OB
03
Table I. Standard Deviation in the Measurement of Calcium Using Glyoxal bis(2-hydroxyanil)
-
-
350
400
450
500
550
600
650
700
W A V E LENGTH, m a
Figure 1. Absorption spectra of calcium glyoxal bis(2-hydroxyanil) in chloroform I .
Llie amount of calcium that will ordinarily occur in the reagents ~ i i not l contribute to the error of measurement since the blank compensates for color from that source. The absorption maximum was determined with a Cary Model 14 recording spectrophotometer. The absorption falls off rather sharply on both sides of 535 mp, as shown in Figure 1. ,411 of the colorimctric measurements were made a t
.
that wave length. The color coniplex obeys Beer's law over the range 0 to 10 Pg Once the standard curve is plotted, i t is necessary to run only one or two points to define the curve. ACKNOWLEDGMENT
The authors are indebted t,o Glen F.
Micrograms of Calcium Per Milliliter Taken Found Found. 0.50 0.50 f 0.016 0.50 f 0.005 1 . 0 0 1.00 i 0,020 1.00 i 0.010 3 00 3.00 i 0.030 3.00 i 0.025 5.00 5 00 i 0 010 $5 00 + 0 048 7 00 7 00 =t0 000 7 00 L 0 065 10 00 10 00 zk 0 110 10 00 i 0 070 a I n a mixture of Ca, M g , Sr, and Fe.
Bailey for determining the wave length of maximum absorption. LITERATURE CITED
(1) Bayer, E., Ber. deut. chem. Ges. 90,
2325 (1957). (2) Goldstein, D., Stark-Mayer, C., Anal.
Chim.Acta. 19, 437 (1958). RECEIVEDfor review May 28, 1960. Accepted September 12, 1960. Mention of manufacturers and commercial products does not imply recommendation by the Department of Agriculture over others of a similar nature not mentioned.
Spectrophotometric Determination of Indium in Zinc and Zinc Oxide T. A. COLLINS, Jr., and J. H. KANZELMEYER Zinc Smelting Division, Si. Joseph l e a d
Co., Monaca, Pa.
b A spectrophotometric method for determining microgram quantities of indium in zinc and zinc oxide has been developed. A preliminary separation is made by extracting indium into isopropyl ether from 6M HBr and reextracting it into water. The indium, in an aqueous solution containing hydroxylamine and KCN a t pH 9, is extracted with 0.002% dithizone in CHC13. The absorbance a t 510 mp follows Beer's law to concentrations of a t least 1.5 pg. of indium per ml. A precision of 2.6y0 relative error was measured for samples containing 0.0007 to 0.0 1 % of indium.
T
HE most sensitive spectrophotometric method for the determination of trace quantities of indium is the extraction procedure employing dithizone ( 5 ) . May and Hoffman (3)outlined the optimum conditions for this determination. They used a rather lengthy separation by extraction with 8-quinolinol to eliminate the interference of zinc, lead, tin. and thallium, Kosta and Hoste ( 2 ) separated traces of indium from large quantities of zinc
by extraction of the indium into isopropyl ether from 6 M aqueous HBr solutions. Other workers ( 1 , $, 6) have found bromide extractions useful for separations of indium from a number of elements. I t appeared that the combined bromide separation and dithizone determination would give a rapid and accurate method for traces of indium in zinc-based materials. A satisfactory procedure is reported in this paper for the measurement of indium in zinc metal and zinc oxide. Interference from elements normally found in these materials is also discussed. EXPERIMENTAL
Apparatus and Reagents. A Beckman Model B spectrophotometer and l-cm. borosilicate cells were used. The p H of solutions was adjusted using a Beckman Zeromatic p H meter. Reagent grade chemicals and deionized water were used. Hydrobromic Acid, 6N. Add 600 ml. of HBr to 300 ml. of water. If appreciable bromine color is apparent, shake with 7 5 ml. of isopropyl ether for
2 minutes and discard the organic layer. Store in a brown screw-capped bottle. Hydroxylamine Hydrochloride Solution (loyo). Dissolve 50 grams of N H 2 0 H . H C l in water and dilute to 500 ml. Prepare every other day. Dithizone in Chloroform (0.002%). Prepare a stock solution by dissolving 26 mg. of dithizone in 500 ml. of CHC13 (shake vigorously!). Dilute 100 ml. of stock solution to 260 ml. to obtain the 0.00270 solution used for extraction. Store both solutions in the refrigerator. Buffer Mixture. Titrate 150 ml. of 10% hydroxylamine hydrochloride solution to p H 9.0 with 1 S iYH40H (requires about 270 ml.). Add 40 ml. of 5% KCN solution and dilute to 500 ml. with water. Shake for 2 minutes with 10 ml. of 0.0027,, dithizone in CHCI, and allow to stand 1 hour before discarding the organic layer. This quantity is sufficient for 10 samples. Procedure. Weigh samples containing 2 to 100 pg. of indium and 1.0 0.1 gram of zinc into 100-ml. beakers. Cover samples with water and dissolve by gradual addition of 10 ml. of concentrated HC1. Add 3.0 ml. of 70% HC104, cover with watch glasses, and evaporate a t moderate heat to strong fumes of HC104. Continue heating
*
VOL 33, NO. 2, FEBRUARY 1961
245
Table 1.
Distribution Coefficients for Extractions from HBr Solutions with Isopropyl Ether
Ion Indium
Concn., pg./Ml. 5
M Zn(ClO&
... ... ...
Zinc Lead Cadmium
20 mg./ml. 1 mg./ml. 600
until samples completely solidify on cooling, leaving no residual liquid (approximately 5 minutes). Rinse watch glasses and beakers with 25 ml. of 6 N HBr, dissolve salts, and transfer to 125-ml. separatory funnels. Rinse beakers with a n additional 25 ml. of 6 S HBr. Extract the indium from the combined solutions with 25 ml. of isopropyl ether by shaking 2 minutes. Discard the aqueous layer. Wash the ether phase by shaking 2 minutes with a fresh 10-ml. portion of 6h' HBr, which is then discarded. Re-extract the indium into the aqueous phase by shaking with 25 ml. of water. M7hen the layers have separated completely, transfer the aqueous (lower) phase, or an aliquot thereof containing less than 20 pg. of indium, into a second set of separatory funnels which contain 50 ml. of the buffer mixture. Mix thoroughly and allow t o stand 1 hour for complete reduction of iron. Add, by pipet, 20.0 ml. of 0.002% dithizone in CHC13 and shake for 2 minutes. Within 15 minutes, but after the layers have completely separated, transfer a portion of the CHC& layer to 1-cm. borosilicate cells and measure the absorbance a t 510 mp us. a blank which has been run through the procedure. Read micrograms of indium from a curve of absorbance us. indium concentration, constructed as follows: Prepare a series of standard samples which contain 0, 1, 2, 3, 4 . and 6 ml. of indium solution (5 pg. of In per ml.) and 5.0 ml. of zinc chloride solution (0.2 gram of Zn per ml.). (Use indiumfree zinc metal or ZnO in preparing the zinc chloride solution.) Carry these samples through the entire procedure, beginning in the first paragraph with the addition of 3.0 ml. of HC104. Subtract the absorbance of the zinc blank (0 indium sample) from that of each of the other samples and plot net absorbance us. indium concentration. The molar absorptivity of indium dithizonate is 6.12 X lo4 liter mole-' cm.-l Absorbance of these solutions should be measured within about a half hour after extraction because of their limited stability toward light. RESULTS A N D DISCUSSION
Extraction of Indium Bromide Complex. Previously published work indicated t h a t indium could be separated from zinc by ether extraction 246
ANALYTICAL CHEMISTRY
0.18 0.76 0.30 0.30 0.30
M HBr 3.5 5.5
6.0 6.0 6.0 6.0 6.0
6.0
M HClO,
...
...
0.3 0.3 0.3 0.3 0.3 0.3
K
(El,) --
0.54 12.4 16.5
48 32 0,0072
0.016
0.014
from 6 S HBr. Separations from lead and cadmium nere also of interest because these elements interfere with t h e determination of indium by dithizone a t p H 9. The d a t a of Kosta and Hoste ( 2 ) indicate that thc extraction of indium is affected by large changes in acidity, zinc Concentration. etc., as well as by changes in the concentration of total bromide. Verification of these factors is shown in the data of Table I. Extraction of indium is greater for 6 M HBr than for lower concentrations. The extraction of indium increases with the addition of zinc to concentrations of about 0.2M Zn, but further increase reduces the extraction. A small excess of HC104 does not appear to have a profound effect on the extraction, although large amounts of acid cause a decrease. Also shown in Table I are the extraction coefficients for zinc. lead, and cadmium in 6.OM HBr. An extraction followed by a washing with 6.OM HBr will eliminate the interference of moderate amounts of lead and cadmium and large amounts of zinc. Under the conditions selected as most convenient [6.03f HBr, 0.3M Zn(C104)z,and a minimum excess of HC104]the calculated loss of indium through the extraction (60j0), washing (3%), and re-extraction into water (1%) would give an over-all loss of about 9%. Experimental observations showed that less than 0.002% of the zinc and 0.1% of the lead and cadmium originally present is found in the final aqueous solution together with 92.0 to 92.5% of the indium. Extraction of Indium Dithizonate. May and Hoffman (3) selected a p H range of 8.5 to 9.5 and a K C S concentration of 0.08M or less as optimum conditions for the dithizone extraction of indium into CHC1,. If hydroxylamine is used to reduce the interference of iron and an NH40H-NH4C1 buffer is used to control the pH, the concentrations of these reagents also influence the extraction. Hydroxylamine enhances the extraction of indium by dithizone; a decrease from 0.3J!l (used in this procedure) to 0.1M of hydroxylamine decreases the extraction of indium 15%. KCN suppresses the extraction; a
10% increase in indium color is obtained by reducing the CN- concentration from 0.04M (used in this procedure) to 0.02M. At the same time, this change increases the interference from iron. The buffer suppresses the extraction; an increase in NHdOH concentration from 0.07M (used in this procedure) to 1.OM a t a pH of 9.0 causes a 40% reduction in the extraction of indium dithizonate. It is advantageous to use a comparatively weakly buffered solution for this determination. The only acid normally present is the 0.01 to 0.02M HBr which is stripped from the isopropyl ether along with the indium bromide. Sample Preparation. The combined HBr-ether and dithizone-CHC13 extractions are subject to interference from aisenic, antimony, and tin. Elimination of these elements by selective volatilization of their chlorides was attempted by dissolving t h e sample (200 pg. of indium and 1 gram of zinc) in an excess of concentrated HC1 and evaporating to dryness. Only 65% of the original indium was recovered. Addition of 2.0 ml. of concentrated H2S04 prior to evaporation increased the indium recovery to 70 to 80%, but elimination of the interfering elements n.as not complete. The amount of each element which gave a dithizone color equivalent to 1 pg. of indium was: 6 pg. of arsenic, 17 pg. of antimony, and 33 pg. of tin. Evaporation of HC1 solutions with HClO4 and the subsequent careful volatilization of the excess HC10, yielded a reproducible recovery of 89% of the indium present. ,\mounts of arsenic, antimony, and tin which will report as 1 pug. of indium with this treatment are in excess of 500 pg. of each. Interferences. If t h e combined procedures of evaporation with HC104, ether e.rtraction from HBr solution, and dithizone extraction into CHCl3 are applied, interfering amounts of diverse elements (in milligrams) are: Zinc Lead Cadmium
1300 3 5
Arsenic Antimony Tin
>0.50 >0.50
>0.50
These cause a 5% error in the determination of 20 pg. of indium. As much as 250 pg. of iron or copper causes no detectable interference. Thallium interferes, but may be easily separated by a prior extraction with isopropyl ether from 1-V HBr. Following the thallium extraction, sufficient 9M HBr is added to increase its concentration to 6,V and the normal indium method is followed. Determination of Indium i n Other Materials. The procedure, as written, is not directly applicable t o high-iron drosses, zinc concentrates,
calcincs, sinters, residues, and othcr niiscellaneous smelter materials. Treatmerit of such samples n-ith H N 0 3 before evaporation with HClO, is recommended to avoid explosion hazards. Large amounts of iron may be extracted by 25 nil. of isopropyl ether from the perchlorate residue dissolved in 7 V HC1. Following the iron separation, evaporate residual ether froin the aqueous layer and add 0.5 ml. of HClO,. Evaporate to remove HC1 and excess HCIOl and proceed with the HBr extractions. One gram of ascorbic acid added to the HBr phase 10 minutes prior to adding the isopropyl ether reduces the interference of iron. For high-lead or high-copper materials, use two separate 5-ml. HBr washes rather than a single 10-ml. portion. Any of these modifications is likely to change the over-all efficiency of extraction. Consequently, for accurate results, it is neccssary to prepare the standard curve by (wrying standard samples through the w t i r e procedure with 11hirh the unlrnonn samples are to be treated. Accuracy and Reproducibility. Suitable standard samples are not a v d a h l c for checking the accuracy of this ni(Jt1iod. A series of production sam1)les was run in quadruplicate by the dithizone eytraction procedure. The results. shown as samples 5 to
~
Table II.
NO.
1
2 3 4 5 6 m
;3
9 10
Accuracy and Reproducibiiity of Indium Determination s,
70,
% In,
Relative Error
% In, Polarographic
0,000675 0.00116 0.00476 0.00938 0.00595 0.00468 0,00192 0,00190 0.00225 0,00894
4.75 0.52 0.90 1.39 1.50 0.77 1.50 0.63
...
Estimat,ed std. dev.
2.57
Sample Type Metal Metal Metal Metal Metal Metal Oxide Oxide Oxide Oxide
Dithizone
10 of Table 11, indicate a satisfactory correlation with the indium concentration as obtained by polarographic means. The standard deviation for the relative error of all the samples in Table I1 is 2.6%, a figure which includes any nonhomogeneity of the samples as well as errors of measurement by the method. -4 scries of eight synthetic samples containing 20 pg. of indium and 1 gram of zinc had a coefficient of variation of 1.6. LITERATURE CITED
(1) Hudgrns, J. E., ?;elson, L. G., Ax.4~.
CHEK24, 1472 (1952).
5.40
2.40
...
... 0.00545 0.00465 0.00187
0.00213 0,00228 0.00594
% Diff. ... ... ... 0,00050 0.00003 0,00005 0.00023 0.00003 0.00000
Av. 0.00014
(2) Kosta, L., Hoste, J., Mikrochim. Acta 416, 790 (1956). (3) May, I., Hoffman, J. I., J . Wash. A c a d . Sci. 38.329 11948). (4) Xorrison, G. H.,‘Freiser, H., “Solvent Extraction in Analytical Chemistry,” pp. 131-3, Wiley, New York, 1957. (5) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp, 87112, Interscience, New York, 1950. ( 6 ) Sunderman, D. K.,Ackerman, I. B., Meinke, R. W.,AXAL.CHEM.31, 40-3 (1959). RECEIVEDfor review June 20, 1960. Accepted October 5, 1960. Presented in part at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 2, 1959.
Spectrochemical Determination of Boron in Saline Waters R. C. REYNOLDS, JR.,’ and JOHN WILSON Research Cenfer, Pan American Pefroleum Corp., Tulsa, Okla.
b A spertrochemical method is described for the determination of trace amounts of boron in saline waters. High voltage spark excitation of the natural liquid is accomplished by the rotating disk method; beryllium is used as an internal standard. The technique covers the range of 0.4 to 8 p.p.m. of boron in sea water; the standard error of the method is computed to b e about *3%. The method offers the advantages of simplicity and rapidity while maintaining adequate sensitivity and precision.
T
HE
SPECTROCHEMICAL
METHOD
described here !vas developed to provide a rapid, sensitive, and precise method for determining the boron contents of natural saline waters. Other analytical methods of adequate precision and sensitivity have been used for the determination of boron in trace
quantities. Of these, colorimetric methods are the most widely reported (8, 9, I d , 15’). Colorimetric techniques are capable of greater precision than the usual spectrochemical methods. However, spectrochemical techniques are usually more rapid and are not subject to interference by trace elements and organic materials; matrix effects are a variable, but inasmuch as these effects are associated with major constituents, suitable calibration procedures can be developed that allow the matriv effects to be evaluated. Other spectrochemical procedures (11) for the determination of boron in brines are designed to provide for determination of additional elements. It is difficult to select a n internal standard that is suitable for such a multipurpose technique; one element must serve as a n internal standard for several elements, all of which have different excitation and
emission characteristics. Furthermore, the excitation conditions used must produce usable spectra of several elements. These conditions do not necessarily represent optimum stability and intensity of the emission of any one of the elements being determined. The technique reported here is concerned only with the determination of boron. The internal standard (beryllium) was selected because i t \Tas known to be particularly suited to boron analysis (IO). The excitation conditions 17-ere adjusted to piovide optimum stability and intensity of boron emission. The resulting technique provided a standard error of 2.8%, which is comparable to colorimetric methods (9).
Present address, Department of Geol-
ogy, Dartmouth College, Hanover, N. H. VOL. 33, NO. 2, FEBRUARY 1961
247
