Both arsenic and mercury can volatilize during sample preparation in open container systems, so you must use a closed system, preferably a microwave digestion apparatus. Both hair and fingernails will dissolve completely in a small volume of concentrated nitric acid, typically 5 g of nitric acid for 0.2 g of hair, using microwave digestion. Care must be taken so that the sample does not vent (overpressure) during digestion, which would result in loss of these volatile elements. If a microwave digestion system is not available, other closed or semi-closed digestion systems (Paar bomb or reflux condenser open system) could be employed.

Arsenic could be determined using either hydride generation AA or electrothermal AA. The latter is the simpler procedure and should be tried first. The nitric acid matrix is ideal for electrothermal measurements. The most sensitive absorption line at 193.7 nm should be used and an ashing study should be performed to ascertain that no arsenic is lost during the atomization step. A multipoint calibration curve should be prepared using standards matched in acid concentration to the samples.

You are using an AA instrument that employs Zeeman background correction, and you observe the peak shape shown at the left for arsenic in the hair samples. What is the problem?

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