Output potential, volts 1000 Capacitance, mfd. 32 Inductance, mh. 490 Resistance, ohms 30 Discharge point control, 90 degrees The exposure conditions used \?-ere: Preburn None Exposure, seconds 12 3 Analytical gap, mm. Slit width, microns 20 With the intensity control filters at the primary slit set to provide approxiniately 50% light transmittance on the iron line 4017.15 A. in the developed spectrogram, the proper transmittance values of lead 4057.82 A. are obtained. The emulsion calibration curve is obtained by using a two-step split field filter in the 3900- to 4100-A. region, a sample of iron being used to provide the calibrated spectrum. The spectrum is recorded on Spectrum Analysis No. 1 film, which is developed in Eastman D19 developer for 3 minutes a t 70' F. and placed in a 3y0acetic acid stop bath for 10 seconds. It is fixed for 1 minute in Kodak rapid liquid fixer. After a 1-minute wash, the film is dried by infrared radiation in a stream of warm air. The film is placed in a projection-type microphotometer to measure the transmittance of the spectral lines.
suitable in covering the range of 0.05 to 0.50Y0 lead. A plot of the log intensity ratio of these analytical lines versus the per cent concentration for each of the synthetic standards prepared as described above provides a straight-line working curve having an index of o.14y0 lead. Precision. The reproducibility of determinations made on three films under closely related conditions provided a measure of the precision of t h e method. A sample containing o.27y0 lead was analyzed a total of 46 times. The coefficient of variation observed was 4.7870. Accuracy. A measure of the accuracy of determinations may be obtained by considering differences between the results of determinations
made by spectrochemical methods and those made by routine chemical methods. A comparison of the lead values by the two methods on 84 samples is summarized in Table I for the concentration range 0.08 to 0.48. These data provided sufficient confidence to use the method for routine control purposes. The level of the solution in the cupped electrodes should be carefully controlled as this is normally the cause of the greatest deviation. Duplicate analyses are made on the solution from each sample, and one control standard is analyzed in duplicate on each film. As high as 80 determinations have been made by one man in 8 hours, indicating the usefulness of this technique. ACKNOWLEDGMENT
Table 1.
+ or -
Lead Values
Dev. from Chemical No. of Value Samples 0.00 20 0.01 31 0.02 21 5 0.03 0.04 3 0.05 4 Av. concn., % 0.23 .4v. diff., % 0.0143 Av. dev., % 6.21
DISCUSSION
Curve. T h e analytical lines used in this study, lead 4057.82 A. and iron 4017.15 A . , were found to be Working
% of Total Samples 24.0 36.0
The authors wish to thank David Stewart, John Rea, and George Rudolph for their assistance in performing many of the chemical analysis. LITERATURE CITED
25.0
6.0
4.0
5.0
Woodruff, J: F., J. Opt. SOC.Amer. 40, RECEIVEDfor review hlarch 16, 1957. Accepted June 21, 1957.
Spectrochemical Determination of Trace Impurities in Commercial G r a d e Ammonium Chloride K. W. BEYER and 0. T. AEPLI Pennsalt Chemicals Corp., Wyandoffe,
Mich.
b A method was developed for determining trace metallic impurities in commercial grade ammonium chloride. After removal of the ammonium chloride by sublimation, the impurities with the internal standards are placed on a graphite electrode. The electrode is excited by a 2300-volt alternating current arc. The spectra are recorded on a photographic plate. For quantities of about 1 p.p.m. the agreement is within +0.04 p.p.m.
B
P USING a
medium quartz spectrograph, it was possible to determine trace quantities of nickel, copper, iron, and lead in commercial grade ammonium chloride quickly and accurately. These metallic impurities are fixed by the addition of 1% phosphoric acid and concentrated by removal of the ammonium chloride by sublimation.
The residue is dissolved in nitric acid and evaporated nearly to dryness. The silica is removed by hydrofluoric acid. An acid sodium nitrate buffer with zinc and bismuth as the internal standards is added to the residue. Excitation is obtained by a &ere high voltage alternating current arc. MATERIALS
The internal standards were prepared from either the spectrochemically pure metals or the salts of the metals. All other chemicals were reagent grade or redistilled liquids from borosilicate glass apparatus similar to Corning Glass Works, Corning, N. Y., Catalog KO. 3380. The buffer solution contains 5 mg. of bismuth and 50 grams of sodium nitrate per liter. The internal standard solution contains 1.7 grams of zinc acetate per liter, equivalent to 0.6 mg. of zinc per ml.
PROCEDURE
A 25-gram sample of ammonium chloride is placed in a 100-ml. Vycor evaporating dish, and 10 ml. of 1% phosphoric acid is added. If the sample is not made wet with the phosphoric acid, inconsistent low results will be obtained. The treated sample is dried in an electric oven a t 130' C. for 1 hour. A longer drying time will produce a hard mixture which cannot be easily broken. After drying, the mixture is broken into about '/*-inch pieces, which are placed in a 20-ml. platinum crucible and slowly sublimed. The residue is dissolved in 5 ml. of redistilled nitric acid and evaporated almost to dryness. Upon further evaporation with about 1 ml. of hydrofluoric acid and a few drops of redistilled nitric acid, the silicic acid is removed. Finally, a few drops of redistilled nitric acid, 1.0 ml. of the buffer solution, and 1.0 ml. of the zinc acetate internal standard solution are added to the residue. The solution in the platinum crucible is VOL. 29, NO. 12, DECEMBER 1957
1779
Table I.
Wave Length of Spectral Lines, Concentration Range, and Interfering Lines
Table 111.
Precision of Method Concn. Av.
KO. of
Internal Standard
Element -4.
A.
Zn 3075.90
Si 3050.82
Si 3054.32 Fe 3047.61 Pb 2833.07
Si 3413.48
C u 3247.54 Fc 2483.27 In excess of 10 p.p.111.
Table II.
Element Copper Sickel Lead
Iron
Quantity Added, P.P.11. 0 13 0 20 0 46 0.40 1.00 1.50 0.40 0.90 1.30 1.00 3.00 8.0
- _. ~
Interfering Element
A. Fe" 3075. 72 Fe" 3075.72
0.2-2.0 0.8-8.0 0.2-6.0 0.1-0.5 0,5-4.0 0 g2.0 0 1-0.8 4.0-15
Zn 3075.90 zn 3075.90 Bi 2887.98 Bi 2897.98 Zn 3282.33 Z n 3282. 3 3 I3 2897.98
Pb 2663.17
'
Concn. Range, P.P.M.
c1 12 0 18
0 46 @ .38 1.1
1.45 0 . 30 0.82
1,l5 0 88 2.8 7.6
thoroughly miwd by gentle rotation of the crucible. One drop of the solution is placed on the top of each of the 1/4-inch graphite electrodes, previously treated with 2 drops of redistilled kerosine. This treatment prevents seepage of the solution into the elcctrodps. The treated electrodes are dried nt 130" C. for about 1 hour. It is advisable to keep the coated electrodes in the oven until just prior to use, because of the hygroscopic nature of the sample. The electrode with the sample is transferred to the electrode holder and preburned for 15 seconds nith a 2300-volt arc a t 2.5 amperes. A
:i 0 I:, 0 19 0 48 0 .3 9 c1. 86 1.50 0 38 (1 . !I3 1.20 0.93
2.!1 7.8
80 25 30 30 25
Lead Iron
Range, P.P.M.
Deviation,
0 14 0 50 2.00 0.50 1.50 5.00
i13
e 7
,c
i 6 1.8 1 8
1 8
=t7
Fe" 3 i 1 3 , 1 4 . , .
...
Quantity Found, P.P.11. 2 0 12 0 1s 0 51 0.44 0.93 1.55 0.41 0.86 1.20 1.1 3.1 8.1
Ticlcel
Fen 2832,44
Accuracy of Method
1
Element Detns. Copper 30
-1V.
Sumericd Difference
0 12 0 18 0 48 0.41 0.96 1.50 0.36 0.87 1.18 0.97 2.9 7.8
-0 01 -0 02 1 0 02 i0.01 -0.04 0.00 - 0 04 -0.03 -0.12 -0 03 -0.10 - 0 20
30-second exposure a t 5.0 amperes with a 1.O-nini. arc gap is used. The slit width is 30 microns and the spectra are recorded on a n Eastman 33 plate, which is processed for 5 minutes in a D-19 developer a t 68" F. with continuous agitation. The plates are ealibatcd with a step slit, using a Beckman poiver supply and hydrogen lamp for the light source. After the photographic plate has been processed, the spectrograms are evaluated with the densitometer. The quantities of trace elements are read from the analytical curves, which are constructed by plotting parts per million of the element against the re-
epective element per internal standard log intensity ratios. The \lave lengths of the spectral lines, the concentration ranges used, and the interfering elements are slio\\ n in Table I. RESULTS
To determine the accuracy of the niethod, a knon-n quantity of each deinent n a s added to spectrochemically pure samples of ammonium chloride. The results showing the difference betn een the quantities added and found are listed in Table 11. For quantities less than 1 p.p,m., the agrecnient is within 20.04 p.p.m. Samples of ammonium chloride xei e :iiialyzed 25 or 30 times in order to hnd the precision of the method. The average deviation from each element analyzed is about ilo%, as shou 11 in Table 111. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Pennsalt Chemicals Corp. for permission to publish this article. RECEIVED for review January 14, 1!956. .Iccepted July 18, 1957. Sixth annual Pittsburgh Conference, A1nalyticalChemistry Group, Pittsburgh Section, ;IJIERICAS CHEMICAL SOCIETY, and Spectroscopy Society of Pittsburgh, Pa., March 19%.
X-Ray Diffraction Powder Data of Some Normal Alkyl Dithiol Esters of Sebacic Acid D. A. LUTZ and L. P. WITNAUER €asfern Regional Research loboratory, Philadelphia 1 8, Pa. RICHARD SASIN and GEORGE S. SASIN Drexel lnstitute o f Technology, Philadelphia 4, Pa.
b X-ray diffraction powder data were obtained for n-alkyl dithiol esters of sebacic acid. All the individual compounds can be easily distinguished and identified b y the diffraction data. The esters crystallize in tilted monomolecular layers. Long spacings increase regularly with increase in hydrocarbon 1780
ANALYTICAL CHEMISTRY
chain length, forming two series, one for odd- and one for even-membered series of the alkyl ester groups.
M
of the dithiol esters of longchain fatty acids are solid crystalline materials a t ordinary teniperatures, suitable for characterization by AKT
x-ra) diffraction. In this paper the xray diffraction p o d e r patterns of methyl. u-amyl, n-heptyl, n-octyl, nnonyl, n-decyl, n-undecyl, and n-dodecyl dithiol sebacic esters are reported. EXPERIMENTAL
All the dithiol compounds used were
