Development of novel detection reagent for simple and sensitive determination of trace amounts of formaldehyde and its application to flow injection spectrophotometric analysis

In this paper, a novel detection reagent for formaldehyde determination is proposed, and is applied to a simple and highly sensitive flow injection method for the spectrophotometric determination of formaldehyde. The method is based on the reaction of formaldehyde with methyl acetoacetate in the presence of ammonia. The increase in the absorbance of the reaction product was measured at 375 nm. An inexpensive light emitting diode (LED)-based UV detector (375 nm) was, for the first time, used. Under the optimized experimental conditions, formaldehyde in an aqueous solution was determined over the concentration range from 0.25 to 20.0 × 10⁻⁶ M with a liner calibration graph; the limit of detection (LOD) of 5 × 10⁻⁸ M (1.5 μg L⁻¹) was possible. The relative standard deviation of 12 replicate measurements of 5 × 10⁻⁶ M formaldehyde was 1.2%. Maximum sampling throughput was about 21 samples/h. The effect of potential interferences such as metals, organic compounds and other aldehyde was also examined. The analytical performance for formaldehyde determination was compared with those obtained by the conventional acetylacetone method, which uses visible absorption spectrophotometry. Finally, the proposed method was successfully applied to the determination of formaldehyde in natural water samples.     

A simple and rapid spectrophotometric method for determination of ultra trace amounts of thallium(III) with 4-(4'-N,N-dimethylaminophenyl) urazole as a new reagent

A simple and selective spectrophotometric method is proposed for the determination of ultra trace amounts of Tl(III). The reported method is based on the oxidation of 4-(4'-N,N-dimethylaminophenyl)urazole (DAPU) to the corresponding triazolinedione (TAD) by Tl(III) at pH 4.0. The reaction was monitored spectrophotometrically by measuring the increasing color of TAD compound at 514 nm by the fixed-time method. At a given time of 2.0 min at 30 degrees C, the working range of calibration was 5.0 x 10(-8) - 2.0 x 10(-5) M Tl(III) and detection limit of 5.0 x 10(-8) M was obtained. The influences of pH, reagent concentration, ionic strength and temperature were studied. The effect of diverse ions on the determination of Tl(III) by the proposed method was also investigated. Thallium in real samples was determined by this method, with satisfactory results.     

Simultaneous spectrophotometric determination of cyanide and thiocyanate after separation on a melamine-formaldehyde resin

A simple indirect spectrophotometric method for the determination of cyanide, based on the oxidation of the cyanide with chlorine (Cl(2)) is described. The residual chlorine is determined by the color reaction with o-tolidine (3,3'-dimethylbenzidine). The maximum absorbance for Cl(2) is at 437 nm. A linear calibration graph (0-4.0x10(-5) M CN(-)) is obtained under optimal reaction conditions at room temperature and pH 11-12. The stoichiometric mole ratio of chlorine to cyanide is 1:1. The effective molar absorptivity for cyanide is 5.87x10(4) l mol(-1) cm(-1) at pH 1.6. The limit of quantification (LOQ) is 3.6x10(-7) M or 9.4 ppb. Effects of pH, excess reagent, sensitivity, reaction time and tolerance limits of interferent ions are reported. The method was applied to the determination of cyanide in a real sample. The basic interferent usually accompanying CN(-), i.e. thiocyanate, is separated from cyanide by sorption on a melamine-formaldehyde resin at pH 9 while cyanide is not retained. Thiocyanate is eluted with 0.4 M NaOH from the column and determined spectrophotometrically using the acidic FeCl(3) reagent. The initial column effluent containing cyanide was analyzed by both the developed chlorine-o-tolidine method and the conventional barbituric acid-pyridine (Spectroquant 14800) procedure, and the results were statistically compared. The developed method is relatively inexpensive and less laborious than the standard (Spectroquant) procedure, and insensitive to the common interferent, cyanate (CNO(-)).     

A facile spectrophotometric method for the determination of selenium.

A rapid and sensitive spectrophotometric method is described for the determination of trace amounts of selenium using Variamine Blue (VB) as a chromogenic reagent. The proposed method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine, which oxidizes Variamine Blue to form a violet-colored species having an absorption maximum at 546 nm. Beer's law is obeyed in the range 2-20 g of selenium in a final volume of 10 ml. The molar absorptivity and Sandell's sensitivity were found to be 2.6 x 10(4) l mol-1 cm-1 and 0.003 microgram cm-2, respectively. The optimum reaction conditions and other analytical parameters were evaluated. The effect of interfering ions on the determination is described. The proposed method has been successfully applied to the determination of selenium in real samples of water, soil, plant materials, human hair, and synthetic samples of cosmetics and pharmaceutical preparations.     

Catalytic resonance scattering spectral method for the determination of trace amounts of Se

A new catalytic kinetic method has been proposed for the determination of Se from 8.0x10(-9) to 8.0x10(-8) M, using the fact that Se(IV) can catalyze the slow reaction between KClO(3) and phenylhydrazine sulfate (PH) in 0.1 M H(2)SO(4) solution at 100 degrees C. The reduction product of ClO(3)(-), Cl(-), reacts with Ag(+) to form (AgCl)(n) nanoparticles. The nanoparticles exhibit a maximum resonance scattering spectral peak at 470 nm. The intensity of resonance scattering light at 470 nm is linear with respect to the Se concentration, using the fixed-reaction time procedure. The factors influencing the determination of Se were examined. This catalytic resonance scattering spectral method has been applied to the analysis of Se in real samples, with satisfactory results.     

Spectrophotometric reaction rate method for determination of barbituric acid by inhibition of the hydrochloric acid-bromate reaction

A new kinetic-spectrophotometric method was developed for the determination of barbituric acid. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.9x10(-7) M and calibration rang is 1x10(-6)-6.0x10(-4) M barbituric acid. The linearity range of the calibration graph is depends on bromate concentration. The relative standard deviation of seven replication determination of 5.6x10(-6) M barbituric acid was 1.8%. The influence of potential interfering substance was studied.     

A simple spectrophotometric method for the determination of copper in industrial, environmental, biological and soil samples using 2,5-dimercapto-1,3,4-thiadiazole.

A simple spectrophotometric method is presented for the rapid determination of copper at a trace level using 2,5-dimercapto-1,3,4-thiadiazole (DMTD) as a new spectrophotometric reagent. The method is based on the reaction of non-absorbent DMTD in a slightly acidic (0.002-0.014 mol dm(-3) sulfuric acid) aqueous solution with copper(II) to produce a highly absorbent greenish-yellow chelate product that has an absorption maximum at 390 nm. The reaction is instantaneous and the absorbance remains stable for 24 h. The average molar absorption coefficient and Sandell's sensitivity were found to be 5.65 x 10(4) dm3 mol(-1) cm(-1) and 10 ng cm(-2) of CuII, respectively. Linear calibration graphs were obtained for 0.1-20 microg cm(-3) of CuII; the stoichiometric composition of the chelate is 1:2 (Cu:DMTD). A large excess of over 50 cations, anions and complexing agents (e.g. tartrate, oxalate, citrate, phosphate, thiourea, SCN-) do not interfere in the determination. The method was successfully used for the determination of copper in several Standard Reference Materials as well as in some environmental water samples, biological samples, soil samples and solutions containing both copper(I) and copper(II) and complex synthetic mixtures. The method has high precision and accuracy (s = +/-0.01 for 0.5 microg cm(-1)).     

Silver-enhanced reduction of 2,3,5-triphenyl-2H-tetrazolium by semicarbazide for the spectrophotometric determination of traces of silver(I).

A sensitive spectrophotometric method for the determination of silver is described. The reaction involves a silver-enhanced reduction of 2,3,5-triphenyl-2H-tetrazolium chloride by semicarbazide hydrochloride to yield a pink-colored product with maximum absorption at 510 nm. Beer's law is obeyed in the concentration range of 0.02-0.34 microg cm(-3) of silver, and the molar absorptivity is 4.51 x 10(5) l mol(-1) cm(-1). The optical parameters, optimum reaction conditions and interference studies have been described. The method has been applied to the determination of silver in photographic film waste water and in synthetic samples.     

Peroxidase-catalysed luminol chemiluminescence method for the determination of glutathione

A luminol chemiluminescence (CL) method was developed for the determination of glutathione (GSH). GSH was indirectly determined by measuring the amount of hydrogen peroxide formed during the Cu(II)-catalysed oxidation of GSH with oxygen. The amount of hydrogen peroxide formed was continuously measured using the Arthromyces ramosus peroxidase-catalysed luminol CL reaction. The CL intensities at maximum light emission were linearly correlated with the concentration of GSH over the range 7.5 x 10(-7)-3.0 x 10(-5) M. The detection limit for GSH was about 10 times better than that of the spectrophotometric method using Ellman reagent.     

Spectrophotometric determination of mercury in environmental sample and fungicides based on its complex with o-carboxy phenyl diazoamino p-azobenzene

In the present method a new reagent o-carboxyphenyl diazoamino p-azobenzene has been synthesised for the determination of mercury spectrophotometrically. The method is based on the reaction of mercury with the reagent in alkaline medium where the reagent is in the aci-form. The purple violet coloured dye-mercury complex showed an absorption maxima at 540 nm. Beer's law is valid over the concentration range of mercury from 0.08 to 0.8 mug ml(-1) (0.08-0.8 ppm). The molar absorptivity and Sandell's sensitivity were found to be 2.22x10(5) mol(-1) cm(-1) and 0.0009 mug cm(-2), respectively. The method has been successfully applied to the determination of mercury in air, water, soil and fungicide samples.     

Flow-injection determination of 9,10-phenanthrenequinone with catalytic photometric detection

A catalytic photometric method with a flow-injection system is described for the determination of 9,10-phenanthrenequinone. It is based on the catalytic effect of 9,10-phenanthrenequinone on the redox reaction of 1,2-dinitrobenzene with formaldehyde under alkaline conditions. 9,10-Phenanthrenequinone at the 5.0 x 10(-8)-5.0 x 10(-6)M level can be determined at a rate of 20 samples/hr. The detection limit is 1.0 x 10(-8)M (40 pg in a 10-microl injection).     

Fluorescent quenching method for determination of trace hydrogen peroxide in rain water

A simple and sensitive fluorescent quenching method for the determination of trace hydrogen peroxide (H(2)O(2)) has been proposed to determine hydrogen peroxide in rain water sample. The method is based on the reaction of H(2)O(2) with 3,3'-diethyloxadicarbocyanine iodide (DI) to form a compound which has no fluorescence in acetate buffer solution (pH 3.09). The maximum emission wavelength of the system is located at 604 nm with excitation at 570 nm. Under the optimal conditions, the calibration graph was obtained between the quenched fluorescence intensity and hydrogen peroxide concentration in the range of 5.0 x 10(-7) to 9.0 x 10(-4) mol L(-1). The proposed method was applied to determine H(2)O(2) in rain water samples, and the result was satisfactory. The mechanism involved in the reaction was also studied.     

二甲酚橙-溴酸钾体系催化动力学光度法测定微量甲醛

在硫酸介质中,溴酸钾在甲醛的催化作用下能氧化二甲酚橙褪色,其褪色程度与甲醛含量成正比,从而建立了光度法测定微量甲醛的新方法。方法的最大吸收波长为435 nm,在50℃水浴中反应10 min,甲醛含量在0～20μg/mL内呈线性关系。方法应用于废水中微量甲醛的测定,相对标准偏差为4.34%,回收率在91.0%～102.8%之间。     

Fluorimetric determination of cerium with paracetamol

A simple, sensitive and selective method for determination of cerium(IV), based on the oxidative reaction between cerium(IV) and paracetamol, has been developed. The fluorescent species is an oxidation product of paracetamol and has excitation and emission maxima at 265 and 360 nm, respectively. The fluorescent intensity of the system is linear over the range 2.0 x 10(-7)-8.0 x 10(-6)M Ce(IV). The method has been applied in the determination of Ce(IV) in synthetic mixtures and ores with good accuracy being achieved.     

Spectrophotometric determination of copper in alloys using naphthazarin

Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone; Naph) is proposed as a chromogenic reagent for the spectrophotometric determination of copper(II). The polynuclear complex has a mole ratio of Cu:Naph=4:6 in a 50% v/v ethanol/water medium containing 0.1 M ammonium acetate and 1.5% (w/v) sodium dodecyl sulfate. The copper-naphthazarin complex shows an absorption maximum at 330 nm with a molar absorptivity of 1.84x10(4) l mol(-1) cm(-1). Beer's law is obeyed up to 4.5 ppm of copper(II). The method was applied for copper determination in alloy samples with satisfactory results.     

Flow-injection determination of ascorbic acid and cysteine simultaneously with spectrofluorometric detection.

A simple and sensitive spectrofluorometric method was developed for the simultaneous determination of ascorbic acid and cysteine by a flow-injection system. This method is based on the reduction of Tl(III) with ascorbic acid or cysteine in acidic media, producing fluorescence reagent, TlCl3(2-) (lambdaex = 227 nm, lambdaem = 419 nm). The injected sample solution was divided into two separate streams. The first stream was treated with Tl(III) at pH 3.0 and then passed through a 270 cm reaction coil to the flow cell of the spectrofluorometer, where the fluorescence intensity was measured. This signal is related to ascorbic acid and cysteine concentration. The second part of the injected sample solution was treated with Tl(III) in HCl solution and then passed through a 50 cm reaction coil to the flow cell and the fluorescence intensity was measured. This signal is related only to cysteine. Thus, the ascorbic acid content was determined directly by the difference according to the calibration curve. Ascorbic acid and cysteine can be determined in the range of 1 x 10(-6) to 5.0 x 10(-5) M, at a rate of 16 samples per hour. The limits of detection (S/N = 3) were 8 x 10(-7) M for ascorbic acid and 7 x 10(-7) M for cysteine. The influence of potential interfering substances was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in real samples.     

Kinetic spectrophotometric method for the determination of ranitidine and nizatidine in pharmaceuticals

An accurate and simple kinetic method is described for the determination of ranitidine and nizatidine in pure form and in pharmaceuticals. The method is based on the reaction of the compounds with 7-chloro-4-nitrobenz-2-oxa-1,3-diazole in pH 7.4 borate buffer at 60 degrees C for a fixed time of 25 min for both compounds. The absorbance of the reaction product is measured at 495 nm for ranitidine and nizatidine. Calibration graphs were linear over the concentration range of 2-20 microg/mL, with limits of detection of 0.13 (3.7 x 10(-7) M) and 0.25 microg/mL (7.5 x 10(-7) M) for ranitidine and nizatidine, respectively. The proposed method was applied successfully to the determination of ranitidine in tablets and ampoules with average recoveries of 100.26+/-0.69 and 100.29+/-0.59%, respectively, and to the determination of nizatidine in capsules with an average recovery of 104.26+/-0.44%. The results obtained are in good agreement with those obtained by the other methods used for comparison. A proposal of the reaction pathway is also presented.     

High-performance liquid chromatographic method for determining trichothecene mycotoxins by post-column fluorescence derivatization

The method described here is based on a separation of deoxynivalenol, nivalenol and fusarenon-X on a C18 column using aqueous acetonitrile, and successive post-column fluorescence derivatization involving an alkaline decomposition to form formaldehyde and modified Hantzsch reaction with methyl acetoacetate and ammonium acetate (lambda ex = 370 nm and lambda em = 460 nm). By this method, 5-10 ng of the standard trichothecenes could be determined. By employing a clean-up procedure with a florisil column and a Sep-Pak CN cartridge, 61.4-96.9% recoveries were obtained for deoxynivalenol and nivalenol added to corn, wheat and barley at concentration levels of 0.05-1 ppm.     

The fluorimetric determination of formaldehyde

A sensitive fluorimetric procedure for formaldehyde has been developed. The method, which can measure 0.01 μg formaldehyde, is based on the Hantzsch reaction between acetylacetone, ammonia, and formaldehyde. The product, 3,5-diacetyl-I,4-dihydrolutidine, is colored yellow and fluoresces yellow green. Infra-red spectra indicate that this compound is ionic in dilute solution and aggregated in concentrated solution. The Hantzsch reaction may be extended for the assay of other aldehydes, amines, and β-diketones.     

Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.