Quality assurance of sampling and analytical instruments

1. Quality assurance of sampling and analytical instruments Lecture Notes IH&S 725 Dr. Myers, C.I.H.

2. Sampling Three basic sources of variability Analytical Workplace IH&S 725 Dr. Myers C.I.H.

3. Sampling Variability Results fromtwo types of error • Random or Statistical Errors • Systematic Errors IH&S 725 Dr. Myers C.I.H.

4. Workplace • Random • Systematic IH&S 725 Dr. Myers C.I.H.

5. Sampling Train • Random • Systematic IH&S 725 Dr. Myers C.I.H.

6. Analytical • Random • Systematic IH&S 725 Dr. Myers C.I.H.

7. Managing and minimizing systematic error • Most important for IH to control • Calibrate • Check sampling train integrity • Use blanks and control samples • Periodic employee sampling • Sample different conditions IH&S 725 Dr. Myers C.I.H.

8. Flow Calibration • Primary standards - Best • Secondary standards – OK IH&S 725 Dr. Myers C.I.H.

9. Check sampling train integrity • Properly assembled filter cassettes • Tight connections • Tubing with no leaks • Pump diaphragms intact, etc… IH&S 725 Dr. Myers C.I.H.

10. Blanks and control samples • Field blank IH&S 725 Dr. Myers C.I.H.

11. Blanks and control samples • Media blank IH&S 725 Dr. Myers C.I.H.

12. Blanks and control samples • Reagent blank • Spikes IH&S 725 Dr. Myers C.I.H.

13. Preparing spikes – Problem # 1 • To complete the sampling campaign you've undertaken you desire to collect a “spiked” sample in your lab at a known SO2 concentration and send it to the analytical lab with your field samples. In order to do this you must create a volume of air having a known SO2 concentration. What volume of SO2 gas must you add to a 100-liter gas-sampling bag to produce a SO2 concentration of 500 ppm? IH&S 725 Dr. Myers C.I.H.

14. Solution for problem #1 IH&S 725 Dr. Myers C.I.H.

15. Preparing spikes – Problem # 1b • What mass of SO2 would you expect the lab to report back to you for this sample if you had sampled 10 liters of the “standard SO2 mixture” on the spiked filter? IH&S 725 Dr. Myers C.I.H.

16. Solution to Problem # 1b IH&S 725 Dr. Myers C.I.H.

17. Preparing spikes – Problem #2 • We are sampling for methylene chloride and want to prepare a series of spiked samples that range in concentrations of 10% and 50% of the PEL value for a sample volume of 1L. • We need to prepare a volume of methylene chloride at known concentration IH&S 725 Dr. Myers C.I.H.

18. Solution to problem #2 IH&S 725 Dr. Myers C.I.H.

19. IH&S 725 Dr. Myers C.I.H.

20. Periodic employee sampling • Regular intervals e.g. every 6 months • Randomly select employees of the same SEG • Sample as many workers as the budget allows – not 1 or 2 unless your budget restricts you to that • Sample highest priority SEGs IH&S 725 Dr. Myers C.I.H.

21. Sample different conditions • Sample different shifts and different days of the week especially if weekend shifts are different from those used during the week • Sample different times of the year • Sample under different run capacities within what is considered normal, etc… IH&S 725 Dr. Myers C.I.H.

22. Managing and minimizing random errors • Can’t eliminate so we account for them in statements of uncertainty • Use coefficients of variability • Confidence intervals, etc… IH&S 725 Dr. Myers C.I.H.

23. Cumulative Error or Total Coefficient of Variation Typical CV for a sampling pump is assumed to be .05 IH&S 725 Dr. Myers C.I.H.

24. Example of using CVT • If the NIOSH method 1005 for methylene chloride reports a method overall precision (CVA) of 0.076 and we assume a pump CVP of 0.05 then the total CVT will be? IH&S 725 Dr. Myers C.I.H.

25. Solution for CVT example IH&S 725 Dr. Myers C.I.H.

26. Application of the CVT • You sample methylene chloride for 4 hrs at a flow rate of .15LPM and have a reported mass of 35ug. Report your concentration and its relative standard deviation. IH&S 725 Dr. Myers C.I.H.

27. Answer IH&S 725 Dr. Myers C.I.H.