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The PE 2400 is a conventional elemental analyzer. It operates by flash
combustion of the specimen encapsulated in tin cups or disks whereby the
specimen is completely combusted at a temperature of 1760 °C. The resulting
gases are chemically scrubbed of the halogens (and of sulfur in the CHN
mode) and are separated in a GC column. Detection is conducted by a thermal
conductivity detector (TCD). Total C, H, and N are calculated with a
precision of 0.1µg. Element ratios are more significant since they minimize
instrument error. Molar element ratios may be reliably reported for up to
three decimal places.
Specimen size is limited by the total carbon content. The analyzer is
optimized to handle 1–2 mg specimens with a total carbon content
between 80 and 200 µg total carbon. The specimens should be ground to the
consistency of talc and well homogenized (a grinding mill is available).
Fibrous materials, such as roots, may need to be frozen down to cryogenic
temperatures to facilitate successful grinding. Liquid samples of 5 µl size
may either be freeze dried or, more conveniently, absorbed in an inert
material in tin capsules. Solid samples may be weighed (to 1µg) with a
micro balance interfaced to the analyzer. Glass filters need to be rolled
very compactly in tin disks to minimize jamming the injector.
A 66 position auto sampler allows programming of the analyzer for batch
runs of capsule samples. However, filter samples must be introduced
manually, one at a time. Normally, a combination of at least 10-12 blanks,
standards, and standard checks must be run before samples are analyzed.
Each run takes approximately six minutes and every batch of ten samples is
bracketed by a reference and a blank run. Analysis cost does not include
tin capsules, tin disks, or glass filters.
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