JEP20120200007_38548421_教学案例设计_教学研究_教育专区.pdf

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1、Journal of Environmental Protection,2012,3,187-193 http:/dx.doi.org/10.4236/jep.2012.32023 Published Online February 2012(http:/www.SciRP.org/journal/jep)187Direct Cadmium Monitoring in Cigarette Filters Leachate by Molecular Fluorescence Mara Carolina Talio1,Tristn A.Bonfiglioli2,Marta O.Luconi2,Li

2、liana P.Fernndez1,2*1Instituto de Qumica de San Luis(INQUISAL-CONICET),Chacabuco y Pedernera,San Luis,Argentina;2rea de Qumica Analtica,Facultad de Qumica,Bioqumica y Farmacia,Universidad Nacional de San Luis,San Luis,Argentina.Email:*lfernandunsl.edu.ar Received November 17th,2011;revised December

3、15th,2011;accepted January 17th,2012 ABSTRACT This work proposes a new direct flourimetric methodology for cadmium traces quantification based on its association with azo-reagent SPADNS and rhodamine B dye.Experimental variables that influence on fluorimetric sensibility were optimized using uni-var

4、iation assays.The calibration graph using zeroth order calibration was linear from 0.192 to 1.26 104 gL1,with a correlation coefficient of 0.99.Under the optimal conditions,it was obtained a limit of detection of 0.057 gL1 and a limit of quantification of 0.192 gL1.The method showed good sensitivity

5、,adequate selectivity with good tolerance to foreign ions,and was applied to the determination of trace amounts of cadmium in filters leachates coming from unsmoked,automatically smoked and smokers smoked cigarettes with satisfactory results.The proposed method represents an innovative application o

6、f luminescence to metal analysis comparable in sensitivity and accuracy to atomic spectroscopies.Keywords:Cadmium Traces;SPADNS;Rhodamine B;Molecular Fluorescence;Cigarette Filters Leachate 1.Introduction Tobacco smoke is an aerosol consisting of solid/liquid droplets(particulate phase)in a gaseous

7、phase generated by the combustion of its components at high temperature 1.More than 4000 compounds have been identified in environmental tobacco smoke 2,3.Cigarette filter was introduced in 1954,when doctors and researchers announced a possible link between lung diseases and smoking 4,5.The presence

8、 of a“filter”on the end of a cigarette implied a theoretical reduction of harmful smoke constituents entering their smoker body,introducing the concept of“safe smoking”.Although the principal purpose of filters is to absorb some of the harmful chemicals of tobacco smoke,a filter has its own chemical

9、s that affect smokers and the envi-ronment.Nowadays,butts or cigarette filters are the main source of waste in the world,discarding on average 4.5 trillion cigarette butts each year 6.Due to they are made of acetate,a non-biodegradable material,they re-main long time in the environment being a poten

10、tial source of contamination.When smokers do not discard cigarette butts properly,the butts can end up in water systems,where they pollute the water by leaking out the toxically substances they were designed to retain and preconcentrate.Cadmium is a known carcinogen and is one of the components of t

11、obacco 7.It has been proved quanti-tatively that exposure to cigarette smoke is harmful to both active and passive smokers.It can cause alterations in the enzymatic,renal,respiratory and digestive systems,with a very long half-life.Smokers may absorb amounts comparable to normal daily intake in the

12、diet,i.e.from 0.1 to 0.2 mg inhaled cadmium per cigarette,with ab-sorption of approximately 50%.Cadmium traces determination result a main topic in environmental,monitoring control processes and toxico-logical-clinical areas.They are frequently determined by atomic techniques such as atomic absorpti

13、on spectrome-try,inductively coupled plasma(ICP)-atomic emission spectrometry and ICP-mass spectrometry associated to a previous preconcentration step 8-11.Particularly,cad-mium determination in biological and environmental sam-ples at ultra-trace levels,have been supported by ET-AAS with in-atomize

14、r trapping 12.The application of molecular fluorescence in cadmium traces determination has put in evidence analytical ad-vantages such as high sensitivity,proper selectivity and wide dynamic range when it is associate to separation/preconcentration step 13,14.Taking into account the development of

15、simple,fast,sensitive and precise methodologies for cadmium traces determination results imperative,the aim of present work *Corresponding author.Copyright 2012 SciRes.JEP Direct Cadmium Monitoring in Cigarette Filters Leachate by Molecular Fluorescence 188 is to propose an alternative methodology t

16、o traditional atomic spectroscopies for cadmium monitoring in filter leachates,not including any separation/preconcentration step,using an instrument accessible in control laborato-ries.Fluorimetric determination of cadmium is based on the formation of a ternary association complex with SPADNS azo-r

17、eagent and rhodamine B,a methyl-xan-thene dye(RhB).2.Experimental 2.1.Reagents Stock solutions of Cd(II)1 105 molL1 were prepared by dilution of 100 gmL1 standard solution plasma-pure(Leeman Labs,Inc.).Buffer acetic/acetate(Mallinckrodt Chemical Works,New York,Los Angeles,St.Louis,USA)1 102 molL1 so

18、lution was prepared.This solution was adjusted to the desired pH,with aqueous NaOH(Mallinckrodt Chemical Works)using a pHmeter(Orion Expandable Ion Analy-zer,Orion Research,Cambridge,MA,USA)Model EA 940.Stock of RhB solution 1 106 molL1(Fluka AG,Chemische Fabrik,Buchs SG,Switzerland)and SPA-DNS(tris

19、odium salt of 2-(4-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic,Merck,Darmstadt,Germany)1 106 molL1 solution were weekly prepared by dis-solution of the appropriate amount of each,in ultrapure water.The stability of solutions was checked by spec-trophotometric measurements.All used reagen

20、t were analytical grade.2.2.Apparatus Spectrofluorimetric measurements were made using a Shimadzu RF-5301 PC spectrofluorophotometer equipped with a 150 W Xenon lamp and 1.00 cm quartz cells.2.3.General Procedure An adequate aliquot of filter leachate solutions(25 L-250 L)coming from unsmoked,automa

21、tically smoked or smokers smoked cigarettes,Cd(II)aliquot(0.19 gmL1-1.26 104 gmL1),100 L buffer acetic-acetate solu-tion 1 10-2 mol L-1(pH=5.8),250 L RhB(1 106 molL1)and 100 L SPADNS(1 106 molL1)were placed in a 10 mL glass volumetric flask.The whole mixture was diluted to 10 mL with ultrapure water

22、.Fluo-rescent emission was measured at em=384 nm(exc=228 nm).2.4 Sampling Procedure and Sample Treatment Smokers were advised respect to the correct filter collec-tion.Then of smoking the cigarette and to put out it on a clean glass ashtray,each smoker collected his filters ari-sing from a unique ci

23、garette brand in a polyethylene re-cipe.In order to prevent environmental humidity,recipes were immediately closed with plastic cap.Next,samples were remitted to laboratory for their immediately exami-nation.For other side,cigarettes were automatically smoked by connection to a vacuum pump.Filters o

24、f unsmoked cigarettes were also assayed;fil-ters were extracted to cigarettes from recently opened packages.Filters were carefully dismantled,wasting paper,ash and tobacco remains;then,they were immediately weighted.Afterward,each filter was put in leachate solution pre-pared with1 mL of buffer acet

25、ic/acetate 1 102 molL1 pH 4,and 9 mL of ultra pure water.Each filter was separately leachated during 1 minute,with continuous manual shake.An adequate aliquot of each leachate solution was used to apply general proce-dure.All used glass materials were previously washed with a 10%v/v HNO3 solution an

26、d then with ultrapure water.3.Results and Discussion 3.1.Fluorescent Spectra The fluorescence of SPADNS-Cd(II)system was ex-plored in aqueous medium without satisfactory results re-spect to sensitivity.Taken into account that previous studies have exposed the feasibility of formation of ter-nary com

27、plexes between metallic ions,SPADNS and RhB dyes 15,the effect of RhB addition on SPADNS-Cd(II)system was examined.The obtained results showed an important enhancement of the fluorescent signal for the ternary system;this fact supports the formation of a ter-nary association complex between Cd(II),S

28、PADNS and RhB,with an extra advantage respect to the sensibility of the luminescent response as can be seen in Figure 1.3.2.Optimization of Experimental Condition for Cd(II)-RhB-SPADNS System In order to find the optimum experimental conditions for Cd(II)-RhB-SPADNS association formation,experimen-t

29、al parameters such as pH,nature and concentration of buffer solution,concentrations of chelating reagent,dye concentrations,solvent,that affecting the complexation reaction were consecutively investigated.The first parameter examined was the pH;this para-meter plays a unique role on metal-chelate fo

30、rmation and the subsequent metal determination.The results illus-trated in Figure 2,showed that at pH above 5.5,a maximum in fluorescence signal was obtained.Due to this behavior,the pH value of 5.8 was selected as work-ing value for the following experiences.Copyright 2012 SciRes.JEP Direct Cadmium

31、 Monitoring in Cigarette Filters Leachate by Molecular Fluorescence 189 Figure 1.Fluorescent spectra of SPADNS-RhB and Cd(II)-SPADNS-RhB systems.Conditions:1 108 molL1 SPA-DNS,2.5 108 molL1 RhB,pH 5.8 buffer acetic/acetate.Other experimental conditions are described under proce-dures.A:SPADNS-RhB sy

32、stem;B:Idem A+Cd(II)1.26 gL1;C:Idem A+Cd(II)2.5 gL1;D:Idem A+Cd(II)5.1 gL1;E:Idem A+Cd(II)7.7 gL1;F:idem A+Cd(II)10.2 gL1.Figure 2.Influence of buffer acetic/acetate concentration on cadmium association complex with SPADNS and RhB.Conditions:1.26 gL1 Cd(II),1 108 molL1 SPADNS,2.5 108 molL1 RhB.Other

33、 experimental conditions are described under procedures.The effect of different buffers on the fluorescence sig-nal of Cd(II)-RhB-SPADNS ternary system was tested.The most enhanced fluorescent emission was obtained using buffer acetic/acetate.The fluorescence response was studied within acetic/aceta

34、te concentration range from 4 104 to 0.5 molL1.The best performance and optimal stability was achieved for a buffer concentration 1.2 104 molL1.The concentration effect of SPADNS chelating reagent and the dye RhB on the quantification of Cd(II)were subsequently studied and the results are presented

35、in Fi-gures 3 and 4,respectively.With these results,a SPA-DNS concentration of 1 108 molL1 and RhB of 2.5 108 molL1 were chosen as optimal for following as-says.4.Analytical Parameters 4.1.Calibration Curve Calibration curve for different concentration levels of Cd(II)0.192-1.2 104 gL1 was attempted

36、 applying the de-veloped methodology.Table 1 summarizes the main characteristics of the calibration plot and optimized ex-perimental conditions,which sustain the proposed pro-cedure for quantification of Cd(II)traces.The limits of detection(LOD)and quantification(LOQ)were calculated in accordance to

37、 the formulas given by the official compendia methods 16,using the relation k(SD)/m where k=3 for LOD and 10 for LOQ.SD represents the standard deviation from 15 replicate blank responses and m is the slope of the calibration curve.4.2.Interferences Study The effect of foreign ions on the recovery o

38、f Cd(II)was tested.Different amounts of common cations in samples were added to the test solution containing 1.26 gL1 of Cd(II)and the developed procedure was applied.An ion was considered as interferent,when it caused a variation in the fluorescent signal of the sample greater than 5%.The tolerance

39、 limits of various foreign ions are given in Table 2.These results demonstrate that large excess amounts of some common cations and anions do not in-terfere on the determination of trace level of Cd(II).5.Applications In order to study the usefulness of the proposed meth-odology,it was applied to th

40、e determination of Cd(II)in filter samples of ten different cigarette blends,which had been smoked by smoker subjects and automatically smoked.Additionally,in order to establish the contribu-tion of filter materials on Cd(II)contents,unsmoked fil-ters were also analyzed.Filters were treated with dif

41、ferent leachating solutions.An ideal leachating solution must fulfill with two essen-tial conditions:To leach selectively the Cd(II)analyte.To show maximum fluorescent emission of ternary association Cd(II)-SPADNS-RhB.With this objective,buffers TRIS(pH 4.5,6.0 and 7.0)and acetic/acetate(pH 4.0,5.0

42、and 6.0)were assayed.Buffer acetic/acetate pH 4.0 were selected as optimal,fulfilled with mentioned requirements.Other optimized variable was the contact time of fil-ters with leachating solutions.Experiences were carried out varying contact time from 30 s to 10 min.The best results respect to sensi

43、tivity and selectivity were obtained for 1 min of contact time.For minor contact times,poor repeatability was obtained.For superior contact times,Copyright 2012 SciRes.JEP Direct Cadmium Monitoring in Cigarette Filters Leachate by Molecular Fluorescence Copyright 2012 SciRes.JEP 190 Figure 3.Effect

44、of SPADNS concentration on the determination of cadmium.Conditions:1.26 gL1 Cd(II),2.5 108 molL1 RhB,pH 5.8 buffer acetic/acetate.Other experimental conditions are described under procedures.Figure 4.Effect of RhB concentration on the determination of cadmium Conditions:1.26 gL1 Cd(II),1 108 molL1 S

45、PADNS,pH 5.8 buffer acetic/acetate.Other experimental conditions are described under procedures.Table 1.Experimental conditions and analytical parameters for cadmium determination.Parameters Studied Range Optimal conditions pH 4.0-6.7 5.8 Buffer acetic/acetate 4 104-0.5 molL1 1.2 104 molL1 SPADNS co

46、ncentration 1 109-1.5 107 mol L1 1 108 molL1 RhB concentration 1 109-8 107 molL1 2.5 108 molL1 LOD-0.057 gL1 LOQ-0.192 gL1 LOL-0.192-1.26 104 gL1 Calibration sensitivity-7 108 Lg 1 r2-0.999 Direct Cadmium Monitoring in Cigarette Filters Leachate by Molecular Fluorescence 191 Table 2.Study of toleran

47、ce.Foreign ion*Fluorescent emission CV 3CO 127.651 0.03 24SO 128.980 0.02 3NO 126.355 0.04 Cl 128.098 0.01 F 132.432 0.02 K1+131.331 0.01 Na1+128.188 0.05 Zn2+131.221 0.07 Fe3+127.537 0.01 Ca2+126.877 0.10 Pb2+132.509 0.05 Cd2+130.278 0.04 Mg2+126.077 0.07 Mn2+127.344 0.12 Cu2+126.321 0.09 Co2+127.6

48、54 0.03(*)1000/1 interferent/Cd(II)ratio.spectral interferences were observed.The accuracy of the methodology was evaluated using the standard addition method.Adequate volumes of lea-chate solutions were spiked with increasing amounts of Cd(II)(0.192-15.0 gL1).The reproducibility of the method was e

49、valuated repeating the proposed methodo-logy,four times for each sample.The recoveries of Cd(II)in each type of sample based on the average of replicate measurements are illustrated in Tables 3-5;the obtained results showed that the proposed method was appropriate for determination of Cd(II)in studi

50、ed filter cigarettes samples.Taking into account these results and considering per-mitted maxima limits for Cd(II)concentration for drink-ing water by EPA(Environmental Protection Agency,5 gL1)and WHO(World Health Organization,3 gL1)17,it can be concluded that filters represent a severe problem of e