Gas chromatographic method for analysis of 2,4-D in wheat: interlaboratory study

A procedure is described for the determination of 2,4-D (2,4-dichlorophenoxyacetic acid) in dried green plant material. Samples are first extracted with dilute sodium hydroxide, and then after acidification and solvent extraction, the residues are methylated using boron trifluoride-methanol reagent. The methyl ester of 2,4-D is cleaned up on a Florisil column and quantitated using a gas chromatograph equipped with an electron capture detector. Six laboratories made quadruplicate determinations on control, dried green wheat check samples, on 4 similar samples fortified at the 0.50 ppm level, and on 4 samples fortified at the 1.00 ppm level with 2,4-D. Based on the data from 5 laboratories, the plant fortifications of 0.50 and 1.00 ppm yielded average interlaboratory recoveries of 2,4-D of 83.3 and 88.2%, respectively. The procedure also has potential for the determination of 2,4-D in wheat straw and wheat grain.     

Leak in evaporated milk by anodic stripping voltammetry and atomic absorption spectrophotometry: cooperative interlaboratory study

The results of a cooperative study on the determination of lead in evaporated milk, using a double blind referee technique, are reported. This study was designed to determine the normal variability of methods currently used for lead analysis by canned food industry laboratories. Twenty-three laboratories participated in this study. Each laboratory was instructed to use atomic absorption spectrophotometry (AOAC 25.065), anodic stripping voltammetry, or carbon rod atomic absorption spectrophotometry. Overall, the results appear to be in close agreement with the spiking levels. The coefficient of variation for all laboratories was 36.0% at the 0.15 ppm lead level and 16.8% at the 0.40 ppm lead level.     

Gas-liquid chromatographic determination of diethylstilbestrol in molasses-based liquid feed supplements.

A gas-liquid chromatographic (GLC) method is described for the determination of diethylstilbestrol (DES) in molasses-based liquid feed supplements, using dienestrol diacetate as the internal standard. A sample equivalent to 110 mug DES was diluted, acidified with dilute sulfuric acid, extracted with chloroform, and subjected to basic sodium acetate cleanup. The bis-(trimethylsilyl) acetamide derivative was prepared and determined by GLC. Interfering peaks and/or low recoveries were found to be related to emulsions and the procedure incorporates centrifugation to minimize these.     

Determination op fluoride in plant samples by a potentiometric method and near‐infrared reflectance spectroscopy

Abstract

The determination of fluoride in plant materials was studied using a specific ion electrode following extraction using either deionized water or 0.1 M perchloric acid.

When the extracting agent was water, the amount of fluoride determined was generally 37% less than that obtained using perchloric acid. However, a close relationship was observed between the amounts extracted by either procedure. When perchloric acid is used, the method was found to be precise (variation coefficient 0.74%), accurate (average recovery 98.67%) and sensitive enough to be used in the routine analysis of plant materials.

The determination of fluoride by near‐infrared reflectance analysis (NIRA) was also used which gave generally acceptable results.     

Flame absorption spectroscopic determination of cadmium, copper, iron, lead, and zinc in mussels

A rapid method is proposed for determination of Cd, Cu, Fe, Pb, and Zn in mussel samples. The elements are extracted with concentrated nitric acid in borosilicate glass tubes at 90 degrees C for 1 h, and determined by flame atomic absorption spectroscopy. Detection limits for a 300 mg sample corresponded to 0.3 microgram Cd/g, 0.7 microgram Cu/g, 33 microgram Fe/g, 0.7 microgram Pb/g, and 6 micrograms Zn/g. The coefficient of variation for 20 independent analyses was 7% for Cd, 7% for Cu, 6% for Fe, 14% for Pb, and 8% for Zn. Recoveries were 107 +/- 3% for Cd, 90 +/- 3% for Cu, 94 +/- 1% for Fe, 90 +/- 5% for Pb, and 96 +/- 3% for Zn. The accuracy of the method was determined by analyzing NBS Oyster Tissues.     

Determination of acidic herbicides and related compounds in water and soil by capillary gas chromatography using a nitrogen-phosphorus detector

Methods are described for the determination of acidic herbicides and related compounds in water and soil. Eight acidic herbicides and related compounds were extracted from water using either dichloromethane or an XAD-2 resin column. The acidic moieties were derivatized with 2-cyanoethyldimethyl(diethyl)aminosilane. The derivatized compounds were separated using capillary gas chromatography and quantitated using a nitrogen-phosphorus detector. Extraction from water using dichloromethane or an XAD-2 resin column resulted in recoveries greater than 90% at 0.1 ppb with an average coefficient of variation (CV) of 6%. In soils extracted with aqueous acetonitrile-acetic acid and partitioned into dichloromethane, recoveries at 500 ppb were greater than 75% with an average CV of 3.3%. The methods are rapid and there are few interferences.     

Determination of aluminum in plant tissue digests using a catechol violet colorimetric method

Abstract

A procedure is described for the colorimetric determination of Al in acid digests of plant tissue using catechol violet as the chromogenic reagent. Components of plant tissue digests were examined for interference in the determination of Al using the described procedure. For highest accuracy, Al standards should contain macroelements, microelements, and acid at concentrations generally typical of those present in acid digests of the plant tissue being analyzed. Using the described procedure, recovery of Al added prior to digestion was 99.1% and 97.1% for National Bureau of Standards SRM 1571 (orchard leaves) and SRM 1572 (citrus leaves), respectively.     

Separation and determination of diesel contaminants in various fish products by capillary gas chromatography.

A semiquantitative capillary column gas chromatographic method is described for the determination of diesel fuel contamination in various canned seafood products. The diesel contaminants are separated from the fish sample by steam distillation, with little carry-over of interfering intrinsic materials such as fish oils. The diesel fuel is extracted from the condensate with n-hexane, and the extract is analyzed on an SPB-1 fused silica capillary column. The efficiency of recovery of diesel fuel added to canned seafood at levels of 40-400 ppt ranged from 72 to 102%. With the additional step of concentrating the hexane extract, the sensitivity of this procedure may be increased at least 10-fold. This procedure can detect the differences among diesel fuel grades No. 1, 2, and 5, and variations within diesel grade No. 2, and thus may be useful in determining the type of petroleum contaminants present in various canned fish products.     

Gas chromatographic profile analysis of basic nitrogen-containing aromatic compounds (azaarenes) in high protein foods

A method is described for the determination of basic nitrogen-containing polycyclic aromatic compounds (N-PACs, azaarenes) in meat. The enrichment procedure includes liquid-liquid partition (dimethylformamide-water-cyclohexane), extraction of N-PACs by sulfuric acid, reextraction after neutralization by cyclohexane or, alternatively, by nonadsorbing ion exchange chromatography. Further purification is performed by column chromatography on Sephadex LH 20 using a closed system to avoid sample contamination by laboratory pollutants. N-PACs are analyzed by capillary gas chromatography and measured by comparing to the corresponding peak areas of an internal standard (e.g., 10-azabenzo(a)pyrene). The limit of detection of this method ranges from 0.1 to 0.4 ng for benzacridines, dibenzacridines, and their methyl derivatives. The results of a collaborative study, stimulated by IUPAC, are reported: Coefficients of variation for the various azaarenes were 4.0-13.6% for the check analysis and 10.4-25.4% for a spiked ham sample. Consequently, IUPAC suggests this procedure as a recommended method.     

Atomic absorption spectrophotometric determination of tin in canned foods, using nitric acid-hydrochloric acid digestion and nitrous oxide-acetylene flame: collaborative study

Twenty-six collaborators participated in a study to evaluate an atomic absorption spectrophotometric (AAS) method for the determination of tin in canned foods. The 5 foods evaluated were meat, pineapple juice, tomato paste, evaporated milk, and green beans, each spiked at 2 levels. The concentration range of tin in the samples was 10-450 micrograms/g, and each level was sent as a blind duplicate. Statistical treatment of results revealed no laboratory outliers and 6 individual or replicate-total outliers, accounting for 3.3% of the data. Repeatability (within-laboratory) coefficient of variation (CVo) ranged from 2.2 to 48%, depending on the tin level and food evaluated. For samples containing greater than or equal to 80 micrograms/g of tin, repeatability CV averaged 5.6% including outliers and 3.7% after their rejection. Overall among-laboratories coefficient of variation (CVx) varied from 3.3 to 58%; at levels greater than or equal to 80 micrograms/g, it averaged 7.3% with outliers and 5.3% after their rejection. Recovery of tin, based on spiking levels, ranged from 100.0 to 112.8% and averaged 105.4%. Detection limit range is 2-10 micrograms/g, and lower quantitation limit is 40 micrograms/g. This method has been adopted official first action.     

Determination of heavy metals in foods by anodic stripping voltammetry after sample decomposition with sodium and potassium nitrate fusion.

A method is described for the simultaneous determination of several heavy metals in foods. The sample is predigested with nitric acid and decomposed completely by heating with a mixture of sodium and potassium nitrates. The resultant melt containing the metals is then dissolved in dilute nitric acid. After the pH is adjusted to an appropriate value, the metals, such as cadmium, copper, lead, and zinc, are determined by anodic stripping voltammetry. The average recoveries of these metals added to 5 commodities were 98, 98,96, and 104%, respectively. The relative standard deviations, based on data from analyses of a commodity containing measurable levels of copper, lead, and zinc, were 12.0, 13.0, and 9.7%, respectively.     

Comparison of several methods for determining free iron in soils

In the previous paper (1), for determining free iron in paddy soils the writers proposed a new method in which free iron was removed by reduction with sodium hydrosulfite in disodium ethylendiamine tetraacetate solution. As described in that paper, many methods have been proposed up to the present time. In this paper the writers are to compare their method with some of those methods, especially with both methods using sodium hydrosulfite and dilute hydrochloric acid and using hydrogen sulfide and dilute hydrochloric acid. The latter method has generally been employed for free iron determination of paddy soils in Japan.     

Semiautomated method for the analysis of formulations of chlorpheniramine maleate and brompheniramine maleate.

The determination of chlorpheniramine maleate and brompheniramine maleate in tablets, capsules, injections, and elixirs has been automated. The active ingredient is dissolved in dilute HCl. The dilute acid solution is sampled, made basic with dilute NaOH, and extracted with isooctane. The isooctane phase is resampled and the drug is re-extracted into dilute HCl. The absorbance of the acidic aqueous layer is monitored at 265 nm. The method is an automated version of the general USP XIX assay for salts of organic nitrogenous bases. The results from the semiautomated procedure agree well with the USP XIX and NF XIV official methods. Recoveries were 100% from an authentic tablet material. The system is linear from 0 to 300% of declared potency. The procedure is free from common excipient and dye interferences. Precision data are included for both the automated and official methods.     

Improved cleanup for liquid chromatographic analysis and fluorescence detection of aflatoxins M1 and M2 in fluid milk products

A rapid method is described for extraction and cleanup of raw and processed milk for determination of aflatoxins M1 and M2 by using a C18 Sep-Pak/silica gel cleanup column combination. Aflatoxins are separated by normal phase liquid chromatography and their concentrations are determined by fluorescence detection in a silica gel-packed flow cell. Recoveries ranged from 99 to 103% with coefficients of variation less than 2% for M1 levels of 0.117-1.17 ng/mL added to raw milk. Similar recoveries were obtained for M2. The coefficient of variation for analysis of 5 subsamples of naturally contaminated milk was less than 1%. Agreement with the official method is satisfactory. Each sample requires less than 25 mL solvent and 10 min actual handling time. Sample chromatograms show no interferences in the M1-M2 elution region and no late-eluting peaks, which permits spacing injections at 13-20 min intervals. Aflatoxin levels as low as 0.03 ppb may be determined by this procedure. Extracts have also been analyzed by thin layer chromatography.     

Predicting sediment metal concentrations in lakes without point sources 1

Surficial sediments (0 to 2 cm) from 189 sites in 52 Quebec and Ontario lakes were analyzed for Al, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn by atomic adsorption spectrometry after extraction in dilute aqua regia. Empirical models using sediment texture (water content), site morphometry (depth) and geology (categorical variables) as predictors explain 82 to 87% of the between-site and between lake variation in sediment concentrations of Cu, Cr, Ni, Pb, and Zn, and 52 to 68% of the variation of Al, Co, Fe, and Mn. Over a broad geologic range, geologic variables are only significant in models predicting Co, Cr, and Ni. These three elements are low in concentration in lakes with catchments on the Grenville shield, while Cr and Ni are enriched in catchments containing ophiolite geology. These models explain both between-site and between-lake variation in sediment metal concentrations, and due to the lack of geologic influence on most metals, may be valid for other regions. The models appear promising as a means to identify point source contamination without assumptions about the relevant sediment fractions or inter-element relationships.     

Spectrofluorometric determination of BAY Vp 2674 residues in poultry tissues

A spectrofluorometric (SPF) method is described for determination of residues of BAY Vp 2674 in chicken and turkey tissues. The drug is extracted from tissues with dichloromethane-methanol. The organic extract is concentrated to near dryness and cleaned up by a series of partitionings with n-hexane, then dichloromethane against pH 2 buffer and dichloromethane against pH 12 buffer. The drug is partitioned into dichloromethane from pH 7 buffer and concentrated to dryness. The residue is dissolved in pH 3.5 buffer for SPF analysis at 282 nm (excitation) and 445 nm (emission). Recoveries of BAY Vp 2674 added to chicken and turkey tissues at levels of 0.05, 0.1, and 0.2 ppm range from 86 to 92% with a coefficient of variation of 3.4-10.1%. Detection limit is 0.02 ppm. A liquid chromatographic confirmatory procedure is also described, with ultraviolet and fluorescence detection.     

Headspace gas chromatographic method for determination of ethanol in canned salmon: collaborative study

Six laboratories collaboratively studied a headspace gas chromatographic method for determination of ethanol in the aqueous phase of canned salmon. Ethanol is determined by a headspace sampling technique with tert-butanol as the internal standard, using a gas chromatograph equipped with a Super Q column and a flame ionization detector. With outliers excluded, the mean recoveries from samples spiked with 25.1 and 78.4 ppm ethanol were 112 and 110%, respectively. For the 4 sample pairs quantitated, repeatability coefficients of variation ranged from 1.42 to 4.25% and reproducibility coefficients of variation from 2.55 to 8.09%, with 3 of the 4 reported values less than 5%. The method has been adopted official first action.     

Computerized gas-liquid chromatographic method for content uniformity analysis of dicyclomine hydrochloride capsules and tablets

An automated, computerized method is presented for the content uniformity determination of dicyclomine hydrochloride capsules and tablets, using up to 4 automatic sampler-equipped gas chromatographs interfaced with a minicomputer. A 3% OV-17 column is used with anthracene as an internal standard. Five sample injections are bracketed by standard mixtures containing about 90 and 110% of the labeled dicyclomine hydrochloride. Data are taken on-line simultaneously from each gas chromatograph and a computer-generated report is produced. Calculations use a BASIC program with linear fit of the 90 and 110% standard mixture. Individual tablet or capsule results are printed in milligrams and per cent declared, including summary calculations of average, high, low, standard deviation, and coefficient of variation. The GLC results are comparable (within 1%) to those obtained using the USP procedure.     

Simultaneous assay for six alkaloids in opium, using high-performance liquid chromatography.

A method is described for the quantitative determination of morphine, codeine, cryptopine, thebaine, papaverine, and narcotine in opium by high-performance liquid chromatography. The alkaloids are isolated from a dilute acid extract by adsorption on an Amberlite XAD-2 resin column and eluted first with methanol and then with chloroform-methanol (3+1). After solvent removal by reduced pressure evaporation, the alkaloids are redissolved in chloroform-methanol (3+1). The sample solution, plus brucine as an internal standard, is injected onto a Corasil II column and eluted with hexane that is gradient programmed with a solution of chloroform-methanol-diethylamine (100+300+1). The absorbances of the separated alkaloids are continuously monitored at 254 nm, using a flow-through ultraviolet double-beam photometer.     

Simultaneous determination of oxytetracycline, tetracycline, and chlortetracycline in milk by liquid chromatography

A simple, rapid procedure is described for the simultaneous quantification of 3 tetracycline drugs in bovine milk. Samples are prepared by dilution with an EDTA/phosphate buffer solution and filtration through a molecular weight cutoff filter. Analytes are concentrated on-column using a reverse-phase gradient elution system of oxalic acid, acetonitrile, and methanol. The limits of quantitation are approximately 15-50 ng/mL and the limits of detection are 10-20 ng/mL, depending on the compound. For oxytetracycline, over the range 50-1200 ng/mL, the average recovery and intralaboratory coefficient of variation were 97% and 4.1%, respectively. Over the same range, these parameters were, respectively, 97% and 5.0% for tetracycline, and 89% and 6.4% for chlortetracycline. The applicability of this procedure is demonstrated by separation and detection of incurred tetracycline residues in milk from treated animals.