Gas chromatographic-chemiluminescence method for determination of volatile N-nitrosamines in minced fish-meat and surimi-meat frankfurters: collaborative study

A collaborative study was carried out on a solid-phase extraction method for separating volatile N-nitrosamines, particularly N-nitrosodimethylamine (NDMA), from combination minced fish or surimi-meat frankfurters with detection by gas chromatography-chemiluminescence (thermal energy analyzer). The results from the 10 collaborators were evaluated using the most recent AOAC guidelines for determining outliers and for the analysis of variance. For NDMA, repeatability standard deviations, sr, ranged from 0.56 to 2.25; repeatability relative standard deviations, RSDr, ranged from 8.9 to 11.5%. Reproducibility standard deviations, SR, for NDMA ranged from 1.40 to 6.49, and reproducibility relative standard deviations, RSDR, ranged from 24.2 to 28.9%. Our data compared favorably to the reproducibility (RSDR) curve of Horwitz. The method has been adopted official first action by AOAC.     

Gas chromatographic method for determination of p,p'-DDT in DDT technical and formulated products: collaborative study

A gas chromatographic (GC) method for determination of p,p'-DDT in technical and formulated products was developed and it performed well in an initial small collaborative study among 4 laboratories. Samples are dissolved in chloroform, and p,p'-DDT is separated on an OV-210 column and determined by GC analysis with flame ionization detection. 2,2'-Dinitrobiphenyl is used as an internal standard. The method was subjected to an international collaborative study with 10 participating laboratories. Collaborators received matched pairs of technical DDT products and of water-dispersible powder, emulsifiable concentrate, and dustable powder formulations. Relative standard deviations for reproducibility (RSDR) for the paired samples were 1.16, 1.48, 2.08, and 1.80%, respectively. The method has been approved interim official first action by AOAC as a CIPAC-AOAC method.     

Gas chromatographic determination with electron capture detection of residual ethylene oxide in intraocular lenses

A sensitive method is described to determine trace quantities of ethylene oxide (EO) in EO-sterilized intraocular lenses (IOLs). An IOL is dipped in ethanol containing 0.25 ppm propylene oxide (PO) in a 4 mL vial, 2 drops of freshly distilled hydrobromic acid is added through a septum, and the mixture is warmed at 50 degrees C for 24 h. It is then neutralized by vigorous shaking with sodium bicarbonate, dehydrated with anhydrous sodium sulfate, and filtered. The filtrate is injected into a gas chromatograph with electron-capture detection, and the peak height ratio of ethylene bromohydrin/propylene bromohydrin is measured. EO residue is calculated from the calibration curve obtained through a similar procedure with the standard EO/PO solutions. The limit of determination is 0.04 microgram/lens (ca 2.0 ppm). When EO residue levels were determined for IOLs sampled at 3 different aeration periods after sterilization, we found that 9 days of aeration was necessary to meet the U.S. Food and Drug Administration proposed limit for EO residue in IOLs.     

Gas chromatographic determination of deoxynivalenol in wheat

Modifications to a published method are described for the determination of deoxynivalenol (DON) in wheat by gas chromatography with electron capture quantitation of the heptafluorobutyrate derivative. In the modified method, DON is extracted by shaking the sample with methanol-water on a wrist-action shaker, followed by filtration through rapid flow paper. One concentration step is eliminated, and a hexane wash is incorporated to remove toluene from the silica gel column. Recoveries of DON from wheat samples spiked at 0.1, 0.5, and 1.0 ppm ranged from 77.3 to 86.3% and averaged 81.5%.     

Gas chromatographic determination of pentachlorophenol in gelatin

A method is described for the determination of pentachlorophenol (PCP) in gelatin. The method employs acid and heat to hydrolyze the gelatin matrix, a base partition and wash for separation and cleanup, and a reacidification and extraction with hexane for direct determination of PCP, without preparation of a derivative, using gas chromatography (GC) with a 1% SP- 124ODA liquid phase and a 63Ni electron capture detector. Recoveries averaged 106% for fortifications between 0.02 and 1.0 ppm. The limit of quantitation is 20 ppb. The limit of detection is 4-6 ppb. The method, which has undergone a successful intralaboratory trial, is simple and rapid, and requires only general laboratory reagents and equipment. GC of the acetate derivative of PCP is used for confirmation of identity.     

Gas chromatographic determination of picloram in fish

A simple method for determining picloram in fish is described. The sample is homogenized with ethyl acetate, acidified with 1N HCl, and extracted twice more with ethyl acetate. Ethyl acetate fractions are pooled, derivatized with diazomethane, cleaned up by column chromatography, and analyzed by electron capture gas chromatography. Rainbow trout exposed to 14C-picloram were used to evaluate the efficiency of 2 methods of extraction and to provide data on the rate of uptake and the bioconcentration factor. The detection limit for this method is 5 ng/g, using a 4 g sample.     

Gas chromatographic determination of glucono-delta-lactone in foods

A method is described for the gas chromatographic (GC) determination of glucono-delta-lactone in foods. A sample was homogenized with 60-70 degrees C water and filtered. The filtrate was buffered with NH4OH-NH4Cl pH 10 solution, and was passed through a QAE-Sephadex A25 column. The column was washed with water and glucono-delta-lactone was eluted with 0.1N HCl. An aliquot of the eluate was evaporated to dryness and derivatized with pyridine, N,O-bis(trimethylsilyl)trifluoroacetamide, and trimethylchlorosilane at room temperature. GC separation of glucono-delta-lactone as the TMS derivative was performed on a 2% OV-17 column at 180 degrees C. Recoveries from bread, jelly, soybean curd, and other foods fortified with 0.1% glucono-delta-lactone ranged from 92 to 106%, with standard deviations from 2.2 to 9.8%. The detection limit was approximately 0.025%.     

Gas chromatographic method for determination of fenitrothion in fenitrothion technical and in formulated products: collaborative study

A gas chromatographic (GC) method for determination of fenitrothion in fenitrothion technical and formulated products has been subjected to a collaborative study with 7 participating laboratories. Formulations are extracted with chloroform containing dibutyl sebacate as an internal standard and are analyzed by gas chromatography using an OV-210 column. Collaborators were furnished matched pairs of technical product and water-dispersible powder and emulsifiable concentrate formulations. Relative standard deviations for reproducibility (RSDR) for the paired samples were 0.54, 1.00, and 1.56%, respectively, for technical fenitrothion, water-dispersible powders, and emulsifiable concentrates. The method has been approved interim official first action as an alternative to the present official first action AOAC method 6.A19-6.A24, which uses a polyphenyl ether, 6 ring (PPE-6R) column packing and fluoranthene as internal standard.     

Gas chromatographic determination of clopidol in chicken tissues

A method has been developed for the determination of clopidol residues in chicken tissues. After extraction and cleanup, clopidol is esterified in a 2-phase system to clopidol propionate, which is determined by gas chromatography. The 2-phase system includes, in addition to the clopidol dissolved in methanol, aqueous borax solution, hexane, propionic anhydride, and pyridine. Use of these reagents precludes the use of explosive or carcinogenic chemicals in the derivatization step, and the method is therefore suitable for routine laboratory analysis. Levels of 0.5 ppb clopidol in tissue can be determined.     

Gas chromatographic determination of cholesterol in egg products

A method has been developed for quantification of cholesterol in fresh egg yolks, spray-dried egg yolks, fresh whole eggs, and spray-dried whole eggs. The method uses saponification followed by petroleum ether extraction of cholesterol. Separation of organic and aqueous layers is enhanced by sodium chloride. Petroleum ether extracts are dried under nitrogen and redissolved in chloroform-methanol (2 + 1) for injection into a gas chromatograph. Cholesterol is separated and quantitated on a high temperature capillary column coated with 5% diphenyl and 95% dimethyl polysilicone crosslinked gum. The method was compared with the current AOAC method 17.017-17.022, and results indicated no significant difference (alpha = 0.05). However, the proposed method allowed separation and analysis of 16 samples in 7 h while the current AOAC method allowed separation and analysis of only 4 samples in 9 h.     

Gas chromatographic determination of total iodine in foods

A gas chromatographic (GC) method has been developed for determination of total iodine in foods, based on the reaction of iodine with 3-pentanone. Organic matter of a sample is destroyed by an alkaline ashing technique. Iodide in a water extract of the ash residues is oxidized to free iodine by adding dichromate in the presence of sulfuric acid. Liberated iodine is reacted with 3-pentanone to form 2-iodo-3-pentanone, extracted into n-hexane, and then determined by gas chromatography with an electron-capture detector. Recoveries of iodide from spiked food samples ranged from 91.4 to 99.6%. Detection limit for iodine is 0.05 micrograms/g.     

Gas chromatographic determination of oxalic acid in foods

A new quantitative gas chromatographic (GC) method has been developed for the determination of oxalic acid in foods. Solid sample is extracted with water (soluble oxalic acid) or 2N hydrochloric acid (total oxalic acid) at room temperature. An aliquot of sample extract is evaporated to dryness, and the oxalic acid in the residue is methylated with 7% hydrochloric acid-methanol. The reaction mixture is extracted with chloroform, and dimethyl oxalate is quantitated by GC. Recovery of oxalic acid added to liquid samples averaged 100.6%; recoveries from extracts of solid samples were 96.2-99.5 and 97.2-100.1% for water and hydrochloric acid extractions, respectively. Results are shown for determination of oxalic acid in spinach and beverages. The technique is simple, rapid, and accurate, and small samples may be used. The limit of determination is 20 micrograms.     

Gas chromatographic, liquid chromatographic, and titrimetric procedures for determination of glycerin in allergenic extracts and diagnostic antigens: comparative study

Three methods for the determination of glycerin are examined as applied to several allergenic extracts and diagnostic antigens. The liquid chromatographic procedure uses a sulfonic acid functional PSDVB resin (Aminex HPX-87H), a mobile phase of 0.013N H2SO4; and refractive index detection. The titrimetric procedure involves oxidation of glycerin with sodium metaperiodate followed by potentiometric titration of the resulting formic acid with sodium hydroxide. Samples are quantitated by comparing the equivalence point obtained from the sample to those obtained from a series of standards. The gas chromatographic procedure includes a column of 5% Carbowax 20 M on 80-100 mesh Chromosorb WHP; p-cresol was used as an internal standard. The 3 procedures are shown to be valid for the majority of product types examined. A positive interference was encountered in the titrimetric analysis of a tuberculin purified protein derivative that contained simple sugars. Recoveries of added glycerin ranged from 95.0 to 100.2% by the liquid chromatographic method, from 98.7 to 101.4% by the gas chromatographic method, and from 99.8 to 101.6% by the metaperiodate oxidation method when interference from simple sugars was not present. Coefficients of variation determined from 8 replicates of samples that contained glycerin were 2.2% or less for the liquid chromatographic method, 2.3% or less for the GC method, and 3.6% or less for the metaperiodate oxidation method.     

Liquid chromatographic method for determination of water in soils

Abstract

A simple, rapid, and sensitive liquid Chromatographic (LC) method for the determination of water in soils was developed. In this method, water is extracted from soil with anhydrous methanol and injected into an LC system including a cation‐exchange column in the H form. The eluent is 1.0 mM transcinnamaldehyde in acetonitrile‐methanol (40:60). The detection scheme is based on the effect of water on the equilibrium established when trans‐cinnamaldehyde and methanol react in the H⁺ column to form cinnamaldehyde dimethylacetal and water. The equilibrium of the reaction is shifted towards the trans‐cinnamaldehyde (absorbs strongly at the detection wavelength, 300 nm) when water is introduced into the column. The extent of the shift and the resulting change in absorbance at 300 nm are proportional to the amount of water present.

Application of the method to a wide range of soils and of clay minerals containing from 0.7 to 25% water showed that the results of the LC method agreed closely with those of the gravimetric method. The LC method is accurate, precise, relatively free from interference, requires a small sample size, and gives a linear calibration graph over approximately three orders of magnitude of water concentrations. A single operator can perform approximately 80 analyses in a normal working day.     

Liquid chromatographic method for determination of citreoviridin in corn and rice

Citreoviridin, a neurotoxic mycotoxin, has been found as a natural contaminant in corn left unharvested in the southeastern United States and in rice of several Asian countries, including Japan. A reliable analytical method for the quantitative determination of citreoviridin in corn and rice is described. Corn or rice is extracted with dichloromethane, and the extract is partially purified on silica and amino solid-phase extraction (SPE) columns. The extract is analyzed for citreoviridin by normal-phase liquid chromatography, using a mobile phase of ethyl acetate-hexane (75 + 25) at 1.5 mL/min and a fluorescence detector to measure the yellow fluorescence (388 nm excitation, 480 nm emission). With a 100 microL injection loop, the relationship between concentration and injection volume is linear for 20-60 microL injections. Recoveries of citreoviridin added to yellow corn at 10-50 ng/g were 91.0-96.9%; recoveries from white corn (10-50 ng/g added) were 96.8-102.8%. Recoveries of 5000 ng/g added to white corn were 89.0%, indicating that heavily contaminated samples can be assayed by the method. Minimum detection limits were 10 ng for citreoviridin standard and 2 ng/g for citreoviridin added to corn. White rice fermented with Penicillium citreo-viride (1524 ppm) was mixed with and serially diluted with uncontaminated ground corn to obtain citreoviridin-contaminated corn (ca 25 ppb). When the samples were assayed by the method, a mean level of 24.4 +/- 1.65 ppb (6.5% coefficient of variation) was obtained. Four fermented rice food samples and 3 commercial rice samples were investigated.(ABSTRACT TRUNCATED AT 250 WORDS)