Report
to aid the process. I n wet digestion, liquid conditions are maintained throughout and the oxidation is car ried out by various oxidizing agents in solution, usually oxidizing acids. The relative merits of these oxi dation methods have been studied extensively (8—11). However, much conflict of opinion still remains as to which is to be preferred. M a n y in vestigators are convinced t h a t the ideal method for ashing biological material has yet to be devised. Thiers {12) states t h a t "there is no single procedure for wet ashing which will effectively handle a va riety of biological materials." D r y ashing is recommended for its sim plicity and relative freedom from positive errors and because large samples can be handled. W e t di gestion is considered superior in terms of rapidity, the low tempera tures maintained, and the freedom from loss by retention. The poten tial errors of dry oxidation are vol atilization of elements and losses by retention on the walls of the vessel. Adsorbed metals on the vessel m a y in turn contaminate future samples. The major error attributed to wet digestion is the introduction of im purities from the reagents necessary for the reaction. This problem has been minimized as commercial acids have become available in greater purity. For example, lead contam ination can be less t h a n 10 parts per billion (13). A mixture of nitric, sulfuric, and perchloric acids has been successfully used to digest samples for chromium analysis at the 10 ppb level. High purity acids are commercially available. G. F . Smith Co., for example, supplies acids distilled and stored in Vycor glass. Perchloric and sulfuric acids from this source have been found to be quite free from copper contami nation (14) • Gorsuch (10) has summarized from the literature the methods used by approximately 250 investigators for the destruction of organic m a t ter. W e t digestion and dry ashing procedures arc used about equally. Direct ashing is the most common method followed by wet digestion with nitric and sulfuric acids. Other methods include wet digestion with nitric, sulfuric and perchloric acids, with nitric and perchloric
Guaranteed resolution — 280 eV
FWHM
Δ . simultaneous, non contact, non destructive real time x-ray analyzer. Quite a mouthful. As implied, we are talk ing about an important technical innovation. Unlike conventional x-ray analysis, the new instrument simultaneously depicts curves for all elements in a speci men instead of one spectral line at a time. A low level radioactive source excites the sample and characteristic xrays are emitted by each element present. These x-rays are resolved by a semiconductor radiation detector and con verted into an x-ray energy histogram. T h e area under the individual spectral peaks is proportional to the a m o u n t of each element present. T h e technique is highly linear mak ing rapid identification of u n k n o w n elements possible. C o m p o n e n t flexibility permits installation in electron probe microanalyzers. Unlike conventional x-ray analyzers, the new system is compact, utilizes ordinary power outlets, is considerably faster and but a fraction of the investment. However, the resolution is not as good and only elements above atomic number 19 can be resolved and separated. For more information contact:
ANALYTICAL
kevex
CHEMISTRY DIVISION Kevex C o r p o r a t i o n , 898 Mahler Road, Burlingame, C a l i f o r n i a Telephone: (415) 697-6901 Circle No. 4 on Readers' Service Card
94010
VOL. 4 1 , NO. 1, JANUARY 1969
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