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R C Doerr

Publications and source records attributed to R C Doerr.

At least 19 recordsLinked to original sources
PubMed1982

Chemiluminescence detection of nitrite in nonfat dried milk powders.

Determination of nitrite in nonfat dry milk powders by chemiluminescence detection was compared with a colorimetric method specifying Griess reagents. The chemiluminescent technique requires no sample preparation, is free from apparent interferences, and is sensitive to 25 ppb nitrite. Statistical analysis shows no difference at P = 0.05 between the colorimetric and chemiluminescent methods, based on the analysis of 16 commercial nonfat dry milk samples.

Animals↗
PubMed1982

Interaction between sample preparation techniques and three methods of nitrite determination.

Meat samples containing nitrite and varying concentrations of ascorbate, cysteine, and sodium chloride were prepared for nitrite analysis. The methods used were the AOAC method of dilution and heating; the addition of mercuric chloride, charcoal, and Carrez reagents at 2 different pH values; and direct analysis of sample supernatants with no treatment (control). The effect of these initial conditions and preparation methods on measured nitrite was determined by using 3 different Griess reagent combinations and chemiluminescent and differential pulse polarographic techniques. Systematic variations were observed in samples treated with mercuric chloride, while the addition of Carrez reagents had little or no effect. Best results were obtained by the AOAC dilution/heating method under alkaline conditions, or by charcoal addition followed by chemiluminescent or colorimetric nitrite determination. Statistical analysis of the nitrite concentrations determined in the several samples showed that these 3 procedures were precise to about 5-6% CV, which was not significantly different from the CV value of 4% determined from replicate analyses.

Indicators and Reagents↗
PubMed1977

Determination of N-nitrosoproline at the nanogram level.

Two sensitive detection systems are described for the quantitative determination of a nonvolatile nitrosamine, nitrosoproline. One procedure involves denitrosation followed by derivatization of amino product, proline, with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl). The highly fluorescent NBD-proline compound formed is then identified and quantitated by either thin-layer chromatography or high-pressure liquid chromatography (HPLC). In the second system, the volatile methyl ester of the intact nitrosoproline is prepared, then detected by gas-liquid chromatography (GLC), and confirmed by combined gas-liquid chromatography and mass spectrometry (GLC-MS). Both methods permit the quantitative detection of less than 10 ng of nitrosoproline. However, the HPLC fluorescence technique is approximately ten times as sensitive as the GLC method.

Chromatography, Gas↗
PubMedDate not supplied

Apparent mutagenicity of N-nitrosothiazolidine caused by a trace contaminant.

The identification of N-nitrosothiazolidine (NTHZ) in smoked meat products prompted us to evaluate this compound for mutagenicity by the Salmonella assay. NTHZ was prepared in 99 + % purity by the nitrosation of the cysteamine-formaldehyde reaction mixture without isolation and purification of the resulting amine, and from thiazolidine, directly. Mutagenic activity was observed with TA100 without metabolic activation in the former, but not the latter preparation. An examination of the precursors, reaction intermediates, and HPLC separation of the NTHZ from the mutagenic product demonstrated that the genotoxic activity resulted from a synthesis-produced trace contaminant.

Animals↗
PubMedDate not supplied

Gas chromatographic method for determination of dimethylamine, trimethylamine, and trimethylamine oxide in fish-meat frankfurters.

A method is described for analysis of minced fish-meat and surimi-meat frankfurters for dimethylamine (DMA), trimethylamine (TMA), and trimethylamine oxide (TMAO) using a headspace-gas chromatographic technique. After simple acid extraction and addition of NaOH, the headspace was directly injected into a gas chromatograph by a gas-tight syringe. DMA and TMA were separated on a Chromosorb 103 column and detected by a flame ionization detector. TMAO was measured as TMA after Zn reduction. Repeatability of the method for DMA, TMA, and TMAO was 6.6, 1.0, and 18.8 ppm, respectively. The method was applicable to Alaska pollock-meat and Atlantic menhaden-meat frankfurters, unwashed, and washed mince and surimi.

Analysis of Variance↗
PubMedDate not supplied

Determination by liquid chromatography with electrochemical detection of cysteamine and cysteine, possible precursors of N-nitrosothiazolidine.

A method is described that is selective, sensitive, rapid, and accurate for the quantitative measurement in meat products of both cysteamine and cysteine, potential precursors for N-nitrosothiazolidine (NTHZ) and N-nitrosothiazolidine-4-carboxylic acid (NTHZC), respectively. In general, a ground meat sample is homogenized with acetonitrile-formate buffer in the presence of dithiothreitol, and then is centrifuged, filtered, and recentrifuged in a disposable microfilter. The thiols are quantitated by liquid chromatography using an amperometric detector equipped with a gold/mercury electrode, operated in the oxidative mode. Cysteamine was found in 6 of 20 samples of raw pork belly in concentrations ranging from 150 to 450 ppb, and cysteine was found in all samples in concentrations ranging from 2.4 to 36.5 ppm. Analysis for the thiols and their corresponding nitrosamines--NTHZ and NTHZC--of bacon before and after processing showed no correlation between cysteamine and cysteine levels before processing nor with nitrosamine levels after processing. Liquid chromatography with electrochemical detection was found to be an extremely selective technique to measure the 2 free sulfhydryl compounds in a complex food substrate.

Animals↗
PubMedDate not supplied

Liquid chromatographic determination of zoalene and its metabolites in chicken tissues with electrochemical detection.

A procedure is described for the quantitation of Zoalene (3,5-dinitro-o-toluamide) and its 2 major monoamino metabolites in chicken tissues. The method includes blender extraction of tissue with chloroformethyl acetate (1 + 1), adsorption of the drug and metabolites on neutral alumina, and subsequent elution of the residues with pH 3.5 formate buffer-methanol (6.5 + 3.5). Recovered residues were separated on a 5 micron C18 column with the alumina eluting solvent as the LC mobile phase. The parent drug and metabolites were detected and quantitated with an electrochemical detector in the reductive mode with a minimum level of reliable measurement of 0.1 ppm. Overall mean recoveries greater than 85% were obtained with Zoalene and its 2 monoamino metabolites in breast, thigh, and liver tissues fortified with 0.25-2.00 ppm. The results on tissues from chickens fed a diet containing 0.0125% Zoalene are presented.

Animals↗
PubMedDate not supplied

Effect of residual ascorbate on determination of nitrite in commercial cured meat products.

Residual ascorbate in cured meat slurries results in different amounts of pigment being produced from different Griess reagent combinations. The phenomenon was used to study residual ascorbate in commercial cured meat products which had a variety of textures, acidities, moisture and meat content, fat, homogeneity, initial nitrite, and processing conditions. Diluting and heating the samples according to the AOAC procedure did not completely eliminate the ascorbate interference, but making the sample alkaline did. Determining nitrite separately in supernate and precipitate from the first dilution showed the effect of heating to be the elimination of interferences and solubilization or extraction of nitrite from the precipitate.

Animals↗