Spectrophotometric determination of polyacrylamide in waters containing dissolved organic matter

Using polyacrylamide (PAM) to reduce soil erosion in irrigated land has increased rapidly in recent years. A simple and reliable method to measure the PAM concentration in waters containing dissolved organic matter (DOM) is of great importance in assessing the fate and efficiency of PAM application. In this research, an analytical method to determine the PAM concentration of waters with correction for DOM interference was developed and tested. The method is based on a combination of determining the total concentration of amide groups by the N-bromination method (NBM) and determining the DOM content spectrophotometrically. The total concentration of amide groups of both PAM and DOM was determined by NBM at 570 nm. The DOM moiety, which is proportional to DOM concentration, was determined by spectrophotometry using a UV 254-nm wavelength. The actual PAM concentration of a water sample (soil extract containing PAM in this study) was obtained from NBM readings subtracted by the interferential DOM contribution using a correction curve. Analysis of PAM in two soil-water samples showed that the recoveries ranged from 94 to 100.3% for the 2 mg/L PAM sample and from 98.4 to 101.4% for the 10 mg/L PAM sample with various DOM concentrations. The coefficients of variation were <6% in all cases.     

Spectrophotometric determination of silicon in soil solutions by flow injection analysis: Reduction of phosphate interference

Abstract

A flow injection analysis (FIA) procedure for the determination of dissolved silica (0.04–20 mg/L Si) in aqueous solution has been optimized to reduce phosphate interference. Determinations are based on measurement of absorbance at 790 nm of heteropoly molybdenum blue formed by reduction with ascorbic acid at room temperature. Phosphate did not interfere in a 15‐fold excess. The optimized procedure was tested on soil solutions isolated by centrifugation of various horizons from a Typic Haplohumod. Si concentrations of 1.3–4.8 mg/L Si were found with a variation coefficient of about 2. Results obtained compared well with those obtained by a manual reference method and a proprietary FIA method except in solutions high in dissolved humic material where slightly higher values were obtained by the optimized method. In a standard addition mode the optimized method yielded 5–15% lower values than in the ordinary mode. This difference was reduced by persulfate oxidation of organic matter. Soil solutions investigated were very low in phosphate but phosphate spiking experiments demonstrated that phosphate interference was less than in model solutions matched in metal ion concentrations and insignificant in solutions low in humic material and with less than 10 mg/L P. Dissolved silica was unstable in a solution isolated from an organic horizon of high biological activity.     

Spectrophotometric determination of cyanoglucosides in cassava

A new method is reported for determination of cyanoglucosides in cassava. The method is simple, rapid, and sensitive. Ten g cassava tuber is homogenized with warm (65-70 degrees C) 80% ethanol (1 + 6, w/v) to extract cyanoglucosides (CNG). The ethanol is evaporated, and an aliquot of the extract (0.1-0.2 mL) is incubated with added linamarase in pH 6.0 phosphate buffer for 15 min at 30 degrees C. The reaction is stopped by adding 0.2 N sodium hydroxide, the solution is neutralized, and cyanide is estimated by adding chloramine T and barbituric acid-pyridine reagent and measuring the absorbance at 570 nm. Complete CNG extraction and rapid inactivation of endogenous linamarase is possible with 80% ethanol. There is no interference from extractives in the linamarase reaction or in the estimation of cyanide. Recovery of added linamarin (as cyanide) is 98% by this assay. The minimum detection limit of cyanide in the assay is 0.1 micrograms/mL.     

Automated mercury determination in waters

A rapid technique for dissolved Hg determination in water at ultra-trace level is described. It consists of the automatisation of the cold-vapor/gold amalgamation/atomic fluorescence technique, which allows the determination of 8 samples per hour with an analytical precision of 5 % and a 0.1 ng.l^?1 detection limit for a 45 ml sample. It is suitable for Hg determination in most of the natural waters.     

Spectrophotometric determination of substrate-borne polyacrylamide

Polyacrylamides (PAMs) have wide application in many industries and in agriculture. Scientific research and industrial applications manifested a need for a method that can quantify substrate-borne PAM. The N-bromination method (a PAM analytical technique based on N-bromination of amide groups and spectrophotometric determination of the formed starch-triiodide complex), which was originally developed for determining PAM in aqueous solutions, was modified to quantify substrate-borne PAM. In the modified method, the quantity of substrate-borne PAM was converted to a concentration of starch-triiodide complex in aqueous solution that was then measured by spectrophotometry. The method sensitivity varied with substrates due to sorption of reagents and reaction intermediates on the substrates. Therefore, separate calibration for each substrate was required. Results from PAM samples in sand, cellulose, organic matter burnt soils, and clay minerals showed that this method had good accuracy and reproducibility. The PAM recoveries ranged from 95.8% to 103.7%, and the relative standard deviations (n = 4) were <7.5% in all cases. The optimum range of PAM in each sample is 10-80 microg. The technique can serve as an effective tool in improving PAM application and facilitating PAM-related research.     

Spectrophotometric determination of phosphine residues in rice

Phosphine residues were determined in 2 types of rice samples, raw polished and parboiled. The yellow chromophore due to phosphine from raw polished rice had 2 absorption maxima, a strong one at 370-380 nm and a weaker one at 400-410 nm. The chromophore from parboiled rice also had 2, one at 390-400 nm and the other at 410-420 nm. A closed system containing rice and a phosphine tablet or powder yielded 93-99% recovery of fortified phosphine. At any given dose of phosphine, parboiled rice retained a higher amount of residue after aeration than did raw polished rice.     

Spectrophotometric determination of organic carbon in soil

Abstract

A detailed study was made of the well‐known organic carbon determination that is based on measuring the absorbance of the green chromium(III) complex generated when organic matter is oxidized by potassium dichromate in acidic medium. The green chromic colour proved to be unstable, turning slowly to a violet colour. It was also found that chromic sulphate exerts a catalytic influence on the decomposition of excess dichromate. Based on this work, a modified method was developed which is simple, rapid, and very accurate when working under carefully controlled conditions.     

Spectrophotometric determination of tolbutamide in tablets.

Two spectrophotometric methods, Glenn's method of orthogonal function and the basic dye method, are described for determing tolbutamide in tablets without interference from the tablet excipients. In Glenn's method, the absorbance of tolbutamide in 95% ethanol is measured in the vicinity of 250--270 nm at 4 nm intervals and the p2 coefficient is calculated. The coefficient is linearly related to concentration within a range of 0.1--0.4 mg/mL. Tolbutamide gives a complex of a ratio 1:1 with basic dye Brilliant Cresyl Blue (BCB) or Safranin T (ST). The complex is easily extracted with chloroform. The absorbance of the chloroform extract is measured against either a blank or reference experiment. The latter is obtained by using a specific concentration of tolbutamide: 0.4 mg/mL in tolbutamide-BCB or 0.024 mg/mL in tolbutamide-ST. The ST complex method is more sensitive compared with the other methods. When the t-test is applied, the results of the proposed methods are more accurate than those of the traditional ultraviolet spectrophotometric method.     

Determination of phosphate in waters by flow injection analysis

A flow injection system for the determination of phosphate in natural water samples is reported. Phosphate is reacted with molybdate ion and Rhodamine B in an acid medium to yield a complex whose absorbance is monitored at 586 nm. The method thus developed is applicable to the determination of phosphate ion at the ppb level at a sampling rate of 55 samples hr^?1.     

Spectrophotometric determination of vitamin A in oils and fats

A spectrophotometric method for determining vitamin A based on interaction with 50% trichloroacetic acid solution in dichloromethane was developed. The blue reaction product had a maximum absorption at 620 nm and obeyed Beer's law over the concentration range of 0.5-5.0 microgram retinol/ml solution. The molar absorptivity of the reaction product was 1.58 X 10(5). As much as 100 microgram vitamin D2, and beta-carotene up to 12 times the vitamin A concentration, did not interfere with the determination. The results obtained from the determination of vitamin A in cod liver oil and butter showed excellent agreement with the Carr-Price method, 43.013(d).     

Spectrophotometric determination of urea in sugar cane distilled spirits

Urea is an important precursor in the formation of ethyl carbamate, a known carcinogen in alcoholic beverages. Ethyl carbamate has recently been detected at high concentrations in sugar cane distilled spirits, but little is known about the concentration of urea in these beverages. The objectives of this study were to validate methodology for the determination of urea in sugar cane distilled spirits, to determine the levels in 68 samples from different regions within the state of Minas Gerais, Brazil, and to examine the relationship between the concentrations of urea and ethyl carbamate. The method, based on the reaction of urea with 1-phenyl-1,2-propanodione-2-oxime and spectrophotometric quantification at 540 nm, provided linear response from 0.5 to 15.0 mg/L. No purification of the sample was required. The limits of detection and quantification were 0.1 and 0.5 mg/L, respectively. Urea was detected in 69% of the samples at levels varying from 0.50 to 5.10 mg/L. There was no significant difference on the levels of urea in samples from different regions of the state. No significant correlation between the levels of urea and ethyl carbamate was observed for the samples analyzed.     

Rapid field determination of nitrate in natural waters

Abstract

Brucine, an organic reagent used for nitrate determinations, proved stable for at least one year when dissolved in methanol. This makes possible a consistently accurate and rapid method for field determinations of nitrate in clear solutions with a minimum of equipment. The method is also useful in the laboratory for determining nitrate in water or soil extracts. It is quicker and simpler than other colorimetric methods and more sensitive to low concentrations than the nitrate electrode.     

Spectrophotometric determination of allylisothiocyanate in mustard seed oil.

Allylisothiocyanate is determined spectrophotometrically after reaction with 2,3-dichloro-1,4-naphthoquinone. For pure samples, the color intensity is proportional to allylisothiocyanate content in the range 0.8-3.0 mg/ml reaction mixture. A modified procedure is used to estimate allylisothiocyanate content of mustard seed oil. The reaction is linear for allylisothiocyanate concentrations in the range 40-240 mug/ml reaction mixture. Two mustard seed oil samples contained 0.995 not equal to 0.020 and 0.981 not equal to 0.019% allylisothiocyanate.     

Spectrophotometric determination of piperazine and its salts in pharmaceuticals

A spectrophotometric determination of piperazine and some of its salts is described. The method depends on the UV measurement of the N-nitroso derivatives formed by the interaction of piperazine with nitrous acid. The chromophore is developed by heating the reaction mixture at 80 degrees C for 15 min, at pH 2.3--2.6. Beer's law is obeyed in the range 1--15 micrograms/mL.     

Spectrophotometric determination of some catecholamine drugs using metaperiodate

A rapid spectrophotometric procedure for the determination of isoprenaline salts, levodopa, dopamine hydrochloride, and dobutamine hydrochloride, either in the drug substances or in pharmaceutical formulations, is described. The method is based on the development of orange, red, or violet products with sodium metaperiodate in an aqueous alcoholic medium. The reaction is suggested to proceed via oxidative cyclization of the catecholamine to form an aminochrome. The wavelengths of maximum absorption range from 465 to 520 nm. The structure of the cyclization product was confirmed by ultraviolet, infrared, and nuclear magnetic resonance spectroscopy and microanalysis data.     

Spectrophotometric determination of cyclamate in foods: NMKL collaborative study

A spectrophotometric method for the determination of cyclamate was collaboratively studied in 9 laboratories. Ethyl acetate is added to extract cyclamate from acidic aqueous solution into water, and the cyclamate is then quantitatively converted to N,N-dichlorocyclohexylamine by adding excess hypochlorite. N,N-Dichlorocyclohexylamine is determined by measuring its UV absorption at 314 nm. Six samples, 3 soft drinks with cyclamate levels of 0.36-0.47 g/kg and 3 jams with levels of 1.23-1.50 g/kg, were included in the study. Average recoveries of cyclamate were 99.7% in the soft drinks and 103.8% in the jams. Reproducibility coefficients of variation were 6.7% for the soft drinks and 4.4% for the jams.     

Spectrophotometric determination of strychnine and brucine in liquid galenicals.

A rapid method is presented for determining strychnine and brucine in liquid galenicals. At pH 5.0, both strychnine and brucine are complexed with methyl orange. After treatment with 0.1N NaOH, the liberated alkaloids are determined spectrophotometrically, using the 2-wavelength method of analysis. The method has been successfully applied to the analysis of 4 batches of nux vomica tincture, nux vomica acid, and nux vomica alkaline mixtures. The method has a relative standard deviation of 0.52%.