Anal. Chem. 1992, 64, 3101-3108
9101
Determination of Chromium(I I I) and Chromium(V1) in Water Using Flow Injection On-Line Preconcentration with Selective Adsorption on Activated Alumina and Flame Atomic Absorption Spectrometric Detection Michael Sperling, Shukun XU,+and Bernhard Welz' Department of Applied Research, Bodenseewerk Perkin-Elmer GmbH, W -7770 uberlingen, Germany
A rapld and sensitive method for the speclecseiective determlnation of chromium( III)and chromium(V1) in water samples by flame atomic absorption spectrometry uslng online precconcentratlonon a mlcrocolunnpacked with activated aiumlna (acldk form) has been developed. Sequential species-seiectlve sorption was poorlbie by using the CiarkLubs buffer systems with pH 7 for Cr( III)and pH 2 for Cr(VI). The proconcentratedspecies were eluteddlrectly from the column to the nebuiizer-burner system uslng 1.0 moi/L nitrlc acid and 0.5 moi/L ammonia for Cr(II1) and Cr(VI), respectively. The retention efficiency was better than 80% for Cr( III)and better than 00 % for Cr(VI), giving a senrltlvlty enhancement of 25 for a 9mL sample loading. The effect of concomitant species was investigated, and satisfactory recovery of 00-106% could be obtained from natural water samples. Linear caiibratlon for both spedes was established over the concentratlon range 10-200 pg/L with detectlon limits (9 8 ) of 1.0 and 0.8 pg/L for Cr(II1) and Cr(VI), respectively.
INTRODUCTION There is a rapidly increasing demand for fast and reliable analytical methods for the determination of chemical forms of elements in environmental samples. The interest in chromium is governed by the fact that ita toxicity depends critically on ita oxidation state: While chromium(II1) is considered essential for mammals for the maintenance of glucose, lipid, and protein metabolism,' chromium(V1) is known to be toxic to humans.2 Cr(II1) and Cr(V1) enter the environmentas a result of effluent discharge from steel works, electroplating, tanning industries, oxidative dyeing, chemical industries, and cooling water towers.' The metal may also enter drinking water supply systems from the corrosion inhibitors used in water pipes and containers or by contamination of the underground water from sanitary landfill leaching. Therefore it is of major concern to understand the behavior of chromium in natural aquatic systems. In view of the difference between the oxidation states, and in order to follow the pathways for interconversion in the environment, it is increasingly important to monitor the concentration of the individual chemical species as well as the total concentration of chromium in the environment. Traditional methods for the speciation of inorganic chromium, are, however relatively time-consuming, involving species separation based on solvent extraction? coprecipitation,4 electrochemical sep-
* To whom correspondence should be addressed.
+ On leave from the Flow Injection Analysis Research Center, Institute of Applied Ecology, Academia Sinica, Shenyang, 110015, China. (1) Ottaway, J. M.; Fell, G. S. Pure Appl. Chem. 1986,58, 1707. (2) Nriagu, J. 0.;Nieboer, E. Chromium in the Natural and Human Enuironment; Wiley: New York, 1988. 0003-2700/92/0364-3101$03.00/0
aration? ion solid-phaseextraction,8pgorselective volatilization in combination with graphite furnace atomic absorption spectrometry (GFAAS)."J Many methods are based on the determination of Cr(V1) and total chromium because Cr(1II) is kinetically inert, calling for a conversion step. The conversion of metal species from one form to another can have serious drawbacks including incomplete conversions (particularly at low concentrations), introduction of contamination by the oxidationlreduction agenta, interferences from other metals present, and generally, complex and time-consuming sample pretreatment procedures. Of the numerous methods developed for chromium speciation, those which physically separate the individual species followed by direct quantitation are preferred because they are relatively fast and require only minimal sample pretreatment. This last factor is particularly important because prolonged sample manipulation may affect the chromium species distribution significantly.11 During the past decade, problems inherent in manual sample manipulation could be overcome, at least in part, by hyphenated techniques such as HPLC or FIA coupled to photometricor spectrometric detection techniques, which are summarized in Table 1.12-2s Detection limita given in Table I are based on 3 s and were ~~
(3) Sugiyama, M.; Fujino, 0.;Kihara, S.; Matsui, M. Anal. Chim.Acta 1986,181, 159. (4) Lan, C.-R.; Tseng, C.-L.; Yang, M.-H.; Alfassi, Z. B. Analyst 1991, 116, 35. (5) Issa, R. M.; Abdel-Nabey,B. A.; Dadek, H.Electrochim. Acta 1968,
-1.7-, 1R37 ---..
(6) Johnson, C. A. Anal. Chim.Acta 1990,238, 273. (7) Mazzucotelli, A.; Minoia, C.; Pozzoli, L.; Ariati, L. At. Spectrosc. 1983, 4, 182. (8) Miyazaki, A.; Barnes, R. M. Anal. Chem. 1981,53,364. (9) Morocco, M. T.; Newman, G.P.; Syty, A. J.Anal. Atom. Spectrom. 1990,5, 29. (10) Dungs, K.; Fleiachhauer, H.; Neidhart, B. Fresenius' Z. Anal. Chem. 1985,322, 280. (11) Florence, T. M.; Batley, G.E. CRC Crit. Rev. Anal. Chem. 1980, 9, 219. (12) deAndrade, J. C.;Rocha,J.C.;Baccan,N.Analyst 1985,110,197. (13) deAndrade, J. C.;Rocha, J.C.;Baccan,N.Analyat 1984,109,645. (14) Ruz, J.; Rim, A.; Luque de Castro, M. D.; Valdrcel, M. Freseniw' Z. Anal. Chem. 1985,322,499. (15) Lynch, T. P.; Kernoghan, N. J.; Wilson, J. N. Analyst 1984,109, 839. (16) Syty, A.; Christensen,R. G.;Raine,T. C. J. AnaLAtom. Spectrom. 1988, 3, 193. (17) Krull, I. S.; Panaro, K. W.; Gereheim, L. L. J. Chromatogr. Sci. 1983, 22, 460. (18)Urasa, I. T.; Nam, S. H. J. Chromatogr. Sci. 1989,27, 30. (19) Shah, A,; Devi, S. Anal. Chim.Acta 1990,236,469. (20) Milosavljevic, E. B.; Solujic, L.; Nelson, J. H.; Hendrix, J. L., Microchim. Acta 1985,111,353. (21) Syty, A.; Christensen, R. G.; Rains, T. C. At. Spectrosc. 1986,7, 89. (22) Hirata, S.; Umezaki, Y.; Ikeda, M. Anal. Chem. 1986,58, 2603. (23) Cox, A. G.; Cook, I. G.;McLeod, C. W. Analyst 1985,110, 331. (24) Cox, A. G.; McLeod, C. W. Anal. Chim. Acta 1986,179,487. (25) Ahmad, S.; Murthy, R. C.; Chandra, S. V. Analyst 1990,115,287. (26) Sperling, M.; Yin, X.;Weh, B. Analyst 1992, 117, 629.
0 1992 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
Table I. Comparison of Published Methods for the Selective Determination of Chromium(II1) and/or Chromium(V1) by
On-Line Separation Techniques. Cr species Cr(VI)
Cr(T) Cr(VI) Cr(T) Cr(W
Cr(T) Cr(II1)
technique
FI-W FI-W FI-UV FI-UV FI-UV FI-FAAS HPLC-FAAS
F,, l/h ng ng
DPC oxidat, Ce(1V) DPC
ng ng
oxidat, Ce(1V)
V,,mL
RSD,%
0.164 0.164
3.0 (100pg/L) 2.0 (200pg/L)
