Showing papers in "Journal of AOAC International in 1982"

Recovery of endogenous selenium from fish tissues by open system dry ashing.

Abstract: Quantitative recovery of endogenous selenium from fish tissues following dry ashing techniques has not been confirmed. An open system dry ashing procedure, using oxidative fusion with Mg(NO3)2 X 6H2O in the presence of MgO, was tested for recovery of selenium from National Bureau of Standards (NBS) Reference Materials (tuna and oyster) and selected fish tissues. Recovery after dry ashing and hydride analysis was complete from NBS Bovine Liver, Tuna, and Oyster Tissues, as well as from Food and Drug Administration cod, haddock, perch, and flounder research materials. Endogenous selenium, injected into rainbow trout (Salmo gairdneri) as 75Se, was recovered after ashing from liver, ovaries, gastrointestinal tract, muscle, bile, and carcass, 3 and 10 days post-injection. Results indicate that open vessel oxidative fusion is a rapid, simple technique applicable to quantitative recovery of selenium from organoselenium compounds that exist in various aquatic species. The diluted digestate is readily amenable to conventional hydride generation analysis.

Food analysis for lead using furnace atomic absorption and a L'vov platform.

Abstract: Furnace atomic absorption is a very sensitive method for determination of lead and other trace metals in a variety of samples, but it is prone to matrix interferences. A major improvement in the method is achieved by the use of a L'vov platform, a small piece of graphite placed inside the furnace tube, onto which the sample solution is pipetted. The temperature of the platform rises more slowly than that of the tube wall during the atomization cycle, and sample vaporization is delayed until the furnace atmosphere is at a high and nearly constant temperature. The resulting atomization behavior is more consistent and less matrix-dependent for numerous analyte elements, including lead. Results are further improved by addition of ammonium phosphate to all samples and standards as a matrix modifier. For example, in comparing analyte sensitivity (slope of the absorbance vs concentration curve) in a variety of food sample types to the sensitivity in dilute HNO3, the average lead response showed 60 +/- 15% suppression due to the sample matrices. Use of the L'vov platform and matrix modifier virtually eliminated the suppression and improved the precision.

Comparison of rapid high pressure liquid chromatographic and CB methods for determination of aflatoxins in corn and peanuts.

Abstract: A method is described for the rapid determination of aflatoxins in corn and peanut samples by high pressure liquid chromatography. The method was compared with the current CB method (AOAC 26.026). For 7 samples of corn and 14 samples of peanut meal and peanut butter, the correlation between methods is 0.991, and no significant difference exist between methods, using the Student's t-test at 15.7% alpha-risk.

Mineral oil vacuum distillation method for nitrosamines in fried bacon, with thermal energy analyzer: collaborative study.

Abstract: Nine laboratories participated in a collaborative study of a method for determining 6 nitrosamines, dimethylnitrosamine, diethylnitrosamine, dibutylnitrosamine, nitrosopiperidine, nitrosopyrrolidine, and nitrosomorpholine, in the 5-17 ppb range. The coefficients of variation for repeatability were 10.8, 8.5, 10.4, 8.5, 8.7, and 7.8% with corresponding coefficients of variation for reproducibility of 16.4, 12.0, 13.6, 10.8, 11.2, and 10.3% and recoveries of 89.6, 91.6, 84.7, 90.0, 89.6, and 88.1%, respectively. The method was adopted official first action.

Determination of background levels of lead and cadmium in raw agricultural crops by using differential pulse anodic stripping voltammetry.

Abstract: A method is described for the simultaneous determination of ultratrace levels of lead and cadmium in selected agricultural crop samples by differential pulse anodic stripping voltammetry. Samples are dry ashed at high temperature with H2SO4 as an ashing aid. Techniques are described to control the lead and cadmium blank levels of 2 ng and 0.4 ng, respectively. Typical relative standard deviations for the crop analyses are 13% at 100 ng/g and 25% at 10 ng/g for lead, and 5% at 100 ng/g and 10% at 10 ng/g for cadmium. The lowest quantifiable level, based on 3 g dry sample, is 2 ng/g for lead and 1 ng/g for cadmium. Recovery studies, precision studies, and analyses of NBS Standard Reference Materials demonstrate the accuracy and reproducibility of this technique. A summary of results for over 1700 crop samples is reported.

Liquid chromatographic determination of aflatoxins in artificially contaminated cocoa beans.

Abstract: A high pressure liquid chromatographic method is described for the extraction and determination of aflatoxins in artificially contaminated cocoa beans. Aflatoxins were extracted by using a CB extraction, column cleanup, and chromatography on a reverse phase column with UV detection at 365 nm for aflatoxins B1 and G1 and fluorescence detection for aflatoxins B2 and G2 (365 nm excitation and 455 nm emission). Recoveries from artificially contaminated cocoa beans of various roast conditions ranged from 77.50 to 107.35%. CV values ranged from 4.87 for G1 to 7.66 for G2 (n = 8). The method can be used for cocoa beans ranging from no roast to a heavy roast (12 min at 400 degrees F).

Fish species identification by thin layer agarose isoelectric focusing and densitometric scanning.

Abstract: Examination of sarcoplasmic proteins of fish by thin layer polyacrylamide gel isoelectric focusing as a means of fish species identification is a powerful and reliable technique, but it displays a number of disadvantages. These problems include the care required when handling acrylamide monomer (a neurotoxin), the mechanical skill needed in molding the gel, the difficulties in ensuring correct gel polymerization, and the extensive destaining periods. Specially treated agarose has been used to obtain protein patterns for an interval of pH 5-8. The patterns so produced were scanned by a densitometer in the visible range after completing staining and destaining. Most of the problems associated with polyacrylamide gels have been overcome by using agarose as a support medium.