Polarographic behaviour of metal chelates of o,o'-dihydroxyazo dyes.

The nature of complexes between various o,o'-dihydroxyazo dyes and metal ions, and their applications in polarographic chemical analysis, are described and discussed.

Decomposition of thiosulphate in acidified oxidants.

The Wollack procedure has been used to study the competition between oxidant and acid for the thiosulphate ion. In concentrated hydrochloric acid solutions of iodine, iodate and chloramine-T, polythionates are the chief products, whereas in acid permanganate substantial amounts of other products occur. Both the concentration of the acid and the acid anion affect the course of the reaction in these solutions. Production of polythionate, an acid-decomposition product, suggests that acid decomposition successfully competes with oxidation.

The determination of tervalent chromium and iron in chromic acid.

Chromic acid is analysed for tervalent chromium by separation of Cr(III) from Cr(VI) by precipitation as the hydrous oxide, with Zn(OH)(2) as a carrier. The hydrous oxide is collected by centrifugation and dissolved in perchloric acid, then Cr(III) is complexed with 1,2-diaminocyclohexanetetra-acetic acid and measured spectrophotometrically at 540 mmicro. Repetitive analysis of a sample of chromic acid showed 93 ppm of Cr(III) (s = 13, n = 9). Iron in chromic acid is also separated as the hydrous oxide, then dissolved in HCl, reduced to Fe(II) with hydroxylamine hydrochloride, complexed with bathophenanthroline disulphonic acid and measured spectrophotometrically at 533 mmicro. Repetitive analyses of a sample of chromic acid showed 2-6 ppm of iron (s = 0.35, n = 8).

Determination and differentiation of nitrilotriacetic acid and ethylenediaminetetra-acetic acid.

Ethylenediaminetetra-acetic acid (EDTA) and nitrilotri-acetic acid (NTA) can be differentiated and determined by titration with metal ions to visual metallochromic dye end-points. EDTA can be determined without interference from NTA, either by titrating with copper(II) at pH 5 using PAN indicator, or by titrating with iron(III) at pH 6 and 70 degrees using Tiron indicator. The total chelating power (EDTA + NTA) can be determined either by titrating with lead(II) at pH 4.4 using dithizone indicator, or by titrating with iron(III) at pH 3.5 using Tiron indicator ; NTA is determined by difference. The lowest concentration at which NTA can be determined in EDTA by titration to the iron(III)-Tiron end-point is about 1 wt.%. The apparent stability constants of the iron(III)-Tiron complexes under the conditions of the titration at pH 3.5 and pH 6 have been determined using the method of continuous variations.

Liquid chromatographic determination of urea in water-soluble urea-formaldehyde fertilizer products and in aqueous urea solutions: collaborative study.

Water soluble urea-formaldehyde (UF) fertilizers, manufactured by complex reaction of urea and formaldehyde, typically contain varying amounts of unreacted urea. A liquid chromatography method for the analysis of urea in these products, and in aqueous urea solutions, was collaboratively studied. An amine chromatography column was used to separate the unreacted urea from numerous UF reaction products present in these liquid fertilizers. Unreacted urea was determined by using external urea standards with UV detection at 195 nm. The standards and test samples were prepared in the mobile phase of 85% (v/v) acetonitrile in water. Ten laboratories analyzed 5 different UF-based commercial products containing unreacted urea in the range of 6 to 17% by weight, and 5 different concentrations of urea in water equivalent to commercial products of that nature. The aqueous urea solutions contained 2-20% urea (w/w). The range of s(R) values for the 5 UF-based commercial fertilizers was 0.49-1.02 and the %RSD(R) was 1.94-6.14. The s(R) range for the 5 urea solutions was 0.10 to 0.79 and the %RSD(R) range was 2.54 to 4.88. The average recovery of urea from the aqueous urea solutions was 96-103%. Therefore, this method is capable of monitoring urea nitrogen manufacturers' label claims and total nitrogen claims in those cases where urea is the sole source of plant food nitrogen. Based on the collaborative study data, the authors recommend this method be approved for AOAC Official First Action status.

Twenty four-hour monitoring of incontinence and bladder function in a community hospital.

We wished to determine whether 24-hour monitoring of urinary incontinence without video urodynamics would provide adequate information for treatment. Twelve subjects with urinary incontinence (seven women and five men) were investigated, average age 75 years (range 44 to 89 years). Setting was a community hospital (80 beds), a nursing home, and a lodge, 60 miles from the nearest assessment center. Twenty four-hour monitoring consisted of 2 hourly preweighed pad changes, postchange weighing, Uroflow set-up in subject's bathroom, fluid intake record, and 1 postvoid residual ultrasonogram. All subjects had history and physical and evaluation of medications. Findings included probable urge incontinence, stress incontinence, chronic retention with overflow, and normal bladder function. Recommendations included oxybutynin chloride, timed toileting, timed fluid restriction, diuretic manipulation, intermittent catheterization, pessary, and surgery. At 6 weeks, 25% (4/12) were better (three with urge incontinence and one after operation for stress incontinence). Video urodynamics were conducted only for the patient with stress incontinence after operation. We suggest that 24-hour monitoring is noninvasive, is less disruptive and less expensive than video urodynamics, and provides adequate information for initial treatment in many patients with urinary incontinence.

Comments on AOAC dry ash method for digestion of mineral-mix feeds.

Phosphorus in feeds or mineral mixes containing monobasic calcium phosphate cannot be determined accurately if the sample is subjected to the dry ash procedure described in AOAC method 7.125-7.128. HCl-insoluble calcium metaphosphates are formed at the high temperature required for ashing.

Liquid chromatographic determination of aflatoxins, ochratoxin A, and zearalenone in grains, oilseeds, and animal feeds by post-column derivatization and on-line sample cleanup.

A liquid chromatographic method using on-line sample cleanup, reverse flow analytical column loading, gradient elution, and postcolumn derivatization with iodine permits direct, rapid determination of aflatoxins B1, B2, G1, and G2, as well as ochratoxin A and zearalenone. Limits of quantitation are 5 ppb for the aflatoxins and ochratoxin A and 30 ppb for zearalenone. This procedure performs well as a multimycotoxin screen for cereal grains and oilseeds, with more limited success in complete animal feeds.

Iron sulfate and feed pelleting to detoxify free gossypol in cottonseed diets for dairy cattle.

Thirty-two lactating cows were fed ad libitum diets with 1) 18.7% soybean meal, 2) diet 1 plus 500 ppm supplemental Fe from FeSO4.H2O, 3) 15% whole cottonseed, or 4) diet 3 plus 500 ppm Fe from FeSO4.H2O. Dry matter intakes were similar except for cows fed diet 2, which was lower. Cows fed whole cottonseed diets ingested 23 g/d of free gossypol per cow. Free gossypol apparently excreted was lower than its intake. Iron excretion was similar to Fe intake. Blood metabolites and productive performance did not differ among the diet groups. No signs of gossypol toxicity were observed. Twelve neonatal Holstein male calves were fed a commercial milk replacer for 4 wk, then were allowed ad libitum access to diets with 1) 27% soybean meal, 2) 50% whole cottonseed, or 3) diet 2 plus 500 ppm Fe from FeSO4.H2O. Dry matter intakes were similar but slightly lower for calves fed diet 3. Daily individual intakes of free gossypol from diets 2 and 3 were 2 g, which was lower than the expected 4 g due to an apparent effect of pelleting. Blood metabolites did not differ among the groups, and calves averaged about .6 kg of daily gain on these diets. A follow-up study showed that pelleting reduced free gossypol by as much as 70% in whole cottonseed and by 48% in cottonseed meal. Pelleting represents a mechanism to decrease the toxicity of gossypol in cottonseed products.