Digestion of biological sample

Urine samples for Pb and Cd analysis were digested with H O, (50%, stabilized, from Fisher) and HNO3 (67-70%, double sub-boiling quartz-distilled in Teflon bottles, NIST) to destroy most of the organic material present. Initially, the urine sample (1 mL) was treated with concentrated HNO3 and was allowed to stand at room temperature for about 1 h. The specimen was subsequently heated at 50 °C on a hot-plate to reduce the volume 

The simpler method for blood Pb required 200 pL from a whole blood sample drawn into a metal-free tube containing EDTA as an anticoagulant. This sample is mixed with internal standard and vortex mixed briefly. Then, with gentle vortex mixing, 400 pL of 4 m HNO3 are added dropwise. The sample is centrifuged at 1760 g for 10 min and the supernate transferred to a clean tube. The pH is adjusted to 7-9 with concentrated NH4OH. This solution is then ready for the chelate preparation step. 

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Two methods were examined for digestion of biological samples prior to trace element analysis. In the first one a nitric acid-hydrogen peroxide-hydrofluoric acid mixture was used in an open system, and in the second one nitric acid in a closed Teflon bomb. The latter method was superior for Ge determination, however, germanium was lost whenever hydrogen fluoride had to be added for disolving sihcious material. End analysis by ICP-AES was used for Ge concentrations in the Xg/g range13. 

C. Y. Zhou, M. K. Wong, L. L. Koh, Y. C. Wee, Microwave digestion of biological samples with tetramethylammonium hydroxide and ethylenediaminetetraacetic acid for element determination, Talanta, 43 (1996), 1061D1068. 

Kojima, I., Uchida, T., lida, C. Pressurized microwave digestion of biological samples for metal determination. Anal. Sci. 4, 211-214 (1988)... 

Graber, C., Bemdt, H. Development of a new high temperature/high pressure flow systems for the continuous digestion of biological samples. J. Anal. At. Spectrom. 14,683-691 (1999)... 

The greatest advantage of on-line digestion methods over batch methods is that they minimize the problem of acid fumes produced during the digestion of biological samples in the traditional Teflon vessels used in batch treatments. Gas evolution in the on-line methods, however, can lead to problems resulting in pressure build-up and disturbances... 

The ability of microwaves to heat water very fast was discovered during the Second World War and the first application of microwaves in the field of sample preparation was described in 1975. Microwave energy was used for the digestion of biological samples in Erlenmeyer flasks. The digestion time was decreased from 1-2 hours to 5 min to 15 min. 

Although this survey is focused upon methods for analysis of biological samples, it will also, to some extent, touch upon methods so far only described for analysis of aqueous solutions, but which may be applicable to wet digests of biological samples. On the other hand, it is out of the scope of this survey to cover all of the huge number of methods published during the last decades. 

Today atomic spectrometric methods are sufficiently sensitive and selective so that they are the method of choice for the determination of beryllium. These techniques can be applied directly to acid digests of biological samples. Electrothermal atomization is better suited than flame atomization for the determination of the low concentrations of beryllium usually found in clinical specimens. A review of different techniques for the atomic spectrometric determination of beryllium was recently published [32]. 

The method described may be adapted to a wide range of biological samples and food-stuff s. It may be found necessary to warm the sample in concentrated HNO3 to effect complete digestion, and also to use rather more HNO3 than that recommended above. 

A microwave-heated, flow-through digestion container (coiled Teflon tubing) was design for a commercial (Prolabo A300) focused microwave system (instead of microwave oven) and applied to the on-line preparation of biological samples, including milk, blood, and urine [108]. 

Heltai, G., Percsich, K. Moderated pressure microwave digestion system for preparation of biological samples. Talanta 41, 1067-1072 (1994)... 

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