Sampling in Analytical Chemistry

How to achieve a sample for analysis
Achieving a sample for Quality Control
Analysis depends upon Sampling
The Method of sampling is very important

1. Sampling MUHAMMAD ARSLAN ROLL NO. 37 ORGANIC SECTION

2. Sampling An important factor for Quality Control Analysis Depends upon Sampling

3. Sampling and Method of Analysis Type of Analysis depends on The Size of Sample

4. Sampling How to achieve a sample for analysis Achieving a sample for Quality Control Analysis depends upon Sampling The Method of sampling is very important

5. Sampling A number of types of samples Grab Samples Gross Samples Representative Samples Analysis Samples Lab Samples

6. Grab Samples A  grab sample , also known as a  catch sample , consists of a single sample taken at a specific time.  The most common and easy type of sample. For example, you took a grab sample when you collected a beaker of raw water and tested it for pH.   Grab samples do provide an immediate sample. Preferred for some tests such as pH, DO and total residual chlorine.

7. Grab Samples A number of limitations  It may not be completely representative of the entire flow.  Composition of sample may vary with time, place or environment Grab samples must be collected carefully to make them as representative as possible.  Mixing two or more grab samples may not give a result which averages the characteristics of the samples. 

8. Representative Sample A small quantity of something such whose characteristics represent as accurately as possible the entire batch, lot, population or universe. Small size Composition similar to Whole A number of grab samples mixed

9. Gross Samples A number of increments taken from a larger quantity of a material to be analyzed Bulk Sample OR Lot sample A large sized representative sample Represent the whole as a relatively small fraction Composition similar to the Matrix Degree of heterogeneity of the whole

10. Laboratory Sample The Sample taken to laboratory for analysis Smaller size Representative Sample

11. Analysis Sample Part of Lab sample to be analyzed Representative Sample Smaller size Part is analyzed and rest stored for Archiving and re-checking

12. Size of Sample Minimum amount of sample required/sufficient for analysis For reliable, accurate and reproducible results Ingamell’s sampling constant ks = Ingamell’s sampling constant (mass of sample for 1% sampling uncertainty at 68% confidence level) R = RSD (%) Sampling variance is inversely proportional to size of sample

13. Minimum Number of Samples The number of individual sample increments needed to achieve a given level of confidence in the analytical results n = no of samples t = value of t s s = sampling variance Gaussian distribution – centered around For Random distribution (Poisson Distribution)

14. Sampling How to perform a sample? Nature of material Type of analysis Confidence Level Statistics Systematic Errors – Minimum possibility

15. Solids Variability in sample matrix – maximum Diffusion – minimum Maximum number of samples to be mixed for representative sample Size reduction Grab sampler Auger samler A shovel A hand cart etc..

16. Liquids More diffusion compared to solids More homogeneity Easy sampling Pure liquids – Grab sample is Rep. Sample. Solutions – Depends on composition A number of samples to be mixed for Rep sample Mixing is easy Glass or plastic bottles

17. Gases Diffusion – maximum Sampling – difficult Composition depends upon a number of factors Time Direction of wind Speed of wind Height Environmental factors Area of sampling Traffic etc.

18. Gases Evacuated glass or plastic bottles A glass syringe Absorption train

19. Transportation Sample to be transported to laboratory according to the GLP and the QA program Refrigerated Ambient conditions Pre-treated according to the requirements

20. Processing of Sample The Sample Preparation Dissolution Digestion Extraction Filtration Evaporation

21. Dissolution For solid samples Suitable solvent Easy dissolution No interference in the analysis

22. Filtration To separate the solid/insoluble/precipitate or crystals from the liquid or mother liquor Gravity filters Vacuum filters Buchner funnels

23. Digestion Acid digestion Sulfuric acid Nitric acid Perchloric acid and nitric acid Base digestion Microwave digestion

24. Extraction Liquid – Liquid extraction Solid Phase extraction Based on distribution coefficient Continuous extraction “Chromatography” Pre-concentration of dilute samples

25. The Analysis The suitable method to be adopted for the purpose Considering the GLP, QA and the available/prescribed facilities

26. Questions

27. Thanks

28. The Value of q

29. The value of t

30. The value of F