Anal. Chem. 1991, 63, 427-432
Table 111. Precision of the GFAAS Determination of Gd in Several Tissues tissue
Nn
kidney muscle liver liver
6
mean f
SD, pg g‘’
72.0 f 3.0 4.00 f 0.15 3.97 f 0.083 0.92 f 0.095
6 6 6
RSD 4.3 3.7 2.4 10.3
N u m b e r of analvses.
Table IV. Recovery of the GFAAS Determination of Gd in Different Tissues and Biological Fluids tissue kidney liver liver muscle lung spleen brain serum urine heart (I
Nu
added, pg
4 4 4 4 4 4 4 4 4 4
8.00 4.00 1.00 4.00 2.00 4.00 1.00 6.00 8.00 1.50
found, pg
7.40 f 0.37 3.87 f 0.15 0.92 f 0.13 3.78 f 0.17 1.84 f 0.08 3.85 f 0.13 0.93 f 0.14 5.80 f 0.41 7.50 f 0.45 1.40 f 0.07
We found the characteristic mass (m,) of Gd to be lo00 pg while we found the GFAAS detection limit defined as 2SD to be 2060 pg. Compared to other GFAAS methods for the determination of Gd (5, 7, l o ) ,the proposed method is more sensitive and has proven to be suitable for measuring Gd levels found in pharmacokinetic experiments in the rat. Further examination is required to determine whether the proposed procedure can also be used for the determination of lanthanoids other than Gd. ACKNOWLEDGMENT The secretarial work of E. Snelders and graphic design of D. De Weerdt are greatly appreciated.
recovery, %
92.5 99.3 92.0 94.4 92.0 96.3 93.0 96.7 93.8 93.3
N u m b e r of analvses.
prepared from the stock standard solution. The recovery values ranging from 92.0% to 99.3% (Table IV) show that the Gd-DOTA complex was almost completely extracted with the proposed method. This indicates that after digestion the Gd present as Gd-DOTA was completely converted to its ionic form.
427
LITERATURE CITED
,-
(1) Van de Vyver, F. L.; Peersman, G. V. Magn. Res&. Imaging 1990, 8 , 333-340. (2) Bousquet, J.-C.; Saini, S.; Stark, D. D.; Hahn, P. F.; Nigam, M.; Wittenberg, J.; Ferrucci, J. T. Radiology 1988, 166, 693-698. (3) Wedeking, P.; Tweedle, M. Nucl. Med. B i d . 1988, 15, 395-402. (4) Grobenski, Z. Fresenius Z . Anal. Chem. 1978, 289. 337-345. (5) Haines. J. At. Spectrosc. 1986, 7 , 161-174. (6) L’vov, B. V.; Nikolaev, V. G.; Norman, E. A. J . Anal. Chem. USSR (Engl. Trans/.) 1988, 79, 46-52. (7) Sen Gupta. J. G. Talanta 1984, 37, 1053-1056. (6) Sen Gupta, J. G. Manta 1985, 32, 1-6. (9) Yao, J. Y.; Huang, 8. L. Can. J . Spectrosc. 1986, 3 7 , 77-80. (10) Slavin, W.; Carnrick, G. R. At. Spectrosc. 1985, 6 , 157-160. (11) Slavin, W.; Manning, D. C.; Carnrick, G. R. At. Spectrosc. 1981, 2 , 137-145. (12) Komarek, J.; Sommer, L. Talanta 1982, 29, 159-166. (13) Korkisch, J. Modern Methods for the Separation of Rarer Metal Ions; Pergamon Press: New York, 1969. (14) Mitchell, J. W.; Banks, C. V. Talanta 1972, 19, 1157-1169. (15) Welz, B. Fresenius Z .Anal. Chem. 1986, 325, 95-101.
RECEIVED for review July 30, 1990. Accepted November 28, 1990.
Simultaneous Photometric Flow Injection Determination of Sulfide, Polysulfide, Sulfite, Thiosulfate, and Sulfate Kim Sonne and Purnendu K. Dasgupta*
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
The titie determination scheme has been developed for application to aqueous samples of importance to the petroleum industry. Sulfur(-11) is determined by acidification to produce H,S and gas diffusion into alkaline Na,[Fe(CN),NO]; in the same manifold, sulfur produced upon acidification from poiysulfides Is measured turbidimetrically and gives a measure of [S(O)]. Sulfite Is mesaured by acidification to produce SO,, gas diffusion, and bleaching of a pararosaniline receptor. Thiosulfate is measured by dialyzing the sample after on-line tretment with Zn2+ and HCHO and bleaching KMnO, with the dialyzate. Sulfate is measured by the turbidimetric BaSO, method; the fouHng of optical windows Is prevented by the use of a sheath-flow cuvette.
INTRODUCTION Water is an integral part of operations involving the drilling, recovery, and processing of petroleum. It may be present naturally (suspended with oil in the subsoil, called brine or reservoir water) or used to displace the oil (injection water),
to make the drilling process smoother (drill fluid water), or to remove the 0.06-8 wt % sulfur present in crude oil by treatment at elevated temperatures and pressure (hydrotreater water). Large amounts of water containing significant concentrations of sulfur-bearing ions, often generically referred to as “sour water” or “produced water”, result from such operations (1, 2 ) . The nature of the sulfur species in such samples is variable and can range from sulfide, polysulfide, thiosulfate, and sulfite to sulfate depending on the availability of oxygen. Most typically, more than one ion is present, with sulfide/polysulfides being dominant. For proper recycling, treatment, or disposal of such waters, a determination of the sulfur anions is necessary. Ideally, practical analytical systems for this determination should also be deployable in the field. Classical approaches to the simultaneous determination of sulfur anions, e.g., titration, spectrophotometry, or polarography (3-6), typically involve differential assays, reaction of the sample for example with iodine under different conditions. The need for extensive manipulation of samples, the integrity of which is highly susceptible to oxygen exposure, subtraction of large numbers from each other, and substantial time investment per sample limit these approaches. Liquid chro-
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matography would appear to be a logical solution to this problem and Story (7) has indeed demonstrated the successful determination of a large number of sulfur anions with postcolumn reaction detection. However, more recent work by Uddin (8)shows that polysulfides cause major problems with chromatographic determinations by decomposing into elemental sulfur and sulfide. Not only does this make it impossible to obtain meaningful values for the two most important analytes in sour water samples but also the usable life of an expensive chromatographic column is severely shortened. Flow-injection analysis (FIA) offers unique opportunities to appoach the present problem (9, 10). The use of membranes allows selective gas diffusion or effective on-line dilution of otherwise intractably large analyte concentrations. The availability of relatively compact pumps with a large number of individual pumping channels makes possible transportable analyzers utilizing a number of reaction chemistries simultaneously. The determination of specific sulfur anions by FIA is hardly new. Numerous direct, indirect, and catalytic methods relying on atomic absorption, chemiluminescence, colorimetry, fluorometry, potentiometry, turbidimetry, and voltammetry developed variously for sulfide, thiosulfate, sulfide, and sulfate have been described; citations are available in monographs providing a complete listing of the FIA literature ($11). However, only the work of Burguera and Burguera (12) has attempted the simultaneous determination of several sulfur anions, sulfide, sulfite, and sulfate, in the presence of each other, using a relatively uncommon technique, molecular emission cavity detection. In this paper, we show the simultaneous photometric flow-injection determination of sulfide, polysulfide, thiosulfate, sulfite, and sulfate, taking advantage of different chemical reactivities, differing pK,'s and volatilities of the various sulfur-containing acids, and kinetic differences. PRINCIPLES The pK,, values for HzS04,HZS2O3, SO,.H,O, H2S, and H,S, (a representative polysulfide for which reliable data are available) are respectively
