Food analysis coupled technique

Coupled LC-LC can separate high-boiling petroleum residues into groups of saturates, olefins, aromatics and polar compounds. However, the lack of a suitable mass-sensitive, universal detector in LC makes quantitation difficult SFC-SFC is more suitable for this purpose. Applications of multidimensional HPLC in food analysis are dominated by off-line techniques. MDHPLC has been exploited in trace component analysis (e.g. vitamin assays), in which an adequate separation for quantitation cannot be achieved on a single column [972]. LC-LC-GC-FID was used for the selective isolation of some key components among the irradiation-induced olefinic degradation products in food, e.g. dienes and trienes [946],... 

Figure 16.1. Coupled techniques used in speciation analysis of foods.

In the field of food analysis, milk was the real matrix in which several metabolites have been analysed by the use of the microdialysis sampling technique. Acetylcholine, glucose and glutamate were analysed by Yao et al. [189], coupling a microdialysis probe with an on-hne enzymatic reactor and a Pt electrode coated with a 1,2-diaminobenzene polymer. 

Treatment of ICPAES from different perspectives and to varying degrees of comprehensiveness appears in a number of chapters in volumes not solely dedicated to ICP-AES, but treating spectrometry and analysis in general. An early excellent chapter on ICP-AES is by Tschopel (1979) on plasma excitation in spectrochemical analysis, in Wilson and Wilson s Comprehensive Analytical Chemistry. A very brief historical introduction to ICP-AES, basic principles and considerations of absorption and emission lines, and applications to food analysis is in a book on modern food analysis (Ihnat (1984), and Van Loon (1985), in his practical analyst-oriented book on selected methods of trace analysis biological and environmental samples includes a chapter (pp. 19-52) on techniques and instrumentation including ICPAES. Moore (1989) (Introduction to Inductively Coupled Plasma Atomic Emission Spectrometry) provides... 

The most commonly used methods for speciation analysis of iodine in tissues and food are chromatographic techniques, such as anion exchange, size exclusion and reverse-phase chromatography, coupled with ICP-MS detection. 

It is also expected that applications of multidimensional LC x LC techniques in food analysis will continue to grow. These techniques provide extraordinary gains in separation power that make them ideal for the analysis of complex matrices such as foods. Although the coupling of different chromatographic separations is not new, the technological development has led, above all, to an increase of comprehensive applications, in which the whole sample is analyzed in two independent dimensions, reducing the sample preparation steps. 

Supercritical fluid extraction as a sample preparation technique in food analysis has become increasingly popular in recent years. The usefulness of using supercritical fluids to investigate wine aroma has been demonstrated by both offline SFE and coupled SFE-GC [13]. 

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

HPLC has been recommended as a cleanup and fiactionation procedure for food samples prior to analysis by GC/ECD (Gillespie and Walters 1986). The advantages over the AOAC-recommended Florisil colunrn are that it is faster, requires less solvent, and gives better resolution. HPLC coupled with various detectors MS, MS/MS, UV/electrochemical detector, or UV/polarographic detection has been tested as a rapid, simplified separation and detection system to replace GC (Betowski and Jones 1988 Clark et al. 1985 Koen and Huber 1970). Recoveries, detection limits, and precisions were generally good, but further work is needed before the techniques are adopted for general use. 

High performance spectroscopic methods, like FT-IR and NIR spectrometry and Raman spectroscopy are widely applied to identify non-destructively the specific fingerprint of an extract or check the stability of pure molecules or mixtures by the recognition of different functional groups. Generally, the infrared techniques are more frequently applied in food colorant analysis, as recently reviewed. Mass spectrometry is used as well, either coupled to HPLC for the detection of separated molecules or for the identification of a fingerprint based on fragmentation patterns. ... 

Applications SFE-SFC solves problems in such diverse areas as polymers/monomers, oils/lubricants, foods, pharmaceuticals, natural products, specialty chemicals, coatings, surfactants and others. Off-line SFE-SFC survives alongside on-line determinations of additives, because of the need for representative sample sizes. Off-line SFE-SFC was used for extraction of AOs from PP [102]. In cases where the analyst wishes to perform further analysis on the extracted species, it is useful to be able to isolate the extract from the solvent. The ability to remove the solvent easily is particularly important when SFE is coupled on-line to chromatographic techniques, but is equally important for trace analysis when it is useful to concentrate... 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

On-line NPLC-GC-FID and/or FUR analysis has been used in discriminating between paraffin waxes and paraffin oils present in, or migrating between, food packaging and food simulants FID was used for quantitation [967]. In a typical application, online coupled LC-GC-F1D has also been used for the analysis of food contamination by mineral oil from printed cardboard [968]. The technique has revealed that many foods are contaminated with mineral oil products. Grob et al. [969] have determined mineral oil in canned food by on-line LC-LC-GC-F1D. DEHP was determined in salad oil by means of conventional LC-GC [970]. HPLC-GC-MS/MS (ion trap) can serve highly useful purposes in areas of applications such as impurity... 

As in the case in the analysis of food samples, the introduction of relatively inexpensive MS detectors for GC has had a substantial impact on the determination of methylxanthines by GC. For example, in 1990, Benchekroun published a paper in which a GC-MS method for the quantitation of tri-, di-, and monmethylxanthines and uric acid from hepatocyte incubation media was described.55 The method described allows for the measurement of the concentration of 14 methylxanthines and methyluric acid metabolites of methylxanthines. In other studies, GC-MS has also been used. Two examples from the recent literature are studies by Simek and Lartigue-Mattei, respectively.58 57 In the first case, GC-MS using an ion trap detector was used to provide confirmatory data to support a microbore HPLC technique. TMS derivatives of the compounds of interest were formed and separated on a 25 m DB-% column directly coupled to the ion trap detector. In the second example, allopurinol, oxypurinol, hypoxanthine, and xanthine were assayed simultaneously using GC-MS. 

In this chapter, the main analytical techniques and the methods currently employed in industrial and research laboratories for the analysis of important classes of additives are reviewed. The use of both gas chromatographic and liquid chromatographic methods coupled with mass spectrometry features prominently. Such methodology enables the sensitive and specific detection of many types of organic additives in polymeric materials to parts per billion (jig/kg) levels. Much of the development of these methods has been undertaken as part of research into the migration or extraction of species from food-contact and medical materials [5-7], This chapter also includes some discussion on the analysis of residual monomers and solvents. 

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