Page 143 - Inorganic Mass Spectrometry - Fundamentals and Applications

~~ductively Coupled Plasma Mass Spectrometry 133

ment patterns, Therefore, isotope dilution-based concentration measurements
have often been used [298-3021.

The low detection limits and rapid, multielement analysis provided by ICP-MS
make it particularly attractive for environmental applications, in which high
sample throughput is often essential, For several elements, including Pb, the
maximum acceptable levels have decreased as the ability to measure lower and
lower concentrations has improved. ICP-MS measurements are used to assess
environmental quality, including meeting legislated requirements; to investi-
gate the natural sources and transport of elements; and to identify sources of
pollutants.

Nonsaline Water Analysis

River, stream, and lake water; groundwater; as well as atmospheric precipitation
are commonly analyzed by using ICP-MS [303]. Often the samples can be run
directly or after simple filtration or centrifugation to remove suspended particu-
lates [304]. Typically samples can be preserved by the addition of l% to 2%
concentrated nitric acid by volume [305]. Nitric acid is preferable to hydrochloric
or sulfuric acid because of the lack of molecular ion spectral overlaps from nitric
acid or its reaction products in the ICP, as discussed earlier. In most cases
preconcentration or separation is unnecessary. In some cases preconcentration and
removal of chlorides from the sample are advantageous and can be done by using a
simple flow injection approach [306].
ICP-MS is widely used to assess drinking water quality. Environmental
Protection Agency (EPA) methods 200.8 and 1638 the analysis of drinking and
for
waste waters use ICP-MS [30’7-3091. Sources of Pb in drinking water can be
assessed from Pb isotope ratios. In one study, 206Pb(207Pb, 206PbPo8Pb, 207Pb(208Pb
isotope ratios in tap water were compared to those of plumbing materials [3 101.
The authors were able to conclude that the copper pipe and solder were the main
sources of Pb.
In some cases, ultrasonic nebulization or preconcentration is used to en-
hance detection limits. As, Se, and Sb were measured in cloud water; detection
limits were 20, 100, and 20 pg/mL, respectively, using pneumatic nebulization
and four to five times lower using ultrasonic nebulization [3 1 l] In another study
[312], activated charcoal from a l-L sample volume was used to preconcentrate
Pd and Pt in fresh waters. Detection limits were 0.3-0.8 ngL. An automated on-
line preconcentration system based on a cationic resin (AG50W-X8) was used to
measure Cd, Pb, Ni, Cu, and Zn, A preconcentration factor of 30 was obtained
even with a sample throughput of 20 samples per hour [3 131.