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

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

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

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

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

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

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

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

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

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

IH&S 725 Dr. Myers C.I.H. 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 SO 2 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 SO 2 concentration. What volume of SO 2 gas must you add to a 100-liter gas-sampling bag to produce a SO 2 concentration of 500 ppm?

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

IH&S 725 Dr. Myers C.I.H. Preparing spikes – Problem # 1b What mass of SO 2 would you expect the lab to report back to you for this sample if you had sampled 10 liters of the “standard SO 2 mixture” on the spiked filter?

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

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

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

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. 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. 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. 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. Example of using CV T If the NIOSH method 1005 for methylene chloride reports a method overall precision (CV A ) of and we assume a pump CV P of 0.05 then the total CV T will be?

IH&S 725 Dr. Myers C.I.H. Solution for CV T example

IH&S 725 Dr. Myers C.I.H. Application of the CV T 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. Answer