Biomedical subjects

R S Ferrera

Publications and source records attributed to R S Ferrera.

3 recordsLinked to original sources

PubMedDate not supplied

Improved reagent for detection of allantoin in thin-layer chromatographic method for urine stains on foods and packaging.

Ten detection reagents known to react with either primary amine groups or indole derivatives were tested to improve sensitivity for allantoin (ALN) and indican (IND) in the official AOAC thin-layer chromatographic method for urine metabolites (44.175-44.177). The lowest levels found using the official method were 500 ng ALN and 6 ng IND. The best reagent was p-dimethylaminocinnamaldehyde (pDMAC), which yielded intensely colored spots with both compounds. The lowest amounts consistently found were 125 ng ALN and 13 ng IND. pDMAC was also used as an overspray for ALN after the spray specified in the official method, p-dimethylaminobenzaldehyde (pDMAB), was applied. This resulted in a detection limit of 250 ng. The overspray procedure was incompatible with IND detection, but provided an easy way to gain slightly greater sensitivity for ALN when use of pDMAB gave negative or borderline results. The combined use of pDMAC for ALN, and the official sprays (pDMAB and sodium acetate) for IND, maximized sensitivity for both compounds.

Allantoin↗

PubMedDate not supplied

Improved spray reagent for thin layer chromatographic method for detecting uric acid: collaborative study.

A collaborative study was conducted to validate the substitution of an improved single spray in the official AOAC thin layer chromatographic method for identifying uric acid (UA) from bird and insect excreta. The proposed reagent, which is a dilute aqueous solution of ferric chloride and potassium ferricyanide, requires neither a heating step nor a pH indicator. Its preparation time, specificity, and sensitivity to low levels (5-50 ng) of UA were compared with those of the official sprays. The improved spray took 1/5 as long to prepare as the official sprays. Neither the proposed spray nor the official sprays gave false positive reactions with compounds similar to UA. For bird and insect excreta samples, at the 95% confidence limits, the false negative rate was between 0 and 9.7% for the proposed spray and between 0.7 and 18.7% for the official sprays. Sensitivity results showed that the proportion positive for the proposed spray was significantly higher (P less than 0.05) than for the official sprays at the 15 ng UA level. The proposed changes have been adopted official first action.

Animals↗

PubMedDate not supplied

Use of urease-bromothymol blue-agar method for large-scale testing of urine on grain and seeds.

The current AOAC method (963.28) for large-scale (50 g) testing of urine on grain is based on the reaction of sodium in urine with magnesium uranyl acetate. Detection of sodium suggests that urine is present and that a test for urea is appropriate. Urea is detected with urease-bromothymol blue-paper and is confirmed through its reaction with xanthydrol to form dixanthylurea crystals, which are detected microscopically. The initial nonspecific test for sodium can be influenced by the presence of salt or other sodium compounds. Furthermore, the magnesium uranyl acetate spray used in Method 963.28 potentially exposes the analyst to the aerosol of a volatile, toxic uranium compound. Excess reagents and analyzed test portions must be disposed of as radioactive waste. In addition, Method 963.28 requires several steps to determine the presence of urea. The alternative AOAC method (972.41) tests for the presence of urea from urine on individual seeds. Urea is enzymatically decomposed to ammonia and carbon dioxide by urease. Liberated ammonia shifts the pH, changing the color of the indicator in the agar from yellow to blue. This study adapts Method 972.41 to larger test samples. Up to 25 g grains and seeds are sprayed with urease test agar instead of being individually immersed in the urease test agar. The modified method was used to analyze urea on seeds and grains of 24 plants from 4 families. The method has a limit of detection of one seed contaminated with 1 microgram urea.

Aerosols↗