to the amount of strontium present and thus increase the precision of the strontium determination. With our apparatus, 300 pg. of strontium is needed to produce a peak height above background equal to the background. The ratio, I B r / I R b , is in turn affected by experimental errors, the chief of which is caused by the inhoniogeneous nature of the sample. Since the resin occurs as discrete particles and the strontium and rubidium are not absorbed equally on each particle of the column, there n-ill be a statistical mixing error that nill depend on a number of factors including the amount of excess resin in the column, the particle size of the resin, and the fraction of pellet effectively contributing to the fluorescence intensity. In any case, the number of particles containing strontium and rubidium, or both, mill be small, and only R fraction of the total pellet nill be
sampled by the exciting x-rays. The internal standard does not in general correct completely for the error because the affinity of the rcsin for the unknown and standard is not the same, and the two elements will not be equally distributed through the resin. An attempt to assess the relative magnitude of the mixing error in comparison to the counting and weighing errors was made by measuring Isr/IRb ten times on a single preparation but grinding, mixing, and repressing the pellet between readings. The variance in I B r / I R b was 19.41 x 10-5 in this case, while the variance of ten individual pellets was 39.26 X 10-5. The variance due to counting was 7.70 X 10-5. Even if counting and preparation errors w r e made insignificantly small, the standard deviation due to mixing statistics would be 37* in amount of strontium.
ACKNOWLEDGMENT
The author is grateful to Paul Shanley and Judith Dubchansky for carrying out much of the experimental work. LITERATURE CITED
(1) Birks,
4,.
S., “X-Ray Spectrochemical Analysis, Interscience, Ken- York, 1959. (2) Collin, R. L., J . Am. Chern. SOC.81, 527.5 (1959).
( 3 j GEGbb, W.T., Zemany, P. I>, iyature 176,221 (1956). (4) Pfeiffer, H. G., Zemany, P.I)., Ihzd., 174, 397 (1964). ( 5 ) van Niekerk, J. X., de Wet, J. F., Wybenga, F. T., ANAL.CHEM.33, 213 (1961).
RECEIVED for revien- July 11, 1960. -4ccepted December 20, 1960. Work done in part under U. S. Atomic Energy Commission Contract AT(30-1)-901. Also supported in part by Research Grant C-3003 from the National Cancer Institute of the National Institutes of Health.
Spectrochemical Determination of Trace Elements in Inorganic Salts Using a ConcentrationPrecipitati on Tech nique RICHARD
L. DEHM, WALTER G. DUNN,
and EDWIN R. LODER’
Industrial laborafory, Eastman Kodak Co., Rochester 4, N. Y.
b A concentration procedure using two quinolinol organic precipitants, 8 (oxine) and 2-mercapto-N-2-naphthylacetamide (thionalide), is used in conjunction with a spectrographic procedure for the simultaneous determination of seven elements in potassium bromide, potassium chloride, potassium iodide, potassium nitrate, sodium bromide, sodium chloride, and sodium nitrate. Copper, iron, lead, manganese, nickel, tin, and zinc are determined in the range of 0.1 to 5 p.p.m. The precipitation is carried out in a hot solution at pH 9; aluminum is used as a carrier element.
-
D
spectrographic examination of the inorganic sodium and potassium salts using direct current arc excitation was found to be too insensitive to detect the majority of the impurities at the level a t which they are normally present, which is usually less than 1 p.p.m. This is probably due to the fact that the alkali metals, having low ionization potentials, lower the average energy of the discharge and suppress IRECT
Present address, hiaumee Chemical Co., Toledo, Ohio.
lines of elements having high ionization potentials. Owens ( 8 ), in a summary of spectrographic methods for trace analysis, recommends the high-voltage, alternating current arc as the most appropriate spectra excitation source for use with inorganic materials. This source has been used for the analyses of sodium hydroxide (1, 3, l l ) , sodium bicarbonate, and sodium chloride solutions (1, l a ) . A solution alternating current arc technique has been used for the analyses of sodium salts, both organic and inorganic, by first converting them to sodium nitrate (9). These procedures failed to give the desired sensitivities for nickel, lead, and zinc below the 1-p.p.m. level and led to the investigation of concentration procedures. Of particular interest JYas a precipitation procedure, prior to spectrographic examination, developed by Mitchell and Scott (5-7). I n their procedure 14 trace elements were concentrated by precipitation with 8-quinolinol, tannic acid, and thionalide in a solution buffered to p H 5.1, containing aluminum as the carrier element. Heggen and Strock (4)reported a similar procedure using indium as the carrier and as the internal standard. Pickett and
Hankins (IO) coinpared the efficiency of these two elements using radioisotopes and reported no differences in carrier characteristics. The concentration procedure described in this report uses two organic precipitants, 8-quinolinol and thionalide. The precipitation is carried out in a hot solution a t p H 9, using aluminum as the carrier element. The spectrographic procedure employs a direct current arc for excitation of the total ash in a matrix of graphite and lithium carbonate with germanium and bismuth as internal standards, REAGENTS
Oxine (8-quinolinol) solution, 5.0% in 2N acetic acid. Thionalide f2-merca~to-iV-na~hthvlacetamide) solution (K*and K Laboratories, 177-10 93rd Ave., Jamaica 33, N. Y.), 1.0% in glacial acetic acid, prepared just before use. Glacial acetic acid, redistilled using a quartz still. Aluminum solution, 11 grams of A1C12.6H10 Der liter of distilled water. A m m o n i u i hydroxide, reagent grade, 28% NHB. Matrix Ratio. 50 LizCOa 1.0 GeOz 40 graphite 0.30 Bi203:
+
+
VOL. 33, NO. 4, APRIL 1961
+
607
Table
Manganese Lead Tin
Nickel Iron
d
Internal Standard Line, A. Ge 3269. 4gb Ge 3039.06" Bi 3397.21d Bi 3397.2 1 Bi 3397.21d Ge 3039.06" Ge 3039,06" Ge 3039.06" Bi 2897. 97d Bi 2897. 97d Ge 2754. 5gb Ge 2754. 5gb Ge 2754.59* Ge 3039.06" Ge 3039.06" Ge 3039.06' Ge 3039.06" Ge 3039.06"
3273.96" 2961. 16c 3345.02c 3345.O d 3345.02b 2949. 2OC 2949. 20d 2949. 20h 2802. OOG 2802. OOd 2863.32c 2863. 32d 2863.32* 3134. loc 3134.10d 3134. lob 3n21 07d 3021 . 0 i b
Zinc
0
Spectral Line Pairs and Analytical Ranges
Analytical Line, A.
Element Copper
a
I.
Concn. Range, P.P.M. by Wt. of Sample 0.1-1 0.5-5 0.1-0.2 0.2-2 1 -5 0.1-0.4 0.2-1 1 -5 0.1-0.6 0.4-5 0.1-0.2 0.1-1 0.6-5 0.1-0.2 0.1-1 1 -5 0.1-1 0.5-5
1.2%. Transmittance step. 5%. Transmittance step. 100%. Transmittance step.
207&. Transmittance step.
Table
II.
Precision and Recovery of Elements Added to Potassium Bromide
Copper
Iron
Nickel
Lead
Zinc
Manganese Tin
Series I. Simultaneous precipitations. Spectrograms recorded on two photographic plates 0.5 P.P.R.I. Added
Mean Std. dev. Coeff. of var., %
2.00 2.20 2 0.5 2.25 2.20 2.25 2.15 0.10 4.7
0.46 0.43 0.45 0.43 0.47 0.45 0.02 4.5
0.40 0.43 0.47 0.40 0.47 0.43 0.04 9.3
0.49 0.54 0.53 0.48 0.53 0.51 0.03 5.9
2 P.P.M. Added 2.17 2.22 2 12 2.22 1.97 1.67 2 32 2.37 2.42 2.37 2.12 2 02 2.22 2.11 0.16 0.25 11.8 7.2
0.51 0.51 0.50 0.50 0.52 0.51 0.01 2.0
0.43 0.44 0.45 0.43 0.43 0.44 0.01 2.3
0.49 0.52 0.53 0.47 0.50 0.50 0.02 4.0
0.48 0.50 0.48 0.47 0.49 0.48 0.01 2.1
1.82 1.97 2 12 1.82 2.12 1 92 1 96 0.13 6.6
1.79 1.76 1.71 1.66 1.76 1.66 1.72 0.05 2.9
1.95 2.05 2.15 2.00 2.00 1*95 2 01 0 . os 4.0
2.10 2.15 2.20 2.25 2 25 2 20 2.19 0.06 2 7
2 32 1.82 1.?2 1.62 1.92 1.88 0.27 14.3
1.88 2.00 1.83 2.17 1.92 1.96 0.13 5.2
1.80 1.80 2.00 2 50 1.90 2.00 0.29 14.5
2.10 2.15 1.80 2.30 2.20 2.11 0.19 9.0
Mean Std. dev. Coeff. of var., yo Series 11. Single precipitations. Spectrograms recorded on separate photographic plates over a period of several weeks 2 P.P.M. Added
Mean Std. dev. Coeff. of var., %
1.95 1.90 1.90 1.55 2.05 1.87 0.19 10.2
2.05 1.74
i.73
2.26 2.34 2.02 0.28 13.8
1.70 2.18 1.75 1.62 2.30 1.91 0.31 16.2
PRECIPITATION PROCEDURE
Dissolve 10 grams of the salt in 50 ml. of distilled water contained in a beaker. Add, by pipet, 1.0 ml. of the aluminum solution, 1.0 ml. of the oxine solution, 5.0 ml. of ammonium hydroxide, and 2.0 ml. of the thionalide solution, swirling the sample solution after each addition. Cover the beaker with a watch glass and heat at 80' to
608
ANALYTICAL CHEMISTRY
85' C. on a steam bath for 1.5 hours. Agitate the solution frequently to aid in coagulation. Place the beaker in an ice bath for 1 hour without agitation. Filter the cold solution through a Yo. 542 Whatman filter paper, 2.0 em. in diameter, contained in a No. 3 Gooch crucible. Wash the precipitate with distilled water, rinsing all the clinging precipitate onto the paper. Continue suction until the filter cake is
nearly dry. Transfer the filter paper and precipitate, without washing, to a No. 0 porcelain crucible. Ash in a muffle furnace, starting a t room temperature, and slowly raise to 500' C Approximately 3 hours are required to bring the ash to a light brown color. Transfer the ash to a small boron carbide mortar containing 10 mg. of matrix and mix thoroughly. Pack the total mix into the crater of a highly purified graphite electrode. Treat a n-ater-reagent blank in the same manner as the sample with every set of determinations. SPECTROGRAPHIC PROCEDURE
The sample electrode is a high purity graphite rod 0.180 inch in diameter. The undercut cup is 0.0938 inch deep and 0.125 inch in diameter. This electrode is arced as the anode. The cathode is a pointed, high purity graphite rod inch in diameter. Excitation is by direct current arc, using 8 amperes for GO seconds and maintaining an electrode gap of 2 mm. A rotating four-step sector wheel, transmitting approyiniately 100, 20, 5 , and 1.2% of the incident light, is placed in front of the slit to aid in bringing all the lines employed in the photometry within a usable density range. The spectra are recorded on Kodak Spectrum iinalysis No. 1 plates The SA No. 1 emulsion is calibrated by the two-step method (d). After the exposed plate has been properly processed and densitometered, the intensity ratios of the analytical line pairs listed in Table I are calculated, The element concentrations are then determined from the appropriate analytical curves. The trace element content of the sample is corrected for any of the element impurities found in the water-reagent blank. ANALYTICAL CURVES
The analytical curves were obtained by adding standard solutions of the element salts to clean potassium bromide solutions and treating them by the complete procedure. Curves of concentration us. intensity ratio were plotted for each element. Clean potassium bromide was prepared by applying the precipitation procedure to hrge qusntities of the salt which was then rccovered from the filtrate by cooling in a dry ice-acetone bath. The recovered salt was washed n-ith alcohol and chloroform to remove traces of the organic reagents. PRECISION STUDIES
The precision of the method was determined by taking aliquots of a clean potassium bromide solution and adding to them standard solutions of the seven elements. I n Table 11, Series 1, are listed the results of five determinations a t 0.5 p.p.m. and six determinations a t 2.0 p.p.m. all made a t the same time and recorded on two photographic plates. The coefficients of variation obtained are representative of those t o
'
be expected for duplicate determinations. A second precision series was run n-hich incorporates most of the variable conditions usually associated with a spectrographic procedure over a longer period of time (Table 11, Series 2). Each series of the seven elements represents a single determination photographed on one plate. The data cover a period of several weeks. The coefficients of variation listed for the seven elements are believed to be representative of those t o be expected over longterm operation. DISCUSSION
Since the procedure has been applied only to neutral salts, the pH of the precipitation has been controlled by the accurate addition of reagents and control of heating conditions with strict adherence to the specified time intervals. The p H of each sample solution prior to the filtration step was found to be betueen 9.0 and 9.2. The alkaline earths are precipitated a t this pH but, since they are present only a t the trace level in the salts tested, rejection is not required. This n a s not the case with the material studied by Xlitchell, where they were a major constituent. A fixed neight of the buffer-internal standard mixture n as added to each sample ash, since the major portion of the ash neight is contributed by the aluminum carrier. The variation in the weight of the ash, as a result of trace element variations in the sample, was not considered significant enough to warrant the additional n-ork involved in weighing all samples. The spectrographic matrix of lithium carbonate, germanium oxide, and graphite has been used successfully in this laboratory for several years in the
semiquantitative analysis of general unknowns. Germanium is used as the internal standard. In the development of this procedure, running plates showed germanium to be a satisfactory internal standard for copper, iron, manganese, nickel, and tin, but not for the more volatile elements, lead and zinc. Bismuth was added as an internal standard for these more volatile elements and on the basis of further running plates was shown to be satisfactory. The arcing period was terminated after 60 seconds to keep the background low near the zinc 3345.02-8. line, thereby increasing its detectability. The reagents, after careful preparation, are stored in polyethylene bottles. All glassware is thoroughly m-ashed with hydrochloric acid before use. Other precautions normally exercised in a spectrographic laboratory are observed, to prevent any contamination of the reagents or the samples. The absolute sensitivities on the electrode n ere determined using standards of the element oxides mixed in aluminum oxide and treated as an ashed precipitate. Lead, tin, manganese, iron, copper, and nickel were detected a t the level of 0.1 fig. This absolute sensitivity has not been obtained for the total procedure because of the contribution of the reagent blanks. On the basis of these tests it is felt that further purification of reagents would increase the sensitivity of this method another five- or tenfold. Extensive recovery studies were not made. Semiquantitative measurements were used to determine the best recovery conditions and, although these measurements were not accurate enough to prove complete recoveries, for practical purposes recoveries by this method
are complete. Chemical cross checks have also substantiated this. APPLICATIONS
It is expected to extend the method to include other inorganics such as the hydroxides, carbonates, and sulfites. Elements other than the seven studied are also precipitated by this procedure, although none of them has been investigated. It is frlt that the procedure could be extended to include trace determinations of cadmium, calcium, cobalt, chromium, and magnesium, since the respective metal oxinates are precipitated in this pH range. LITERATURE CITED
(1) Boettner, E. A., IND.ENG.CHEM., ANAL.ED. 13, 861-4 (1941). (2) Churchill, J. R., Zbid., 16, 653 (1944). (3) Duffendack, 0. S., Wolf, R. A., Ibid., 10, 161-4 (1938). (4) Heggen, G. E., Strock, I,. W ,AXAL. CHEW25, 859 (1953). (5) Mitchell, R. L., “Emission Spectro-
chemical Analvsis.” in “Trace Ana!-
ysis,” J. H. Yoe and H. J. Koch, eds.,
Wiley, h’ew York, 1957. (6) Mitchell, R. L., Scott, R. 0 , A p p l . Spectroscopy 11, 6 ( 1957).
(7) Mitchell, R. L., Scott, R. 0 , Spectrochim. Acta 3, 367 (1948). (8) Owens, J. S., IND.EKG. CHEM., A N A L . ED. 11, 59 (1939). (9) Perry, V. G., Weddel!, k4’. A I . , Wright, E. R., ANAL. CHEW 22, 1516-18
( 1950). (10) Pickett, E. E., Hankins, B. E., Zbid., 30,47 (1958). (11) Wilson, M. F., in ‘‘Methods for
Emission Spectrochemical Analysis,” p. 352, Am. SOC. Testing Materials, Philadelphia, Pa., 1957. (12) I b i d . , p. 355.
RECEIVED for review July 11, 1960. Accepted Pl‘ovember 21, 1960. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 4, 1960.
The Jet Fumigator G. L. ROUNDS, J. H. HOEFFERLE, E. F. GARNER, and H. J. MATO! Air Control and Research Department, Kaiser Steel Corp., Fontana, Calif.
b The description and operation of a device for generating parts per billion or parts per million concentrations of gas for fumigation chamber atmospheres are described (Patent application No. S.N. 766292). The device uses a Beckman flame spectrophotometer burner. The fuel used for combustion is hydrogen, with air supplying the oxidant. The gas must b e dissolved in a solvent which will not produce objectionable pyrolytic decomposition products in passing through the flame. Water is ised as a solvent for hydrogen fluoride in vegetation fumigations.
I
involving corrosive and toxic atmospheres, difficulty is encountered since minute quantities of the agent must be metered into large volumes of air passing through an enclosure. The common method of metering gaseous agents is to incorporate some form of volume displacement ( 2 , 3, 6 ) . Besides being restricted to the use of gaseous materials, some volumetric displacement devices have the disadvantage of being batch operations. The device described operates continuously and is not limited to the use of gaseous fumigants. Solutions which produce liquid or solid aerosols upon N MANY STUDIES
passing through the hydrogen-air flame might also be incorporated effectively if pyrolysis does not produce objectionable products. DESCRIPTION
The operation of the device is based upon the aspirating characteristics of the burner used in the Beckman flame spectrophotometer. This burner is designed to be used with either oxygen or air as the oxidant and aspirating medium, and either hydrogen or acetylene as the fuel. For use as a fumigator, hydrogen and air were chosen: VOL. 33, NO. 4, APRIL 1961
609
