Stable isotope techniques for assessing labile Cu in soils: development of an L-value procedure, its application, and reconciliation with E values

Isotopic techniques have become a valuable tool for assessing the lability or potential availability of elements in soil. Until now, work on soil Cu has been limited to E-value methods where soil solution extracts are obtained by physical means due to the very short (12.4 h) half-life of the radio isotope 64Cu. However, a stable isotope method has recently been developed for determining soil Cu E values that utilizes enhancement of the 65Cu isotope in soil and measurement of the subsequent ratio with 63Cu. We have developed an L-value technique for soil Cu, where plants are used to sample the soil solution and therefore give a direct measure of the plant available Cu. The L-value technique developed was then compared, and found to be equivalent, with E values using equilibration periods up to and including the growth period of plants in the L-value method.     

Evauation of lysinoalanine determinations in food proteins

Summary A comparison is made between lysinoalanine (LAL) determinations both with an automatic amino acid analyzer (AAA) and with thin layer chromatography-densitometry (TLC) in different types of food and food ingredients, taken from the Dutch market.Generally there is a reasonable agreement between the LAL content obtained by both methods. However, some results indicate that a single technique is not always conclusive about the real identity of the ninhydrin-positive compound at the same position as LAL on the chromatogram. By TLC for instance, in yeast a content of about 800 mg of LAL/kg in protein is found, but according to the AAA method no LAL is present. In heated milk and milk products the LAL content determined by the TLC method is also higher than that found by the AAA method.This is caused by a preceding unknown ninhydrinpositive compound in TLC, occurring in all heated milk products and practically coinciding with LAL. In the AAA technique similar interferences of unknown ninhydrin-positive compounds could be avoided by choosing a suitable elution temperature; however, application of this temperature modification to foaming agents gave no satisfactory results.

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Auswertung von Lysinoalaninbestimmungen in Lebensmittelproteinen

Zusammenfassung Um zwei Bestimmungsmethoden von Lysinoalanin (LAL) miteinander zu vergleichen, wurden Analysen sowohl mit einem automatischen. Aminosäureanalysator als auch mit Dünnschichtchromatographie-Densitometrie, mit verschiedenen in den Niederlanden käuflichen Lebensmitteltypen und Ingredienten durchgeführt.Daraus ergibt sich eine ziemlich gute Übereinstimmung im LAL-Gehalt nach beiden Methoden. Einige Resultate deuten jedoch darauf hin, daß eine einzelne Methode nicht immer eindeutig ist, was die Identität der auf Ninhydrin positiv reagierenden Verbindung, bei gleicher Position im Chromatogramm als LAL angesprochen, betrifft.In Hefe z. B. fand man mit Dünnschichtchromatographie einen Gehalt von etwa 800 mg LAL/kg Protein, mit dem Aminosäurenanalysator jedoch kein LAL. Auch in erhitzter Milch und Milchprodukten ist der LAL-Gehalt, bestimmt mit Dünnschichtchromatographie, höher als der mit dem Aminosäurenanalysator gefundene Wert. Die Ursache ist, daß bei der Dünnschichtchromatographie von erhitzten Milchprodukten eine unbekannte auf Ninhydrin positiv reagierende Verbindung dem LAL-Fleck vorangeht, der praktisch mit dem LAL zusammenfällt. Um Störung durch unbekannte Verbindungen dieser Art beim Aminosäurenanalysator zu vermeiden, kann man eine geeignete Elutionstemperatur wählen. Bei einigen Schaummitteln jedoch erhält man durch Temperaturveränderung keine gute Trennung.

     

Spectroscopic techniques coupled with chemometric tools for structure and texture determinations in dairy products

Structure conditions both textural and flavour properties of cheeses and dairy products. Until recently, delineating the structure of the food matrices and the interactions between components in dairy products has been impaired by the lack of techniques. More and more evidence shows that front face fluorescence spectroscopy and attenuated total reflection infrared spectroscopies may be valuable techniques. These spectroscopic techniques remove methodological locks and allow the structure at molecular level and the dynamics of “real dairy products” to be investigated.Over the last few years, we gave most of our interest to the delineation of the molecular structure of dairy products and to the understanding of the relationships between structure and texture in cheese. The analysis of large spectral collections recorded for dairy products using multivariate analysis techniques such as principal component analysis, factorial discriminant analysis and canonical correlation analysis makes it possible to extract relevant information related to the molecular structure of proteins and fats in semi-hard cheeses, the interactions between dairy product components and the relation between structure and texture of soft and semi-hard cheeses. The presented data show that the texture of a dairy product is a reflection of its structure at the molecular level.     

Proposal of new analytical procedures for heavy metal determinations in mussels, clams and fishes

New analytical procedures and sample mineralizations for the determination of copper, lead, cadmium, zinc and mercury in matrices such as mussels, clams and fishes are proposed. An H₂SO₄ HNO₃ acidic mixture was used for the determination of copper, lead, cadmium and zinc. In the case of mercury, the sample digestion was performed using a concentrated supra pure H₂SO₄ K₂Cr₂O₇ mixture and the results compared with those from other conventional methods. Differential pulse anodic stripping voltammetry (DPASV) was employed for simultaneously determining copper, lead, cadmium and zinc, while the mercury determination was carried out by cold vapour atomic absorption spectrometry (CV-AAS) with reduction with SnC₂, using an innovative method for sample dissolution. The analytical quality control procedures have been verified on three reference standard materials: Oyster Tissue NIST 1566, Mussel Tissue BCR-CRM 278 and Cod Muscle BCR-CRM 422. For all the elements in the certified matrices, the precision, expressed as relative standard deviation (s_r     

Correction

These notes have been prepared by Mr Bernard Faulks, the Technical Manager of Chichester Dairies (St Ivel). We think that they will be helpful to members who have, for the first time, been asked to give a paper to a Society meeting, and also to more experienced members who would like a check list to help them to put over their material more effectively. - Editor     

Effect of modifiers for As,Cu and Pb determinations in sugar-cane spirits by GF AAS

Palladium plus magnesium nitrates with and without Ir, Ru and W were evaluated for the simultaneous determination of As, Cu and Pb in cachaça by graphite furnace atomic absorption spectrometry. For 20 μL of sample, 5 μL Pd(NO₃)₂ and 3 μL Mg(NO₃)₂ dispensed together onto the Ir-coated platform of the THGA, analytical curves in the 0–30.0 μg L⁻¹ As, 0–1.50 mg L⁻¹ Cu and 0–60.0 μg L⁻¹ Pb were built up and typical linear correlation coefficients were always better than 0.999. The limit of detection was 1.30 μg L⁻¹ As, 140 μg L⁻¹ Cu and 0.90 μg L⁻¹ Pb. As, Cu and Pb contents in 10 cachaça samples agreed with those obtained by ICP-MS. Recoveries of spiked samples varied from 96% to 106% (As), 97% to 112% (Cu) and 92% to 108% (Pb). The relative standard deviation (n = 12) was typically 2.7%, 3.3% and 1.9%.