Method For Determination Of Urea Research Articles

Spectrophotometric methods for the determination of urea in real samples using silver nanoparticles by standard addition and 2nd order derivative methods

In this work, we have developed simple, sensitive and inexpensive methods for the spectrophotometric determination of urea in urine samples using silver nanoparticles (AgNPs). The standard addition and 2nd order derivative methods were adopted for this purpose. AgNPs were prepared by chemical reduction of AgNO3 with hydrazine using 1,3-di-(1H-imidazol-1-yl)-2-propanol (DIPO) as a stabilizing agent in aqueous medium. The proposed methods were based on the complexation of AgNPs with urea. Using this concept, urea in the urine samples was successfully determined spectrophotometric methods. The results showed high percent recovery with ±RSD. The recoveries of urea in the three urine samples by spectrophotometric standard addition were 99.2%±5.37, 96.3%±4.49, 104.88%±4.99 and that of spectrophotometric 2nd order derivative method were 115.3%±5.2, 103.4%±2.6, 105.93%±0.76. The results show that these methods can open doors for a potential role of AgNPs in the clinical determination of urea in urine, blood, biological, non-biological fluids.

Validation of a LC–MS Method for the Determination of Urea Contamination in Market Teas

Tea is one of the most widely consumed beverages in the world preceded only by water. In some culture style of tea plant, urea fertilizer is sprayed on tea leaf in order to increase crop output; besides, in some processing method of green tea, urea is illegally added to maintain tea’s vivid color. The above-mentioned process may unavoidably cause urea residue, and prolonged or repeated exposure of body to urea may cause adverse effects. In this work, an easy and reliable hydrophilic interaction liquid chromatography/mass spectrometry analytical method for determination of urea in tea was firstly validated; the method exhibited a linear response from 4 to 60 μg mL−1 (R 2 > 0.9996), the limit of quantitation for urea is 4 μg mL−1, the mean recoveries of urea spiked at levels of 10 and 20 μg mL−1 were 95–110 %, and the relative standard deviations of intra- and inter-day measurements were less than 7.8 %. The method was later successfully applied to the analysis of urea residue in some market tea samples. The result showed that there is obvious urea contamination in some market teas, and the contamination percentage is especially high in green tea samples. Among the samples investigated, urea was detected at concentration ranges of 24.02–46.02 mg/kg. Some attention should be paid on the health effect resulting from such urea contamination in tea.

Determination of Urea in Atmospheric Aerosols and Natural Waters - A Cation Exchange Method

An ion exchange chromatographic method has been developed for the determination of urea in freshwater, rainwater, and water-extracted aerosol samples. The method provides a fast and reliable way to determine the concentration of urea without the use of harmful chemicals or large amounts of time devoted to sample preparation. The method utilizes a Dionex IonPac CS12 cation exchange column and UV detection at 190 nm. A comparison between the new method described in this manuscript and a previously published method for urea determination in rainwater and water-extracted aerosol samples is also presented. This comparison shows potential interferences from other organic N compounds similar to urea when using the previously published method. Tests utilizing various pH values and the enzyme urease also confirmed the ability of the new method to determine the concentration of urea within atmospheric aerosols and natural waters.

A Fluorometric Determination of Urea With Urease

ABSTRACT A sensitive fluorometric method was developed for the determination of urea. The method was based on the hydrolyzation of urea catalyzed by urease with pH and the change of fluorescence intensity of sodium fluorescein as a pH sensitive dye in the enzymatic reaction. The increase in fluorescence intensity of sodium fluorescein was measured at λex= 490 nm and λem= 514 nm. Under the optimum conditions the assay responded linearly to urea concentration in the range of 0.25 to 3 mM with a correlation coefficient of 0.996. This study also demonstrated the feasibility of a fluorometric method for urea determination with fiber optic detection. The probe response also displayed good linearity in the range of 0.10 to 1.75 mM urea.

Determination of arginase activity in macrophages: a micromethod

We propose a modification of Schimke's method for urea determination as a valuable micromethod for measuring arginase in activated macrophages. The method exhibits the following advantages: (a) it uses small amounts of samples (approximately 25 000 macrophages per assay); (b) it does not interfere with other related metabolites that are also present in the activated macrophage such as citrulline or arginine; (c) saturating concentrations of the substrate arginine can be used; and (d) it is much more sensitive than Schimke's method and can detect small amounts of urea, in the order of 0.02 μmol.

Potentiometric determination of urea with perchloric acid in acetic anhydride

A potentiometric method for the quantitative determination of urea is proposed. Urea is titrated with perchloric acid in acetic anhydride solvent. This method is rapid and less costly than the semi-micro Kjeldahl method. In addition, its accuracy is nearly identical with that of Kjeldahl's method. An analysis of a given sample is completed in about 30 min.

A modified manual method for the determination of urea in seawater using diacetylmonoxime reagent

A manual method for the quantitative determination of urea in seawater was developed based on the reaction of urea with diacetylmonoxime. Critical factors include the treatment of collection bottles, sample storage, pre-filtration techniques, water purification, reaction temperature and reproducible cooling of samples during analysis. The limit of detection was 0·14 μg-at urea-N 1 −1 with Beer's Law being obeyed in the range tested of 0–15 μg-at urea-N 1 −1 . The precision (±1 SD) of replicate samples of 1,2 and 15 μg-at urea-N 1 -1 was 0·024, 0·019 and 0·03 μg-at urea-N 1 −1 ( n = 10) respectively.

Flow Injection Analysis for the Determination of Urea in Cow’s Milk

An inexpensive and easily automated flow injection method for determination of urea in cow’s milk was evaluated. Urea is hydrolysed by urease and in a gas diffusion cell the ammonia formed passes a membrane into an indicator solution. The resulting colour change of the indicator is measured at 590 nm. The repeatability of the analysis, expressed as the coefficient of variation (C.V.), was between 0.5 and 1.2%. Measured (y) and expected (x) milk urea concentrations after addition of known amounts of urea were related according to the equation y = 1.00× – 0.12 with a C.V. for the regression of 1.8%. Recommended amounts (0.02 %) of the preservative bronopol (2-bromo-2-nitropropane-1,3-diol) added to the milk did not affect the results (P > 0.05).

Evaluation of a reflectance photometric method for determination of urea in blood, plasma, or serum.

Evaluation of a reflectance photometric method for determination of urea in blood, plasma, or serum.

Analytical application of the urease method for determination of urea in the presence of biuret

Biuret does not interfere in the urease-catalysed hydrolysis of urea.

Determination of urea in natural water by an improved Newell method

The method for determination of urea in sea water proposed by Newell et al. was re-examined in detail and partly modified. The following method is recommended.To 25 mlof a sample solution are added 3 g of sodium chloride for fresh water or 2 g for sea water (Fig. 1), 3 mlof concentrated sulfuric acid and 1 mlof the mixed reagent (4.0 g of diacetyl monoxime, 0.05 g of semicarbazide hydrochloride and 15 g of MnCl24H2O in 200 mlof water). The solution is allowed to stand for 90 min at 70°C (Fig. 2). After cooling in running water, the absorbance is measured at 520 mμ against water using a 5-cm cell. The blank is measured by the same procedure with distilled water for fresh water or artificial sea water for sea water. The common ions in natural water and nitrogen-containing compounds do not interfere as seen in Table I. Although citrulline, which is produced by decomposition of arginine, gives a positive error, it is unlikely that such amount of citrulline exsists in natural water. The molar extinction coefficient for urea is 22000. The relative standard deviations were 3 and 5% at the concentration of 86 and 43 μg urea/l, respectively.

Determination of urea in water by electric conductivity measurement after decomposition by urease

Colorimetric method for determination of urea in aqueous solutions using urease and Nessler reagent is the standard process, especially in the clinical analysis. In this method, however, the color is unstable and a careful control of conditions is necessary for obtaining accurate results.The method proposed here is to determine urea by a measurement of electric conductivity of the solution after the decomposition of urea by glycerine extract of urease. It is applicable to the concentration range from 1 to 104ppm of urea in water. The method is simple and accurate, although further developments are necessary for removing influences by a number of ions present in sample solutions.

Determination of Urea in Blood and Urine with Diacetyl Monoxime-Glucuronolactone Reagent

Abstract A simple method for determination of urea in blood and urine with diacetyl monoximeglucuronolactone reagent is presented. The stability of the color produced permits analysis of a large number of samples at one time. Deproteinization of blood is accomplished with sodium tungstate and alum.

Colorimetric Determination of Urea in Feeds

Abstract A collaborative study was undertaken this year on the DMAB method for the colorimetric determination of urea in dry corn samples, which was compared with method 22.023-22.024. The DMAB method uses p-dimethylami-nobenzaldehyde as the color producer for spectrophotometry measurement. Mean values showed excellent recovery by both the official procedure and the DMAB procedure. Over-all standard deviation and coefficient of variation for all three dry corn samples containing urea indicated greater precision and accuracy by the DMAB procedure; collaborators expressed preference for this method. Further work is recommended to finalize the determination of urea in feeds.

A spectrophotometric method for determination of urea

If phenazone is substituted for perchloric acid or arsenic pentoxide in the diacetylmonoxime reaction for urea determination, a colored product is formed, apparently from a double condensation of phenazone with diacetylmonoxime and urea. The color has a maximum absorption at 460 mμ. Beer's law is followed for concentrations of urea ranging from 0.1 to 2 μg/ml in the final reaction mixture. The sensitivity is very high ( E 1 cm 1% 5.900), the color is stable, and the reaction seems to be specific. It is very simple and is routinely performed on an amount of filtrate corresponding to 10 μl of blood.

Corrections-Conductivity Method for Determination of Urea

Corrections-Conductivity Method for Determination of Urea

Conductivity Method for Determination of Urea

Conductivity Method for Determination of Urea

Nitrogen Solutions Analysis, Rapid Method for Determination of Urea in Nitrogen Solutions

Nitrogen Solutions Analysis, Rapid Method for Determination of Urea in Nitrogen Solutions

Spectrophotometric Method for Determination of Urea

Spectrophotometric Method for Determination of Urea

A Note on the Distillation of Ammonia in the Folin and Wu Method for the Determination of Urea in Blood

A simple modification of the distillation procedure in the Folin and Wu method for the routine determination of urea in blood has proved extremely helpful for our hospitals. The changes proposed resulted from an attempt to overcome the trouble which some workers, particularly students and others of little experience in the laboratories, had encountered with the distillation process of the original method. The principal causes of difficulty were (1) frothing in the distillation tube with the carrying over of some of the contents, (2) sucking back of the distillate, and (3) blowing out of the distillate from the receiving tube by steam as a result of too rapid distillation. Elimination as far as possible of these potential sources of error in the original procedure has met with considerable success. We have abandoned the use of the loosely fitting rubber stopper on the long arm of the bent glass tubing to hold the 25 cc. graduated receiving test tube* in position. Instead, we place this test tube in a 600 cc. beaker filled with cold water and bring it into place for distillation by raising the beaker so that the end of the glass tubing comes well below the surface of the 0.05 normal hydrochloric acid in the receiving test tube. The beaker is held in position during the distillation by a wooden block of suitable size.