20-, and 150-pg. amounts of fluoride as illustrated by the following data:
Table 111.
Direct Titration Results for Fluoride
Fluoride Found Sample City water Demineralized water with 100 pg. F added Water extract A Water extract B
F,
Added
Found
1 3 10 20 150
1 2. 3
io
20,20, 19 151
Some common interferences studied are listed in Table 11. Approximate concentration in the final solution and per cent relative error in titrant volumes
Table 11.
Anion Added
c1-
NOa-
C1O4POa-3
so,-'
Interference Data
Concn. of hdded Anion in Final soln., $& Relative Error P.P.M. 50 pg. F 200 pg. F +1.5 Nil 40 360 385 285 0.1 0.06 9 2
+1.5 f3.0 f0.7 -3.0 -0.7 1-12.5 +0.8
f0.5 f2.5
...
...
+i:5
...
rg.
P.P.M.
25, 23
0.10, 0.09
100, 100, 96 18 (4detns.) 7 ( 8 detns.)
at the 50- and 200-pg. fluoride levels are given. Fluoride in aqueous samples can be separated from most interfering substances by the Willard and Winter distillation (6) or by some other suitable means. This method has been used successfully in the author's laboratory for over three years. During this time the slopes of the linear calibration curves-sensitivity of the method-varied from 0.8 to 0.7. This change is attributed to variation in ambient temperature a t the time of preparation of reagents and consequent variation in thorium content of the reagents. It causes no decrease in the accuracy of the method as long as the recommended standardization procedures are followed. Typical direct titration results are
0 . 3 8 , 0 . 3 8 , 0.37 0.12 14 detns.) 0 . 0 3 (8 detns.)
given in Table I11 for various routine aqueous samples. LITERATURE CITED
(1) Dean, J. A,, Buehler, & H., I.Hardin,
L. J., J . Assoc. 0.j'icial Agri. Chenaists
40. 949 119571. \
,
(2) Gwirtsman, J., Mavrodineanu, Coe, R. R., ANAL. CHERI. 29, (1957). (3) Klingman, D. IT., Hooker, D. Banks, C. V., Ibid., 27, 572 (1955). (4) Ma, T. S., Gwirtsman, J., Ibid., 140 11937). (5) Mavrodkeanu, R., Gwirtsman, J., Contribs. Boyce Thompson Inst. 18, 181 (1956). ( 6 ) Willard, H. H., Winter, 0. B., ANAL. CHEM.5. 7 11933). I~
I
W.P. PICKHARDT Polychemicals Department E. I. du Pont de Nemours &- Co. Wilmington, Del.
Nature of Extraneous Peaks in Gas Chromatographic Analysis of Gira rd-T kola ted Car bonyls SIR: The use of Girard-T reagent [ (carboxymethy1)trimethyl-ammonium
chloride, hydrazide] by this laboratory for the isolation of carbonyls from multifunctional group mixtures, as described by Teitelbaum (4) and applied by Stanley et al. (S),results in the appearance of a great many extraneous peaks when the carbonyl fraction is analyzed by gas chromatography. These impurities have been traced to the formalin used for regeneration of the carbonyls. The terpenoid fraction of cold pressed orange oil, after being separated from the terpene fraction (1, 2) contained aldehydes, ketones, esters, and alcohols. This terpenoid fraction was treated with Girard-T reagent as described by Stanley et al. (3) with regeneration of the aldehydes using formalin. The residue, containing the aldehydes, was analyzed by gas chromatography (column 16-feet x '/,-inch Silicone 200 Fluid coated 30- to 60-mesh firebrick, temperature programmed 50' to 150' C. a t 2.9' C. per minute, helium flow rate 50 ml. per minute, hot wire thermal conductivity cell). The curve is reproduced in Figure 1. The components represented by the individual peaks were isolated and determined by infrared spectro864
ANALYTICAL CHEMISTRY
photometry. The chromatogram indicated the presence of octanal (peak g), nonanal (peak ll), decanal, and citronellal (peak 13), which were aldehydes isolated from the orange oil terpenoid fraction, The remaining peaks were attributable to the Girard-T process
except peak 7 , which may contain material from the terpenoid fraction in addition to an impurity introduced by the Girard-T process. Figure 2 shows a chromatogram of the extract obtained from a blank Girard-T run which was carried out
48
60
72
04
TIME, MIN
Figure 1. reagent
isolation of carbonyls from orange oil using Girard-T
Lu
I n
YI
a a
W
10
a
0 W
0
12
24 TIME,
Figure 2.
36
40
60
0
12
MIN.
48
36
72
BO
TIME, MIN.
Chromatogram of Girard-T blank
identically to the procedures used for the isolation of carbonyls from the terpenoid fraction. Comparison of peak retention times with those in Figure 1 serve to illustrate that the extraneous materials originated in the chemicals introduced in the Girard-T procedure. Infrared comparisons of material representing peaks having the same retention time further corroborate their identity as having originated in the procedure. Figure 3 shows a chromatogram of purified octanal which had been extracted by the use of the Girard-T process. The added octanal served to align more closely the results of Figure 1. Most of these impurities are introduced into the carbonyl residue directly from the formalin solution. Commercial formalin was extracted with isopentane and the dried extract chromato-
24
Figure 3.
Determination of octanal using Girard-T reagent
grammed. The components represented by the individual chromatographic peaks gave infrared spectra identical to many of the extraneous peaks in Figure 1. A volume of isopentane equal to that used in the Girard-T process waa evaporated to 1 ml. and chromatogrammed. The chromatogram showed traces of impurities appearing in the proximity of the solvent region. An amount of Girard-T reagent equivalent to that used in the process was extracted with isopentane. The ckromatogram of concentrated solvent showed traces of impurities attributable to the solvent. Octanal, purified by gas chromatography, was treated with Girard-T and regenerated with formalin which had been extracted with isopentane. The residue after stripping was chromatogrammed showing no extraneous peaks
other than those traceable solvent.
to the
LITERATURE CITED
(1) Clark, J. R., Bernhard, R. A,, Food Research 25,389 (1960). (2) Kircbner, J. G., Miller, J. M., Ind. Eng. C h a . 44,318(1952). (3) Stanley, W. L., Ikeda, R. M., Vannier, S. H., Rolle, L. A., J . of Food Sci. 26,43 (1961). (4)Teitelbaum, C. L.,J . Org. Chem. 23, 646 (1958).
G. L. K. HUNTER ROBERT F. ST RUCK^ U. S. Fruit and Vegetable Products Laboratory Southern Utilization Research and Development Division Winter Haven, Fla. Present Address: Southern Research Institute, Birmingham, Ala.
Spectrophotometric Determination of Rhenium in Tungsten Alloys SIR: The spectrophotometric determination of rhenium as the yellow ReO(CKS)4 complex (4) requires prior separation from interfering elements by means such as solvent extraction (1, 3) or precipitation (6). I n the determination of molybdenum by a similar method, interference of tungsten is prevented by adding citric acid to form the stable W(VI) chelate (2). As tungstenrhenium alloys are substantially free of molybdenum, the need for a chemical separation can similarly be avoided. EXPERIMENTAL
Apparatus. Beckman Model D U spectrophotometer with 1-cm. Corex cells. Reagents. Tartaric acid solution. Dissolve 500 grams of D-tartaric acid
and 90 grams of N a 2 W 0 4 . 2 H 2 0 in water and dilute t o 1 liter. Clarify the solution by shaking with a few grams of activated carbon and filter. Sodium thiocyanate solution. 100 grams per liter. Stannous chloride solution. Dissolve 100 grams of SnClz.2Hz0 in 500 ml. of concentrated HC1 and dilute to 1liter. Procedure. The alloy sample, 0.4 to 0.5 gram containing from 0.1 to 2074 rhenium, is dissolved in a platinum capsule with HIYO3 and H F ( 5 ) ,and the solution is evaporated just to dryness by warming, on a hot plate at 80' to 100' C. The residue is dissolved in water with the addition of a few drops of 6N NaOH solution and diluted to 500 ml. A 5-ml. aliquot is pipetted into a 100-ml. volumetric flask and diluted to approximately 50 ml. Next, 10 ml. of the tartaric acid solution is added, followed by 5 ml. of the NaCNS solution
and 10 ml. of the SnClz solution. The flask is filled to the mark and allowed to age for 30 minutes before measuring the transmittance a t 385 mq. using a reagent blank as reference. If the coloration is faint, indicating a low rhenium content, the procedure is repeated with a 25- or 50-ml. aliquot. The rhenium content is then found from a calibration curve prepared by similarly treating known dilutions of pure ammonium perrhenate. For alloys of approximately known compositions, a sample weight is taken to contain from 0.5 to 2.0 mg. of rhenium, and its solution is run in entirety. RESULTS
Table I lists the results obtained by this procedure for a series of tungsten alloys. The values in the second VOL. 34, NO. 7, JUNE 1962
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