Simultaneous determination of planar chlorobiphenyls and polychlorinated dibenzo-p-dioxins and -furans in Dutch milk using isotope dilution and gas chromatography—high-resolution mass spectrometry

A method is described for the simultaneous determination of planar chlorobiphenyls and dioxins in milk using isotope dilution and gas chromatography—high-resolution mass spectrometry (GC-MS). The method is based on gel permeation chromatography, alumina clean-up and carbon chromatography and is highly automated, making a high sample throughput possible. Data on recovery, accuracy and reproducibility of results obtained with quality control samples are presented. Data for both dioxins and planar chlorbiphenyls from the analysis of samples of Dutch milk from several areas in the Netherlands are also presented. Possible interference of the chlorobiphenyls in the determination of the dioxins in the GC-MS method is discussed.     

Evaluation of dialysis as a technique for the removal of lipids prior to the GC determination of ortho- and non-ortho-chlorobiphenyls, using 14C-labelled congeners.

Dialysis was evaluated as a non-destructive clean-up technique to isolate chlorobiphenyls (CBs) from fish-oil prior to further analysis. 14C-CBs were used to study the transfer processes of the CBs across polyethylene membranes. Single step processes using equilibrium dialysis were compared to a dynamic method of refluxing solvent. The dynamic method reduced the duration of the separation to 8 h. The transfer of CBs and the lipids was dependent on temperature and nature of the analyte with smaller molecules being dialysed substantially faster than larger molecules. An optimised dynamic method was used to compare the dialytic clean-up with a traditional method using sulfuric acid-impregnated silica for the determination of CBs in a laboratory reference material. Labelled recovery standards for each individual congener are recommended in combination with dialysis as a method for clean-up.     

Retention times of fifty one chlorobiphenyl congeners on seven narrow bore capillary columns coated with different stationary phases

Retention times of fifty one important chlorobiphenyl congeners have been determined on seven narrow bore GC columns coated with different stationary phases. The retention times of the chlorobiphenyls relative to tetrachloronaphthalene were plotted for different column combinations; the plots generated can be used to choose an optimum column combination for the multidimensional gas chromatographic separation of the chlorobiphenyls.     

Universal extraction/clean-up procedure for screening of pesticides by extraction with ethyl acetate and size exclusion chromatography

Size exclusion chromatography (SEC) is used as a clean-up procedure after extraction of pesticides with the compatible solvent ethyl acetate. Recoveries better than 90% are obained for oranochlorine and organophosphorus pesticides, fungicides and chlorobiphenyls from fats, fish oils, vegetables, fruits, cereals and liver. A comparison with other procedures is made. The use of a 10-mm i.d. SEC column provides the same limits of determination as those attainable with commercial systems by requires only 15% of the amount of solvents normally used.     

Spectral tolerance determination for multivariate optical element design

Recent reports from our laboratory have described a method for all-optical multivariate chemometric prediction from optical spectroscopy. The concept behind this optical approach is that a spectral pattern (a regression vector) can be encoded into the spectrum of an optical filter. The key element of these measurement schemes is the multivariate optical element (MOE), a multiwavelength interference-based spectral discriminator that is tied to the regression vector of a particular measurement. The fabrication of these MOEs is a complex operation that requires precise techniques. However, to date, no quantitative means of determining the allowable design/ manufacturing errors for MOEs has existed. The purpose of the present report is to show how the spectroscopy of a sample is used to define the accuracy with which MOEs must be designed and manufactured. We conclude this report with a general treatment of spectral tolerance and a worked example. The worked example is based on actual experimental measurements. We show how the spectral bandpass is defined operationally in a real problem, and how the statistics of the theoretical regression vector influence both the bandpass and the minimum tolerances. In the experimental example, we demonstrate that tolerances range continuously between 1 (totally tolerant) to approximately 10(-3) (0.1% T) in this problem.     

Comparison of the results for the analysis of individual chlorobiphenyl congeners in various interlaboratory exercises

A comparison is made between interlaboratory studies in which individual chlorobiphenyls (CBs) are measured in fish and sludge samples. The target coefficient of variation (CV(R)) between laboratories at CB levels of 0.01–1.0 mg/kg should be in the order of 20–30%. An improvement in the CV(R) is clearly shown in studies in which a learning program, paying attention to the optimization of gas Chromatographic operating conditions, is included. For standard solutions, where no interference problems of the matrix occur, excellent CV(R)s are obtained in the order of 6%. In fish oil CV(R)s of 10–30% and in sludge CV(R)s of 20–30% are reached.     

Resolution method for overlapping peaks based on the fractional-order differential

Equations between the differential order and the maximum of the fractional-order differential for the specified peak signals are developed based on the variation of the maximum of the specified peak signals at different orders. Also, equations between the differential order and the zero-crossing of the fractional-order differential of the specified peak signals are proposed according to the variation of the zero-crossing of the specified peak signals at different orders. Characteristic paramters of the Gaus- sian peak, Lorentzian peak, and Tsallis peak can be estimated using estimator I and estimator II which are obtained by the equations above. As a result, a new method is presented to resolve the overlapped peaks signal. Firstly, a fractional-order differential of the specified peak signals is obtained with the fractional-order differentiation filter. Then, characteristic paramters of the specified peak signals can be extracted using estimator I and estimator II. Finally, the Tsallis peak is used as a model to assign the overlapping peak signals correctly. Experimental results show that the proposed method is efficient and effective for the simulated overlapping peaks and detected overlapping voltammetric peak signals.     

Spectral tolerance determination for multivariate optical element design

Recent reports from our laboratory have described a method for all-optical multivariate chemometric prediction from optical spectroscopy. The concept behind this optical approach is that a spectral pattern (a regression vector) can be encoded into the spectrum of an optical filter. The key element of these measurement schemes is the multivariate optical element (MOE), a multiwavelength interference-based spectral discriminator that is tied to the regression vector of a particular measurement. The fabrication of these MOEs is a complex operation that requires precise techniques. However, to date, no quantitative means of determining the allowable design/ manufacturing errors for MOEs has existed. The purpose of the present report is to show how the spectroscopy of a sample is used to define the accuracy with which MOEs must be designed and manufactured. We conclude this report with a general treatment of spectral tolerance and a worked example. The worked example is based on actual experimental measurements. We show how the spectral bandpass is defined operationally in a real problem, and how the statistics of the theoretical regression vector influence both the bandpass and the minimum tolerances. In the experimental example, we demonstrate that tolerances range continuously between 1 (totally tolerant) to approximately 10^–3 (0.1% T) in this problem. Received: 21 August 2000 / Revised: 30 October 2000 / Accepted: 4 November 2000     

The method of introducing correction factors into parameters of atom-atom potentials of intermolecular interaction used for calculation of thermodynamic characteristics of adsorption

Different methods of introducing correction factors into parameters of atom-atom potentials of intermolecular interaction used for calculation of thermodynamic characteristics of adsorption by the semiempirical molecular statistical theory were compared. A method of isostructural fragments based on the application of the atom-atom potential corrected for the molecular fragment was suggested for introducing the correction factors. The advantages of this method were demonstrated for chlorobenzenes, chlorodioxines, and chlorobiphenyls. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 681–687, April, 2000.     

Study of the dependency of spectral radiance factor and colorimetric values on geometric tolerances

The CIE has recommended geometric tolerances for the illumination and collection of light in the measurement of reflectance and radiance factor for colorimetry. This investigation is a pilot study to examine the range of results obtained from the measurement of the radiance factor and colour of reflectance standards over these geometric tolerances.     

Validation of the Soleris E. coli method for detection and semi-quantitative determination of Escherichia coli in foods

The performance of the Soleris E. coli method was compared with that of the ISO 7251 most probable number (MPN) and detection reference methods for Escherichia coli. The Soleris E. coli method is a growth-based, rapid, automated system composed of temperature-controlled incubation chambers and photodiode-based optical detection devices for measurement of color changes in a prepared medium vial. A dilution of the test sample homogenate is inoculated directly into the vial. Products of E. coli metabolism alter the color of the medium over time, and this change is monitored by the Soleris instrument. The test is used in a dilute-to-specification or specification monitoring manner in which the result is positive or negative around a desired cutoff (in CFU/g) determined by the dilution and volume of sample homogenate added to the vial. Alternatively, the test is used for zero tolerance determinations (e.g., absence in 25 g) by performing an off-line pre-enrichment step followed by transfer of a portion of the pre-enrichment culture to the Soleris vial. Six E. coli strains originating from food sources were inoculated individually into six food commodities: frozen green beans, Echinacea powder, cocoa powder, sweetened condensed milk, pasteurized liquid egg, and shredded mozzarella cheese. Uninoculated samples were included in each trial. The results obtained by the ISO 7251 detection method and the Soleris E. coli method were shown to be in agreement by Chi-square analysis when the presence of E. coli was determined in 25 g of sample. Results from the Soleris E. coli dilute-to-specification method and the ISO 7251 MPN method were found to be in agreement by probability of detection statistical analysis. In inclusivity testing, 52 of 53 E. coli strains were detected within 24 h. Only a non-thermoduric strain of serotype O157:H43 was not detected. In exclusivity testing, all 31 strains tested produced negative results. Results of ruggedness experiments show that accurate results can be obtained even when the operating temperature of the Soleris instrument is set beyond normal tolerances. The internal and independent laboratory studies demonstrated that the Soleris E. coli method could be successfully utilized as an alternative to the reference methods, with a significant time savings of 2 to 3 days.     

Identification in residue analysis based on liquid chromatography with tandem mass spectrometry: Experimental evidence to update performance criteria

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is one of the most widely used techniques for identification (and quantification) of residues and contaminants across a number of different chemical domains. Although the same analytical technique is used, the parameters and criteria for identification vary depending on where in the world the analysis is performed and for what purpose (e.g. determination of pesticides, veterinary drugs, forensic toxicology, sports doping). The rationale for these differences is not clear and in most cases the criteria are essentially based on expert opinions rather than underpinned by experimental data. In the current study, the variability of the two key identification parameters, retention time and ion ratio, was assessed and compared against requirements set out in different legal and guidance documents. The study involved the analysis of 120 pesticides, representing various chemical classes, polarities, molecular weights, and detector response factors, in 21 different fruit and vegetable matrices of varying degrees of complexity. The samples were analysed non-fortified, and fortified at 10, 50 and 200 μg kg⁻¹, in five laboratories using different LC-MS/MS instruments and conditions. In total, over 135,000 extracted-ion chromatograms were manually verified to provide an extensive data set for the assessment. The experimental data do not support relative tolerances for retention time, or different tolerances for ion ratios depending on relative abundance of the two product ions measured. Retention times in today’s chromatographic systems are sufficiently stable to justify an absolute tolerance of ±0.1 min. Ion ratios are stable as long as sufficient response is obtained for both product ions. Ion ratio deviations are typically within ±20% (relative), and within ±45% (relative) in case the response of product ions are close to the limit of detection. Ion ratio tolerances up to 50% did not result in false positives and reduced the false negative rate for pesticides with product ions in the low S/N range to <5%. Without ion ratio criterion, two false positives were obtained in 105 non-fortified samples. Although the study has been conducted for pesticides residues in fruits and vegetables, the impact of these findings is believed to extend towards other application areas and possibly support adjustment or consolidation of criteria across other analytical domains.     

Adaptive Evolution of Saccharomyces cerevisiae with Enhanced Ethanol Tolerance for Chinese Rice Wine Fermentation

High tolerance towards ethanol is a desirable property for the Saccharomyces cerevisiae strains used in the alcoholic beverage industry. To improve the ethanol tolerance of an industrial Chinese rice wine yeast, a sequential batch fermentation strategy was used to adaptively evolve a chemically mutagenized Chinese rice wine G85 strain. The high level of ethanol produced under Chinese rice wine-like fermentation conditions was used as the selective pressure. After adaptive evolution of approximately 200 generations, mutant G85X-8 was isolated and shown to have markedly increased ethanol tolerance. The evolved strain also showed higher osmotic and temperature tolerances than the parental strain. Laboratory Chinese rice wine fermentation showed that the evolved G85X-8 strain was able to catabolize sugars more completely than the parental G85 strain. A higher level of yeast cell activity was found in the fermentation mash produced by the evolved strain, but the aroma profiles were similar between the evolved and parental strains. The improved ethanol tolerance in the evolved strain might be ascribed to the altered fatty acids composition of the cell membrane and higher intracellular trehalose concentrations. These results suggest that adaptive evolution is an efficient approach for the non-recombinant modification of industrial yeast strains.     

Interlaboratory studies of the determination of selected chlorobiphenyl congeners with capillary gas chromatography using splitless- and on-column injection techniques

The Community Bureau of Reference has organized a collaborative interlaboratory project to improve the analytical protocol for some specific chlorobiphenyls (CBs) within the European Community (EC). A series of test procedures were prescribed to optimize the gas chromatographic conditions for splitless and on-column injection, which substantially improved the quality of data. Important parameters included the initial column and injector temperatures and the choice of the polarity of the stationary phase. In a study with cleaned eel-fat extracts, coefficients of variation for reproducibility CV(R) ranging from 11 to 24% at the 0.04–0.3 mg/kg level per CB congener were obtained. No significant difference could be found between splitless- and on-column injection.     

Development of a rapid screening test for veterinary sedatives and the beta-blocker carazolol in porcine kidney by ELISA

Sedatives and tranquillisers are frequently used to reduce stress during the transportation of food producing animals. The most widely used classes of sedatives include the butyrophenone azaperone, the phenothiazines acepromazine, propionylpromazine, chlorpromazine and the [small beta]-blocker, carazolol. For regulatory control purposes, tolerances for azaperone and carazolol have been set by the European Union as 100 and 25 [micro sign]g kg(-1), respectively. Furthermore, the use of the phenothiazines is prohibited and therefore has a zero tolerance. A method for the detection of residues of five tranquillisers and one [small beta]-blocker using a single ELISA plate has been developed. Kidney samples (2.5 g) were extracted with dichloromethane and applied to a competitive enzyme immunoassay using three polyclonal antibodies raised in rabbits against azaperol, propionylpromazine and carazolol conjugates. In sample matrix, the azaperol antibody cross-reacted 28.0% with azaperone and the propionylpromazine antibody cross-reacted 24.9% with acepromazine and 11.7% with chlorpromazine. In the ELISA, the detection capabilities of the six sedatives, azaperol, azaperone, carazolol, acepromazine, chlorpromazine, and propionylpromazine are 5, 15, 5, 5, 20 and 5 [micro sign]g kg(-1), respectively. The proposed method is a sensitive and rapid multi-residue technique that offers a cost effective alternative to current published procedures, without any concession on the ability to detect sedative misuse.     

Concept of Selectivity and Its Meaning in Analytical Separation Techniques

The ambiguity of the use of selectivity concept in currently available analytical separation techniques (including chromatographic techniques) is pointed out. In all cases when this term is applied, it should be specified for which analyte (or analytes) and with respect to which concomitant component (or components) selectivity is considered in order to eliminate uncertainties of this kind. It should also be specified whether the analysis as a whole, its individual stages, chromatographic systems, or their particular elements (such as columns or phases used in them) are characterized. Corresponding criteria should also be specified for derived terms such as selectivity control, selectivity improvement, etc.     

Study of initiation reactivity of some plastic explosives by vacuum stability test and non-isothermal differential thermal analysis

On the basis of measurements of 18 high explosives by means of the Czech Vacuum Stability Test (VST) STABIL, a relationship has been specified between the results of this test and those of Russian manometric method. The said relationship was used to predict the Arrhenius parameters (E_a and log A values) of four plastic explosives based on RDX and one high explosive based on PETN (Semtex). The slopes E_aR⁻¹ of Kissinger's equation were specified by means of non-isothermal differential thermal analysis (DTA) and evaluation of the measurement results by means of the Kissinger method. The role played by binders and plasticizers in thermal decomposition of nitramines was pointed out on the basis of relationship between the E_a values obtained from VST and the E_aR⁻¹ values obtained from DTA, both for plastic explosives, eight nitramines, Composition B and PETN. The relationships between the E_aR⁻¹ values and thermostability threshold was specified for the given group of explosives. The relationship classify some of the studied plastic explosives as belonging to nitramines with steric hindrance in the molecule (CPX, TNAZ and HNIW). The relationship between E_aR⁻¹ values and drop energies, E_dr, sharply differentiates between plastic explosives and individual nitramines. From the relationship between the E_dr and D² values it was found that the increasing performance of the studied nitramines and plastic explosives is connected with the decrease in their impact sensitivity. Also specified are the approximate linear dependences between the peak temperatures of exothermic decomposition of all the explosives studied and their ignition temperatures, T_ig, or critical temperatures, T_c; these dependences were applied to prediction of T_ig and T_c of both the studied plastic explosives and some of the nitramines.     

A compression moulding technique for thick sheets of thermoplastics

A common requirement in plastics testing is the compression moulding of flat sheets with very small thickness variations, so as to obtain test specimens within specified tolerances. This is not always easy to achieve, especially with polymers exhibiting high mould shrinkage, particularly where relatively thick sheets are required.A moulding technique is described which involves the use of thermal insulation around the edge of the mould, and which produces flat sheets of high-density polyethylene with uniform thickness up to 25 mm or greater.     

Determination of planar chlorobiphenyls in animal fat

The occurrence of the highly toxic non-ortho substituted (planar) chlorobiphenyls (CBs) at low levels in wildlife, (human) fat, and fish generates the need for a routine analytical procedure. The use of a fully automated system for the separation of planar and non-planar CBs, consisting of a gel permeation chromatography system, a sample preparation system employing extraction columns, and a porous graphitic carbon HPLC column is described, and tested with horse fat. Gas chromatography on capillary columns, with electron-capture or high resolution mass spectrometric detection, is used for quantitation of the CBs.