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A spectrophotometric assay method for vanadium in biological and environmental samples using 2, 4-dinitrophenylhydrazine with imipramine hydrochloride

A spectrophotometric assay method for vanadium in biological and environmental samples using 2, 4-dinitrophenylhydrazine with imipramine hydrochloride
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  Environ Monit Assess (2012) 184:181–191DOI 10.1007/s10661-011-1957-2 A spectrophotometric assay method for vanadiumin biological and environmental samplesusing 2,4-dinitrophenylhydrazinewith imipramine hydrochloride Naef Ghllab Saeed Al-Tayar · P. Nagaraja · R. A. Vasantha · Ashwinee Kumar Shresta Received: 9 February 2010 / Accepted: 9 February 2011 / Published online: 6 April 2011© Springer Science+Business Media B.V. 2011 Abstract  Asimple,rapid,andsensitivemethodin-volving the interaction of 2,4-dinitrophenylhydrazinewith imipramine hydrochloride in presence of va-nadium (V) in sulfuric acid medium has been pro-posed for the determination of vanadium. Thepurple-colored product developed showed an ab-sorption maximum at 560 nm and was stable for24 h. The working curve was linear over theconcentration range of 0.1–2.8  µ  g ml − 1 , with sen-sitivity of detection of 0.0124  µ  g ml − 1 . Molar ab-sorptivity and Sandell’s sensitivity were found tobe 2.6 × 10 4 l/mol cm and 0.0039 µ  g cm − 1 , respec-tively. The accuracy of the proposed method wasassessed by Student’s  t   test and variance ratio  F  test, and the results were on par with the reportedmethod. The method was successfully used in thedetermination of V in water, human urine, soil,and plant samples, and it was free from interfer-ence by various concomitant ions. N. G. S. Al-Tayar · P. Nagaraja ( B ) · A. K. ShrestaDepartment of Studies in Chemistry, Universityof Mysore, Manasagangotri, Mysore570 006, Indiae-mail: profpn58@yahoo.comR. A. VasanthaDepartment of Chemistry, Teresian College,Mysore, India Keywords  Vanadium · 2,4-Dinitrophenylhydrazine · Imipraminehydrochloride · Spectrophotometry · Environmental samples · Biological samples Introduction Vanadium (V), though a useful element in themanufacture of printing inks, pigments, in glassindustries, in cleaning and repairing of oil firedboilers, particularly in electricity power stations(Hirayama and Leyden 1986; Meier and Werner1989; Chau 1992), is considered to be the index element in urban environmental pollution, espe-ciallyinairpollution(LangardandNorseth1986).Vanadiumreleasedintotheenvironmentfromva-nadium refineries, iron, steel industries, and burn-ing of fossil fuels enters the air and settles eitheron the soil or water. Food contaminated with va-nadium from soil, when consumed, is storedprimarilyinfattytissues,theninkidney,spleen,orbone and is excreted through urine. Vanadiumpentaoxide dust and fume cause gastrointestinaland respiratory disturbances, conjunctivitis, phar-yngitis,andpersistentcough(ZenzandBerg1967).Even vanadium in trace amounts ( ≈ 0.5 mg L − 1 )was found to inhibit cholesterol synthesis and in-crease the oxidation of fatty acids of liver phos-pholipids (Stokinger 1981), which may result innervous depression, vomiting, diarrhea, irritation  182 Environ Monit Assess (2012) 184:181–191 of mucous membranes, and bronchopneumonia.However, laboratory and epidemiological evi-dence suggest that vanadium may be beneficial inthepreventionofheartdisease(Eatonetal.1995). The toxicity of vanadium depends on its oxi-dation state. Vanadium in  + 5 state is found tobe more toxic than  + 4 state (Patel et al. 1990). Vanadium in trace amounts (at microgram perliter level) serves as an essential component fornormal cell growth in plants and is found tobe toxic at higher concentrations (Rehder 2003).Vanadium acts as a growth-promoting factor andhelps in fixation and accumulation of nitrogen inplants (Taylor and Van Staden 1994). However,at higher concentration, it becomes potentially adangerous chemical pollutant that can play havocwith the productivity of plants, crops, and theentire agricultural system. Therefore, greater em-phasis is made for the determination of vanadiumin biological and environmental materials.Many methods for the determination of vana-dium have been reported. The usual way todetermine vanadium content in environmentalsamples is to use spectrometric methods suchas atomic absorption spectrometry (Chakrabortyand Das 1994), inductively coupled plasma–massspectrometry (Noguchi 2008), inductively coupled plasma–atomic emission spectrometry (Danzaki1992; Osamu Noguchi et al. 2009; Hakim et al. 2007), inductively coupled plasma–optical emis-sionspectrometry(Wuilloudetal.2000),voltame- try (Ensafia and Naderi 1997), high-performance liquid chromatography (Wang et al. 1995), spec- troflurimetry (Kawakubo et al. 1995), ion chro-matography inductively coupled plasma–opticalemission spectrometry (Coetzee et al. 2002), andETAAS (Saavedra et al. 2004). However, thesetechniques require highly expensive instrumentsfor routine analysis, which every laboratory can-not afford. Some of the reported methods re-quire specific electrodes. The catalytic methodsreported, though highly sensitive (Mohamed andFawy 2000; Ensafi et al. 1999), lack simplicity and/or time consuming. Hence, accurate deter-mination of vanadium at microgram levels usingsimple, rapid, and cost-effective technique is of paramount importance.Severalspectrophotometricmethodshavebeenreported in the literature for the determinationof vanadium in environmental and biologicalsamples, using various reagents such as 1,8-diaminonaphthalene (Gao et al. 2000), 4-(2- pyridylazo) resorcinol (Abbas et al. 2001), 2- (5-chloro-2-pyridylazo)-5-dimethylaminophenol(Zucchi et al. 1998),  N  , N  ′ -bis(2-hydroxyl-3-sulfopropyl)-tolidine (Shigenori et al. 2003),2-(2-quinolylazo)-5-diethylaminophenol (Qiufenet al. 2004), variamine blue (Kiran Kumar andRevanasiddappa 2005), tannic acid (Serrat andMorell 1994), dopamine hydrochloride (SureshKumara et al. 2007),  p -methyldibromoarsenazowith potassium bromate (Zhai et al. 2008), andthionine and potassium bromate (Linshan et al.2007).Manyofthesemethodsaretedious,requireextraction, involve the use of activators for cat-alytic photometric determination, and suffer frominterference by a large number of diverse ions.In order to determine vanadium at microlevels in environmental and biological samples,an attempt was made to develop a simple,rapid, and reliable spectrophotometric methodinvolving oxidative coupling reaction of 2,4-dinitrophenylhydrazine (2,4-DNPH) with imipra-mine hydrochloride (IPH) in presence of V insulfuric acid medium. Materials and methods InstrumentsSystronics spectrophotometer model 106 with 1-cm matched glass cell was used for all spectralmeasurements.Reagents and solutionsAll the chemicals used in the analysis were of ana-lytical reagent grade or of highest purity. Doubledistilled water was used throughout the experi-ment for dilution of the reagents and samples.Glass vessels were cleaned by washing with acid-ified solution of K 2 Cr 2 O 7 , followed by washing  Environ Monit Assess (2012) 184:181–191 183 withconcentratedHNO 3  andrinsingseveraltimeswith distilled water.Standard stock solution of V (100  µ  g ml − 1 )Standard stock solution containing 100  µ  g/ml of V was prepared by dissolving 0.2393 g of ammo-nium meta vanadate (E-Merck, India) in 1,000-mlvolumetric flask and diluted up to the mark with0.01 M HCl. Working solutions were prepared byappropriate dilution of the standard solution.2,4-Dinitrophenyl hydrazineA 1% ( w / v ) solution of 2,4-DNPH was preparedby dissolving 1 g of 2,4-DNPH (SD Fine Chemi-cals, India) in 10 ml concentrated H 2 SO 4 , dilutedup to 100 ml with double distilled water andstored in refrigerator maintaining temperature of 0–10 ◦ C. The solution thus stored was stable for10 days.Imipramine hydrochlorideA 0.1% ( w / v ) solution of IPH was prepared bydissolving the requisite amount of IPH (BDH,England) in water and stored in dark-coloredbottle in refrigerator maintaining temperature of 0–10 ◦ C. The solution thus stored was stable for1 month.Sulfuric acid (1:1)This solution was prepared by diluting a knownvolume of concentrated sulfuric acid (RanbaxyLaboratories Ltd., Hariana, India) with equal vol-ume of double distilled water.Solutions of foreign ionsSolutions containing suitable concentrations of potentially interfering ions were prepared in dis-tilled water or in appropriate solvent to assesstheir interference if any, in the determination of vanadium.Other solutionsAll other solutions used in the experiment like or-thophosphoric acid, acetic acid, hydrochloric acid,sulfamic acid, and sodium fluoride were preparedby dissolving requisite amounts of the reagents indistilled water.General procedureTo a series of 10-ml standard flasks which con-tained1–28 µ  gofV,1mlof(0.1%)ofIPHreagentsolution, and 1 ml of (1%) 2,4-DNPH reagentsolution were added. The mixture was shakenthoroughly and kept aside for 2 min. The solutionin each standard flask was then made up to themark with 1:1 sulfuric acid. The purple color wasformed instantaneously after addition of sulfuricacid and had a maximum absorbance at 560 nm.The absorbance was measured against the corre-sponding reagent blank, and the calibration graphwas constructed.Determination of vanadium in water samplesWater samples from different sources in the en-vironment (100 ml each) were collected, filtered,and analyzed for vanadium content by the pro-posedmethod,andresultswerenegativeforV.Tothese samples, known amounts of V were spikedand analyzed by the proposed procedure.Determination of vanadium in human urineUrine samples were filtered through WhatmanNo. 1 filter paper and stored in plastic contain-ers without adding any preservative. The sam-ples were analyzed immediately to avoid possiblespecies transformation or interconversion. About50 ml of the urine sample were concentrated to5 ml by evaporation. To this solution was spikeda known amount of vanadium and mixed with5 ml of concentrated HNO 3  and 5 g of K 2 SO 4  andheated to dryness. The process was repeated twoto three times and then HNO 3  (1:3, 25 ml) wasadded to the residue and digested on a water bath  184 Environ Monit Assess (2012) 184:181–191 for 30 min. The contents were again evaporatedto dryness, cooled, and the residue was dissolvedin water and filtered (Suresh Kumara et al. 2007).The mixture was diluted to a known volume withwater and vanadium content in urine was deter-mined by the proposed method.Determination of vanadium in soil sampleThe soil samples collected represented the uppertop soil layer with a thickness of 20 cm. The sam-ples were dried and ground in a tungsten carbidemilling system to a grain size of less than 200  µ  m.Sodium carbonate solution (25 ml of 0.1 M) wasadded to accurately weighed (0.25 g) soil sampletaken in a glass beaker. The contents were boiledfor 15 min and filtered through Whatman No. 1filter paper. The precipitates were washed severaltimes with 0.1 M Na 2 CO 3  with distilled water.The final volumes of sample solutions were madeto 25.0 ml with distilled water (Mandiwana andPanichev 2004). The resulting solution was thenanalyzed by the proposed method.Determination of vanadium in plant samplesTheplantleaf(grass)samplewaswashedwithdis-tilled water to get it free from adhering soil. It wascarefully wiped with filter paper before taking itsweight.Na 2 CO 3  solution(25ml,0.1M)wasaddedto accurately weighed 0.25 g plant sample takenin a 50-ml glass beaker. The contents were boiledfor 15 min and filtered through Whatman No. 1filter paper. The precipitates were washed severaltimes with 0.1 M Na 2 CO 3  followed by distilledwater. The final volumes of sample solutions wereadjusted to 25.0 ml with distilled water (Panichevet al. 2006). The resulting solutions were analyzed by the proposed method. Results and discussion V oxidizes 2,4-DNPH at room temperature toform daizonium cation which immediately getscoupled with IPH in sulfuric acid medium result-ing in the formation of a purple-colored species.Absorption spectra of colored speciesThe proposed method involved the formation of purple-colored species. The wavelength of maxi-mum absorbance of the colored species was iden-tified by scanning the sample over the range of 400–800nm for differentconcentrations of V. Theoptimum wavelength for maximum absorbancewas found to be at 560 nm, at which the reagentblanksshowedslightabsorbanceornoabsorbanceas shown in Fig. 1.Optimization of reaction conditionsTo enhance the performance of the proposedmethod for the determination of V, effect of IPHand 2,4-DNPH was studied by using a fixed con-centration of V in 10-ml standard flasks. It wasfound that 0.1% IPH in the range of 0.2–2 ml wasneeded for getting maximum color intensity.Hence, 1 ml of 0.1% IPH was selected for all fur-ther studies. Different volumes of 1% of 2,4-DNPH were tested, and reliable results wereobtained in the range of 0.2–2 ml of 1% of 2,4-DNPH. Hence, 1 ml of 1% of 2,4-DNPH was,therefore, used for further experiments. Similarexperiments were carried out with the above-selected concentrations of IPH and 2,4-DNPH tostudy the effect of different acids on the forma-tion, sensitivity, and stability of the colored spe-cies.Acidslikehydrochloricacid,orthophosphoric 470 490 510 530 550 570 590 610 630 650 670 690 Wavelength (nm)       A     b    s    o    r     b    a    n    c    e Reagents Blank 0.75 µg/ ml Vanadium+Reagents1.5 µg/ ml Vanadium+Reagents2.25 µg/ ml Vanadium+Reagents Fig. 1  Absorption spectrum of Vanadium with 2,4-DNPHand IPH  Environ Monit Assess (2012) 184:181–191 185 acid, sulfuric acid, and acetic acid were used attheir optimum concentrations. It was observedthat acetic acid did not give color, whereas hy-drochloric acid gave color with less sensitivity andlinearity. Although orthophosphoric acid gavegoodcolor,itlackedlinearity.Hence,sulfuricacid(1:1) was selected which gave the best results withrespect to sensitivity, linearity, and stability of the purple colored species. The calibration graphsfor the different acids used for the determinationof various concentrations of V within Beer’s lawrange were plotted and are shown in Fig. 2.Analytical featuresUnder the optimum conditions, the calibrationgraph for the determination of vanadium in therange of 0.1–2.8  µ  g ml − 1 has given a coefficientregression of 0.9993 (Fig. 3). The molar absorp-tivity and Sandell’s sensitivity were calculatedand found to be  2 . 6 × 10 − 4 l mol − 1 cm − 1 and0.0039  µ  g cm − 1 , respectively. The detection limitand quantification limit were found to be 0.0124and 0.0376  µ  g ml − 1 , respectively. Ten replicatedeterminations for 1.5  µ  g ml − 1 of V were takento calculate the relative standard deviation whichwas found to be 0.23%. Beer’s law range, molarabsorptivity, Sandell’s sensitivity, and other pa-rameters of the oxidation coupling mixture aregiven in Table 1. The precision and accuracy of  the method was studied by analyzing the reactionmixture containing known amount of the citedreagents within Beer’s law limit. The low values 0.4 0.8 1.2 1.6 2 2.4 Vanadium (V) concentration µg/ ml       A     b    s    o    r     b    a    n    c    e 1:1 Sulphuric acid1:2 Hydrochloric acid1:1 Orthphosphoric acid Fig. 2  Effect of different acids on the color development y = 0.2539x - 0.0028R 2  = 0.9993 0 0.10. 2 Vanadium Concentration (µg/ml)       A     b    s    o    r     b    a    n    c    e Fig. 3  Beer’s law graph for vanadium with 2,4-DNPH andIPH obtained for relative standard deviation and alsofor the error indicated high accuracy of the pro-posed method.Effect of non-target speciesThe effect of various non-target species in thedetermination of V was investigated. Solutioncontaining 1.5  µ  g ml − 1 of V and different concen- Table 1  Optical parameters of the determination of vana-dium with IPH and 2,4-DNPHParameters CharacteristicColor Purple λ max  (nm) 560Stability (h) 24Beer’s law range ( µ  g ml − 1 ) 0.1–2.8Molar absorptivity (l mol − 1 cm − 1 ) 2.6 × 10 4 Sandell’s sensitivity ( µ  g cm − 2 ) 0.0039Optimum photometric range ( µ  g ml − 1 ) 0.2–2.6Detection limit ( µ  g ml − 1 ) 0.0124Quantification limit ( µ  g ml − 1 ) 0.0376Regression Equation a Correlation coefficient 0.9993Slope (a) 0.2539Intercept (b) 0.0028Standard deviation b 0.0036Relative standard deviation b (%) 0.23Reaction time (min) 2 a Y   = ax + b  where  x  is the concentration of vanadium inmicrograms per milliliter and  Y   is the absorbance b Ten replicates measurements
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