Highly selective spectrophotometric flow-injection determination of trace amounts of bromide

Spectrochimica Acta Part A 60(2004)2053–2057Highly selective spectrophotometric flow-injection determination of trace amounts of bromide by catalytic effect on the oxidation ofm -cresolsulfonephthalein by periodateAli A.Ensafi∗,B.Rezaei,S.NourooziCollege of Chemistry,Isfahan University of Technology,Isfahan 84156,IranReceived 12May 2003;received in revised form 12May 2003;accepted 6November 2003AbstractA new flow-injection method is reported for the determination of bromide.The method is based on catalytic effect of bromide on the oxidation of m-cresolsulfonephthalein by periodate in acidic media.The reaction was followed spectrophotometrically by measuring the decrease in absorbance at 528nm.The influence of pH,reagent concentration and manifold variables on the sensitivity was studied.Under optimum conditions,a calibration graph was obtained in the range of 0.160–20.00␮g ml −1bromides with a limit of detection of 0.150␮g ml −1bromide.The relative standard deviation for ten replicate measurement of 1.0␮g ml −1bromide was 2.1%.The influence of potential interfering ions on the selectivity was studied.The method successes to measure bromide in the presence of other halide ions.The method was used to measure bromide in river water and tap water.©2003Elsevier B.V .All rights reserved.Keywords:Bromide;Catalytic;m -Cresolsulfonephthalein;FIA1.IntroductionBromide is trace element in natural waters and biological fluids in the concentration range of 10−4to 10−8M.For this purpose,catalytic methods are considered to be most suit-able because of the high sensitivity and sufficient accuracy.Several catalytic-spectrophotometer methods have been re-ported for determination of bromide [1–7],some of these methods [1–5]based on the catalytic effect of bromide on the iodine-permanganate reaction,are sensitive,but chloride ions interfere seriously.The other method based on catalytic effect of bromide on the oxidation of pyrocathecol violet by hydrogen peroxide [6],but iodide ion interferes seriously.Tomiyasu et al.[7]have been reported a sensitive methods for determination of bromide using tetrabase-chloramine T reaction,but the method has narrow linear calibration range and suffer many interfering ions such as iodide at ng ml −1specially.Flow-injection analysis widely used as a simple and convenient approach to rapid analysis,in which varying∗Corresponding author.Tel.:+98-311-3912351;fax:+98-311-3912350.E-mail address:ensafi@cc.iut.ac.ir (A.A.Ensafi).the flow rate of the solution and the length of reaction coil can easily control the reaction time.The application of a flow-injection technique to catalytic method should offer a reproducible,rapid and rather convenient procedure for routine determinations of trace amount of bromide.Some flow-injection methods have been reported for de-termination of bromide [8–13],but these methods were not sensitive enough to determine bromide at trace lev-els or suffer from interfering ions especially iodide and chloride.This paper describes a FI-spectrophotometric procedure for the determination of bromide,by its catalytic on the oxidation of m-cresolsulfonephthalein with periodate.The method has been successfully applied to the determination of bromide in river and tap water samples.2.Experimental 2.1.ReagentsAll the solution was prepared using reagent grade chem-icals.Double distilled water was used for preparation of solutions.1386-1425/$–see front matter ©2003Elsevier B.V .All rights reserved.doi:10.1016/j.saa.2003.11.0032054 A.A.Ensafiet al./Spectrochimica Acta Part A60(2004)2053–2057Fig.1.Manifold system used for bromide determination.A bromide solution,500␮g ml−1was prepared by dis-solving0.0745g KBr(Merck)in water in a100ml volumet-ricflask.The working solutions were prepared by diluting this solution with water daily,m-cresolsulfonephthalein solution,0.001M,was prepared by dissolving0.0382g of the reagent(Merck)in mixture of EtOH/H2O(0.10/1.0), in a100ml volumetricflask.Sodium periodate solution, 0.100M,was prepared by dissolving 2.1389g NaIO4 (Merck)and diluting to100ml with water in a100ml volumetricflask.2.2.ApparatusA manifold diagram of theflow system employed is shown in Fig.1The decrease in absorbance was measured with Shimadzu Model6A V,equipped with theflow-through cell of(20ul inner volume)1.0cm optical path,its out-put was connected to Shimadzu signal processing(Model C-R4AX Chromatopac).A12-channel peristaltic pump (Desaga,Model PLG)with three silicon rubber tubes (1.0mm i.d.)was used.PTFE mixing joints and PTFE tub-ing(1.0mm i.d.)was used for the connections and for the mixing coil.The controlled water bath(Gallen-Kamp,BLG, 220V)was used at a given temperature of40±0.1◦C. Sample solutions were injected using a rotary Rheodyne valve with a sample loop of200l.2.3.ProcedureAs shown in Fig.1,H2O(R1),m-cresolsulfonephthalein (R2)and mixture of HCl/IO4−(R3)solutions were pumped at13.5ml h−1for each channel via a peristaltic pump.The standard solution-containing(160–20,000ng ml−1Br−) sample was injected into a carrier stream(H2O)at point S. The sample stream was directly treated with other reagents and passed toflow cell of the spectrophotometer where the decrease in absorbance at528nm is measured.3.Results and discussionThe oxidation reaction of m-cresolsulfonephthalein (MCP)with periodate in acidic media is so slow.On the other hand,the oxidation reaction goes to the fast in the presence of bromide ion at trace levels.The reaction can be followed spectrophotometrically by measuring thedecrease Fig.2.Variation of absorbance of m-cresolsulfonephthalein–periodate sys-tem with time in the presence of bromide.Conditions:MCP,7.8×10−5M; periodate,0.0010M;HCl,0.80M;Br−,0.500␮g ml−1;temperature, 30◦C;time interval for each scan,60s.in absorbance of MCP at528nm(Fig.2).By increasing bromide concentration,the absorbance of the reagent at characteristic band decreased linearly at afixed time of the initiation of the reaction.In order to maximize the sensitivity,the influence of acid type and concentration,reagents concentration,and mani-fold variables on the reaction was studied.Signal of bro-mide in hydrochloric acid medium is larger than other acidic (H2SO4,HNO3,H3PO4)media.The influence of hydrochlo-ric acid concentration on the peak heights was studied with 7.05×10−5M(MCP),6.0␮g ml−1Br−and0.025M IO4−. Fig.3shows that by increasing HCl concentration,the sen-sitivity increased.Therefore,1.4M HCl was selected. Fig.4shows the effect of MCP concentration on the sen-sitivity(peak height)with the1.4M HCl,6.0␮g ml−1Br−and0.025M IO4−.The results show that the sensitivity in-creased by increasing MCP concentration up to7.0×10−5M Fig.3.Influence of HCl concentration on the sensitivity.Conditions: MCP,7.0×10−5M;Br−,6.0␮g ml−1;periodate,0.025M;flow rate, 1.0ml min−1for each channel;Reaction coil length,200cm;Sample volume,20␮l;temperature,40◦C.A.A.Ensafiet al./Spectrochimica Acta Part A 60(2004)2053–20572055Fig.4.Influence of m -cresolsulfonephthalein on the sensitivity.Conditions:such as Fig.3with 1.4M HCl.whereas greater amount of the reagent cause decrease in sensitivity by increasing of noise.Therefore,7.0×10−5M of MCP was selected for the study.The influence of periodate concentration on the sensitivity was studied with the optimum concentration of HCl and MCP in the presence of 6.0␮g ml −1Br −(Fig.5).The results show that the sensitivity increased by increasing periodates concentration up to 0.070M,and then level off.Therefore,0.070M IO 4−was selected for further study.The effect of temperature on the sensitivity was checked in the range of 22–60◦C with the optimum reagent concen-tration and 6.0␮g ml −1Br −.The results showed that peak height increases by increasing temperature up to 40◦C,and then it’s decreased.Therefore,40◦C was selected.The sample volume injected into the carrier line has sig-nificant effect on the peak height.The signal increaseduponFig.5.Effect of periodate concentration on the sensitivity.Conditions:such as Fig.4.Fig.6.Influence of sample injection volume on the peak height.Condi-tions:such as Fig.4with 0.070M periodate.increasing the sample volume,but this increasing is slowly and cause broadening of the peaks.Thus,for the rate of anal-ysis and peak shape (sharper)200␮l for the sample volume is selected (Fig.6).The peak height depends on the residence time of the sample zone in the system,e.g.on the total flow rate and length of reaction coil.The effect of the pump flow rate was checked over the range 0.5–1.5ml min −1.The signal decreased with increasing flow rate.This is due to the fact that at higher flow rate,the residence time was decreased,thus oxidation reaction and the consumption of MCP is decreased,thus causing decreasing peak heights.From the results,and for best peak shape (sharper)and rate of analysis,the flow rate of 0.7ml min −1is chosen for study (Fig.7).The increase of reaction coil length on the sensitivity was studied at a constant flow rate.Increase in length of reaction coil from 150to 335cm increased the sensitivity,which is related to the longer residence time for the reaction mixture,whereas a longer reaction coil does not affect sensitivity,but only cause peak broadening.Thus,base on the results shown in Fig.8,250cm for the reaction coil length was selected as the optimum.4.Calibration graph and reproducibilityFig.9shows typical flow signals for the injection of 1.00and 5.00␮g ml −1bromide solution obtained under the opti-mum conditions using the flow system shown in Fig.1.The calibration graph was linear from 0.160to 20.00␮g ml −1bromide with regression coefficient of r 2=0.9989.By using the signal to noise ratio equal to 3as a limiting requirement,the experimental detection limit was found to be 0.150␮g ml −1.The precision of the method was tested by injection of 15samples.2056 A.A.Ensafiet al./Spectrochimica Acta Part A 60(2004)2053–2057Fig.7.Effect of pump flow rate on the peak heights.Conditions:such as Fig.4.Fig.8.Influence of length of the reaction coil on the sensitivity.Condi-tions:such as Fig.4with flow rate of 0.7ml min −1for each channel.The standard deviations for 15replicate determinations of 1.00and 5.00␮g ml −1bromide were 3.48and 2.1%,re-spectively.The sampling rate was 27h −1.5.Influence of interferenceThe effect of more than 25ions on the determination of 1.00␮g ml −1Br −was studied.The tolerance limit was de-fined two time of standard deviation of determination ofTable 1Interferences in the determination of bromide (1.00␮g ml −1)SpeciesTolerance limit (W ion /W Br −)Pb(II),Mn(II),Al(III),Cr(VI),Mo(VI),F −,CH 3COO −,NO 3−,SO 4−,PO 4−,C 2O 42−,CO 32−,HCO 3−,ClO 3−1000Ni(II)600Fe(III)300Sn 2+,SO 32−200Cu(II),I −150Hg(II)60As(III)50SCN −351.00␮g ml −1bromide (in the absence of interfering ions).Table 1shows that many ions;especially iodide did not in-terfere with bromide.Ions,which are to participate in redox reactions as either oxidizing or reducing agent such as S 2−and BrO 3−,cause serious interference.6.Determination of bromide in water sampleIn order to test the applicability of the method,the proce-dure was applied to the determination of bromide in river and tap water samples after passed through a filter paper (What-man No.1)and then through a column (10cm ×1.0cm)containing cation exchange resin.The determinations were made by standard addition method.The results are shown in Table 2that shows good agreement between added bromide and recoveries.A.A.Ensafiet al./Spectrochimica Acta Part A60(2004)2053–20572057 Table2Determination of bromide in real samplesSample no.Bromide added(␮g ml−1)Bromide found(␮g ml−1)Recovery(%)River water10.00.05–20.80.841053 1.2 1.251044 1.6 1.641025 2.0 1.9397Tap water10.000.0–20.800.775973 1.20 1.231024 1.60 1.59995 2.00 1.9999.5 Dimeh spring water(Isfahan)10.00.04–20.800.841003 1.20 1.19984 1.60 1.62995 2.00 2.0299.57.ConclusionThe method described is significant with respect to the development of simple manifold for determining traces of bromide in the presence of other halide.Its simplicity,ex-cellent reproducibility,freedom from some interference ions and broad range of bromide determination are coupled with the high speed of the FIA technique.AcknowledgementsThe authors are acknowledging to the Center of Excel-lency of IUT and Research Council for support of this work.References[1]M.J.Fishman,M.W.Skougstad,Anal.Chem.35(1963)146.[2]G.S.Pyne,M.J.Fishman, 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