Modifications to the commercial hydride generator,
manufactured by Spectrametrics, resulted in improved operating
procedure and enhancement of the arsenic and germanium signals.
Experiments with arsenic(III) and arsenic(V) showed that
identical reiults could be produced from both oxidation states.
However, since arsenic(V) is reduced more slowly than
arsenic(III), peak areas and not peak heights must be measured
when the arsine is immediately stripped from the system
(approximately 5 seconds reaction). When the reduction is
allowed to proceed for 20 seconds before the arsine is stripped,
peak heights may be used. For a 200 ng/mL solution, the
relative standard deviation is 2.8% for As(III) and 3.8% for
As(V). The detection limit for arsenic using the modified
system is 0.50 ng/mL.
Studies performed on As(V) standards show that the
interferences from 1000 mg/L of nickel(II), cobalt(II),
iron(III), copper(II), cadmium(II), and zinc(II) can be
eliminated with the aid of 5 M Hel and 3% L-cystine.
Conditions for the reduction of germanium to the
corresponding hydride were investigated. The effect of
different concentrations of HCl on the reduction of germanium to
the covalent hydride in aqueous media by means of NaBH
4
solutions was assessed. Results show that the best response is
accomplished at a pH of 1.7. The use of buffer solutions was
similarly characterized. In both cases, results showed that the element is best reduced when the final pH of the solution after
reaction is almost neutral. In addition, a more sensitive
method, which includes the use of (NH4)2S208' has been developed.
A 20% increase in the germanium signal is registered when
compared to the signal achieved with Hel alone. Moreover, under
these conditions, reduction of germanium could be accomplished,
even when the solution's pH is neutral. For a 100 ng/mL
germanium standard the rsd is 3%. The detection limit for
germanium in 0.05 M Hel medium (pH 1.7) is 0.10 ng/mL and 0.09
ng/mL when ammonium persulphate is used in conjunction with Hel.
Interferences from 1000 mg/L of iron(III), copper(II),
cobalt(II), nickel(II), cadmium(II), lead(II), mercury(II),
aluminum(III), tin(IV), arsenic(III), arsenic(V) and zinc(II)
were studied and characterized. In this regard, the use of
(NH4)ZS20S and Hel at a pH of 1.7 proved to be a successful
mixture in the sbppression of the interferences caused by iron,
copper, aluminum, tin, lead, and arsenic. The method was applied
to the determination of germanium in cherts and iron ores.
In addition, experiments with tin(IV) showed that a 15%
increase in the tin signal can be accomplished in the presence of
1 mL of (NH4)2S20S 10% (m/V)
