Spectrophotometric Procedure for the Determination of Tin in Complex Materials Using 8-Quinolinol and Phenylfluorone SIR: I n an evaluation of analytical procedures for the determination of tin in the 10-p.p.m. range or less, there are at least three suitably sensitive colorimetric reagents. These reagents, phenylfluorone (3, 4, 7 ) , toluene-3,4 dithiol (2) and pyrocatechol violet (6), are however, subject to many interferences. T o apply any of these reagents to the determination of tin in complex materials such as rock samples would require some efficient prior separation. Such techniques as distillation of tin or the use of ion exchange or solvent extraction have been studied in the past. I n terms of analytical procedures that would be amenable to a high volume of differing complex materials, solvent extraction was selected for further investigation. Prior separation by solvent extraction has two broad divisions: isolation of the element by its extraction into the organic phase by a highly selective reagent or the removal of the bulk of the interference as by a broad spectrum reagent that uniquely does not complex the desired element. I n the case of tin, both possibilities exist. The use of acetylacetone in chloroform can be used to extract large amounts of many elements, while
Table 1.
Impurity, mg. Al, 100
Sn, a. 0
10
cu, 100
0
10 Fe, 100
0
10 Ni, 100
0
10 Ti, 2
0
Ti, 4
0
Ti, 5
0
Ti, 4
10
Ti", 11
0
10 Q
10 drops HZ02,
290
ANALYTICAL CHEMISTRY
leaving tin uncomplexed in the aqueous phase. On the other hand, in an acid solution, 8-quinolinol (1, 6) forms extractable complexes with few elements, molybdenum and tin being notable exceptions. Furthermore, the tin complex is only extractable in the presence of choride ion. Under these special conditions, tin can be isolated, although a colorimetric determination in the ultraviolet would be lacking in sufficient sensitivity for the purpose outlined previously. Investigations to evaluate the combination of the acetylacetone and 8quinolinol prior separations with a sensitive colorimetric determination using phenylfluorone were planned. The combination of solvent extraction and colorimetric determination must retain the simplicity and ease of operation that is required for the handling of multiple analyses. EXPERIMENTAL
Apparatus. T h e absorbance measurements were made with a Beckman Model D E spectrophotometer using 5-cm. cells. T h e p H measurements were made with a Beckman Model 76 p H meter. Reagents. 8-Quinolinol 4%, adjusted t o p H 0.85 with H z S 0 4 ; am-
Effect of Impurities Absorbance
0.586 0.586 1.182 1.182 0,580 0.584 i ,i52 1.154 0.525 0.530 1.138 1.148 0.520 0.525 1.112 1.103 0.546 0.548 0.551 0.555 0.623 0,628 0.624 0.613 1.175 1.165 0.578 0.583 1.181 1,173
Corrected Absorbance
?4
Recovery
0.586 0.596 0,596
99.6 99.6
0.570 0,572
95.2 95.6
0.610 0.620
101.9 103.6
0.590 0.581
98.6 97.1
0.622 0.612
103,2 102.0
0.601 0.593
100,4 99.1
0.582
0.528
0.522 0.547 0.553 0.622
0.580
monium chloride 20%, adjusted to p H 0.85 with HzS04; gelatin 1%; phenylfluorone (Distillation Products Industries-2,6,7- trihydroxy- 9- phenylisoxanthene-3-one) 0.01 % in methanol and 1 ml. HCl, this solution remains stable for about 1 month; acetate buffer solution, 450 grams of sodium acetate trihydrate and 240 ml. of acetic acid made to 2 liters with water; standard tin solution 1 mg./ml. (dissolve 0.500 gram of reagent grade tin in 50 ml. of hot H2S04 and dilute to exactly 500 ml. with water) if cloudy prepare fresh; standard tin solution 1 pg./ml. in 10% HzSO4; standard tin solution 50 pg./ml. standard tin solution in 10% 2 pg./ml. in pH 0.85 HzS04; standard tin solution 1 pg./ml. in p H 0.85 HzS04; 10%; HzS04pH 0.85; and acetylacetone-CHC13 1: 1 Procedure. ~ - Q U I X O L I N O ExL TRACTION. Solutions containing 0 to 15 pg, of tin are adjusted to a 40- to 50-ml. volume in a small beaker. The p H is then adjusted to 0.85 =k 0.05 with HzS04. The solutions are transferred to separatory funnels using approximately 10 ml. of pH 0.85 solution. Add 25 ml. of 8-quinolinol solution and mix. Add 15 ml. of chloroform and shake for 2 minutes. Discard chloroform layer (contains molybdenum). Add 5 ml. of xH&1 solution and 15 ml. of chloroform. Shake for 2 minutes and reserve chloroform layer. Repeat with a second 15-ml. portion of chloroform. Reserve both extractions in the original beaker. Add 15 ml. of HzS04(10%) and evaporate chloroform on a steam or sand bath; then evaporate on a hot plate to fumes of 803. Destroy organic matter with a few drops of HNOl and HzOZ. Cool and add 15 ml. of water. Transfer with small increments of water (no more than 10 ml. total) to a 50-ml. volumetric flask. PHENYLFLUORONE PROCEDURE.To the solution containing 0-15 pg. of tin and 1.5 ml. of (concd.) in a 15-20 ml. volume, add 5-10 drops of HzOZ, 10 ml. of buffer solution, and 1 ml. of gelatin. Then add exactly 10 ml. of phenylfluorone solution, make to 50 ml. with water and read the absorbance in 30 minutes f 5 minutes in 5-cm. cells at a wavelength of 510 mp with either water or a blank solution in the reference cell. Plot absorbance against the tin content. ACETYLACETONE PROCEDURE. Solutions containing 0-15 pg. of tin and 0.25 ml. of HzS04 (concd.) are adjusted to a volume of 50 ml. with water. ,4dd 10 drops of H202and transfer to a separatory funnel. Add 25 ml. of acetylacetone-chloroform ( 1 : l ) and shake for 2 minutes. Drain the lower layer and discard it. Repeat this extraction with two more 25-ml. portions of acetylacetone-chloroform (1: 1). Reserve the aqueous layer in a small beaker. Add 15 ml. of H2S04(10%) and evaporate on
a hot plate to fumes of SOS. Destroy the organic matter with a few drops of HNOa and H202. Cool and add 15 ml. of water. Transfer with small increments of water (no more than 10 ml. total) to a 50-ml. volumetric flask. Continue as in phenylfluorone procedure. DISCUSSION A N D RESULTS
The procedure involving prior separation of the matrix by acetylacetonechloroforni in the presence of 25.0 mg. of iron or 2.5 mg. of titanium resulted in blanks that were beyond the reading range of the phenylfluorone procedure. No further work in this approach was performed. The procedure using a prior separation of tin with 8-quinolinol was so much more proniising that this approach was carried to a conclusion. The results via this procedure were investigated for completeness of recovery and then in the presence of several common interfering metals. See Table I. The results were satisfactory except with certain limitations in the case of titanium as noted in the data. There is also some indication that
Table II. Analysis of Ore Samples for Tin
Tin, p.p.m. Spectrochemical Colorimetric 7 5 3 1.5 4 3 2 2 1.5 2 1.5
1
6
6 2
3
it is probable that the procedure would be applicable in the presence of many other metals. ACKNOWLEDGMENT
The authors thank Franklin Clark and Blair Roberts of the Bear Creek Mining Co., Kennecott Copper Corp. for the use of their samples and spectrochemical data. LITERATURE CITED
(1) Eberle, A. R., Lerner, S . W., ANAL.
CHEM.34,627 (1962).
recovery of tin is approximately 96% complete when the prior separation is employed. The procedure was applied to eight silicate rock samples and the data were compared to results by eniission spectrometry (Table 11). The results were in good agreement. This procedure appears to be applicable to the deterinination of tin in the low p.p.m. range in complex materials such as silicate rocks. I t also appears to be applicable to the determination of tin in aluminum, iron, nickel, and copper. Other metals were not investigated but
( 2 ) Farnsworth, AI., Pekola, J., Zbid.,
26. 735 1,1954). (3) Luke, C. L., Ibzd., 28, 1273 (1956). (4) Ibid., 31, 1803 (1959). (5) hlotojima, K., Hashitani, II., Ibzd., 33,48 (1961). (6) Ross. W.J., White. J. C.. Ibid.. 33. 421 (1961). ( 7 ) Sandell, E . B., “Colorimetr,i,c Determinat,ion of Traces of Metals, 3rd ed., Interscience, Sew York, 1959. EUGENE N . POLLOCK LAWREKCE P. Z ~ P A T T I Ledgemont Laboratory Kennecott Copper Corp. Lexington 73, Mass. I
,
Identification of Pesticides at Nanogram Level by Extraction p-Values SIR: Electron-capture gas chromatography ( 2 ) has made it possible to analyze for halogenated and thiophosphoryl pesticides a t the nanogram level, the pesticides being identified by retention time. The possibility that plant or animal extractives may contain electron-capturing interferences, the similarity of retention time of some pesticides on a given column, and the low efficiency of certain analytical systems being used in electron capture determinations, make it desirable to have an independent means of confirming or deciding upon the identity of pesticides (3, 5 ) . Although the positive identification of a pesticide in a residue determination is frequently a crucial consideration, few methods are available for making identifications or confirmations of identity a t the nanogram level. A method, based on the distribution of the pesticide between two immiscible phases, has been found applicable at the nanogram and other levels as well. Each pesticide has a characteristic distribution ratio, which in residue analysis has been found practically independent of pesticide concentration and the presence of plant and animal extractives. The procedure is a general one-useful for all pesticides as well as for other compounds. It is convenient and easy to carry out.
Table I. p-Values of Insecticides Determined by single distribution between 5-ml. volunies of immiscible solvents equilibrated at 25.5’ C. Isooctanedimethyl HexaneIsooctaneformamide 857? aq. Isooctane(with 126 90y0 aq. Hexanedimethyl dimethyl dimethyl mg. butter Pesticide acetonitrile sulfoxide formamide formamide extractive) Aldrin 0 73 0 89 0 86 0 38 0 29 Carbopheno thion 0 21 0 35 0 27 0 04 0 0i 0 45 0 40 0 48 Gamma chlordane 0 14 0 16 0 73 0 65 0 56 p,p’-DDE 0 16 0 18 0 45 0 53 0 ,o ‘-DD T 0 42 0 10 0 11 0 40 0 38 0 36 0 08 0 09 P,P’-D,DT 0 45 Dieldrin 0 33 0 46 0 12 0 13 0 55 0 39 0 52 Endosulfan I 0 16 0 17 0 09 0 14 n 06 n” ni 0 13 Endosulfan I1 Endrin 0 35 0 52 0 51 0 iS 0 16 0 77 0 55 0 73 Heptachlor 0 21 0 23 0 29 Heptachlor epoxide 0 35 0 39 0 10 0 11 1-Hydroxychlordene 0 03 0 07 0 06 0 03 0 04 0 12 0 09 Lindane 0 14 0 05 0 06 0 17 0 08 TDE 0 15 0 04 0 04 0 48 Telodrin 0 65 0 63 0 li 0 19
EXPERIMENTAL
like the first 5-ml. aliauot. The ratio
stoppered 10-my. centrifuge tub; an equal volume of lower phase is added; the tube is shaken for about one minute and the upper phase is analyzed exactly
Typical results are given in Table I. I n 62 of the 64 runs the p-values
RESULTS A N D DISCUSSION
VOL. 37, NO. 2, FEBRUARY 1965
291
