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.     

Degradation of pesticides in nursery recycling pond waters

Recycling or collection ponds are often used in outdoor container nursery production to capture and recycle runoff water and fertilizers. Waters in recycling ponds generally have high concentrations of nutrients, pesticides, and dissolved organic matter, as well as elevated salinity and turbidity. Little is known about pesticide degradation behavior in the unique environment of nursery recycling ponds. In this study, degradation of four commonly used pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters from two nursery recycling ponds was investigated at an initial pesticide concentration of 50 microg/L. Results showed that the persistence of diazinon and chlorpyrifos appeared to be prolonged in recycling pond waters as compared to surface streamwaters, possibly due to decreased contribution from biotic transformation, while degradation of chlorothalonil and pendimethalin was enhanced. Activation energies of biotic degradation of all four pesticides were lower than abiotic degradation, indicating that microbial transformation was less affected by temperature than chemical transformation. Overall, the pesticide degradation capacity of recycling ponds was better buffered against temperature changes than that of surface streamwaters.     

Colorimetric determination of arprinocid in feed.

An analytical method has been developed for the determination of arprinocid (9-(2-chloro-6-fluorophenylmethyl)-9H-purin-6-amine) in feed, based upon measurement of the absorbance of the diazo chromophore formed from a product of zinc reduction of the drug in acidic solution. The analyte is extracted from the feed into chloroform in the presence of a pH 7 phosphate buffer and isolated by adsorption chromatography on alumina, followed by partitioning between hexane and 0.15M HCl. The reduction product in the aqueous phase is then treated for colorimetric measurement. This procedure has been applied to determining 0.0010--0.0080% arprinocid in feed with a precision of less than 5% relative standard deviation near the middle of this concentration range. Of 32 feed additives examined, only zoalene and sulfamethazine were serious interferences. A study and discussion of several factors, e.g., reaction time, pH, and amount of zinc metal, that affect the analytical reactions are also included.     

Colorimetric determination of stanozolol in pharmaceutical formulations

In acidic medium, stanozolol reacts with phenoldisulfonic acid to form a stable yellow chromophore, which is quantitated by spectrophotometry at 385 nm. The reaction gives a linear response at concentrations from 5 to 50 micrograms/mL. The method is suitable for routine analytical control of stanozolol and its formulations.     

Colorimetric determination of tetracycline hydrochloride in pharmaceutical preparations

A simple, sensitive, and rapid colorimetric method is presented for the estimation of tetracycline hydrochloride as the pure drug and in formulations. The proposed method is based on the reaction of tetracycline HCl with cupric chloride in an alkaline medium to give a yellowish green solution whose absorbance is measured at 400 nm against a reagent blank. The color obeys Beer's law in the concentration range of 0-20 micrograms/mL. Molar absorptivity and Sandell's sensitivity of the yellowish-green copper complexes of tetracycline HCl are 1.99 X 10(4) L X mol-1 X cm-1 and 0.0241 ppm, respectively.     

Colorimetric determination of caffeic acid in plant materials

A new colorimetric method is described for determining caffeic acid content in plant materials. Caffeic acid is separated by thin layer chromatography from the alcoholic extract, and color is developed using 0.5% aqueous thiosemicarbazide solution under alkaline conditions. The absorbance is read at 475 nm. Lambert-Beer's law is obeyed in the concentration range 0.37-17.5 micrograms caffeic acid/mL. The method is reproducible and has been applied to the estimation of caffeic acid in carrot roots.     

Colorimetric determination of tetracycline derivatives in pharmaceutical preparations

A quick colorimetric method is reported for the determination of tetracycline derivatives such as oxytetracycline hydrochloride (OTCH), chlortetracycline hydrochloride (CTCH), methacycline hydrochloride (MCH), and doxycycline hydrochloride (DCH). The method involves complexation of the above derivatives with cupric chloride in alkaline medium. The yellowish green copper complexes of OTCH, CTCH, MCH, and DCH show maximum absorbance at 395, 410, 400, and 400 nm, respectively. The color intensity obeys Beer's law in the concentration range of 0-20 micrograms/mL.     

Colorimetric determination of diazepam in pharmaceutical preparations.

A colorimetric method is presented for the estimation of diazepam as the pure drug and in formulations. Diazepam is hydrolyzed with 6N HCl to 2-methylamino-5-chlorobenzophenone, which is extracted with chloroform to give a yellow solution whose absorbance is measured at 410 nm against a solvent blank. The color obeys Beer's law in the concentration range of 0-30 mug/ml. In 5 determinations, recovery was 99.0 +/- 1.9%. The method is applicable to pure diazepam and its formulations for oral and parenteral use. No interferences were observed from pyridoxine hydrochloride and commonly used preservatives, vehicles, and colors.     

Colorimetric determination of hydralazine with 9-chloroacridine

A spectrophotometric assay for hydralazine hydrochloride based on the interaction of the drug with 9-chloroacridine has been developed. The interaction shows an absorption maximum at 460 nm and is affected by temperature, heating time, and quantity of acridine reagent used. Color development is maximum when the drug is heated in the presence of a 30-fold molar excess of the acridine in a 50 +/- 1 degree C water bath for 1 hr. The method detects hydralazine hydrochloride in the 10(-5)--10(-6)M range with sensitivity to 0.2 micrograms/mL and 3--4% accuracy. Typical calibration data obtained from linear regression analysis of absorbance at various drug concentrations show r = 0.9997 (n = 6). Hydralazine can be determined in dosage forms that also contain varying quantities of reserpine and hydrochlorothiazide. The 9-chloroacridine method is as sensitive as other spectrophotometric procedures for hydralazine but also more accurate and precise, and involves fewer manipulative steps.     

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.     

Colorimetric determination of propoxur and its residues in vegetables

A method has been developed for the determination of propoxur (o-isopropoxyphenyl N-methylcarbamate) based on the hydrolysis of propoxur with methanolic potassium hydroxide to its phenol and coupling with diazotized 4,4-diaminodiphenyl sulfone. The orange complex formed has an absorption maximum at 500 nm and obeys Beer's law in the range 0.25-5.0 micrograms/mL. The method can be applied to levels as low as 0.5 ppm propoxur from vegetables.     

Potential transformations of chromium in natural waters

A study has been conducted on the transformation of Cr(III) and Cr(VI) in simulated natural water conditions. It has been found that these forms are readily interconvertible under natural water conditions. The results of this study indicate that Cr(VI) is reduced by Fe(II), dissolved sulfides, and certain organic compounds with sulfhydryl groups, while Cr(III) is oxidized by a large excess of MnO₂ and at a slow rate by Oz under conditions approximating those in natural waters. Based on the results of these studies, water quality standards for Cr should be based on total Cr rather than on Cr(VI), as has been frequently done in the past.     

Colorimetric determination of sympathomimetic amines methyldopa and noradrenaline

The chromogenic reagent p-dimethylaminocinnamaldehyde (PDAC) is introduced for the determination of the sympathomimetic amines methyldopa and noradrenaline. The method is based on measurement of the orange color developed when the alkaline solution of methyldopa and noradrenaline is allowed to react with PDAC at pH 5.0. The color developed obeys Beer's law in the concentration range 0.1-1.5 mL of 2 X 10(-3)M solution of noradrenaline and methyldopa. The results are compared with those obtained with another chromogenic reagent, p-dimethylaminobenzaldehyde (PDAB). Determinations on dosage forms of the drugs, using PDAC and PDAB reagents, agreed well with results of determinations by official pharmacopoeial methods.     

Colorimetric method for the determination of lipoxygenase activity

A colorimetic assay for lipoxygenase activity has been developed. The assay is based on the detection of the lipoxygenase reaction product, linoleic acid hydroperoxide, by the oxidative coupling of 3-methyl-2-benzothiazolinone (MBTH) with 3-(dimethylamino)benzoic acid (DMAB) in a hemoglobin-catalyzed reaction. This test reaction is rapid and sensitive, and it offers advantages over other methods for detecting lipoxygenase activity. The assay is capable of detecting activity in a number of crude vegetable homogenates and should be particularly useful where a rapid visual determination of lipoxygenase activity is desired.