Acid-digestion of plant materials

Mortatti et al. [16] has described a method for the determination of total iron in extracts of perchloric acid-nitric acid digests of plant materials. Their method involves flow injection analysis of the 1 10 phenanthroline complex. 

This element has been determined in perchloric acid digests of plant materials by a spectrophotometric procedure as permanganate ion obtained by oxidation with periodic acid or by AAS using the 279.5 nm emission line [28]. 

J.W.B. Stewart, J. Ruzicka, Flow injection analysis. Part V. Simultaneous determination of nitrogen and phosphorus in acid digests of plant material with a single spectrophotometer, Anal. Chim. Acta 82 (1976) 137. 

J. W. B. Stewart and J. Rdiidka, Flow Injection Analysis. Part V. Simultaneous Determination of Nitrogen and Phosphorous in Acid Digests of Plant Material with a Single Spectrophotometer. Anal. Chim. Acta, 82 (1976) 137. 

A comparison of different mineral acids for wet digestion of plant material for AAS analysis was carried out by Dokiya et al. (1975), who concluded that nitric acid was best for the determination of Cu, Mn and Pb by flameless AAS, whereas a nitric sulphuric mixture was best for Fe, Mn, Cu and Zn by FAAS. Most literature reports dissolve plant material in nitric acid (Middleton and Stuckey, 1954) or in nitric and perchloric acids (Isaac and Johnson, 1975 Williams, 1978, Thompson and Wood, 1982). This method will not dissolve aluminium containing particles from soil or other contaminations (Pierson and Evenson, 1988 Ramsey et al., 1991) (see also Standard Reference Materials). 

G. C. L. Araujo, M. H. Gonzalez, A. G. Ferreira, A. R. A. Noggueira, J. A. Nobrega, Effect of acid concentration on closed-vessel microwave-assisted digestion of plant materials, Spectrochim. Acta, 57B (2002), 2121-2132. 

An official method has been published for the determination of magnesium in plant material [27]. A hydrochloric acid digest of the sample is treated with strontium chloride perchloric acid releasing agent and magnesium is determined by AAS using the 285 nm emission line. See Sect. 7.34.1. 

For trace metals other than those described above, it is necessary to use larger samples of plant material. Often digestion with nitric acid, followed by perchloric acid is used to digest upto 2 g of plant tissue, with final dilution to 25 ml. This allows determination of elements such as nickel by flame AAS. However, great care is necessary when using perchloric acid because of the explosion risk. A suitable, wash-down fume hood should be available, or at least an efficient fume scrubbing system. 

Nickel is determined more often, and with better sensitivity, by flame AAS than by flame AFS or AES techniques, even when a nitrous oxide-acetylene flame is employed in AES. The AAS detection limit at 232.0 nm under carefully optimized conditions in an oxidizing air-acetylene flame is about 10 ng ml-1, which is adequate for those environmental applications where a low sol-ution-to-sample weight ratio may be used. For example, if 1 g of plant material is digested with a mixture of nitric acid plus perchloric acid, and the mixture diluted only to 10 ml, nickel may be determined directly by flame AAS. Similarly the... 

S. Wu, X. Feng, A. Wittmeier, Microwave digestion of plant and grain reference materials in nitric acid or a mixture of nitric acid and hydrogen peroxide for the determination of multielements by inductively coupled mass spectrometry, J. Anal. Atom. Spectrom., 12 (1997), 797-807. 

Knight MJ (1980) A Comparison of Four Digestion Procedures not Requiring Perchloric Acid for the Trace-Element Analysis of Plant Material. Argonne National Laboratory, Report ANL/LRP-TM-18, pp. 1-27, Argonne, IL. 

Feng, X., Wu, S., Wharmby, A., and Wittmeier, A., "Microwave Digestion of Plant and Grain Standard Reference Materials in Nitric and Hydrofluoric Acids for Multi-Elemental Determination by Inductively Coupled Plasma Mass Spectrometry," J. Anal. At. Spectrom., 14,1999, pp. 939-946. 

Zarcinas BA, Cartwright B, Spounser LR (1987) Nitric acid digestion and multi-element analysis of plant material by inductively coupled plasma spectrometry. Conunon Soil Sci Plant Anal 18 131-146... 

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