are lower than practical with schlieren optics alone and, thus, errors due to the Johnston-Ogston effect can be reduced.
(3) Hexner, p. E., Radford, L. E., Beams, Natl* Acad* Sei* u* s. 47,
LITERATURE CITED
(5) Lamm, O., 2.physik. Chem. (Leipzig.) A143, 177 (1929). (6) Lansing, W. D., Kraemer, E. O., J . Am. Chem. SOC.57, 1369 (1935). (7) Richards, E. G., Schachman, H. K., J . Phys. Chem. 63, 1578 (1959). (8) Schwert, G. W., J . Bid. Chem. 190, 799 (1951).
(1) Dayhoff, M. O., Perlman, G. E., MacInnes, D. A,, J. Am. Chem. SOC.74,2515 (1952). (2) Harrington, W. F., Schellman, J. A., Compt. Rend. Trav. Lab. Carlsberg, Ser. Chim. 30, 21 (1956).
~ ~ ~ y l ~ ~ $
c. H, w.,M ~ s., ~Stein,~ w.H., J . BWZ. Chem. 219, 623 (1956).
(4) Hirs,
(9) Svensson, H., Acta Chem. Scand. 4,399 (1950). (10) Van Holde, K. E., Baldwin, R. L., ~ J . Phys. , Chem. 62, 734 (1958). (11) Wilcox, P. E., Cohen, E., Tan, W., J . Biol. Chem. 228, 999 (1957). (12) Yphantis, D. A., Ann. N . Y . Acad. Sci. 88, 586 (1960).
C. H. CHERVENKA Spinco Division Beckman Instruments, Inc. Palo Alto, Calif.
Determination of Trace Amounts of Lead in Steels, Brass, and Bronze Alloys by Atomic Absorption Spectrometry SIR: Since the introduction of atomic absorption spectrometry (10, 13) as an analytical tool, many advances have been made, several of which have been discussed in recent reviews by Elwell and Gidley (6), Gilbert (8),and Scribner and Margoshes (11). Applications of this technique to the analysis of trace amounts of lead have been reported for petroleum spirit (a, 9) and urine (16, 16). The determination of larger amounts (0.08-3.2%) of lead in copper base alloys and steels has been described by Elwell and Gidley (5). Other applications to metallurgical analysis have been described by Gidley (7) and Stumpf (18).
The direct spraying of aqueous acid solutions of metal alloys frequently leads to difficulties such as corrosive attack upon the burner head and consequent introduction of metal ions into the flame. Neutralization of the acid, on the other hand, may lead to clogging of the burner head, because of the resulting high electrolyte concentration, and can also reduce the efficiency of spraying by increase of viscosity. As a result it appeared to us that it would be better to extract and concentrate the traces of lead into an organic solvent and spray it directly into the flame. This would have the added advantage resulting from a higher input ratio through the aspiration-type of spray used in this work. This factor has been discussed recently by Dagnall and West (1) in relation to the determination of silver following its extraction from aqueous solutions. EXPERIMENTAL
Apparatus. Absorbance measurements were made with an SP 909A atomic absorption-flame emission spectrophotometer fitted with a lead hollow cathode lamp, Unicam Catalog No. 103898 (Unicam Instruments Ltd., Cambridge, England), equipped with a 0-10-mv. Honeywell-Brown recorder. The absorbance flame-path in this instrument is ca. 7 cm. Air was supplied from a rotary compressor via a regulator, and acetylene gas from a cylinder. 358
ANALYTICAL CHEMISTRY
Procedure. REMOVALOF MAJOR pared saturated potassium iodide soluCOMPONENT.Determination of Lead tion. Pipet 20 ml. of methyl iso-butyl in Sleek. Dissolve a suitable weight ketone into the funnel and shake for 30 of sample (containing 0 to 300 pg. of Pb) seconds to extract the lead. Discard in 10 ml. of concentrated hydrochloric the lower aqueous phase. The organic acid (AR) in a 100-ml. beaker, warming extract may now be passed directly into to assist solution. Oxidize the iron presthe atomic absorption spectrophotoment to Fe(II1) by the dropwise addition eter using the instrumental settings and flame conditions summarized below. of concentrated nitric acid (AR). After cooling, transfer the solution to a 250-ml. The amount of lead present is determined by comparison with a calibraseparating funnel with the aid of a furtion curve prepared by taking synthetic ther 15 ml. of concentrated hydrochloric standard iron-lead (0 to 1.6 ml. lO-3M acid. Add 25 ml. of iso-amyl acetate and extract the bulk of the ferric ion (14) Pb) or copper-lead mixtures through the procedure. The appropriate standard by shaking the funnel for 30 seconds. solution should be taken through the Allow the phases to separate and run the lower aqueous layer into a second procedure with each series of determinaseparating funnel. Repeat the extractions to correct for any slight variation tion with a further 25 ml. of iso-amyl in instrumental response. acetate. Run the aqueous solution back The following flame conditions and into the 100-ml. beaker and evaporate instrument settings were used on the SP to dryness. 900A spectrophotometer. Slit width, 0.20 mm; wavelength, 2833 A.; lamp Baking to hard dryness should be current, 6 ma.; and air pressure, 15 avoided as this will cause low recoveries. p s i . The acetylene pressure was just The purpose of this separation is merely insufficient to give a luminous flame to remove excess acid and, hence, to fawhen the organic extract was being cilitate the control of acidity subsesprayed (manometer reading ca. 3 to 4 quently for the H2Pb14 extraction. cm. of ethylene glycol). The measureDetermination of Lead in Brass/ ments of absorbance were made low Bronze Alloys. Dissolve a suitable down in the flame just above the blue weight of sample (containing 0-300 pg. luminous cones of the burner head. of Pb) in a small volume of concentrated nitric acid (AR) in a 100-ml. beaker, warming to assist solution. Add 10 ml. RESULTS AND DISCUSSION of 5% calcium chloride solution, make ammoniacal, and add 10 ml. of 10% The line a t 2833 A. was found to be sodium carbonate solution; stir well to most suitable for measurements of obtain intimate mixing. Allow the soluatomic absorption due to lead. The tion to stand for 5 minutes and then cenoptimum sensitivity was obtained with trifuge to collect the precipitate. Wash a lamp current of 6 ma. and the best the precipitate thoroughly with water and redissolve it in a small quantity of flame conditions were found when nitric acid, transferring the solution back there was just insufficient acetylene to to the original beaker. Evaporate the cause a luminous flame (Figure 1). solution to dryness observing the preA slit width of 0.20 mm. was used caution mentioned above. The presalthough this factor xas not critical. ence of small amounts of copper ion in The maximum response occurred with the calcium carbonate does not interfere extracted lead iodide solutions when with the method. EXTRACTION AND DETERMINATION. absorbance measurements were made just above the base of the flame (Figure After evaporating the solution to dryness, redissolve the residue in 10 ml. of 2) * 5% (v./v.) hydrochloric acid. Samples It was found that, relative to aqueous containing appreciable amounts of tisolutions, a five- to six-fold increase in tanium or tungsten cannot be redissensitivity was obtained with the ketone solved, but these precipitates do not afextract. This difference, which may be fect recoveries, Transfer the solution accounted for by a higher throughput with the aid of a further 15 ml. of 5% ratio of the ketone extract, was investihydrochloric acid tlo a 250-ml. separating gated a,s follows. funnel and add 2.5 ml. of freshly pre-
6C
.
flame base
20 m
C
P
.-e
0
0 Y
U
o SQ
L
Y
-u Y
L
Y
IO
V
a
0
u
. I
0 405
9
gas
manometer
Figure 1 .
Measurement of 4 X 1 0 % 4 HzPbla In methyl iso-butyl ketone at different absorbance paths obtained b y raising or lowering the burner head
BCS 183/1
Type of sample Mild steel Mild steel Mild steel Mild steel Mild steel Mild steel Mild steel Mild steel Mild steel High tensile brass Cupronickel Bronze
BCS 207/1
Bronze
08917
Stainless steel Stainless steel Stainless steel Sppnge iron Tungsten steel Tungsten steel
No.
BCS 326 BCS 327 BCS 328 BCS 329 BCS 330 BCS 271 BCS 273 BCS 275 BCS 277 BCS 179/1 BCS 180/1
40415 41373
G 7471 MGS 186
setting
Absorbance path
Analysis of Standard Steels, Copper Base Alloys, Stainless Steels, and High Speed Steels
Sample
FMB
head
Figure 2.
Measurement of 6 X 10-4M standard lead nitrate solution a t a fixed air pressure of 1 5 p.s.i. with varying acetylene pressures
Table 1.
IO
8
burner
reading
Air-acetylene ratio
A known volume of distilled water was partly converted into a fine spray by the aspiration spray chamber fitted to the apparatus under the usual conditions (air pressure 15 p.s.i.) and the total time for complete consumption of the water from the supply vessel was recorded together with the volume of water collected a t the outlet to the spray chamber-Le., the amount not converted to a fine spray. The rate of throughput of fine spray to the burner head was then calculated in ml./min. When the experiment was repeated with ketone, it was found that approximately 51/2 times more ketone than water reached the burner head as a fine spray. This reveals clearly that in this instance, as in others, the enhancement is largely due to an increased supply of spray to the flame. The optimum conditions for extraction of H2PbI4 into methyl iso-butyl ketone were obtained from previous publications (5, 4) concerning the development and applications of a spectrophotometric method for determining lead. A number of cations are wholly or partially extracted as their iodides from dilute acid solution with methyl isobutyl ketone. The effect of these foreign ions was examined by preparing standard solutions of lead nitrate containing ca. 1000-fold mole-excesses of these ions and subjecting the solutions to the recommended procedure. Antimony (111) , arsenic(II1) , bismuth,
6
4
I7
13
Found, yo
Average
Certificate value
Spread in certificate
0.0145 0.014 0.012
0.0145
0.014
0.014
0.012-0.017
0.0115
0.012
0.010
0.009-0.012
0.0165 0.0155 0.052 0.051 0.004
0.016
0.016
0.015
0.012-0.018
0.051
0.051
0.05-
0.042-0.053
0.004
0.004
0.003
0.002-0.004
0.0035
0.003
0.003
0.0025
0.0035
0.004
0.004
0.003
0.00150.003
0.006
0.006
0.006
0.005
0.008
0.0075
0.008
0.0065
0.195
0.216
0.209
0.190
0.216 0.0085 0.008 3.60 3.40 0.087 0.081 0.007
0.008
0.008
3.58
0.003-0.006
0.170-0.203
