Page 139 - Inorganic Mass Spectrometry - Fundamentals and Applications

Inducti~ely Coupled Plasma Mass Spectro~et~ l29

Selenium has also been investigated extensively with ICP-MS. It can be
efficiently introduced into the plasma by hydride generation in order to improve
detection limits. The analyte is efficiently transported into the plasma as a gas and
the sample matrix is left behind. The hydride generator design can influence
interferences and sensitivity [258]. Sample cross-contamination was elirninated
when the air bubble normally entrained between samples was removed [258].
Isotope dilution can be used to obtain high accuracy.

Isotope Tracers
Stable isotope tracers can be conveniently measured by using ICP-MS [259,260].
The low ICP-MS detection limits allow small amounts of stable isotope tracers to
be given to subjects, including infants [261].
The first complete study of nickel metabolism in humans involved ingestion
of 10 pg of G2Ni/kg body weight [262]. Isotope dilution (with (jlNi+) was used to
measure 62Ni+ tracer concentrations in blood, urine, and feces. Potential compli-
cations due to contarnination and dietary intake of nickel were eliminated by using
the isotope tracer approach.
ICP-MS allows multiple element isotopic tracers to be monitored simul-
taneously. For example, zinc metabolism in heathly women was investigated by
oral ingestion of a 67Zn trace and an intravenous (i.v.) tracer highly enriched in
70Zn. Ratios of 67Zn to 66Zn and 7OZn to 66Zn in plasma, urine, and feces were
determined to trace the Zn from the oral and i.v. sources independently.

Plant Analysis
Uptake of elements by plants is important in understanding essential nutrients for
plants, potential health concerns for humans and animals that eat the plants, and
use of plants as a remediation agent to remove toxic elements from soils, The
uptake of heavy metals by wheat from fertilizers and sewage sludge applied to
agricultural lands was investigated by using ICP-MS [263].
Wet and dry ashing sample preparation procedures for plant materials and
subsequent analysis by ICP-MS have been assessed [264]. Closed vessel micro-
be
wave digestion nitric acid and added hydrogen peroxide can often employed for
~ssolution of plant materials [265]. H202 helps to allow a higher temperature to
be maintained without excessive pressure buildup as well as reduce the carbon
to
content in the sample. However, impurities in the hydrogen peroxide can degrade
detection limits for some elements [265]. Ultrasonic slurry sampling ETV-ICP-
MS was used to measure Ge, As, Se, Cd, and Pb in plant tissues [266].
Plants such as mung bean seedlings can be used as bioindicators for toxic
elements such as As [26’7]. Analysis of tree rings can provide information on
short-term variations in pollution sources [268]. Elemental “fingerprints” have
also been used to identify sources of plants, including cannabis [269].