E. Jackwerth

Residues from biological materials after pressure decomposition with nitric acid : Part 1. Carbon conversion during sample decomposition

Abstract The degradation of biological sample materials with 69% nitric acid was studied at 180°C in closed PTFE crucibles. Of the organic matrix constituents present in significant concentrations in the biological samples, merely some amino acids (phenylalanine, histidine, tryptophan, methionine) and the double unsaturated fatty acid linoleic acid provide residues of organic compounds which cannot be volatilized at temperatures of up to 130°C. All other constituents of biological materials are either completely mineralized or occur in such low concentrations that their degradation products do not make a significant contribution to the organic residue. The influence of nitrogen dioxide on the success of decomposition is shown. Indications of the mechanism of the degradation reactions are discussed.

Residues from biological materials after pressure decomposition with nitric acid part 2. identification of the reaction products

Abstract During the degradation of biological materials under pressure with 69% nitric acid at 180°C the organic matrix constituents are completely mineralized, with a few exceptions. Apart from sample constituents that occur in such low concentrations that their degradation products do not make a significant contribution to the organic residue, only five substances provide residues of organic compounds that cannot be volatilized at temperatures up to 130°C. On the basis of IR and NMR spectra and results from further analytical studies, it is shown that the phenylalanine contained in the biological sample reacts to give a mixture of isomeric nitrobenzoic acids, histidine to give imidazole-4-carboxylic acid, linoleic acid to give cyclopropane-1,2-dicarboxylic acids and tryptophan to give a mixture of aromatic compounds. Methionine is oxidized to methanesulphonic acid and cystine and cysteine to sulphuric acid. The phosphorus fraction of organic matrix constituents is converted to phosphate in the course of decomposition.

Residues from biological materials after pressure decomposition with nitric acid : Part 3. Influence of reaction products on inverse voltammetric element determination☆

Abstract After the pressure decomposition of biological sample materials with 69% nitric acid at 180°C, organic decomposition products frequently remain, leading to interference effects during inverse voltammetric trace metal determination. It is shown by the example of the determination of Zn, Cd, Pb and Cu by inverse square-wave voltammetry that the interference signals are caused by the two-stage reduction of nitrated benzoic acids to amines at the mercury electrode. Nitrobenzoic acids arise in the degradation of phenylalanine during decomposition. In addition, they also cause, as do oxidation products of tryptophan, an increased current due to hydrogen deposition in the potential range of Zn oxidation. Decomposition solutions of biological materials free from phenylalanine and tryptophan, on the other hand, can be analysed by inverse voltammetry without any interference.

Probenvorbehandlungsstudien mit biologischen und Umweltmaterialien

SummaryThe efficiency of wet digestion with nitric acid at 320 °C by use of the high pressure asher published by Knapp [10] has been studied with a series of biological materials which usually are only incompletely decomposed by pressure digestion at 170 °C in PTFE vessels. For that purpose the residual carbon content of the digestion solution was determined by coulometry after combustion in an oxygen stream. The results verify a complete sample digestion already after digestion times of less than 3 h. By the example of bovine liver it is shown that the inverse voltammetric determination of zinc, cadmium, lead and copper is feasible without any subsequent oxidation by perchloric acid and is free of interferences.

Untersuchungen zur Kohlenstoffbilanz beim Aufschluß biologischer Probenmaterialien mit Salpetersäure

SummaryThe efficiency of wet decomposition methods by use of nitric acid for different biological sample materials was investigated. For that purpose the decomposition rates obtained by pressurized digestion or by digestion in open vessels were determined in dependence on the applied amount of oxidant, temperature and decomposition time. To calculate the decomposition rates the residual amounts of carbon remaining in the decomposed and evaporated samples were measured by coulometric titration of the carbon dioxide after combustion of the residues in a stream of oxygen. The results show that in most cases the sample decomposition with nitric acid remains incomplete even when the parameters are varied in wide ranges.ZusammenfassungAnhand unterschiedlicher biologischer Probenmaterialien wurde die Leistungsfähigkeit der Naßveraschung mit Salpetersäure untersucht. Dazu wurden die durch Druckaufschluß bzw. in offenen Gefäßen erzielten Aufschlußraten in Abhängigkeit von den Parametern Oxidationsmittelmenge, Temperatur und Zeit ermittelt. Zur Berechnung der Aufschlußraten wurde der Restkohlenstoffgehalt der Aufschlußrückstände nach Verbrennen im Sauerstoffstrom als CO2 coulometrisch titriert. Die Ergebnisse zeigen, daß der Aufschluß mit Salpetersäure innerhalb weiter Grenzen der Parameter in fast allen Fällen unvollständig bleibt.

Zur Multi-Elementanreicherung aus eisenhaltigen Böden und Sedimenten

SummaryTraces of Ag, Bi, Cd, Co, Cu, Hg, In, Mo, Ni, Pb, Se, and Zn can be preconcentrated with recoveries Rs ⩾ 95% from soils and sediments of high iron content by collector precipitation with hexamethylene-ammonium-hexamethylenedithiocarbamate and with a small amount of the iron as a collector element. The trace concentrates are analyzed by AAS and XRF. The relative standard deviation of the combined method of sample decomposition, preconcentration and AAS determination (n = 12) is generally about 0.03; the limit of detection (3 s, n = 20) for different elements was found to be between 0.1 and 1 μg·g−1. The accuracy of the method was verified by certified standard material. The power of detection of XRF for the analysis of trace concentrates obtained from soils and sediments is only sufficient for some of the interesting elements.

Trace analysis to determine heavy metal load in lung tissue

SummaryA routine method to determine the presence of partly environmentally relevant trace elements Al, Be, Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in lung tissue is described. The stages of process are preparation of samples conforming to the analysis material, decomposition, and subsequent trace determination by atomic absorption spectrometry. The results obtained from 125 samples show that chemical analysis is an effective aid in identifying and substantiating occupational risks.

Systematic investigations of the multi-element preconcentration from copper by precipitation of the matrix as copper(I) oxide and copper(I) thiocyanate

Abstract Two methods for multi-element preconcentration from copper by reductive matrix precipitation are presented. In systematic investigations on the coprecipitation behaviour of Ag, Al, Au, Bi, Cd, Co, Cr, Fe, Ga, In, Mn, Mo, NJ, Pb, Sb, Se, Sn, Te and Zn during precipitation of the copper matrix as Cu 2 O or CuSCN, the separation parameters were optimized. By combination with a hexamethyleneammonium hexamethylenedithiocarbamate collector precipitation, a concentration of 8 elements (Cu 2 O precipitation) or 13 elements (CuSCN precipitation) in a small volume was achieved. The limits of detection of the procedures are, depending on the element, 0.1–5 μg g −1 for flame atomic absorption spectrometry (AAS) and 0.01–0.1 μg g −1 for graphite furnace AAS. The relative standard deviations are about 3%. The analytical performance of the procedures is compared with that of an electrolytic copper separation.

Zur Multi-Elementanreicherung aus Reineisen und reinen Eisenverbindungen

SummaryTraces of Bi, Cd, Co, Cu, Hg, In, Mo, Ni, Pb, Sb, Se, Sn, Te and Zn are preconcentrated with high recoveries from pure iron metal and iron compounds by collector precipitation with hexamethylene-ammonium-hexamethylenedithiocarbamate and with a small amount of the iron as a collector element. The trace concentrates are analyzed by AAS and ICP-MS. The relative standard deviation of the combined method of sample dissolution, trace preconcentration and flame-AAS determination (N=12) is generally about 0.03; the limit of detection (3 s; N=20) for the different elements was found to be between 0.1 and 1 Μg · g−1.

Comparison of different excitation methods for X-ray spectral analysis

ZusammenfassungDie verschiedenen Anregungsmethoden der Röntgenspektralanalyse mit Protonen, Photonen und Elektronen (PIXE, XRFA bzw. EPMA) werden hinsichtlich ihres Nachweisvermögens, ihrer Präzision und Genauigkeit verglichen. Die Beurteilung der jeweils optimierten Anregungsmethoden basiert auf praktischen Problemen der Spurenanalyse: auf der Analyse von Aluminium, von Blei und von Spurenkonzentraten aus Wasser und Glas. Für dicke homogene Proben erwies sich die XRFA wegen der sehr guten Stabilität der heutigen Geräte als überlegen. PIXE ist vorteilhaft anzuwenden, wenn dünne Proben vorliegen oder wenn eine Probenvorbereitung, wie z.B. eine chemische Voranreicherung, erforderlich ist, die zu einer zusätzlichen Streuung von ⩾ 1% führt, so daβ die hohe Stabilität der XRFA-Geräte nicht mehr zum Tragen kommt. EPMA ist sowohl PIXE als auch XRFA unterlegen, solange nicht die lokale Verteilung von Elementen zu ermitteln ist.SummaryThe different excitation methods of X-ray spectral analysis with protons, photons and electrons (PIXE, XRFA and EPMA, respectively) are compared with regard to detection power, precision and accuracy. The evaluation of the independently optimized excitation methods is based on practical problems of trace-analysis: on the analysis of aluminium, lead and trace-concentrate targets of water and glass. For thick homogeneous samples XRFA turned out to be the best method, because of the very high stability of modern instruments. PIXE is advantageous for thin samples and if some kind of sample preparation like chemical preconcentration is necessary which introduces an additional scatter of ⩾ 1%, so that the high stability of XRFA instruments is no longer effective. EPMA is inferior to both, PIXE and XRFA, in all cases, where information on the lateral distribution of the elements is of no interest.