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Sample preparation and extraction of analytes
JOURNAL
OF FOOD COMPOSITION
AND ANALYSIS
3, 103-104
(1990)
EDITORIAL Sample Preparation
and Extraction
of Analytes
Recent research studies in analytical chemistry have focused on the development of new instrumentation for the separation and detection of analytes, on the use of computers for instrument control and data acquisition, and on the new field of chemometrics. The current state of the art in GLC, HPLC, supercritical fluid chromatography, capillary electrophoresis, atomic absorption and atomic plasma emission spectrophotometry, mass spectrometry, diode array spectrophotometry, various electrochemical detectors, fluorescent detectors, the hyphenated techniques (i.e., GLCmass spectrometry, etc.), artificial intelligence, pattern recognition, and signal conditioning is impressive. All these techniques have the potential to be useful to the food analyst. Similar significant advances have been made in analytical biochemistry and molecular biology. Major advances have been made in the development of highly selective and sensitive probes, particularly in the use of immune-reagents and DNA and RNA probes. Significant improvements have been made in the use of enzymes as reagents and of enzyme amplifier systems. ELISA systems which couple the sensitivity of enzyme assays with the selectivity of the immune systems show considerable potential of becoming the assay system of choice for some food assays. Reports are now being published wherein the new advances in analytical biochemistry, molecular biology, and analytical chemistry have been combined to yield very powerful analytical tools. The sequencing of genes is now possible because of the powerful tools generated by this combination of advanced techniques. Other analytical milestones can be expected from the combination of such advanced techniques. The assay of foods should benefit from the development of these types of advanced techniques. Almost all the advanced techniques described above require clean samples free of interfering compounds. For the most part, it is best if the analytes are dissolved in clear solutions which are themselves compatible with the separation and detection components of the assays. These advanced techniques are perfect for the assay of pure standards or the assay of mixtures of pure standards. Unfortunately, most food samples do not come in such tidy packages. On the contrary, most foods are mixtures of multiphase materials with extremely complex chemical matrices. Before analysts can use today’s marvelous array of analytical tools, they first must extract the analyte from the food sample. However, the development of adequate analyte extraction techniques has lagged far behind the other analytical components of food analysis. Thus those wishing to use the modern analytical tools described above frequently find that the companion sample preparation and extraction techniques are inadequate, untested, or nonexistent. One might say that what are really needed are holistic extraction techniques or maybe even holistic assay techniques. Basically what are needed are extraction procedures that are quantitative and are compatible with the rest of the assay systems. In an ideal extraction procedure the analyte is quantitatively removed from the food 103
OSSS-1575/90$3.00 Copyright 0 1990 by Academic Press, Inc. All n&s of reproduction in any form reserved.
104
EDITORIAI
sample, no analyte remains with the residue, and none is destroyed by the extraction procedure or the inherent biochemical and chemical activities of the sample and of the postextraction conditions. The extract should not contain compounds that would interfere with the separation and detection components of the assays. For example if chromatographic separations are to be used, then the food extract should not contain components which co-elute with the analytes or those which alter the chromatographic behavior of the analytes. If immune reactions and/or enzyme detection systems are used, then components which alter the enzymatic and/or immune reactions are not acceptable. Given the complexity and variability of food matrices, quality control procedures for the extraction steps should be required parts of most assays. Certainly, the sample preparation and extraction procedures should be critically reviewed before they are used or published in reputable scientific journals. It is likely that the development of such sample preparation and extraction systems will require as much effort as the development of the chromatography and detection portions of the assays. Thus it is as appropriate to do research on this branch of analytical biochemistry/chemistry as it is to do studies on separation and detection techniques. Others have recognized these priorities and the Journal has recently published several manuscripts which have dealt specifically with the problems of sample preparation and extraction. Much more published research work in this field is needed. I hope that those working on food analysis will accept the challenge. KENT K. STEWART Blacksburg,
Virginia,
C;.S.A.
OF FOOD COMPOSITION
AND ANALYSIS
3, 103-104
(1990)
EDITORIAL Sample Preparation
and Extraction
of Analytes
Recent research studies in analytical chemistry have focused on the development of new instrumentation for the separation and detection of analytes, on the use of computers for instrument control and data acquisition, and on the new field of chemometrics. The current state of the art in GLC, HPLC, supercritical fluid chromatography, capillary electrophoresis, atomic absorption and atomic plasma emission spectrophotometry, mass spectrometry, diode array spectrophotometry, various electrochemical detectors, fluorescent detectors, the hyphenated techniques (i.e., GLCmass spectrometry, etc.), artificial intelligence, pattern recognition, and signal conditioning is impressive. All these techniques have the potential to be useful to the food analyst. Similar significant advances have been made in analytical biochemistry and molecular biology. Major advances have been made in the development of highly selective and sensitive probes, particularly in the use of immune-reagents and DNA and RNA probes. Significant improvements have been made in the use of enzymes as reagents and of enzyme amplifier systems. ELISA systems which couple the sensitivity of enzyme assays with the selectivity of the immune systems show considerable potential of becoming the assay system of choice for some food assays. Reports are now being published wherein the new advances in analytical biochemistry, molecular biology, and analytical chemistry have been combined to yield very powerful analytical tools. The sequencing of genes is now possible because of the powerful tools generated by this combination of advanced techniques. Other analytical milestones can be expected from the combination of such advanced techniques. The assay of foods should benefit from the development of these types of advanced techniques. Almost all the advanced techniques described above require clean samples free of interfering compounds. For the most part, it is best if the analytes are dissolved in clear solutions which are themselves compatible with the separation and detection components of the assays. These advanced techniques are perfect for the assay of pure standards or the assay of mixtures of pure standards. Unfortunately, most food samples do not come in such tidy packages. On the contrary, most foods are mixtures of multiphase materials with extremely complex chemical matrices. Before analysts can use today’s marvelous array of analytical tools, they first must extract the analyte from the food sample. However, the development of adequate analyte extraction techniques has lagged far behind the other analytical components of food analysis. Thus those wishing to use the modern analytical tools described above frequently find that the companion sample preparation and extraction techniques are inadequate, untested, or nonexistent. One might say that what are really needed are holistic extraction techniques or maybe even holistic assay techniques. Basically what are needed are extraction procedures that are quantitative and are compatible with the rest of the assay systems. In an ideal extraction procedure the analyte is quantitatively removed from the food 103
OSSS-1575/90$3.00 Copyright 0 1990 by Academic Press, Inc. All n&s of reproduction in any form reserved.
104
EDITORIAI
sample, no analyte remains with the residue, and none is destroyed by the extraction procedure or the inherent biochemical and chemical activities of the sample and of the postextraction conditions. The extract should not contain compounds that would interfere with the separation and detection components of the assays. For example if chromatographic separations are to be used, then the food extract should not contain components which co-elute with the analytes or those which alter the chromatographic behavior of the analytes. If immune reactions and/or enzyme detection systems are used, then components which alter the enzymatic and/or immune reactions are not acceptable. Given the complexity and variability of food matrices, quality control procedures for the extraction steps should be required parts of most assays. Certainly, the sample preparation and extraction procedures should be critically reviewed before they are used or published in reputable scientific journals. It is likely that the development of such sample preparation and extraction systems will require as much effort as the development of the chromatography and detection portions of the assays. Thus it is as appropriate to do research on this branch of analytical biochemistry/chemistry as it is to do studies on separation and detection techniques. Others have recognized these priorities and the Journal has recently published several manuscripts which have dealt specifically with the problems of sample preparation and extraction. Much more published research work in this field is needed. I hope that those working on food analysis will accept the challenge. KENT K. STEWART Blacksburg,
Virginia,
C;.S.A.