Rapid acid digestion and simple microplate method for milk iodine determination

Iodine deficiency leads to deficiency of thyroid hormones, which causes mental retardation in infant. Laboratory confirmation is important in its diagnosis. The major problems associated with the existing methods for iodine determination in milk samples are: 1) nonsafe alkaline solution; 2) harsh thermal condition; and 3) extra time required to complete various steps. In this study, a simple and rapid colorimetric method was investigated, which used acid digestion in combination with a rapid microplate reading format method to determine the total iodine content in milk. Sample digestion was done on 50 microL milk in metavanadate/perchloric, at 230 degrees C for 10 min. After digestion, iodine determination was based on the Sandell-Kolthoff reaction. The reaction results were read in 96-well microplates by an enzyme-linked immunosorbent assay (ELISA) reader. The determination range of the assay was between 2 and 40 microg/dL. The within-run coefficient of variation percent in three levels (3, 12, and 36 microg/dL) ranged from 6.7 to 9.3 and between-run coefficients of variation ranged from 8.6 to 12.3%. The results obtained (n=70) by the optimized method have good correlation with the results of alkaline incineration as a reference method (n=70; r2=0.907; y=0.952x+1.77). Recovery tests for accuracy assessment in six levels from 6.2 to 34.2 microg/dL) were between 91.3 and 113%. This method has enabled us to achieve 0.12 microg/dL sensitivity. The results of this study show that a quick acid digestion combined with mild thermal and low sample volume with a quick reading of assay results were the main advantages of the acid digestion and microplate reading format.     

Assessment of iodine intake in mildly iodine-deficient pregnant women by a new automated kinetic urinary iodine determination method.

Maternal iodine deficiency can compromise the thyroid status of the mother, fetus and newborn child. Therefore, it is important to assess the iodine excretion level of groups of pregnant women. In this study we aimed to determine iodine intake in pregnancy using a recently reported automated kinetic method for urinary iodine determination. Urinary iodine measurements of 123 pregnant women (18 first, 28 second and 77 third trimester) were carried out using a new automated kinetic assay based on the Sandell-Kolthoff reaction at 37 degrees C and its kinetic measurement at 340 nm in a random-access automated analyzer after ammonium persulfate digestion at 95 degrees C in a water bath with +/-0.1 degree C precision. Statistical analyses were carried out using SPSS software. Whole group, first trimester, second trimester and third trimester urinary iodine concentrations (mean+/-SD) in pregnant women were 1.13+/-0.81, 1.08+/-0.71, 0.86+/-0.58 and 1.27+/-0.87 micromol/L, respectively. The urinary iodine concentration significantly increased with gestational age (p<0.05). We found that our study group was mildly iodine-deficient according to WHO criteria. Furthermore, the pregnant women were found to be mildly iodine-deficient in the first and third trimesters and moderately so in the second trimester. The only statistical difference was between second and third trimester values (p<0.05). Even though the increased iodine deficiency in the second trimester is not useful for early detection of iodine deficiency in pregnancy, the severity of this deficiency in the second trimester may lead to important effects on thyroid metabolism for both mother and fetus. Our study suggests that the iodine excretion of pregnant women living in iodine-deficient areas could be assessed using this fast and automated method.     

Colorimetric method for determination of urinary methylmalonic acid

The colorimetric method for the determination of methylmalonic acid by coupling with diazotised p-nitroaniline has been re-examined. Extraction of the diazotised product into amyl alcohol and tetra-methyl ammonium hydroxide considerably increases its stability and sensitivity and reduces background absorbance. Preliminary solvent extraction and ion-exchange chromatography are desirable but can be accomplished simply and quickly using very small quantities of urine. In this form, the method is very reliable and gives recoveries of about 95% and a coefficient of variation of about 7%.     

Simple method for determination of thiocyanate in urine.

BACKGROUND: It would be useful to develop a simple kit method for determination of thiocyanate in urine, which could be used to monitor cyanide overload in cassava-consuming populations. METHODS: The method was based on the quantitative oxidation of thiocyanate in acid permanganate at room temperature in a closed vial with liberation of HCN, which reacted with a picrate paper. For semiquantitative analysis in the field, the colored picrate paper was matched with a color chart prepared using known amounts of KSCN. In the laboratory, a more accurate result was obtained by elution of the colored complex in water and measurement of the absorbance at 510 nm. Over the range 0-100 mg/L, there was a linear relationship given by the equation: thiocyanate content (mg/L) = 78 x absorbance. RESULTS: The picrate thiocyanate method gave no interference with urine samples containing protein at less than 7 g/L, 21 amino acids, histamine, glucose, NaCl, urea, blood, and linamarin. For 53 urine samples analyzed by an accurate column method and the thiocyanate picrate method, a regression line gave very good agreement (r(2) = 1. 000). Quantitative recoveries of thiocyanate added to urine samples were obtained with the picrate method. CONCLUSIONS: A simple picrate kit for determination of thiocyanate in urine was developed and is available free of charge for workers in developing countries.     

Simple method for monitoring 24-hour urinary urea nitrogen excretion

The urine urea nitrogen/urine creatinine excretion ratio (UUN/UCr) of a "spot" urine specimen obtained approximately 5 hours after the last meal of the day can be used to accurately calculate the urinary urea excretion for the previous 24-hour period. Because UUN excretion is largely determined by dietary intake of protein nitrogen, this method can be used to estimate dietary protein intake for the previous 24-hour period. Strategies for using this simple method for inexpensively and continuously monitoring dietary protein intake are discussed.     

A method for the quantitative determination of urinary glycosaminoglycans

A method is presented by which the urinary glycosaminoglycans can be isolated in a macromolecular fraction with complete recovery by preparative gel filtration. The urinary glycosaminoglycans can be quantitated by determinations of uronic acid and sulfaminohexose in the macromolecular fraction. Using untreated, random urine specimens of less than 5 ml volume, clinical mucopolysaccharidoses types I, II, and III could be readily distinguished.     

A new method for the determination of urinary poryphrins

The authors present an original method for the quantitative determination of total urinary porphyrins and an electrophoretic separation technique for the identification and fractional determination of uroporphyrins, of coproporphyrins and of the 7, 6, 5 carboxyl groups porphyrins.     

A method for the determination of urinary metabolites of tryptophan

A method is described for the estimation of the urinary tryptophan metabolites, 3-hydroxy-anthranilic acid, l-kynurenine, 3-hydroxy-kynurenine and xanthurenic acid. They were separated by thin-layer chromatography and measured fluorimetrically. In the case of l-kynurenine and 3-hydroxy-kynurenine, the fluorimetric analysis was preceded by hydrolysis with kynureninase, to anthranilic acid and 3-hydroxy-anthranilic acid, respectively. The precision, accuracy and lower limits of sensitivity of the method were determined.