Saturday, 25 February 2017
calibration parameters for HPLC
HPLC is calibrated by the following parameters:
1) Pump calibration
2) Detector Linearity
3)Injector Precision and carryover test
4) Wavelength accuracy by using caffeine and pyrene solution
5) Determine the column oven temp. and sample compartment temp
6) Gradient test
7) Detector noise
In HPLC there must calibrations for Pump, Detector,injector
Pump :- Should calibrated by checking flow accuracy test, Pressure holding test.
Detector :- Should calibrated by checking Linearity test, Detector wavelength accuracy test
Auto sampler :- Should calibrated by Injector Accuracy test,
Carryover test, Injector precision test, carry over test
1) Pump calibration
2) Detector Linearity
3)Injector Precision and carryover test
4) Wavelength accuracy by using caffeine and pyrene solution
5) Determine the column oven temp. and sample compartment temp
6) Gradient test
7) Detector noise
In HPLC there must calibrations for Pump, Detector,injector
Pump :- Should calibrated by checking flow accuracy test, Pressure holding test.
Detector :- Should calibrated by checking Linearity test, Detector wavelength accuracy test
Auto sampler :- Should calibrated by Injector Accuracy test,
Carryover test, Injector precision test, carry over test
About Oral Liquids ( artical help you for your interview preparation for production and QA department in pharmaceutical industry and also in QC department )
The source of the content is Indian pharmacopoeia 2007
Oral Liquids
Elixirs.
Linctuses.
Mixtures.
Oral Drops.
Oral Drops are Oral Liquids that are intended to be administered in small volumes with the aid of a suitable measuring device such as a dropper.
Oral Emulsions.
Emulsions.
Emulsions may exhibit phase separation but are easily reformed on shaking. The preparation remains
sufficiently stable to permit a homogeneous dose to be withdrawn.
Oral Solutions.
Syrups.
Containers.
Tests
Uniformity of content.
Oral Liquids
Oral Liquids are homogeneous liquid preparations, usually consisting of a solution, an emulsion or a suspension of one or more medicaments in a suitable vehicle. They are intended for oral administration either undiluted or after dilution. They may contain auxiliary substances such as suitable dispersing, emulsifying, suspending, wetting, solubilising, thickening, stabilising agents and antimicrobial preservatives. They may also contain suitable sweetening, flavouring and permitted colouring agents. if saccharin, including its sodium and potassium salts, is used as a sweetening agent, its concentration in preparations meant for paediatric use should be restricted so as to limit its intake to 5 mg per kg of body weight.
Oral Liquids other than Oral Emulsions may be supplied as liquids or prepared just before use by dissolving or dispersing granules or powder in the liquid stated on the label. The granules or powder comply with the requirements stated under
Oral Powders.
During manufacture, packaging, storage and distribution of oral liquids, suitable means shall be taken to ensure their microbial quality; acceptance criteria for microbial quality are given in Chapter 5.9.(IP) Oral Liquids should not be diluted and stored; where, however, the individual monograph directs dilution, the diluted Oral Liquid should be freshly prepared irrespective of the nature of the diluent. Diluted Oral Liquids may be less stable physically and chemically than the corresponding undiluted
preparation and should be used within the period stated on the label. Oral Liquids are variously known as Elixirs, Linctuses Mixtures, Oral Drops, Oral Emulsions, Oral Solutions, Oral Suspensions
and Syrups. These terms are defined below.
Elixirs are clear, flavored Oral Liquids containing one or more active ingredients dissolved in a vehicle that usually contains a high proportion of Sucrose or a suitable polyhydric alcohol or alcohols and may also contain Ethanol (95 per cent) or a dilute Ethanol.
Linctuses.
Linctuses are viscous Oral Liquids containing one or more active ingredients dissolved in a vehicle that usually contains a high proportion of sucrose, other sugars or a suitable polyhydric alcohol or alcohols. Linctuses are intended for use in the treatment or relief of cough, and are sipped and swallowed slowly without the addition of water.
Mixtures.
Mixtures are Oral Liquids containing one or more active ingredients dissolved, suspended or dispersed in a suitable vehicle. Suspended solids may separate slowly on keeping but are easily redispersed on shaking.
Oral Drops.
Oral Drops are Oral Liquids that are intended to be administered in small volumes with the aid of a suitable measuring device such as a dropper.
Oral Emulsions.
Oral Emulsions are Oral Liquids containing one or more active ingredients and are stabilised oil-in-water dispersions, either or both phases of which may contain dissolved solids. Solids may also be suspended in Oral
Emulsions.
Emulsions may exhibit phase separation but are easily reformed on shaking. The preparation remains
sufficiently stable to permit a homogeneous dose to be withdrawn.
Oral Solutions.
Oral Solutions are Oral Liquids containing one or more active ingredients dissolved in a suitable vehicle. Oral Suspensions. Oral Suspensions are Oral Liquids containing one or more active ingredients suspended in a suitable vehicle. Suspended solids may slowly separate on keeping but are easily redispersed. In the manufacture of oral suspensions containing dispersed particles, measures shall be taken to ensure a suitable and controlled particle size with regard to the intended use of the
product.
Syrups.
Syrups are viscous Oral Liquids that may contain one or more active ingredients in solution. The vehicle usually contains large amounts of Sucrose or other sugars to which certain polyhydric alcohols may be added to inhibit crystallisation or to modify solubilisation, taste and other vehicle properties. Sugarless syrups may contain sweetening agents and thickening agents. Syrups may contain Ethanol (95%) as a preservative or as a solvent to incorporate flavouring agents. Antimicrobial agents may also be added to Syrups.
Containers.
Oral Liquids may be supplied in multiple dose or single dose containers. Oral Emulsions and Oral Suspensions should be packed in bottles sufficiently wide-mouthed to facilitate the flow of the contents. They are administered either in volumes such as 5 ml, or multiples of 5 ml, or in small volumes (drops). Each dose of a multiple dose Oral Liquid is administered by means of a suitable measuring device which is usually provided with the container.
Tests
Uniformity of content.
Unless otherwise specified, single dose liquids in suspension form or powders or granules presented
in single dose containers and that contain less than 10 mg or less than 10 per cent of active ingredient comply with the following test. For Oral Liquids containing more than one active ingredient, carry out the test for each active ingredient that corresponds to the above conditions. Empty each
container as completely as possible and carry out the test on the individual contents of active ingredients. The test for Uniformity of content should be carried out only after the content of active ingredient(s) in a pooled sample of the preparation has been shown to be within the accepted limits of the stated content. Determine the content of active ingredient(s) of each of 10 containers taken at random using the method given in the monograph or by any other suitable analytical method of
equivalent accuracy and precision. The preparation complies with the test if the individual values thus obtained are all between 85 to 115 per cent of the average value. The preparation fails to comply with the test if more than one individual value is outside the limits 85 to 115 per cent of the average value or if any one individual value is outside the limits 75 to 125 per cent of the average value. If one individual value is outside the limits 85 to 115 per cent but within the limits 75 to 125 per cent of the average value, repeat the determination using another 20 containers taken at random. The preparation complies with the test if in the total sample of 30 containers not more than 3 individual values are outside the limits 85 to 115 per cent and not more than one is outside the limits 75 to 125 per cent of the average value. Uniformity of weight/volume. Unless otherwise specified, Oral Liquids comply with the test for contents of packaged dosage forms . Storage. Store Oral Liquids or powders and granules for the preparation of Oral Liquids in well-closed containers at temperatures not exceeding 30º c Labeling. For Oral Liquids that are supplied as drops, the label states the number of drops per g of preparation if the dose is stated in drops or the number of drops per ml of preparation if the dose is stated in volume. For oral liquids supplied as granules or powder to be constituted before use, the label states
(1) that the contents are meant for preparation of an Oral Liquid;
(2) the directions for preparing the Oral liquid including the nature and quantity of the liquid to be used;
(3) the conditions under which the constituted solution should be stored;
(4) the period during which the constituted Oral Liquid may be expected to remain satisfactory for use when prepared and stored in accordance with the manufacturer’s recommendations;
(5) the strength in terms of the active ingredient(s) in a suitable dose-volume of the constituted preparation.Lupin receives USFDA approval for generic drug to treat sleep disorders
Pharmaceuticals (LPI), US subsidiary of Indian drug maker Lupin, has received the US Food and Drug Administration's (FDA) approval for its Armodafinil tablets indicated to improve wakefulness in adult patients with obstructive sleep apnea, narcolepsy or shift work disorder. Armodafinil is a generic version of Cephalon Inc's Nuvigil tablets.
LPI will begin to promote the product in the US shortly, the company informed the Bombay Stock Exchange (BSE) in a release on Tuesday evening. US FDA has granted approval for four strengths of the tablet—50mg, 150mg, 200mg and 250 mg.
Nuvigil had US sales of $515.6 million, Lupin said, citing IMS data from September 2016.
Lupin's share prices rose 0.82% on Tuesday to close at Rs1,517.05 on BSE, where the benchmark Sensex ended 0.17% higher.
LPI will begin to promote the product in the US shortly, the company informed the Bombay Stock Exchange (BSE) in a release on Tuesday evening. US FDA has granted approval for four strengths of the tablet—50mg, 150mg, 200mg and 250 mg.
Nuvigil had US sales of $515.6 million, Lupin said, citing IMS data from September 2016.
Lupin's share prices rose 0.82% on Tuesday to close at Rs1,517.05 on BSE, where the benchmark Sensex ended 0.17% higher.
about sexual disorders in india
presented a useful discussion on the current status of the
pharmacotherapy of sexual dysfunction. In this context, I observe with
surprise that there has been no survey on sexual dysfunction in India,
much as there has been in other countries.2
Surveys of this nature are necessary to understand the magnitude and
determinants of the problem, especially as may be regionally modulated
by psychosocial, economic and possibly even biological factors.
To illustrate my meaning, I cite four hypotheses.
- Indian men are at a higher risk of coronary heart disease than men in most other parts of the world; a biological risk factor has been postulated. The increase in risk is evident from the fourth decade of life onwards, when most men are still sexually active. As coronary heart disease and erectile dysfunction may share a common aetiology (atherosclerosis), erectile dysfunction attributed to atherosclerosis may be commoner in India than elsewhere in the world.
- The average Indian woman exercises little and therefore, after an active life associated with studentship, tends to become sedentary. As a result, she tends to gain weight from the third decade of life onwards. This physical change is magnified after marriage by repeated childbirth. Furthermore, the average middle class Indian woman often dresses unattractively at home, such as in a billowing nightgown. These biological and behavioural factors could surely be expected to decrease the sexual appeal of a woman and increase the likelihood that her husband will experience erectile failure with her.
- In urban India, women who work in software, business process outsourcing, and other organizations are empowered as never before. Their professional status and financial independence will encourage them to relate more aggressively with their spouses. Indian men are not used to leadership challenges from women in the family; the resultant relationship difficulties could increase the prevalence of erectile dysfunction.
- In urban India, deadlines, targets, long working hours, night duties, and travel responsibilities in various professions ranging from information technology to pharmaceutical promotion could result in physical stress in the individual and emotional stress between a couple; the latter is especially likely when both spouses are employed. The result could be a variety of sexual dysfunctions, starting with a decreased libido.
Many
other possibilies are conceivable, depending on the unique biological,
socioeconomic, moral and behavioural subgroups in the melting pot of
Indian cultures. Sexual function and dysfunction in India, with special
reference to the long-neglected issue of female sexuality, require to be
systematically investigated if this branch of medicine is to become
relevant to the needs of the population
Interview Tips for Pharma Production Jobs
I. Sample Production interview questions
1. Tell me about yourself?
2. Why did you leave your last job?
3. What is your greatest weakness?
4. What experience do you have in Production field?
5. What have you done to improve your Production knowledge in the last year?
6. What have you learned from mistakes on the Production job?
7. What was the best subject that you studied in Operations management during your post graduation?
8. What are the prospects of you becoming successful as a manufacturing planner?
9. What activities are involved in planning?
10. As a manufacturing planner, how will you ensure that you take into account views of all the interested parties during the stage of planning?
11. What should be the performance parameters of a manufacturing planner?
12. What are the threats to the manufacturing sector?
13. Do you think the stage of planning gets completed before implementation begins?
14. Why did choose the profession of a manufacturing process engineer?
15. Which computer languages did you learn during engineering?
16. What are the general issues facing the manufacturing sector?
17. How will you deal with a situation when old but useful equipment needs an expensive maintenance and repair? Will you delay the repair?
18. Do you know computer modeling techniques?
19. Do you prefer working in shifts or having a general shift?
20. What qualities do you have to prove that you are a good manufacturing assembler?
21. How would you recommend working people to assemble work and life?
22. How do you deal with a colleague who is always passing on his work to you only because you are working in the next shift?
23. What is your understanding of an assembly line?
24. With increase in technology, do you think assembly line job will become outdated and men will be replaced by machinery?
25. Do you think firms take enough care to ensure safety of employees working especially in the assembly and production departments?
26. What measures will you take to ensure that an assembly line goes smoothly despite not having enough lubrication in the track?
27. Have you visited any other manufacturing companies to see how their processes are different than yours?
28. What is the meaning of preventive maintenance?
29. What kind of experience do you have working as a technician in the manufacturing sector?
30. What is the reason that your marks decreased to below 65% after your third semester?
31. How good are you at repairing and fitting different parts of cars?
32. What are methods that are used to manage Production?
33. How to maintain Production activities?
34. What are common risks for Production? And how to face?
35. Describe steps to manage Production?
36. How to measure performance of Production activities?
37. What are monitoring methods for Production activities?
38. Describe ISO 9001 for Production?
39. What made you choose to apply to Production…position?
40. Tell me about your last position and what you did?
41. What do you know about the Production…position?
42. What are key tasks for Production…position?
43. What are top 3 knowledge/top 3 skills for Production…position?
44. What are KRAs/output of Production…position?
45. How to measure/appraise your Production…position?
46. What do you know about this company?
47. Describe two or three major trends in your Production field?
48. Did you choose this profession/field?
49. What tertiary qualifications have you attained that related to Production…position?
50. What is the most recent skill you have learned that related to Production…position?
II. Production interview answer tips
1. Identify key goals, tasks, job specs and attributes for Production positions then ask question: How to do, how to become …
2. Listen job interview questions carefully, then ask by your-self: what are things related to Production field before answering.
3. Always ask by yourself: What are proofs that are required for this position?
4. Make a full list of interview questions for Production field: specialized interview questions, common interview questions, interview tips, interview thank you letters, types of job interview questions…
(1)Tell me about yourself
Answers to interview questions: Tell me about yourself
Steps to answer interview questions:
Step 1: Give a brief introduction about yourself:
For example: My name is Peter. I graduated from XYZ University with bachelor degree in Sales. After 5 years working as a Sales Manager, I have well experienced in training, mentoring and motivating other sales personnel to achieve the goals of the Company.
Step 2: Give a brief summary of your experience in your latest positions:
Give a summary of 2-3 latest companies that you have worked for and companies that have helped you succeed with your new jobs.
For example: recently, I have worked for ABC Company as Sales Manager for North-East Region. With my skills from training courses, I developed many sales campaigns which contributed much to the development of new customers and maintenance of current customer base. After 6 months, my sales force and I did regain the company’s market and promote the sales revenue up by 37%.
Step 3: Connect your ability to the employer’s requirements:
Never assume that the employer will by himself be able to connect all of your abilities to the job requirements.
Step 4: Make a concerning question:
With a concerning question, it will help you gain “control” of the interview. You may reduce the stress of the interview with such questions.
For example: I would like to know the strong points of your company’s current Sales force.
(2)Why did you leave your last job?
One of the most frequent questions in any interview is that “Why are you leaving your last job?” or
“Why did you quit your last job?”
“Why did you leave your last job?”
“Why are you leaving your last job?”
…..
1. Some sample answers to the interview question: “Why are you leaving your last job?”
• There is no opportunity to promote in my current job and I’m ready to face a new challenge;
• I have worked there for 04 years with much experience and skills. I want to be promoted but the Company do not offer me that opportunity;
• The company has cut down with its focus on the business line my job is responsible for;
• My family transferred to another region, or, my current workplace is too far away from my home;
• My old company often paid late and had inadequate compensation policy.
2. You should avoid answers that:
• Speak ill of your old boss, colleague, etc.;
• They punished me many times for…
• I did not complete my job.
(3)What is your greatest weakness?
1. Ways to answer:
a) First way: Turning your strong point into weak point.
For example: I am a perfectionist and therefore, I rarely believe in anyone who can work as well as me. As a result, I am afraid to delegate important tasks to others.
This approach has a weak side as that if you are not clever, you will cause the employer to believe that you are cheating him.
b) Second way: Solving your weakness absolutely.
A better approach is that you state one point which was once your weakness, but you have done well to resolve it.
For example: I tended to be a perfectionist, therefore I didn’t like to delegate to others. But I have found out that in order to develop the organization, everyone in the organization must be experienced with many tasks and this is very good for an efficient team work.
2. Steps to answer:
• You need to show it through your attitude and voice: It is really your weakness. And, you may also state some situations how much that weakness has caused you difficulties.
• Give your solution to resolve that weakness, partly or wholly.
• Solutions to a weakness may be training, mentoring, etc
3. Interview Tips for “weakness” question:
• This is a common question in any interview, so don’t try to avoid answering it.
• Never mentioning a weakness that relates to a crucial requirement of the job.
• Don’t try to make up a weakness.
• Don’t say you have no weakness. No one is perfect, therefore, you shouldn’t say you have no weakness.
(4)What experience do you have in this field? or Do you have any actual work experience?
Answer tips
• Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.
• If you are being asked this question from your employer then you can explain your experience. Tell the employer what responsibilities you were performing during your job. You can tell what programs you developed and what modules you worked on. What were your achievements regarding different programs.
Answer sample
I have been working with computers since 2001 I also have a degree in network support/computer repair. I have built my last 3 computers, have work with Dell as an employee. So I have around 15 years experience working with computers.
• Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.
• If you are being asked this question from your employer then you can explain your experience. Tell the employer what responsibilities you were performing during your job. You can tell what programs you developed and what modules you worked on. What were your achievements regarding different programs.
Answer sample
I have been working with computers since 2001 I also have a degree in network support/computer repair. I have built my last 3 computers, have work with Dell as an employee. So I have around 15 years experience working with computers.
1. Tell me about yourself?
2. Why did you leave your last job?
3. What is your greatest weakness?
4. What experience do you have in Production field?
5. What have you done to improve your Production knowledge in the last year?
6. What have you learned from mistakes on the Production job?
7. What was the best subject that you studied in Operations management during your post graduation?
8. What are the prospects of you becoming successful as a manufacturing planner?
9. What activities are involved in planning?
10. As a manufacturing planner, how will you ensure that you take into account views of all the interested parties during the stage of planning?
11. What should be the performance parameters of a manufacturing planner?
12. What are the threats to the manufacturing sector?
13. Do you think the stage of planning gets completed before implementation begins?
14. Why did choose the profession of a manufacturing process engineer?
15. Which computer languages did you learn during engineering?
16. What are the general issues facing the manufacturing sector?
17. How will you deal with a situation when old but useful equipment needs an expensive maintenance and repair? Will you delay the repair?
18. Do you know computer modeling techniques?
19. Do you prefer working in shifts or having a general shift?
20. What qualities do you have to prove that you are a good manufacturing assembler?
21. How would you recommend working people to assemble work and life?
22. How do you deal with a colleague who is always passing on his work to you only because you are working in the next shift?
23. What is your understanding of an assembly line?
24. With increase in technology, do you think assembly line job will become outdated and men will be replaced by machinery?
25. Do you think firms take enough care to ensure safety of employees working especially in the assembly and production departments?
26. What measures will you take to ensure that an assembly line goes smoothly despite not having enough lubrication in the track?
27. Have you visited any other manufacturing companies to see how their processes are different than yours?
28. What is the meaning of preventive maintenance?
29. What kind of experience do you have working as a technician in the manufacturing sector?
30. What is the reason that your marks decreased to below 65% after your third semester?
31. How good are you at repairing and fitting different parts of cars?
32. What are methods that are used to manage Production?
33. How to maintain Production activities?
34. What are common risks for Production? And how to face?
35. Describe steps to manage Production?
36. How to measure performance of Production activities?
37. What are monitoring methods for Production activities?
38. Describe ISO 9001 for Production?
39. What made you choose to apply to Production…position?
40. Tell me about your last position and what you did?
41. What do you know about the Production…position?
42. What are key tasks for Production…position?
43. What are top 3 knowledge/top 3 skills for Production…position?
44. What are KRAs/output of Production…position?
45. How to measure/appraise your Production…position?
46. What do you know about this company?
47. Describe two or three major trends in your Production field?
48. Did you choose this profession/field?
49. What tertiary qualifications have you attained that related to Production…position?
50. What is the most recent skill you have learned that related to Production…position?
II. Production interview answer tips
1. Identify key goals, tasks, job specs and attributes for Production positions then ask question: How to do, how to become …
2. Listen job interview questions carefully, then ask by your-self: what are things related to Production field before answering.
3. Always ask by yourself: What are proofs that are required for this position?
4. Make a full list of interview questions for Production field: specialized interview questions, common interview questions, interview tips, interview thank you letters, types of job interview questions…
(1)Tell me about yourself
Answers to interview questions: Tell me about yourself
Steps to answer interview questions:
Step 1: Give a brief introduction about yourself:
For example: My name is Peter. I graduated from XYZ University with bachelor degree in Sales. After 5 years working as a Sales Manager, I have well experienced in training, mentoring and motivating other sales personnel to achieve the goals of the Company.
Step 2: Give a brief summary of your experience in your latest positions:
Give a summary of 2-3 latest companies that you have worked for and companies that have helped you succeed with your new jobs.
For example: recently, I have worked for ABC Company as Sales Manager for North-East Region. With my skills from training courses, I developed many sales campaigns which contributed much to the development of new customers and maintenance of current customer base. After 6 months, my sales force and I did regain the company’s market and promote the sales revenue up by 37%.
Step 3: Connect your ability to the employer’s requirements:
Never assume that the employer will by himself be able to connect all of your abilities to the job requirements.
Step 4: Make a concerning question:
With a concerning question, it will help you gain “control” of the interview. You may reduce the stress of the interview with such questions.
For example: I would like to know the strong points of your company’s current Sales force.
(2)Why did you leave your last job?
One of the most frequent questions in any interview is that “Why are you leaving your last job?” or
“Why did you quit your last job?”
“Why did you leave your last job?”
“Why are you leaving your last job?”
…..
1. Some sample answers to the interview question: “Why are you leaving your last job?”
• There is no opportunity to promote in my current job and I’m ready to face a new challenge;
• I have worked there for 04 years with much experience and skills. I want to be promoted but the Company do not offer me that opportunity;
• The company has cut down with its focus on the business line my job is responsible for;
• My family transferred to another region, or, my current workplace is too far away from my home;
• My old company often paid late and had inadequate compensation policy.
2. You should avoid answers that:
• Speak ill of your old boss, colleague, etc.;
• They punished me many times for…
• I did not complete my job.
(3)What is your greatest weakness?
1. Ways to answer:
a) First way: Turning your strong point into weak point.
For example: I am a perfectionist and therefore, I rarely believe in anyone who can work as well as me. As a result, I am afraid to delegate important tasks to others.
This approach has a weak side as that if you are not clever, you will cause the employer to believe that you are cheating him.
b) Second way: Solving your weakness absolutely.
A better approach is that you state one point which was once your weakness, but you have done well to resolve it.
For example: I tended to be a perfectionist, therefore I didn’t like to delegate to others. But I have found out that in order to develop the organization, everyone in the organization must be experienced with many tasks and this is very good for an efficient team work.
2. Steps to answer:
• You need to show it through your attitude and voice: It is really your weakness. And, you may also state some situations how much that weakness has caused you difficulties.
• Give your solution to resolve that weakness, partly or wholly.
• Solutions to a weakness may be training, mentoring, etc
3. Interview Tips for “weakness” question:
• This is a common question in any interview, so don’t try to avoid answering it.
• Never mentioning a weakness that relates to a crucial requirement of the job.
• Don’t try to make up a weakness.
• Don’t say you have no weakness. No one is perfect, therefore, you shouldn’t say you have no weakness.
(4)What experience do you have in this field? or Do you have any actual work experience?
Answer tips
• Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.
• If you are being asked this question from your employer then you can explain your experience. Tell the employer what responsibilities you were performing during your job. You can tell what programs you developed and what modules you worked on. What were your achievements regarding different programs.
Answer sample
I have been working with computers since 2001 I also have a degree in network support/computer repair. I have built my last 3 computers, have work with Dell as an employee. So I have around 15 years experience working with computers.
• Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.
• If you are being asked this question from your employer then you can explain your experience. Tell the employer what responsibilities you were performing during your job. You can tell what programs you developed and what modules you worked on. What were your achievements regarding different programs.
Answer sample
I have been working with computers since 2001 I also have a degree in network support/computer repair. I have built my last 3 computers, have work with Dell as an employee. So I have around 15 years experience working with computers.
Atomic absorption spectroscopy
Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state.The technique makes use of absorption spectrometry to assess the concentration of an analyte in a sample. It requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the Beer-Lambert Law
In short, the electrons of the atoms in the atomizer can be promoted to higher orbitals (excited state) for a short period of time (nanoseconds) by absorbing a defined quantity of energy (radiation of a given wavelength). This amount of energy, i.e., wavelength, is specific to a particular electron transition in a particular element. In general, each wavelength corresponds to only one element, and the width of an absorption line is only of the order of a few picometers (pm), which gives the technique its elemental selectivity. The radiation flux without a sample and with a sample in the atomizer is measured using a detector, and the ratio between the two values (the absorbance) is converted to analyte concentration or mass using the Beer-Lambert Law.
n order to analyze a sample for its atomic constituents, it has to be atomized. The atomizers most commonly used nowadays are flames and electrothermal (graphite tube) atomizers. The atoms should then be irradiated by optical radiation, and the radiation source could be an element-specific line radiation source or a continuum radiation source. The radiation then passes through a monochromator in order to separate the element-specific radiation from any other radiation emitted by the radiation source, which is finally measured by a detector.
Atomizers
Atomizers
The atomizers most commonly used nowadays are (spectroscopic) flames and electrothermal (graphite tube) atomizers. Other atomizers, such as glow-discharge atomization, hydride atomization, or cold-vapor atomization might be used for special purposes.
Flame atomizers
The oldest and most commonly used atomizers in AAS are flames, principally the air-acetylene flame with a temperature of about 2300 °C and the nitrous dioxide system (N2O)-acetylene flame with a temperature of about 2700 °C. The latter flame, in addition, offers a more reducing environment, being ideally suited for analytes with high affinity to oxygen.
Liquid or dissolved samples are typically used with flame atomizers. The sample solution is aspirated by a pneumatic analytical nebulizer, transformed into an aerosol, which is introduced into a spray chamber, where it is mixed with the flame gases and conditioned in a way that only the finest aerosol droplets (< 10 μm) enter the flame. This conditioning process is responsible that only about 5% of the aspirated sample solution reaches the flame, but it also guarantees a relatively high freedom from interference.
On top of the spray chamber is a burner head that produces a flame that is laterally long (usually 5–10 cm) and only a few mm deep. The radiation beam passes through this flame at its longest axis, and the flame gas flow-rates may be adjusted to produce the highest concentration of free atoms. The burner height may also be adjusted, so that the radiation beam passes through the zone of highest atom cloud density in the flame, resulting in the highest sensitivity.
The processes in a flame include the stages of desolvation (drying) in which the solvent is evaporated and the dry sample nano-particles remain, vaporization (transfer to the gaseous phase) in which the solid particles are converted into gaseous molecule, atomization in which the molecules are dissociated into free atoms, and ionization where (depending on the ionization potential of the analyte atoms and the energy available in a particular flame) atoms may be in part converted to gaseous ions.
Each of these stages includes the risk of interference in case the degree of phase transfer is different for the analyte in the calibration standard and in the sample. Ionization is generally undesirable, as it reduces the number of atoms that are available for measurement, i.e., the sensitivity.
In flame AAS a steady-state signal is generated during the time period when the sample is aspirated. This technique is typically used for determinations in the mg L−1 range, and may be extended down to a few μg L−1 for some elements.
Electrothermal atomizer
Electrothermal AAS (ET AAS) using graphite tube atomizers was pioneered by Boris V. L’vov at the Saint Petersburg Polytechnical Institute, Russia,[4] since the late 1950s, and investigated in parallel by Hans Massmann at the Institute of Spectrochemistry and Applied Spectroscopy (ISAS) in Dortmund, Germany.[5]
Although a wide variety of graphite tube designs have been used over the years, the dimensions nowadays are typically 20–25 mm in length and 5–6 mm inner diameter. With this technique liquid/dissolved, solid and gaseous samples may be analyzed directly. A measured volume (typically 10–50 μL) or a weighed mass (typically around 1 mg) of a solid sample are introduced into the graphite tube and subject to a temperature program. This typically consists of stages, such as drying – the solvent is evaporated; pyrolysis – the majority of the matrix constituents are removed; atomization – the analyte element is released to the gaseous phase; and cleaning – eventual residues in the graphite tube are removed at high temperature.
The graphite tubes are heated via their ohmic resistance using a low-voltage high-current power supply; the temperature in the individual stages can be controlled very closely, and temperature ramps between the individual stages facilitate separation of sample components. Tubes may be heated transversely or longitudinally, where the former ones have the advantage of a more homogeneous temperature distribution over their length. The so-called stabilized temperature platform furnace (STPF) concept, proposed by Walter Slavin, based on research of Boris L’vov, makes ET AAS essentially free from interference.[citation needed] The major components of this concept are atomization of the sample from a graphite platform inserted into the graphite tube (L’vov platform) instead of from the tube wall in order to delay atomization until the gas phase in the atomizer has reached a stable temperature; use of a chemical modifier in order to stabilize the analyte to a pyrolysis temperature that is sufficient to remove the majority of the matrix components; and integration of the absorbance over the time of the transient absorption signal instead of using peak height absorbance for quantification.
In ET AAS a transient signal is generated, the area of which is directly proportional to the mass of analyte (not its concentration) introduced into the graphite tube. This technique has the advantage that any kind of sample, solid, liquid or gaseous, can be analyzed directly. Its sensitivity is 2–3 orders of magnitude higher than that of flame AAS, so that determinations in the low μg L−1 range (for a typical sample volume of 20 µL) and ng g−1 range (for a typical sample mass of 1 mg) can be carried out. It shows a very high degree of freedom from interferences, so that ET AAS might be considered the most robust technique available nowadays for the determination of trace elements in complex matrices.
Specialized atomization techniques
While flame and electrothermal vaporizers are the most common atomization techniques, several other atomization methods are utilized for specialized use.
Glow-discharge atomization
A glow-discharge device (GD) serves as a versatile source, as it can simultaneously introduce and atomize the sample. The glow discharge occurs in a low-pressure argon gas atmosphere between 1 and 10 torr. In this atmosphere lies a pair of electrodes applying a DC voltage of 250 to 1000 V to break down the argon gas into positively charged ions and electrons. These ions, under the influence of the electric field, are accelerated into the cathode surface containing the sample, bombarding the sample and causing neutral sample atom ejection through the process known as sputtering. The atomic vapor produced by this discharge is composed of ions, ground state atoms, and fraction of excited atoms. When the excited atoms relax back into their ground state, a low-intensity glow is emitted, giving the technique its name.
The requirement for samples of glow discharge atomizers is that they are electrical conductors. Consequently, atomizers are most commonly used in the analysis of metals and other conducting samples. However, with proper modifications, it can be utilized to analyze liquid samples as well as nonconducting materials by mixing them with a conductor (e.g. graphite).
Hydride atomization
Hydride generation techniques are specialized in solutions of specific elements. The technique provides a means of introducing samples containing arsenic, antimony, tin, selenium, bismuth, and lead into an atomizer in the gas phase. With these elements, hydride atomization enhances detection limits by a factor of 10 to 100 compared to alternative methods. Hydride generation occurs by adding an acidified aqueous solution of the sample to a 1% aqueous solution of sodium borohydride, all of which is contained in a glass vessel. The volatile hydride generated by the reaction that occurs is swept into the atomization chamber by an inert gas, where it undergoes decomposition. This process forms an atomized form of the analyte, which can then be measured by absorption or emission spectrometry.
Cold-vapor atomization
The cold-vapor technique an atomization method limited to only the determination of mercury, due to it being the only metallic element to have a large enough vapor pressure at ambient temperature.[citation needed] Because of this, it has an important use in determining organic mercury compounds in samples and their distribution in the environment. The method initiates by converting mercury into Hg2+ by oxidation from nitric and sulfuric acids, followed by a reduction of Hg2+ with tin(II) chloride. The mercury, is then swept into a long-pass absorption tube by bubbling a stream of inert gas through the reaction mixture. The concentration is determined by measuring the absorbance of this gas at 253.7 nm. Detection limits for this technique are in the parts-per-billion range making it an excellent mercury detection atomization method.
Radiation sources
We have to distinguish between line source AAS (LS AAS) and continuum source AAS (CS AAS). In classical LS AAS, as it has been proposed by Alan Walsh,[citation needed] the high spectral resolution required for AAS measurements is provided by the radiation source itself that emits the spectrum of the analyte in the form of lines that are narrower than the absorption lines. Continuum sources, such as deuterium lamps, are only used for background correction purposes. The advantage of this technique is that only a medium-resolution monochromator is necessary for measuring AAS; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined. In CS AAS, in contrast, a single lamp, emitting a continuum spectrum over the entire spectral range of interest is used for all elements. Obviously, a high-resolution monochromator is required for this technique, as will be discussed later.
Hollow cathode lamps
Hollow cathode lamps (HCL) are the most common radiation source in LS AAS.[citation needed] Inside the sealed lamp, filled with argon or neon gas at low pressure, is a cylindrical metal cathode containing the element of interest and an anode. A high voltage is applied across the anode and cathode, resulting in an ionization of the fill gas. The gas ions are accelerated towards the cathode and, upon impact on the cathode, sputter cathode material that is excited in the glow discharge to emit the radiation of the sputtered material, i.e., the element of interest. Most lamps will handle a handful of elements, i.e. 5-8. A typical machine will have two lamps, one will take care of five elements and the other will handle four elements for a total of nine elements analyzed.
Electrodeless discharge lamps
Electrodeless discharge lamps (EDL) contain a small quantity of the analyte as a metal or a salt in a quartz bulb together with an inert gas, typically argon gas, at low pressure. The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp. The emission from an EDL is higher than that from an HCL, and the line width is generally narrower, but EDLs need a separate power supply and might need a longer time to stabilize.
Deuterium lamps
Deuterium HCL or even hydrogen HCL and deuterium discharge lamps are used in LS AAS for background correction purposes.[6] The radiation intensity emitted by these lamps decreases significantly with increasing wavelength, so that they can be only used in the wavelength range between 190 and about 320 nm.
Continuum sources
When a continuum radiation source is used for AAS, it is necessary to use a high-resolution monochromator, as will be discussed later. In addition, it is necessary that the lamp emits radiation of intensity at least an order of magnitude above that of a typical HCL over the entire wavelength range from 190 nm to 900 nm. A special high-pressure xenon short arc lamp, operating in a hot-spot mode has been developed to fulfill these requirements.
Spectrometer
As already pointed out above, there is a difference between medium-resolution spectrometers that are used for LS AAS and high-resolution spectrometers that are designed for CS AAS. The spectrometer includes the spectral sorting device (monochromator) and the detector.
Spectrometers for LS AAS
In LS AAS the high resolution that is required for the measurement of atomic absorption is provided by the narrow line emission of the radiation source, and the monochromator simply has to resolve the analytical line from other radiation emitted by the lamp.[citation needed] This can usually be accomplished with a band pass between 0.2 and 2 nm, i.e., a medium-resolution monochromator. Another feature to make LS AAS element-specific is modulation of the primary radiation and the use of a selective amplifier that is tuned to the same modulation frequency, as already postulated by Alan Walsh. This way any (unmodulated) radiation emitted for example by the atomizer can be excluded, which is imperative for LS AAS. Simple monochromators of the Littrow or (better) the Czerny-Turner design are typically used for LS AAS. Photomultiplier tubes are the most frequently used detectors in LS AAS, although solid state detectors might be preferred because of their better signal-to-noise ratio.
Spectrometers for CS AAS
When a continuum radiation source is used for AAS measurement it is indispensable to work with a high-resolution monochromator. The resolution has to be equal to or better than the half width of an atomic absorption line (about 2 pm) in order to avoid losses of sensitivity and linearity of the calibration graph. The research with high-resolution (HR) CS AAS was pioneered by the groups of O’Haver and Harnly in the USA, who also developed the (up until now) only simultaneous multi-element spectrometer for this technique. The break-through, however, came when the group of Becker-Ross in Berlin, Germany, built a spectrometer entirely designed for HR-CS AAS. The first commercial equipment for HR-CS AAS was introduced by Analytik Jena (Jena, Germany) at the beginning of the 21st century, based on the design proposed by Becker-Ross and Florek. These spectrometers use a compact double monochromator with a prism pre-monochromator and an echelle grating monochromator for high resolution. A linear charge coupled device (CCD) array with 200 pixels is used as the detector. The second monochromator does not have an exit slit; hence the spectral environment at both sides of the analytical line becomes visible at high resolution. As typically only 3–5 pixels are used to measure the atomic absorption, the other pixels are available for correction purposes. One of these corrections is that for lamp flicker noise, which is independent of wavelength, resulting in measurements with very low noise level; other corrections are those for background absorption, as will be discussed later.
Background absorption and background correction
The relatively small number of atomic absorption lines (compared to atomic emission lines) and their narrow width (a few pm) make spectral overlap rare; there are only few examples known that an absorption line from one element will overlap with another[citation needed]. Molecular absorption, in contrast, is much broader, so that it is more likely that some molecular absorption band will overlap with an atomic line. This kind of absorption might be caused by un-dissociated molecules of concomitant elements of the sample or by flame gases. We have to distinguish between the spectra of di-atomic molecules, which exhibit a pronounced fine structure, and those of larger (usually tri-atomic) molecules that don’t show such fine structure. Another source of background absorption, particularly in ET AAS, is scattering of the primary radiation at particles that are generated in the atomization stage, when the matrix could not be removed sufficiently in the pyrolysis stage.
All these phenomena, molecular absorption and radiation scattering, can result in artificially high absorption and an improperly high (erroneous) calculation for the concentration or mass of the analyte in the sample. There are several techniques available to correct for background absorption, and they are significantly different for LS AAS and HR-CS AAS.
Background correction techniques in LS AAS
In LS AAS background absorption can only be corrected using instrumental techniques, and all of them are based on two sequential measurements[citation needed], firstly, total absorption (atomic plus background), secondly, background absorption only, and the difference of the two measurements gives the net atomic absorption. Because of this, and because of the use of additional devices in the spectrometer, the signal-to-noise ratio of background-corrected signals is always significantly inferior compared to uncorrected signals. It should also be pointed out that in LS AAS there is no way to correct for (the rare case of) a direct overlap of two atomic lines. In essence there are three techniques used for background correction in LS AAS:
Deuterium background correction
This is the oldest and still most commonly used technique, particularly for flame AAS. In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background absorption over the entire width of the exit slit of the spectrometer. The use of a separate lamp makes this technique the least accurate one, as it cannot correct for any structured background. It also cannot be used at wavelengths above about 320 nm, as the emission intensity of the deuterium lamp becomes very weak. The use of deuterium HCL is preferable compared to an arc lamp due to the better fit of the image of the former lamp with that of the analyte HCL.
Smith-Hieftje background correction[edit]
This technique (named after their inventors) is based on the line-broadening and self-reversal of emission lines from HCL when high current is applied. Total absorption is measured with normal lamp current, i.e., with a narrow emission line, and background absorption after application of a high-current pulse with the profile of the self-reversed line, which has little emission at the original wavelength, but strong emission on both sides of the analytical line. The advantage of this technique is that only one radiation source is used; among the disadvantages are that the high-current pulses reduce lamp lifetime, and that the technique can only be used for relatively volatile elements, as only those exhibit sufficient self-reversal to avoid dramatic loss of sensitivity. Another problem is that background is not measured at the same wavelength as total absorption, making the technique unsuitable for correcting structured background.
Zeeman-effect background correction
An alternating magnetic field is applied at the atomizer (graphite furnace) to split the absorption line into three components, the π component, which remains at the same position as the original absorption line, and two σ components, which are moved to higher and lower wavelengths, respectively[citation needed]. Total absorption is measured without magnetic field and background absorption with the magnetic field on. The π component has to be removed in this case, e.g. using a polarizer, and the σ components do not overlap with the emission profile of the lamp, so that only the background absorption is measured. The advantages of this technique are that total and background absorption are measured with the same emission profile of the same lamp, so that any kind of background, including background with fine structure can be corrected accurately, unless the molecule responsible for the background is also affected by the magnetic field and using a chopper as a polariser reduces the signal to noise ratio. While the disadvantages are the increased complexity of the spectrometer and power supply needed for running the powerful magnet needed to split the absorption line.
Background correction techniques in HR-CS AAS
In HR-CS AAS background correction is carried out mathematically in the software using information from detector pixels that are not used for measuring atomic absorption; hence, in contrast to LS AAS, no additional components are required for background correction.
Background correction using correction pixels
It has already been mentioned that in HR-CS AAS lamp flicker noise is eliminated using correction pixels. In fact, any increase or decrease in radiation intensity that is observed to the same extent at all pixels chosen for correction is eliminated by the correction algorithm.[citation needed] This obviously also includes a reduction of the measured intensity due to radiation scattering or molecular absorption, which is corrected in the same way. As measurement of total and background absorption, and correction for the latter, are strictly simultaneous (in contrast to LS AAS), even the fastest changes of background absorption, as they may be observed in ET AAS, do not cause any problem. In addition, as the same algorithm is used for background correction and elimination of lamp noise, the background corrected signals show a much better signal-to-noise ratio compared to the uncorrected signals, which is also in contrast to LS AAS.
Background correction using a least-squares algorithm
The above technique can obviously not correct for a background with fine structure, as in this case the absorbance will be different at each of the correction pixels. In this case HR-CS AAS is offering the possibility to measure correction spectra of the molecule(s) that is (are) responsible for the background and store them in the computer. These spectra are then multiplied with a factor to match the intensity of the sample spectrum and subtracted pixel by pixel and spectrum by spectrum from the sample spectrum using a least-squares algorithm. This might sound complex, but first of all the number of di-atomic molecules that can exist at the temperatures of the atomizers used in AAS is relatively small, and second, the correction is performed by the computer within a few seconds. The same algorithm can actually also be used to correct for direct line overlap of two atomic absorption lines, making HR-CS AAS the only AAS technique that can correct for this kind of spectral interferen
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