Anal. Chem. lg83, 55, 212-216
212
RSD, %
This method of continuous measurement of free chlorine is expected to be used in the flow system of a wastewater treatment plant.
meth- meth.
ACKNOWLEDGMENT
Table 11. Results of Tap Water Analyses
sample
concn of free chlorine (X10-5 M) _______ this DPD method method
tap water l a
3.8OC
tap water 2 b
(0.33)d 1.79 (0.02)
od
od
3.98 8.7 (0.13) 1.65 1.4
3.2
The authors thank Yoshihito Kanamaru for assistance with experimental measurements and acknowledge Kimoto Electric Co. for providing the microporous PTFE tubes.
6.1
Registry NO.PTFE, 9002-84-0;Clz, 7782-50-5;HzO, 7732-18-5.
(0.10)
a Tap water from Sakai on Dec. 18, 1981. Tap water Mean value of four deterfrom Sakai on Feb. 8, 1982. Standard deviation is shown in parentheses. minations.
and the result will be published later.
Determination of Free Chlorine in Tap Water. The applicability of the proposed method for measurement of free chlorine in water was demonstrated when two tap water samples, taken on separate days, were analzyed for free chlorine by both this method and the DPD colorimetric method (9). Our method gives results comparable to the standard DPD colorimetric method as shown in Table 11. Samples with 2 x to 6 X 10" M added were analyzed for free chlorine by both methods. The coefficient of correlation between the results was 0.993. However, the DPD colorimetric method is not suitable for the measurement of free chlorine above M, since above this concentration the color becomes unstable. CONCLUSIONS This method appears to have several advantages; (a) The calibration curve is linear over a wide range (10-5-10-2 M). (b) It is a simple procedure that uses only HC1 and NaOH as reagents. (c) It uses direct measurement of free chlorine by UV absorption at 290 nm and therefore the other oxidant, such as monochloramine which interferes with the membrane electrode (10) and probably with the method reported by Balt et al. (13),does not interfere and can be determined separately. Response can be made 30-40% faster by shortening the tubes used in this system. In this case, 20 samples can be analyzed in an hour.
LITERATURE CITED (1) Long, D. F., Ed. "Water Treatment Handbook"; Wiley: New York, 1979; Chapter 15. (2) Klnney, E. C.; Drummond, W. D.; Hanes, B. N. I n "Chemistry of Wastewater Technology"; Rubln, J. A., Ed.; Ann Arbor Science: Ann Arbor, M I , 1977; pp 189-198. (3) Atklns, F. P.; Scherger, A. D.; Barnes, A. R.; Evans, L. F. ,/.-Water Pollut. Control Fed. 1973, 4 5 , 2372-2388. (4) Patterson, W. J. I n "Wastewater Treatment Technology"; Ann Arbor Science: Ann Arbor, M I , 1977; pp 87-102. (5) Marlno, D. F.; Ingle, J. D., Jr. Anal. Chem. 1981, 5 3 , 455-458. (6) Isacsson, U.;Wettermark, G. Anal. Len. 1978, A 11, 13-25. (7) Rlgdon, L. P.; Moody, G. J.; Frazer, J. W. Anal. Chem. 1978, 50, 465-469. (8) Brown, K. D.; Parker, G. A. Anal. Chem. 1979, 51, 1332-1333. (9) "Standard Methods for the Examination of Water and Wastewater", 14th ed.: American Public Health Association: Washinaton, DC. 1975: pp 304-349. (10) Johnson, J. D.; Edwards, W. J.; Keeslar, F. J. ./.-Am. Water Works Assoc. 1978, 70, 341-348. (11) Dlmmock, A. N.; Mldgley, D. Water Res. 1979, 13, 1101-1104. (12) Dlmmock, A. N.; Mldgley, D. Water Res. 1979, 13, 1317-1327. (13) Balt, L.; Stamhuls, E. J.; Joosten, G. E. H. Anal. Chem. 1981, 53, 1799-1801. (14) Nelson, G. R. I n "Water Chlorlnatlon"; Jolley, R. L., Ed.; Ann Arbor Science: Ann Arbor, M I , 1978; pp 345-378. (15) Zimmerman, G.; Strong, F. C. J . Am. Chem. SOC. 1957, 79, 2063-2086. (16) Haas, N. C. Environ. Sci. Technol. 1981, 15, 1243-1244. (17) Prince, A. L. Anal. Chem. 1984, 36,613-616. (18) Patton, J. C.; Crouch, S. R. Anal. Chem. 1977, 4 9 , 466-469. (19) Chapin, R. M. J . Am. Chem. SOC.1934, 56, 2211-2215. 120) . , Youssefl. M.: Zenchelskv. .. S.T. J . Environ. Sci. Health, Part A 1978. A 13, 629-637. (21) Pressley, A. T.; Bishop, F. D.; Roan, G. S. Environ. Sci. Technol. 1972, 6 , 622-628. (22) Kleinberg, J.; Tecotzky, M.; Audrleth, L. F. Anal. Chem. 1954, 2 6 , 1388-1389.
RECENED for review May 28,1982. Accepted October 26,1982.
Quantitative Separation of Gallium from Other Elements by Cation-Exchange Chromatography Tjaart N. van der Walt" and Franz W. E. Strelow National Chemical Research Laboratory, CSIR, P.O. Box 395, Pretoria 0001, Republic of South Afrlca
Trace amounts and up to 1.5 mg of galllum can be separated from up to gram amounts of AI, Cd, Cu, In, Mn, NI, Pb, U(VI), and many other elements by elutlng these elements wlth 8.0 M hydrochlorlc acid from a column contalnlng 13.0 mL (3.0 g) of AG 50W-X4 catlon-exchange resin of 100-200 mesh partlcle size In the H-form. Gallium can be separated from up to 2 g of Iron( I I ) and up to 10 mg of scandlum by eluting the Iron with 8.0 M hydrochloric acid contalnlng 0.30% tltadum( I I I ) chlorlde and eluting the scandlum with 7.0 M hydrochlorlc acid. The retalned gallium is effectlvely eluted wlth 2.5 M hydrochloric acid. Separations are sharp and quantitative.
The quantitative separation of gallium from other elements by ion exchange has received considerable attention in the
last few decades. A summary of some of the various approaches has been given by Strelow (1)recently. Most of the suggested methods have either a limited selectivity, employ reagents which are cumbersome to remove, or work in media in which many elements are insoluble. One of the few methods which has a wider general applicability is anion exchange chromatography in aqueous hydrochloric acid ( 2 ) . Iron(III), uranium(VI), and antimony(V) are among the few elements which accompany gallium. Furthermore, elements with strong tendencies toward chloride complex formation, including zinc, cadmium, and bismuth, are retained by the resin more strongly than gallium. Separation from large amounts (1 g or more) of these elements is therefore not very favorable because large columns are required. Ivanova et al. (3) described ion-exchange chromatographic separations of gallium and about 20 other elements on anion-
0003-2700/83/0355-0212$01.50/00 1983 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 55, NO.2, FEBRUARY 1983
and cation-exchange resins. A scheme for group separations was worked out, and Ga tagether with In, Na, K, and Cs were separated from Fe, Ni, Co, Cu, Mn, Cr, Sc, La, Zn, Al, Ag, Au, As, Sb, W, Mo, and Cd, but the average recoveries were found t o be only between 86 and 98%. Very selective methods for the separation of gallium from other elements were recently published by Strelow ( I , 4 ) . Elements such as :tint, cadmium, indium, copper(II), lead(II), bismuth(III), andl many others with strong tendencies to bromide complex formation are easily eluted with 0.50 M hydrobromic acidl in 80% acetone from a column of AG 50W-X4 cation-exchange resin while gallium is retained quantitatively ( I ) . The gallium is then selectively eluted with 0.20 M hydrochloric acid in 84% acetone. Many elements like uranium(VI), cobalt(II), manganese(II),nickel(11), aluminum, manganese, calcium, and others with relatively low tendencies to chloride complex formation are still retained quantitatively on the resin ( 4 ) . This method separates gallium from practically all other elements, but the separation from iron is not satisfactory because of serious tailing. Only 98-99.5% of the iron is recovered in the iron fraction. Furthermore, many common elements such as aluminum, calcium, and magnesium are retained more strongly than gallium and relatively large columns are therefore required to separate gallium from larger amounts of these elements. A very selective separation of gallium from other elements should be possible by cation exchange chromatography at high hydrochloric acid concentration with AG 50W-X4 resin according to the distribution coefficients published by Nelson e t al. ( 5 ) . Even iron and antimony, after reduction to the divalent and trivalent state, respectively, should be separated. Separation from scandium and thorium should be somewhat critical but possible, but these are rather rare elements. Though a method, based on the above data of Nelson e t al. ( 5 ) ,has been used for preparation of carrier-free gallium radioactive isotopes (6), no general investigation exploring the limits and general applicability of the method seems to have been carried out. I t seems reasonable to expect some behavior different from a normal stoichiometric ion-exchange process. The anion GaC14- or tetrahalide acid, HGaCl,, which exists at high concentrations of hydrochloric acid is unlikely to react with a sulfonic acid exchange group. Distribution coefficients for gallium with the AG 50W-X4 cation exchange resin a t high hydrochloric acid concentration with various amounts of gallium were therefore determined to explore the deviiation from stoichiometric exchange and to estimate the amounts which could be handled by columns of a definite size. From this a very selective method for the separation of gallium from h o s t all other elements in a single column procedure was developed. Results of an investigation of the quantitative aspectai of the separation of gallium from other elements are described and presented in this paper.
EXPERIMENTAL SECTION Reagents and Apparatus. Analytical reagent grade chemicals were used. Water was distilled and then passed through an Elgastat deionizer. Bio Rad AG 50W-X4 sulfonated polystyrene cation exchange resin, with a particle size of 100-200 mesh, was used in the H form. Two types of ion exchange columns were used: one set of columns (type A) were prepared in borosilicate glass tubes (20.0 mm bore, 110 mm long) with a B19 female joint at the top, joined at the other end to a narrower tube (14.4 mm bore, 200 mm long) fitted with a fused-in no. 1porosity glass sinter and a buret tap at the bottom. The other type of columns (type B) were also made in borosilicate tubes (20.6 mm bore, 400 mm long) fitted with a 1319 female joint at the top, and at the other end fitted with a fuged-in no. 1 porosity glass sinter and a buret tap at the bottom. Atomic absorptiinn measurements were carried out with a Varian-Techtron AA-5 spectrophotometer.
21:3
Table I. Distribution1 Coefficients of Gallium on AG 50W-X4 Cation Exchange Resin in Hydrochloric Acid HC1 concn, amt of Ga, M mmol D 7.0 0.01 467 7.0 0.02 348 0.05 239 7.0 0.20 96 7.0 0.01 0.02 0.05
580 472
0.20
117
9.0
0.50 1.00 0.01
66 37.0 630 600 352 130
8.0 8.0 8.0 8.0 8.0 8.0
9.0
0.02
9.0
0.05
9.0
0.20
312
Distribution Coefficients. Coefficients were determined by equilibrating 250 mL of hydrochloric acid solution containing various concentrations of gallium (0.01-1.00 mmol) with 2.500 g of AG 50-X4 resin by shaking for 24 h in a mechanical shaker at 20 A 2 "C. The resin had been dried at 60 "C in a vacuum pistol over silica gel prior to use. After equilibration the resin was separated from the aqueous phase by filtration and the amounts of the gallium in the aqueous phases were determined by atomic absorption spectrophotometry or by complexometric titration. Reference solutions containing the same amounts of gallium used for equilibration were used to calculate the amounix of gallium retained by the resin. The distribution coefficients, D = {[massof element in resin (g)]/[mass of element in solution (g)]) X ([volume of solution (mL)]/[massof dry resin (g)]),were calculated from the results of the equilibrations and are shown in Table I. Elution Curves. The ion exchange columns (type A) were filled with a slurry of AG 50W-X4 resin to a mark at 13.0 mL, volume ( ~ 3 . g0 of dry resin in the H form) and columns of type B were filled to a mark at 43.3 mL (=lo g of dry resin in the H[ form). (a)Elution Curue for 10 mg of Scandium and 1 mg of Gallium1 on 3.0 g of AG 50W-X4 Resin. The resin column (type A) was] equilibrated by passing 50 mL of 8.0 M hydrochloric acid through the resin column. A solution containing 10 mg of scandium and 1mg of gallium in 50 mL of 8.0 M hydrochloric acid was prepared and passed through the resin column. The elements were washed onto the resin with small portions of 7.0 M hydrochloric acid anal scandium was eluted with 250 mL of 7.0 M hydrochloric acid, including washings. Gallium was then eluted with 80 mL of 2.6 M hydrochloric acid, using a flow rate of 4.0 i 0.3 mL/mini throughout. Fractions (10 mL in volume) were collected from1 the beginning of the sorption step with an automatic fraction collector. The excess acid was evaporated on a water bath, and the amounts of the elements in each fraction were determined by atomic absorption spectrophotometry after suitable dilution using the acetylene-nitrous oxide flame and the 294.4- and 391.2-nm lines for gallium and scandium, respectively. The experimental curve i s shown in Figure 1. ( b ) Elution Curve for 2 g of Zron(ZI)and 1.3 mg of Gallium on 3.0 g of AG 50W-X4 Resin. A solution containing 2 g of iron(I1) and 1.3 mg of gallium in 10 mL of 0.50 M hydrochloric acid was treated with sulfur dioxide to reduce any iron(II1)to the divalent state, and then 40 mL of 10 M hydrochloric acid was added and mixed. This solution was passed through the resin column, equilibrated as described above. The elements were washed onto the resin with small portions of 8.0 M hydrochloricacid containing 0.30% of titanium(1II)chloride (solutionA) and iron(I1) was eluted with a total volume of 80 mL of solution A. Residual titanium was then eluted with 90 mL of 8.0 M hydrochloric acid. Finally, gallium was eluted with 90 mL of 2.5 M hydrochloric acid, The flow rate was 4.0 A 0.3 imL/min throughout. Fractions (10 mL in volume) were collected and the amounts of iron and gallium were determined in each fraction by atomic absorption spectrophotometry as described above, using the air-acetylene flame and
214
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
HCI
0
100
300
200
400
mL ELUATE
Flgure 1. Elution curve Sc-Ga with 8.0 M HCI and 7.0 M HCI: 13.0 mL (3.0 g) of AG 50W-X4 resin, 100-200 mesh, H form; column length, 80 mm; diameter, 14.4 mm; flow rate, 4.0 f 0.3 mL/mln.
I -I
E W a
?
03
-
I
P
!!
OL 0
mL ELUATE
Flgure 2. Elution curve Fe(I1)-Ga wlth 8.0 M HCI and 8.0 M HCI0.30% TICI,: 13.0 mL (3.0 g) AG 50W-X4 resin, 100-200 mesh, H form; column length, 80 mm; diameter, 14.4 mm; flow rate, 4.0 f 0.3 mL/min. SORPTION
8,OM H C I - C Z . 5 M H C I A m
9
I
N
Y
-
t t 8
,
Table 11. Analytical Methods Used Ga atomic absorption spectrophotometry; acetylenenitrous oxide flame at 294.4 nm Pb complexometric titration with EDTA, in acetate medium at pH 5.5, xylenol orange as indicator; small amounts of Pb with atomic absorption spectrophotometry, air-acetylene flame at 217.0 nm Mn complexometric titration with EDTA after reduction with ascorbic acid to Mn(II), in ammonia solution in the presence of triethanolamine at pH 10, methylthymol blue as indicator; small amounts of Mn with atomic absorption spectrophotometry, air-acetylene flame at 279.5 nm Ni complexometric titration with DCTA, in ammonia solution at pH 10, murexide as indicator; small amounts of Ni with atomic absorption spectrophotometry, air-acetylene at 232.0 nm sc complexometric titration with DTPA, in acetate medium at pH 5.5, xylenol orange as indicator; small amounts of Sc with atomic absorption spectrophotometry, acetylene-nitrous oxide flame at 391.2 nm Cd complexometric titration with DTPA, in slight excess ammonia, methylthymol blue as indicator; small amounts of Cd with atomic absorption spectrophotometry, air-acetylene flame at 228.8 nm Al complexometric titration with DCTA; excess DCTA and back-titration with zinc solution at pH 5.5, xylenol orange as indicator; small amounts of A1 by atomic absorption spectrophotometry, acetylene-nitrous oxide flame at 309.3 nm gravimetrically as U,O, after precipitation with C0,-free ammonia; small amounts of U(V1) spectrophotometrically with chlorophosphonazo 111 Fe small amounts of Fe by atomic absorption spectrophotometry, air-acetylene flame at 248.3 nm cu complexometric titration with DCTA, in acetate medium at pH 5.5, in the presence of 1 , l O phenanthroline and methylthymol blue as indicator; small amounts of Cu by atomic absorption, air-acetylene flame at 324.8 nm Zn complexometric titration with EDTA, in acetate medium at pH 5.5, xylenol orange as indicator; small amounts of Zn by atomic absorption spectrophotometry, air-acetylene flame at 213.9 nm In complexometric titration with EDTA at pH 2.5-3.0 in the presence of 1,lO-phenanthroline and xylenol orange as indicator; small amounts of In by atomic absorption spectrophotometry, air-acetylene flame at 303.9 nm
Go ca 1,5rng
0
0
zoo
IO0
300
m L ELUATE
Flgure 3. Elution curve Zn-Ga with 8.0 M HCI: 13.0 mL (3.0 g) of AG 50W-X4 resin, 100-200 mesh, H form; column length, 80 mm; diameter, 14.4 mm; flow rate, 4.0 f 0.3 mL/mln.
the 248.3-nm line for iron. The amounts of titanium in each fraction were determined spectrophotometrically as its peroxide complex. The experimental elution curve is shown in Figure 2. ( c ) Elution Curve for 4.0 g of Zinc and 1.5 mg of Gallium on 3.0 g of AG 50W-X4 Resin. A solution containing 4.0 g of zinc and 1.5 mg of gallium in a volume of 50 mL in 8.0 M hydrochloric acid was prepared and passed through a resin column, equilibrated as described above. The elements were washed onto the resin
with small portions of 8.0 M hydrochloric acid and the zinc was then eluted with 130 mL of 8.0 M hydrochloric acid altogether. Gallium was eluted with 100 mL of 2.5 M hydrochloric acid. The flow rate was 4.0 & 0.3 mL/min throughout. Fractions were collected and amounts of gallium and zinc were determined in each fraction by atomic absorption spectrophotometry as described above, using the air-acetylene flame and the 213.9-nm line for zinc. The elution curve is shown in Figure 3. ( d ) Figure 4 shows the elution curves for 2 g of copper and 10 mg of gallium and 2 g of zinc and 20 mg of gallium on 10 g of AG 50W-X4 resin as described above (under ( c ) ) , continuing the elution of copper and zinc until 350 mL of 8.0 M hydrochloric acid had been passed. Quantitative Separations of Synthetic Mixtures. A series of columns containing 13.0 mL of AG 50W-X4 (particle size 1OC-200 mesh) was prepared as described under Elution Curves. Appropriate volumes of standard solutions of gallium and one other element as the chloride in dilute hydrochloric acid were accurately measured out in triplicate, mixed, and adjusted to a
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
215
-.
Table 111. Resulbs of Quantitative Separations of Synthetic Mixtures amt found,a mg
amt taken, mg other element Pb Mn Ni sc sc Cd A1
U
a
amt of other element found in Ga fraction, p g
Ga
other element
Ga
other element
0.0450 0.1007 0.1007 0.5236 0.1007 0.0450 0.1018 0.1023 1.035 0.01036 0.0986 0.01032 0.0986 0.0986
518.9 1003.4 1006.2 9.93 9.72 1125.3 1000.0 999.7 0.0986 1005.3 0.0992 1000.3 4000.1 99.63
0.0001 0.1006 f 0.0003 0.1006 k 0.0003 0.5232 k 0.0020 0.1006 i 0.0003 0.0449 f 0.0001 0.1016 i 0.0004 0.1024 i 0.0001 1.035 :t 0.004 0.01036 i 0.00007 0.0989 i 0.0002 0.01037 k 0.00005 0,0989 f 0.0004 0.0985 i 0,0001
519.0 k 0.4 1003.3 f 0.2 1006.2 i 0.3 9.9% f 0.01 9.71 f 0.01 1125.2 t 0 . 2 1000.0 i 0.1 999.7 t 0.4 0,0989 f 0.0004
0.4-0.5 0.1-0.3 0.8-3.0 8.0-12.3 5.2-10.7 0.58-1.09 3.4-5.8 2.6-3.7
not determined
15.4-19.0
0.0992 i 0.0002 1000.2 i 0.5 4000.1 f 0.9 99.6% i 0.08
0.53-1.63 0.3-2.5 0.2-0.4
0.0450
Fe Fe cu cu Zn In Results are the means of triplicate runs.
i
-.
trophotometry. The amounts of the other elements in the eluates and reference solutions and in the gallium eluates were determined by appropriate analytical methods.
RESULTS AND DISCUSSION
...iill.niiiil.il
0
100
zoo
300
.IO 400
v, 500
m L ELUATE
Figure 4. Elution curve (i)Cu-Ga and (ii) Zn-Ga with 8.0 M HCI: 43.3 mL (10 g) of AG 50W-X4 resin, 100-200 mesh, H form; column length, 130 mm; diameter, 20.6 mm; flow rate, 5.0 f 0.3 mL/min.
volume of about 50 mL containing 8.0 M hydrochloricacid. When 4 g of zinc was present, a volume of 100 mL was used. The standard solution of iron(1l’) chloride in dilute hydrochloric acid was treated with sulfur dioxide before made up to volume. (Three equivalent aliquots of each solution were measured out and kepi, separately as standrvds for comparisonwith the solutions obtained after separation, using simnlar dilutions or volumes for the finall determinations of the elements in the standards and separated solutions.) The mixed solutions were passed through the equilibrated resin columns and washed onto the resin with s m d portions of 8.0 M h:ydrochloiricacid and the other elements, except iron and scandium,were eluted with more 8.0 M hydrochloricacid using 60 mL in total. When separating 4 g of zinc from gallium a total volume of 100 mL of 8.0 M hydrochloric acid was used. When scandium was separated from gallium, the elements were washed onto the resin with small portions of 7.0 M hydrochloric acid and the scandium was eluted with 150 mL of 7.0 M hydrochloric acid in total. When iron(I1) was separated from gallium, the elements were washed onto the resin with small portions of 8.0 M hydrochloric acid containing 0.30% titanium(II1) chloride (eluant A), eluting ithe iron(11)with 80 mL of eluant in total. The eluates were collected from the beginning of the sorption step, and, after the excess acid had been removed by evaporation, were made up to convenient volumes. (Residual titanium was eluted with 50 mL of 8.0 M hydrochloric acid before eluting the gallium.) Gallium was eluted with 4 X 10 mL portions of 2.5 M hydrochloric acid. To suppress ionization of gallium in the flame, we added an appropriate volume of EL potassium chloride solution, to the gallium eluate before evaporating the excess acid in order to have a concentration of 2.0 mg of potassium/mL when diluting to a final volume of 10,50, or 100 mL depending on the amount of gallium present for determination by atomic absorption spec-
The analytical methods used for the determination of thle elements are listed in Table 11, and the results obtained for the quantitative separations are presented in Table 111. Tbe described method provides an excellent means for the highly accurate determination of gallium and its quantitative separation from lead, manganese, nickel, cadmium, aluminum, uranium(VI), iron(II), copper, zinc, and indium. Due to their low distribution coefficients (5) all the remaining elements of the Periodic Table, except gold(II1) and antimony(V), should also easily be separated from gallium. Antimony(II1) should, however, also be separated from gallium. Gallium and thorium can be separated in 2.5 M hydrochloric acid medium[; gallium will pass through the resin, while thorium will ble retained and can be removed quantitatively from the resin by elution with 150 nnL of 5.0 M nitric acid (6). On comparison of the distribution coefficients for thle various amounts of gallium in 8.0 M hydrochloric acid on AG 50W-X4 resin, it is obvious that the sorption of the gallium on the resin is not a stoichiometric sorption but rather a separation between two phases with different thermodynamilc properties. I t was assumed that the equilibrium coefficient obtained from mass action law, k = [Ga3+]resin[H+]3801,/ [Ga3+]ml[H+]3resm, is constant or nearly constant for a gallium load up to 20% of the resin capacity. This assumption seem,s to be reasonable for most cases. Furthermore, the distribution coefficient, D (as defined under “Distribution Coefficients”), a t 0.01 mmol of gallium (ca. 0.25% load a t total adsorption) was taken to be equal to the limiting value of the distribution coefficient a t trace concentration. From the above two equations the distribution coefficients were calculated for various amounts of gallium present. It was found that the experimental values were decreasing much faster than those calculated. The differences are illustrated in Figure 5. Separations are sharp and quantitative and the amount of tailing is insignificant as shown in Figures 1-4. The completeness of the separations is demonstrated by the fact that less than 13 pg of scandium and less than 20 pg of iron, the most critical elements, were found in the gallium fractions when separating ca. 10 mg of scandium and about 1 g of iron, respectively, from gallium. The recoveries of gallium were between 99.8 and 100.3%. The separations can be carried out rapidly and present probably the most selective method available for the separation of gallium from complex mixtureti with other elements. A better sensitivity and considerably
Anal. Chem. 1983, 5 5 , 216-220
216
made up in 0.5 M of either hydrochloric acid or nitric acid. Up to 1.5 mg of gallium can be separated from other elements on 3.0 g of AG 50W-X4 resin, but larger amounts of gallium (up to 20 mg) can be separated from other elements on 10 g of AG 50W-X4 resin as can be seen from Figures 3 and 4, respectively. As little as 10 pg have been separated quantitatively; but there seems to be little doubt that the separation should be applicable to submicrogram amounts and could also be useful for the separation of carrier-free radioisotopes of gallium from irradiated cyclotron targets.
IO00
800 6
o
o
[
~
x
W
h
4
AC A S L C USL A T EACTION D ACCORDING LAW
4 00
3OOL ,
zol u 0
0,2
0,4
0,6
0,8
1,0
MILLIMOLE GALLIUM
Figure 5. Distributioncoefficients of Ga in 8.0 M HCI medium: varlous amounts of Ga on 2.5 g of drled AG 50W-X4, 100-200 mesh, H form; experimental values and calculated according to mass action law.
less background interferences were found with the acetylene-nitrous oxide flame than with the normally used airacetylene flame. The standard and sample solutions should contain 2.0 mg of potassium/mL to suppress ionization and
LITERATURE CITED (1) Strelow, F. W. E. Talanfa 1980, 27,231. (2) Kraus, K. A.; Nelson, F.; Smlth, G. W. J . Phys. Chem. 1954, 5 8 , 11. (3) Ivanova, M. M.; Oglobllna, I . P.; Genel', S. A.; Mitina, V. V.; Kalinin, A. I.; Lambrev, V. G. Zh. Anal. Khim. 1877, 32, 1066. (4) Strelow, F. W. E. Anal. Chlm. Acta 1980, 773,323. (5) Nelson, F.; Murase, T.; Kraus, K. A. J . Chromafogr. 1984, 73,503. (6) Nelrlnckx, R. D.; Van der Merwe, M. J. Radiochem. Radioanal. Lett. 1971, 7,31. (7) Victor, A. H.; Strelow, F. W. E. Anal. Chim. Acta 1982, 738, 265.
RECEIVED for review August 17,1982. Accepted October 20, 1982.
Determination Limits and Distribution Function of Ultraviolet Absorbing Substances in Liquid Chromatographic Analysis of Plant Extracts L. J. Nagels" Laboratorium voor Algemene Scheikunde, RiJksuniversitair Centrum Antwerpen, Groenenborgerlaan 171, 8-2020 Antwerpen, Belgium
W. L. Creten and P. M. Vanpeperstraete Laboratorium voor Experimentele Natuurkunde, Rijksunlversitair Centrum Antwerpen, Groenenborgerlaan 17 1, 8-2020 Antwerpen, Belgium
A study was made of the accuracy of quantltatlve hlgh-performance llquld chromatographic (HPLC) determlnatlons of UV absorblng substances In plant extracts. By use of gradient elution on a reversed-phase column and UV detectlon, 62 extracts from plant leaves were lnvestlgated. The obtained chromatograms provided a dlstrlbution functlon of the relatlve abundance of observed peak areas. A computer slmulatlon of such plant extract analyses permltted the estlmatlon of the real dlstrlbutlon function of component absorbances. By use of the same slmulations, the probablllty that a glven determlnatlon could be performed with success was obtained. These data should be helpful to analysts working on the chromatographic analysls of such samples to estlmate the accuracy of a partlcular determlnatlon In quantltative terms. Reallstlc determlnation llmlts for phenolic compounds In plant extracts were defined and computed. The same method can be applied to the analysis of other blological samples and to other chromatographic technlques.
Qualitative and quantitative determinations of components in biological extracts can be complicated because they are composed of hundreds of products. Analytical chromatographic techniques are powerful tools with which to solve such
problems, eventually in combination with various cleanup procedures. However, these chromatographic methods offer only limited "peak capacities" (n,for definitions see ref 1and 2) to resolve these complex mixtures. Peak capacities can be highly increased by using chromatographic techniques in series (3). Application of these methods could, however, be quite impractical. In chromatography of biological samples, the probability of obtaining an accurate quantitative determination strongly depends on the available peak capacity and on the characteristics of the matrix of interfering substances. Actually, judging the accuracy of a specific chromatographic determination of a component in a biological sample depends on the investigators' experience and intuition. A scientific approach is almost impossible as there are no criteria. Our aim is to express the quality of such a determination in more quantitative terms. As far as we know, no investigations have been carried out in this direction. Therefore we simulated high-performance liquid chromatographic (HPLC) analyses of biological samples by using a microcomputer. The determination of phenolic compounds in plant leaves was taken as a concrete example.
EXPERIMENTAL SECTION Instrumentation. All separations of plant extracts were performed with a Hewlett-Packard 1084B liquid chromatograph, with variable wavelength detector and a recorder-integrator. For
0003-2700/63/0355-0216$01.50/00 1983 American Chemical Society
