Multi-element Analysis of Food by Microwave Digestion and Inductively Coupled Plasma-Atomic Emission Spectrometry

This paper reviews techniques for determining B concentration and isotopic ratio and their application to soil and plant samples. Boron concentration has been determined utilising spectrophotometry, potentiometry, chromatography, flame atomic emission and absorption spectrometry, inductively coupled plasma (ICP) optical emission (OES) and mass spectrometry (MS), and neutron activation analysis using neutron radiography and prompt-γ activation analysis. Isotopic ratios of B have been measured by ICP–MS, thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS). For isotopic measurements, TIMS and SIMS are more sensitive and provide higher degrees of accuracy and resolution than ICP–MS, however, extensive sample preparation and purification, and time-consuming measurements limit their usefulness for routine analyses.

Techniques for boron determination and their application to the analysis of plant and soil samples

A boron-containing compound was administered to tumor-bearing mice and the time-dependent concentration was determined by ICP-AES, ICP-MS and quantitative neutron capture radiography (QNCR). The atomic spectrometric procedures were optimized to minimize analyte losses during microwave digestion. Non-spectroscopic interferences were investigated in detail and appropriate internal standards were established for ICP-MS. The best detection limits achieved for boron were 30 ng ml–1 by ICP-AES and 0.3 ng ml–1 by ICP-MS. The respective determination limits in the digested and diluted tissue samples were 0.4 µg ml–1 and 3 ng ml–1. The results of the spectrometric determinations were confirmed by QNCR of whole-body cryosections of six mice. A brief description of the metabolism of the boron compound is given.

Comparison of Inductively Coupled Plasma Atomic Emission Spectrometry and Inductively Coupled Plasma Mass Spectrometry With Quantitative Neutron Capture Radiography for the Determination of Boron in Biological Samples From Cancer Therapy

Analytical fractionation of silicon compounds in foodstuffs

Fourier transform (1)H-nuclear magnetic resonance (NMR) spectroscopy was suitable for the quantitative determination of polydimethylsiloxanes (PDMS) in wine and edible oil samples. This approach offers highly specific qualitative and quantitative analysis due to silicone-specific location of proton signals linked to carbon atoms located directly next to silicon atoms (0-0.5 ppm), as well as a different location of signals in the range for different organosilicon structures. The method can be used for the control of PDMS at regulatory limits in foodstuffs (10 mg kg(-1)) using hexamethyldisiloxane (HDMS) as an internal standard. Samples were prepared by extraction under suitable conditions to separate the analyte, and with analyte enrichment before (1)H-NMR analysis. Analytical procedures were developed to permit the determination of PDMS at 0.06 mg kg(-1) in wine and at 6 mg kg(-1) in edible oils samples using readily available NMR instrumentation. It was, however, possible to lower the limit of detection to 6 microg kg(-1) for wine and to 60 microg kg(-1) for edible oils using a higher field instrument (500 MHz). Relative standard deviations (S(r)) were obtained for wine (0.028) and for oil samples (0.043), which when compared with values obtained for samples spiked with PDMS (0.021) indicated that the sample preparation was the main factor determining the precision of the method. The average recovery rates for PDMS were 97 and 95% for wine and edible oils, respectively. PDMS was detected in four brands of Italian wine, with Chianti-Rafaello containing the highest concentration (0.35 mg kg(-1)), and in four types of edible oils, highest concentration (11.9 mg kg(-1)) being found in Italian corn oil. None of the levels of PDMS found in the food samples exceeded the permissible standards laid down by the Codex Alimentarius Commission (10 mg kg(-1)), with the exception of the one corn oil sample.

Determination of polydimethylsiloxanes by 1H-NMR in wine and edible oils

Samples of raw noodles in a mixture of nitric acid and hydrogen peroxide were microwave digested in sealed tetrafluoromethaxil (PTFE TFM) vessels. The digests were diluted to volume with distilled water and quantitated by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The recoveries of boron for spikes of 2.5, 250, and 500 micrograms were 88, 101, and 102%, respectively. The quantitation limit was estimated to be 1.5 mg B/kg. The method is rapid and ideally suited to large numbers of samples.

Jurgen L Kacprzak

Papers

Microwave digestion-inductively coupled plasma atomic emission spectrometric determination of boron in raw noodles.

Atomic Absorption Spectroscopic Determination of Dimethylpolysiloxane in Juices and Beer