Preconcentration of Ultra-trace Cadmium with Nanometer-size TiO2 Colloid and Determination by GFAAS

Chinese Chemical Letters Vol. 17, No. 7, pp 933-936, 2006933http://www.imm.ac.cn/jourmalccl.htmlPreconcentration of Ultra-trace Cadmium with Nanometer-size TiO2Colloid and Determination by GFAAS with Slurry SamplingSha Hua QIAN*, Xue Qin LI, Han LIN, Mei XIAO,Hong Bing DENG Luo Jing XIANGCollege of Resource and Environmental Science, Wuhan University, Wuhan 430072Abstract: A novel method of ultra-trace Cd(I) preconcentration with nanometer-size TiO2 colloidand determination by graphite furnace atomic adsorption spectrometry(GFAAS) with slurrysampling was first advanced in this paper. The adsorption efficiency of nanometer-size TiO2colloid for ultra-trace Cd(ID) could reach above 96% in a short time when the pH value wasbetween 5 and 6. Other problems were also studied, such as adsorption capacity, nanometer-sizeTiO2 colloid dosage, effect of coexistent ions., The detection limit(3o) and the relative standarddeviation (R.S.D) of this method were 4.46-103 μg/L and 1.30%(n= 7), respectively. The methodwas sucessfully applied to the analysis of environmental samples with recoveries between 93.8%and 96.4%.Keywords: Nanometer- size TiO2 clloid, Ca(I), GFAAS, slurry sampling.Cadmium- a heavy metal used in coatings, batteries and plastics 一can accumulate inhuman's liver and kidney, causing osteoporosis and cancerl2. The monitoring of itscontent is, therefore, of great importance.But the average concentration of cadmium inwater samples is too low to be determined directly by most existing apparatuses, 0.15μg/L in seawater and less than 1.0 ug/L in most freshwater'. As a result, it comes to bevery important of the separation and enrichment of the cadmium in solution. In recentyears, hydrous aluminium(II) oxide, modified rice husks and other adsorbents coupledwith Perkin-Elmer 2400 CHN microanalyser, furnace atomic adsorption spectrometry(FAAS), atomic adsorption spectrometry(AAS) have been used in the analysis of tracecadmiumNanometer-size material is a new type of functional material received muchattention recently'. The atomic number, area and chemical combination energy ofnanometer-size material's surface increase rapidly with the reducing of radius. Thereforenanometer-size material has strong adsorption capacity. And the adsorption balancecan be reached quickly'. A lot of researchers have used nanometer-size powder as the :adsorbent of trace metals, but there is not any reportnenrmeter-size colloid yets9. Compared with nanometer-size中國煤化工oid ismore dispersive and more stable because of its much sYHCNMHG0nm.* E-mail: Qiansh@whu.edu.cn934Sha Hua QIAN et al. .So it possesses more vigorous adsorbability of most metal ions, and presents betteradsorptive reproductivity.In this study, nanometer-size TiO2 colloid was used to enrich cadmium in aqueoussamples, and the concentration of cadmium was determined by GFAAS with slurrysampling. The main advantages of this method were high adsorption efficiency,extremely short enriching time, needless of filtration and elution, etc. The method issimple, rapid to be used to the determination of ultra-trace cadmium in practical watersamples, and the results were satisfactory.ExperimentalStock solution (100 mg/L) of cadmium was prepared by dissolving 0.0408 g of cadmiumchloride in 5 mL of 1 mol/L HCl solution, and diluting to 250 mL with distilleddeionized water (DDW). Nanometer-size TiO2 colloid 1.24% w/w was provided byInfrared Academe of Wuhan University. Oyster (ESA-2 GSBZ 19002-95) was suppliedby Chinese Environmental Monitoring Terminal.Sample solution was added into a centrifugal tube containing nanometer-size TiO2colloid, the pH of the solution was adjusted, and the solution was centrifuged for 15minutes at the speed of 4000 rpm. The supernate was transferred into a volumetricflask and supplemented with DDW. The resident value of Cd(I) in the solution wasmeasured by GFAAS. 0.1 mL of 1 mo/L HNO3 was added to the residue in theabove- mentioned centrifugal tube, the solution was shaken to be dispersed evenly, thenadjusted to 5 mL with DDW. At last, the content of Cd(I) in the colloid was detectedby GAFFS with slurry sampling.A Hitachi Z 5000 Polarized Zeeman Atomic Absorption Spectrophotometer and aMettler-Toledo 320-S type pH meter were used.The operation conditions were asfollows: hollow cathode lamp current 7.5 mA, wavelength 228.8 nm, slit width 1.3 nmand sample volume 20 μL. The heating procedures were summarized in Table 1.Results and DiscussionIt was difficult to separate the nanometer-size TiO2 colloid if the pH value was lowerthan its isoelectric point 4. And the pH value could not be too high because of thepossible deposition of Cd(OH)2. Test results indicated that the adsorption efficiency ofnanometer- size TiO2 colloid for Cd(I) could reach 96% or higher when the pH valuewas between 5 and 6. And the adsorption balance could be reached immediately thecolloid was added.The adsorption efficiencies of different volumes of nanometer size TiO2 colloid for100 mL 0.6 μg/L cadmium solution were showed in Figure 1. The adsorptionefficiency could reach 96% or higher when the volume of the colloid was only 0.3 mL.Adsorption capacity is very important becaut中國煤化工dsorbent isrequired to quantitatively concentrate the aljion. Weexamined the adsorption capacity of nanometer-YHCNM H.G of caMsolutions with different concentrations. The results were showed in Figure 2. It couldbe seen that the saturation capacity was 11.21 mg/g.Preconcentration of Ultra-trace Cadmium with Nanometer-size TiO2 Colloid 935Figure 1 Effect of nanometer-size TiO2 colloid dosageFigure 2 Adsorption capacity1007 12R 90豈808t70500 0.3 0.6 0.9 1.2 1.5 1.8 2.10 0.2 0.40.6 0.8 1 1.2 1.4 1.6Volume of nanometer-size TiO2 colloid 1Cocentration of solution /mgL1mLThe effects of common coexisting ions on the determination of 50 mL solutioncontaining 0.3 μg Cd(I) were investigated. The results indicated that in exist ofK* (2.1mg), Nat (55.2 mg), Ca2+ (2.2 mg), Mg2+ (6.6 mg), Sr2+ (40.5 Hg), Zn2+ (12 ug), Fe*+ (30μg), Al*+(19 ug), Mn2+ (10 μg), CI (99.4 mg), SO4- (13.3 mg), NO3~ (621 ug), PO,~(130 ug), Br (336.5 μg) and F (6.5 μg), the recovery efficiencies of Cd(II) could reach95.9%-99.2% (n=4).100 mL of solution containing 0.1 μg/L Cd(I) was concentrated to 5 mL andmeasured.The detection limit (3σ) and the relative standard deviation (R.S.D) of thismethod were 4.46*10* μg/L and 1.30%, respectively (n =7).For study of the accuracy of this method, a certified reference material withcadmium content of 4.56土0.48 ug/g, was analyzed. The obtained cadmium contentvalue 4.61 士0.085 μg/g, based on the average of five replicates, was in good agreementwith the certified value. By the way, in order to eliminate the effect of the matrix, thestandard curve was also made in suspended state and determined with slurry sampling,with R=0.99928.The above-mentioned method was applied to cadmium determination in severalwater samples, including Donghu Lake, Yangtse River and tap water. The results werelisted in Table 2.Table 1 Heating proceduresProcedureT/CRamp/sHold/sFlow rate of Ar/ mI /minDrying50-80200200Ashing80-1200025030Atomization1600Cleaning1800中國煤化工MYHCNMHG936Sha Hua QIAN et al.Table 2 Addition/recovery for cadmium determination in water samples(sample volume: 100mL, final volume: 5 mL (n =3))SampleCadmium added (ng)_ Cadmium found (ng)Recovery (%)Donghu Lake6.66士0.1214.17土0.1693.88Yangtse River3.40士0.11013.04士0.3296.40A tap water2.28士0.226.97+0.0793.80ConclusionThis paper presented a novel method to analyze cadmium in aqueous solution of usingnanometer-size TiO2 colloid as adsorbent and detecting by GFAAS with slurry sampling.The results suggested that this method had many advantages, such as simplepreconcentration process, good selectivity, low detection limit, fine accuracy andprecision, free of interference. So it can be successfully used in the determination ofultra-trace amount cadmium in environmental samples.ReferencesBosch, Xavier, Science Now, 2003.P. A. Brown, s. A. Gill, s. J. Allen, Water Res, 2000, 4, 3907.L. Qi, L. Quanmin, Z. Yongcai, Instrum. Anal, 2000, 5, 34.4. R. R. Bell, G. C. Saunders, Applied Geochemistry, 2005, 20, 529.5. T. Tarley, C. Ricardo, C. Ferreira, Microchemical Jourmal, 2004, 77(2), 163.A. Henglein, Chem. Rev, 1989, 89, 1861.K.W. Hipps, Joumal of Chemical Education, 2005, 82(5), 693.8. S.X. Li, N. s. Deng, F. Y. Zheng, Y. z. Huang, Talanta, 2003, 60, 1097.9. E. Vassileva, I. Proinova, K. Hadijivanov, Analyst, 1996, J21, 607.Received 15 December, 2005中國煤化工MYHCNMHG