829
Anal. Chem. 1985, 57,829-833
The second term results from the finite time required for the injected sorbate to pass into the mobile phase. For large values of N , Perry et al. suggest using the approximation ~(~/,)l/2e-N~1-~t/t'~"212
F=
2t1/4(t')3/4
(21)
which under the same conditions should be an equally good approximation to Young's equation. But in a short column where this approximation is not valid, differences brought about by the state of the injected sorbate might be noted.
LITERATURE CITED (1) Glbilaro, L. 0. Nature (London) 1977, 270, 47-48. (2) Buffham, B. A. Proc. R . SOC. London, Ser. A 1973, 3 3 3 , 89-98.
Huang, Jan-Chan; Madey, Rlchard Anal. Chem. 1982, 5 4 , 326-326. Galan, M. A.; Suzukl, M.; Smith, J. M. Ind. Eng. Chem. Fundam. 1975, 14, 273-275. Kucera, Eugene Chromatography 1985, 19, 237-248. Young, J. K. "Gas Chromatography 1957"; Academic Press: New York, 1958; Chapter 2. Wlcar, Stanlslav; Novak, Josef; Ruseva-Rakshieva, Nedjalka Anal. Chem. 1971, 4 3 , 1945-1950. Madey, Richard; Fiore, Ronald A,; Pflumm, Eugene: Stephenson, Thomas Trans. Am. Nucl. SOC. 1962, 5 , 465-466. Underhlll, Dwight W. U S . AEC Report CONF-700816, 1970, pp 600-606. Perry, Robert H. "Chemical Engineers' Handbook", 4th ed.; McGrawHill: New York, 1963; Chapter 2.
RECEIVED September 20,1984. Accepted December 26,1984. This study was supported by NIOSH Grant 1 R01 0H01644-01.
/ ,
Potassium Hydroxide Eluent for Nonsuppressed Anion Chromatography of Cyanide, Sulfide, Arsenite, and Other Weak Acids Tetsuo Okada* and Tooru Kuwamoto Department of Chemistry, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606, J a p a n
Potassium hydroxide solution was found to be an effective eluent for nonsuppressed anion chromatography. Polyvalent ions, SCN-, and CiO,-, which are strongly retained by an anion-exchange resin, could not be quantitatlveiy measured, because potassium hydroxide was too weak an eluent. However, this method was applicable to the determlnation of 15 inorganic monovalent anions (F-, CI-, Ci03-, Br-, Br0,-, I-, IO3-, NO3-, NO,-, CN-, HS-, CNO-, BF,-, siilcate, arsenite). The main advantage is that weak acids of pK, > 7 (cyanide, sulfide, arsenlte, silicate, and phenol compounds) which cannot be detected by conventional Ion chromatography using a conductivity detector can be determined by this method. The detection limits for cyanlde, sulfide, and arsenite were 0.1 ppm, 0.1 ppm, and 0.2 ppm (as As), respectively.
Since ion chromatography (IC) was introduced by Small et al. (1)in 1975, it has been applied to the analysis of anions and cations in various fields (2-6). To improve problems with column efficiency and conductivity detection, other systems for the anion analyses, such as ion-exchange chromatography or reversed-phase chromatography with UV (7, 8), electrochemical (9-12), and atomic absorption spectrometric (13-16) detectors, have been developed recently. However, IC using a conductivity detector is still a powerful method for anion analysis which has often proved difficult and tedious using conventional analytical methods. IC has been applied to the determination of organic (17)and oxo acids (18,19)in addition to some common inorganic anions (F-, C1-, Br-, NOz-, NO3-, etc.). With suppressed IC, weak acids of pK, > 7 could not be detected because the conductance of the effluent was measured in a neutral. or acidic solution (20). Nonsuppressed IC using a basic eluent permitted detection of weak acids but the determination of cyanide, sulfide, and arsenite has been shown to be inadequate. 0003-~00/85/0357-0829$01.50/0
The authors previously reported the nonsuppressed IC of anions using a potassium hydroxide eluent (3,17,21,22). This method has two advantages. First, it is sensitive because of the large ion equivalent conductance of hydroxide ion, and second, weak acids such as phenol (17) and silicic acid (21, 22) can be determined since the separation and detection are carried out in a basic solution. Although this eluent is a weak eluent relative to a carbonate eluent or organic acid eluents, it can quantitatively elute monovalent anions. For example, silicic acid which is essentially a tetravalent ion could be determined, because it dissolved as the monovalent ion (H3Si0,-) in potassium hydroxide eluent (22). In this paper, the applicability of this method to the analysis of some weak acids (cyanide,sulfide, and arsenite) is discussed.
EXPERIMENTAL SECTION Apparatus. A Toyo Soda Model nonsuppressed ion chromatograph HLC-601 equipped with an anion exchange column (50 mm X 4.6 mm id.) packed with TSKgel IC-Anion-PW (particle size 10 1 pm; capacity 0.03 0.005 mequiv/g) was used. HLC-601 consisted of a computer-controlledpump, conductivity detector, a sample injector (100 pL), and an oven. Two separation columns were connected, if necessary. The flow rate was maintained at 1 mL/min under a pressure of 15-25 kg/cm2. The separator columns and a conductivity detector were set in an oven regulated at 30 "C. Reagents. The eluent was prepared daily by dissolving analytical grade potassium hydroxide in distilled deionized water and deaerating it. Stock solutions (1000 ppm) of cyanide and sulfide were prepared weekly by dissolving the analytical grade potassium cyanide and sodium sulfide in water, respectively. Their working standard solutions were prepared daily by diluting the stock solutions with water. A silicate standard solution was prepared according to the previous reports (21,.22).Stock solutions (1000 ppm) of the other inorganic anions were prepared by dissolving their potassium or sodium salts, dried under vacuum at 110 OC overnight if necessary, in water. Standard solutions of heavy metal ions were prepared by dissolving the analytical grade reagents of their nitrate or sulfate salts in water. Working standard so-
*
0 1985 American Chemical Society
*
830
ANALYTICAL CHEMISTRY, VOL. 57, NO. 4, APRIL 1985
0
IO
20
Time, min
Flgure 1. Typical ion chromatogram of seven inorganic anions: 1, fluoride (1 pprn); 2, bromate (3 ppm); 3, chloride (5 ppm); 4, nitrite (3 ppm); 5, cyanate (3 pprn); 6, bromlde (3 ppm); 7, nitrate (10 ppm). The eluent was 1 mM KOH.
lutions were prepared by diluting the stock solutions with water and were stored in plastic bottles.
RESULTS AND DISCUSSION Figure 1 shows a typical ion chromatogram of seven anions obtained with 1 mM potassium hydroxide as eluent. The first large negative peak is the "dip peak" which is caused by sample water, sample cations ion-excluded by the anion exchange resin, and an eluent anion (OH-) replaced by sample anions (23). This peak often interfers with anions which elute rapidly. For example, it restricts the linear range of the calibration curves of fluoride and chloride (17) and interfers with the analysis of silicic acid when the concentration of electrolyte was ten times lager than that of an eluent (22). All elution peaks were detected as negative peaks because of the large ion equivalent conductance of hydroxide ion (198 f2-l cm2mor1 at 25 OC). The analysis of some weak acids (cyanide, sulfide, arsenite, etc.) by this method is discussed below. Cyanide and Sulfide. Because of concern for the toxicity of sulfide and cyanide, many analytical methods for their determination have been investigated. Methods studied include the solid membrane ion selective electrodes using AgI or Ag,S (24,25),polarography (26,27)or amperometry (28) with Ag or Hg electrodes, and direct (29) or indirect spectrophotometry (30). Those methods using silver or mercury, however, have the serious common disadvantages that some ions (e.g., halide ions), which form complexes or insoluble salta with silver and mercury, interfere with the determination and that sulfide and cyanide frequently interfere with the analysis of each other. Therefore, a method is required that separates cyanide and sulfide from each other and from interfering ions. Since sulfide (pK1 = 6.02, pK2 = 14.0) and cyanide (pK, = 9.32) are dissolved as monovalent anions at pH 10-11, they can be quantitatively eluted and detected by nonsuppressed IC using the potassium hydroxide eluent. They eluted between chloride and nitrite and were completely separated from the other anions (Br-, NO3-, I-, F-, etc.). Since it is possible that chloride and nitrite will be present in a sample solution, it is important that these four anions (Cl-, HS-,CN-, NOz-) are separated for accurate determination. Two separation columns were connected in order to enhance efficiency. A marked increase in pressure was avoided because the columns were short (50 mm long) and the packed resin was small and spherical. The actual increase of pressure was below 10 kg/cm2. Figure 2 shows the variation of resolution between pairs of anions eluting adjacently (Cl--HS-, HS--CN-, CN--N02-), with the eluent concentration. The resolution of Cl--HS- and HS--CN- hardly varied with changing the eluent concentration, but that of CN--N02- was affected (the resolution was 1.03 with 0.5 mM KOH and 0.46 with 3 mM KOH). Figure 3 shows the separations of Cl--HS-, HS--CN-, and CN--N02- at various eluent concentrations. An increase
0
1 2 3 Concentration ot KOH , m M
Flgure 2. Variation of resolution between anion pairs eluting adjacently, with the concentration of the eluent: A, CI--HS-; B, HS--CN-; C, CN--NOz-. Two separation columns were connected and used. Zrnin
L Time
Flgure 3. Separations of CI--HS-, HS--CN-, and CN-NOz-: eluent, (A) 1 mM KOH, (B) 1.5 mM KOH, (C) 2 mM KOH, (D) 3 mM KOH; sample, 5 ppm of each anion.
Table I. Anion Interference Study for Cyanide Ion" anion Cl-
ppm ratio (A-/CN-) 1
5 Br-
NOzNOBSa
b
1 10 1 5 1 10 1 2
recovery, 70 103.8 103.3 98.1 97.3 102.5
109.0 100.3 98.8 106.0 115.6
Sample contained 5 ppm of cyanide ion. Eluent was 0.5 mM
KOH. 1.5 mM KOH for other cases.
in the eluent concentration increased the peak heights of these anions but degraded the separations. These facts are also shown in Figure 2. Therefore, as a result of the consideration of the separation and the time required for the analysis, 1.5
ANALYTICAL CHEMISTRY, VOL. 57, NO. 4, APRIL 1985
831
Table 11. Anion Interference Study for Sulfide Ionsa
anion c1-
ppm ratio (A-/CN-)
recovery, %
1
100.4 120.9 105.8 99.4 102.5 98.6 102.1 99.4 97.8 93.5
5
Br-
1
NOT
5 1
5
NO,-
1
5 CN-
1 2
Sample contained 5 ppm of sulfide ion. Eluent was 1.5 mM of
KOH.
Time
Flgure 4. Depression of cyanide peak by Cu2+ retained by the resin. 5 ppm of cyanide was injected.
Table IV. Anion Interference Study for Arsenite Iona
anion
Table 111. Cation Interference Study for Cyanide Ion"
molar ratio (Mzt/CN)
metal ion
logb
Hg(I1) Co(I1) Ni(I1) Cu(I1) Pb(I1)
40.9 19.1 30.2 28 10.3
0.1 0.1 0.1 0.1 0.1 0.5
Zn(I1)
16.8
0.1 1
Cd(I1)
17.1
0.1
ppm ratio (A-/H2AsOJ
silicate
1
5
Fconcn, ppm
recovery, %
3.85 1.13 1.13 1.22 3.98 19.9 1.26 12.6 2.16
C
62.7 35.5 60.0 95.5 80.6 101.7 97.3 102.3
Sample contained 5 ppm of cyanide. Formation constant of cyanide complex (literature value). Small and distorted peak. mM of KOH eluent was used for the following investigation. Tables I and I1 show the interference of anions to the analysis of cyanide and sulfide, respectively. All sample solutions contained 5 ppm of cyanide or sulfide. The interference caused by chemical reactions in the sample solution or the separator column, as occurred in the case of fluoride interference with silicic acid (22),was not observed in either case. Bromide and nitrate which were completely separated from cyanide and sulfide did not interfere even if their concentrations were 25-50 ppm. However, 25 ppm of chloride which did not interfere with the determination of cyanide, caused an increase of 20% in sulfide recovery. Ten parts per million of cyanide caused a decrease of 6.5% in sulfide recovery, and 10 ppm of sulfide also caused an increase of 15.6% in cyanide recovery. Table I11 shows cation interference with cyanide. Hg(II), Cu(II), Co(II), and Ni(I1) seriously interfered but Pb(II), Zn(II), and Cd(I1) did not. Hg(I1) markedly depressed the cyanide peak and even 1.92 X M of Hg(I1) (molar ratio of Hg to cyanide is 0.1) abolished it. The degree of the interference of metal ions (Hg > Ni > Cu > Co > Cd > Zn > Pb) was related to the magnitude of the formation constants of the cyanide complexes (Hg > Ni > Cu > Co > P b = Zn = Cd). The concentration of free cyanide in a sample solution containing metal ions may decrease during IC analysis, because cyanide complexes of metal ions are easily formed in a basic solution. However, Pb(II), Zn(II), and Cd(II), the cyanide complexes of which are comparatively stable, did not depress the peak height of cyanide. Considering these facts, free cyanide must be measured by this method though its concentration may be slightly decreased by the formation of cyanide complexes during IC. As sulfide and heavy metal ions form insoluble salts, sulfide measured by this method must be sulfide free. When only heavy metal ions were injected into this system, they were adsorbed as hydroxides by the anion-exchange resin. These hydroxides were retained in the column and affected the elution of cyanide and sulfide. Figure 4 shows the peak de-
recovery, %
1
5
c1-
1
10
arsenate
1
10
97.1 70.1b 103.7 103.4 100.7 85.2b 98.8 102.5
"Sample contained 5 ppm (as As) of arsenite. bThe peak was broadened. pression of cyanide by Cu(I1) remaining in a column. The recovery of cyanide was 57% a t the first injection after injecting 5 ppm of Cu(I1) and six injections of cyanide were necessary in order to reach the original peak height. Calibration curves for cyanide and sulfide were linear over the ranges 0.5-5 ppm, respectively. The percent deviations were 1.6% and 1.7% a t 5 ppm cyanide and sulfide levels, respectively. Each detection limit was 100 ppb (the detection limit was defined as the concentration corresponding to twice the value of the noise of the base line). For chromatographic methods for cyanide and sulfide, Rocklin et al. (11)determined parts-per-billion levels of these anions with an amperometric detection system, but these anions were determined with detection limits only in the parts-per-million to sub-part-per-million range by the other systems such as potentiometric (31) and coulometric detection (12). Cyanide has also determined by the conductivity detection after conversion to other detectable anions by the following reactions (32, 33). I, HCN = H+ I- ICN
+
+ + NaCN + 2 H 2 0 = NH, + HCOO- + NaS
The italic anions were detected by conventional IC. In both cases, parts-per-million levels of cyanide were detectable. The present method has the following itemized advantages for the determination of cyanide and sulfide compared with these conventional methods. (1) The procedure is simple and safe, because pretreatment is unnecessary and cyanide and sulfide are always in a basic solution. (2) Other anions can be simultaneously determined. (3) The sensitivity is satisfactory compared with the other chromatographic methods. Arsenite. Arsenate (pK, = 2.2, pK2 = 6.9, pK, = 11.5), which is a comparatively strong atid, can be detected by the conventional IC (34),but arsenite (pK1 = 9.2, pK2 = 12.1, pK3 = 13.4) has only been detected by an atomic absorption spectrometric system (15, 16). Arsenite eluted between fluoride and chloride using this system. Table IV shows the interference of anions in the determination of arsenite. Silicate and chloride caused the broadening of the arsenite peak and lessened the peak height, when they were present in high concentration in a sample
832
ANALYTICAL CHEMISTRY, VOL. 57, NO. 4, APRIL 1985
I
Table V. Anions Detected by Conventional IC Using Conductivity DetectorD
t
anions
ref
F-, C1-, Br-, I-, ClOC, BrO;, L
Figure 5.
anion.
L 0
I
I
I
IO
20 30 Time , rnin
Separation of arsenic species. 5 ppm (as As) for each
IO3-, Clod-, NO2-, 1, 18, 19, 36-43 NOC, SCN-, CNO-, Nc, SO>-, S032-, S2032-, PO:-, Po33-,BFC, CrO>-, WOd2-, MOO>-, Se(IV), Se(VI),As(V)
”Phenate, carbonate, and borate solutions were used for suppressed IC (1, 18, 19). Phthalate, tartrate, and citrate solutions were used for nonsupmessed IC (36-43). Table VI. Detection Limits and Linear Ranges of Calibration Curves of Four Weak Acids
32 5 37 I 492 49 5
BF4ISCNClO4-
anion
detection limit, (ppb)
silicate cyanide sulfide arsenite
22 (as Si) 100 100 200 (as As)
Figure 6. Fifteen anions determined by the present method. The eluent was 1 mM KOH.
solution. Arsenite could be determined separately from arsenate which eluted with a longer retention time. Figure 5 shows the separation of arsenite and arsenate. Organoarsenic compounds were not investigated, but the separation of arsenite from organoarsenic species should be possible since separation using the Dionex system and atomic absorption spectrometric detection were reported by Ricci et al. (15). The peak of arsenate was broadened and overlapped with the “absent peak” of carbonate contained in the eluent as an impurity (17,231. Therefore, arsenate could not be determined accurately by this system. The calibration curve for arsenite was linear over the range 0.5-10 ppm (as As). The percent deviation was 1.8% at the 5 ppm As level. The detection limit was 200 ppb, corresponding to that of flame atomic absorption spectrometry (35). Silicate. As mentioned in previous papers (21,221,fluoride, magnesium, and calcium ions interfere with the determination of silicic acid. However, the interference of fluoride ion was reduced by adding boric acid to the sample solution and interference from magnesium and calcium ions was eliminated by pretreatment with a H+ form cation-exchangecolumn. The detection limit was 22 ppb (as Si). This method was practical for the analysis of silic acid and applicable to its determination in natural water. Phenol Compounds. Phenol and its derivatives (cresols, dimethylphenol, and ethylphenol) were detectable by this system as already reported (17).Nitrophenols and picrate were not eluted because of their strong adsorption on the anion-exchange resin. A detailed investigation of phenol compounds was not carried out because UV detection is more practical for these compound than conductivity detection. However, a lo4 M level of phenol compounds was detectable by the present method. There was a possibility that phenol compounds would interfere with the determination of inorganic anions which should be detected by IC. However, the interference was not serious for the determination of most monovalent anions because the retention time of phenol, which eluted most rapidly among the phenol compounds studied, was longer than that of nitrate. Comparison with Conventional IC. Figure 6 shows the retention times of monovalent anions eluted with 1mM KOH. The quantitative peaks for SCN- and C104-were not obtained because their elution was delayed by hydrophobic interactions
I
linear range of calibration curve, ppm 0.1-2.5 0.5-5
0.5-10 0.5-10
L
-il 1
0
10
Time, rnin
Ion chromatogram of four weak acids: 1, silicic acid (1 pprn); 2, arsenite (5 pprn); 3, sulfide (5 ppm); 4, cyanide (5 ppm). Figure 7.
with the resin matrix (a polyacrylic acid resin was used for this study). Similarly, polyvalent anions were not quantitatively eluted by this eluent. It is necessary to use a more concentrated eluent to obtain quantitative elution of these anions retained by the resin. However, the use of such an eluent is impractical, since the noise of the base line increases because of the increase in the background conductance. Table V shows inorganic anions detected by the conventional suppressed and nonsuppressed IC. Some polyvalent anions, which were determined with difficulty by the present method, could be measured by the conventional methods. However, 15 inorganic anions eluting ahead of iodide could be determined by the present method as shown in Figure 6. Above all, this method has an advantage that four weak acids (cyanide, sulfide, silicate, and arsenite) can be simultaneously determined, together with other inorganic anions without the need for selective detection systems. Figure 7 shows an ion chromatogram of these four weak acids. The applicability of this method will be increased by the complete separation of cyanide and sulfide. Although arsenate is not quantitatively measured as mentioned above, arsenite and arsenate can be separately determined by the combined use of this method and other methods (e.g., atomic absorption spectrometry) since arsenite can be determined without interference from arsenate. Table VI shows the detection limits of this method for these
ANALYTICAL CHEMISTRY, VOL.
four weak acids. These values will be improved upon by the elimination of pulses from the pump, temperature deviation in the oven, and the dissolution of carbon dioxide into the eluent. In conclusion, 15 inorganic anions, which included cyanide, sulfide, arsinite, and silicic acid, could be determined with detection limits in sub-part-per-millionby the present method. This method is practical to the analysis of anions which were determined with difficulty by conventional methods and will be applied to the anion analysis in wider fields. Registry No. C103-, 14866-68-3;Br03-, 15541-45-4; IO3-, 15454-31-6;NO,, 14797-55-8;NO,, 14797-65-0;CN-, 57-12-5;HS-, 15035-72-0;CNO-, 661-20-1;BF,, 14874-70-5;H3Si04-,18102-72-2; H~AsO~-, 14102-45-5;S-, 18496-25-8;F-,16984-48-8;C1-, 1688700-6; Br-, 24959-67-9; I-, 20461-54-5; KOH, 1310-58-3.
LITERATURE CITED Small, H.; Stevens, T. S.; Bauman, W. C. Anal. Chem. 1975, 4 7 , 1801-1809. Legrand, M.; Angells, M.; Delmas, R. J. Anal. Chlm Acta 1984, 156, 181-192. Okada, T.; Kuwamoto, T. Bunseki Kagaku 1983, 32. 595-599. Stevens, T. S.; Turkelson, V. T.; Albe, W. R. Anal. Chem. 1977, 4 9 , 1176-1 . .. - 178 . -. Sunden, T.; Llndgren, M.; Cedergren, A.; Siemer, D. D. Anal. Chem. 1983, 55, 2-4. Sevenich, G. J.; Fritz, J. S. Anal. Chem. 1983, 55, 12-16. Rokushika, S.; Qui, 2. Y.; Sun, 2. L.; Hatano, H. J. Chromatogr. 1983, 2 6 0 , 69-76. Reeve, R. N. J. Chromatogr. 1979, 177, 393-397. Wang. C. Y.; Bunday, S. D.; Tartar, J. G. Anal. Chem. 1983, 55, 1617-1619. Pyen, 0. S.; Erdmann, D. E. Anal. C h h . Acta 1983, 149, 355-358. Rocklin, R. D.; Johnson, E. L. Anal. Chem. 1983, 55, 4-7. Glrard, J. E. Anal. Chem. 1979, 5 1 , 836-839. Parks, E. J.; Brlnckman, F. E.; Blair, W. R. J . Chromatogr. 1979, 185, 563-572. Messman, J. D.; Rains, T. C. Anal. Chem. 1981, 53, 1632-1636. Rlcci, G. R.; Shepards, L. S.; Colovos, 0.; Hester, N. E. Anal. Chem. 1981, 53, 610-613. Grabinskl, A. A. Anal. Chem. 1981, 53, 968-968. Okada, T.; Kuwamoto, T. Anal. Chem. 1983, 55, 1001-1004.
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(18) Zolotov, Yu. A.; Shpigun, 0. A.; Bubchikova, L. A. Fresenlus Z . Anal. Chem. 1983. 316. 8-12. (19) Ficklln, W. H. Anal. Lett. 1982, 15, 865-871. (20) Pohl, C. A.; Johnson, E. L. J. Chromatogr. Sci. 1980, 18, 442-452. (21) Okada, T.; Kuwamoto, T. Anal. Lei?. 1984, 17, 1743-1751. (22) Okada, T.; Kuwamoto, T.; Anal. Chem., In press. (23) Okada, T ; Kuwamoto, T. Anal. Chem. 1984, 5 6 , 2073-2078. (24) Pungor, E.; Toth, K. Analyst (London) 1970, 9 5 , 625-648. (25) Cusbert, P. J. Anal. Chlm. Acta 1978, 8 7 , 429-435. (26) Turner, J. A.; Abel, R. H.;Osteryoung, R. A. Anal. Chem. 1975, 47, 1343-1347. (27) Davison, W.; Gabbutt, C. D. J. Electroanal. Chem. 1979, 9 9 , 3 11-320. (28) McCloskey, J. A. Anal. Chem. 1961, 33, 1842-1843. (29) Chambers, W. E.; Coulter, P. D.; Greinke, R. A. "Treatise on Analytical Chemistry"; Kolthoff, I. M., Elving, P. J., Eds.; Wiley: New York, 1978; Part 11, Vol. 10, pp 175-177. (30) Blanco, M.; Maspoch, S. Talanta 1983, 3 1 , 85-87. (31) Wang, W.; Chen, Y.; Wu, M. Analyst (London) 1984, 109, 281-286. (32) DuVal, D. L.; Fritz, J. S.;Gjerde, D. T. Anal. Chem. 1982, 5 4 , 830-032. (33) Dolzine, T. W.; Esposito, G. G.; Rinehart, D. S.Anal. Chem. 1982, 5 4 , 470-473. (34) Hansen, L. D.; Richter, B. E.; Rollins, D. K.; Lamb, J. D.; Eatough, D. J. Anal. Chem. 1979, 5 1 , 833-637. (35) Skoneiczny, R. F.; Han, R. B. "Treatise on Analytical Chemistry"; Kolthoff, I. M., Elving, P. J., Eds.; Wiley: New York, 1978, Part 11, Vol. 10, pp 247-249. (36) Hill, C. J.; Lash, R. P. Anal. Chem. 1980, 52, 24-27. (37) Hoover, T. 6.; Yager, G. D. Anal. Chem. 1984, 56, 221-225. (38) Mackie, H.; Speciale, S. J.; Throop, L J.; Yang, T. J. Chromatogr. 1982, 242, 177-180. (39) Matsushita, S.;Tada, Y.; Baba, N.; Hosako, K. J. Chromatogr. 1983, 259, 459-464. (40) Gjerde, D. T.; Fritz, J. S.; Schmuckler, G. J . Chromatogr. 1979, 186, 509-5 19. (41) Gjerde, D. T.; Schmuckler, G.; Fritz, J. S.J . Chromatogr. 1980, 187, 35-45. (42) Gjerde, D. T.; Fritz, J. S. Anal. Chem. 1981, 5 3 , 2324-2327. (43) Fritz, J. S.; DuVal, D. L.; Barron, R. E. Anal. Chem. 1984, 5 6 , 1177-1 182.
RECEIVED for review October 26, 1984. Accepted December 17,1984. This work has been supported by Grant-in-Aid for Scientific Research (NO. 58470029) from the Ministry of Education, Science and Culture, Japan.
