Environmental Engineering Reference
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21. (a) Sketch and briefly describe the hydride generation atomic absorption (HGAA)
technique for the analysis of arsenic and selenium. (b) What are the operational
parameters that affect the sensitivities?
22. In the U.S. EPA's SW-846 methods: (a) Describe two multielement atomic spectrometric
methods; (b) Describe two most common single element atomic AA; (c) What else
atomization techniques are used for several other elements such as Hg, As, and Sn?
23. A groundwater sample is analyzed for its K by FAA using the method of standard
additions. Two 500 mL of this groundwater sample are added to 10.0-mL DI water. To
one portion, it was added 10.0 mL of 10 mM KCl solution. The net emission signals in
arbitrary units are 20.2 and 75.1. What is the concentration of K in this groundwater
in mg/L and mM?
24. A 5-point calibration curve was made for the determination of Pb in FAA. The
regression equation was: y ¼ 0:155xþ0:0016, where y is the signal output as absor-
bance, and x is the Pb concentration in mg/L. (a) A contaminated groundwater sample
was collected, diluted from 10 to 50 mL, and analyzed without digestion. The
absorbance reading was 0.203 for the sample. Calculate the concentration of Pb in this
groundwater sample; (b) A sediment sample suspected of Pb contamination was
collected. After decanting the overlying water, a 1-g wet sediment sample was digested
and diluted to 50 mL. FAA measurement gave an absorbance reading of 0.350. A
subsample of this wet sediment was taken to measure the moisture content with oven
drying overnight. The moisture was 35%. Report the Pb concentration in sediment
sample on a dry basis.
25. In flameless graphite furnace method, which quantitative method is more appropriate:
(a) Internal standard method; (b) Standard addition methods? Explain.
26. What precautions regarding QA/QC should be made in running a batch of samples in the
automatic sample log (sequence table)?
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