Exchange of Comments: Loss of Mercury during Flameless Atomic Absorption Spectrometry Sir: Issaq and Zielinski ( I ) have recently described a flameless atomic absorption method for the determination of Hg a t nanogram levels. They employed H202 to stabilize the Hg in the atomic absorption graphite furnace during drying cycles of 50-120 s a t 115-140 OC. Since preatomization losses from the furnace have been reported for Pb, Cd, Be, and V ( 2 ) , we investigated potential Hg loss from this technique and have been unable to reproduce either the 1.3% precision or the degree of Hg stabilization in the furnace reported by the authors. All experiments were conducted on the same day utilizing Hg solutions acidified with “ 0 3 to prevent Hg loss to container walls during the analysis. We have used an analytical arrangement similar to that of the authors ( 1 ) : a Perkin-Elmer Model 306 atomic abTable I. Precision of Ha Determination from Seven Solvent Mixtures I
Mean Recorder respone & std deva, cm
Precision,
0.6 f 0.4 0.8 f 0.4 1.2 f 0.3 2.3 f 1.8 13.2 f 4.8
67 50 25 78 36
Working curve
slopeb
Linear correlation coefficientb
0.094
0.780
B. 2% “ 0 3
0.301
0.981
C.
0.362
0.988
Solution
A.
Hg concn, ng/ml
E.
F.
G.
(%I
2%”03 0 50 100 250 500
D.
U/P
+ 2% H202 0 0.0 f 0.0 ... 50 1.7 f 0.3 18 100 3.3 i 0.5 15 250 5.9 f 2.5 42 74 500 8.4 f 6.2 2%H202 0 0.0 f 0.0 ... 50 1.4 f 0.7 50 100 4.6 f 2.4 52 250 7.4 f 2.8 38 500 19.8 f 3.4 17 2%HCl 0 0.0 f 0.0 ... 50 3.0 f 0.4 13 9.7 100 7.2 f 0.7 260 14.4 f 1.0 6.9 500 34.3 f 1.6 4.7 2% H C l f 2% H202 0 0.35 f 0.47 130 50 12.1 f 0.5 4.1 100 22.4 f 3.6 16 250 56.5 f 4.0 7.1 500 off chart ... 2% “ 0 3 + 2% HC1 + 2% H202 0 0.15 0.30 200 50 6.8 f 0.9 13 100 14.2 f 0.7 4.9 250 35.8 f 0.8 2.2 500 61.9 f 2.4 3.9 2% “ 0 3 2% HC1 0 0.0 f 0.0 ... 50 3.6 i 0.8 22 100 6.9 f 1.2 17 19 250 15.1 f 2.9 25 500 31.2 f 7.7
*
+
sorption spectrophotometer equipped with a deuterium background corrector, a Beckman Model 1005 10-in stripchart recorder, a Perkin-Elmer mercury electrodeless discharge lamp, and a Perkin-Elmer HGA-2000 graphite furnace. The results of analyses of 100-111aliquots of seven different solvent combinations a t varying Hg concentrations are shown in Table I. An analytical precision of only 1574% was obtained for solution B, which is the solvent combination recommended by the authors (1). Continuous recording of the output of the atomic absorption unit revealed that Hg was being released from the furnace during the drying cycle from solutions A, B, C, D, and G. Reduction of drying temperatures to as low as 50 “C did not improve the observed precision. I t has been suggested that the peak observed during drying is the result of solvent evaporation ( 3 ) ;however, not only has it not been observed on numerous blanks, but its intensity also increases with increasing Hg concentration, confirming its identification as Hg. We have found that the addition of 2% HCl (v/v) as well as 2% H202 ( v h ) eliminates the initial loss of Hg during drying and permits the use of this flameless technique with reasonable precision as shown for solutions E and F in Table I. We feel that the authors’ ( I ) suggestion of H202 as a stabilizing agent is valuable, but our results indicate the necessity of using HC1 as an additional stabilizer if minimal loss of Hg from the furnace during drying is desired. In conclusion, the use of HCl increases the sensitivity and improves both the precision and detection limit for Hg (cf. mean recorder response and working curve slope for solution B, E, and F in Table I). The linearity of the working curve is also enhanced as shown by the linear correlation coefficients given in the table.
LITERATURE CITED (1) H. J. lssaq and W. L. Zielinski, Anal. Chern., 46, 1436 (1974). (2) W. J. Findlay, A . Zdrojewski, and N. Quickert. Spectrosc. Lett., 7, 355 (1974). (3) H. J. Issaq, private communication, 1975.
0.649
2.30
0.996
0.999
J. W. Owens E. S.Gladney* Los Alamos Scientific’Laboratory P.O. Box 1663 Los Alamos, New Mexico 87545 RECEIVEDfor review May 19, 1975. Accepted December 24, 1975. We gratefully acknowledge support of these studies by the U S . Energy Research and Development Agency.
1.37
0.652
0.998
0.997
Peak heights are normalized to 3X chart recorder expansion. These data are derived from a weighted least-squares regression analysis using a 1/02 weighting scheme.
Sir: Owens and Gladney claim that “An analytical precision of 15-74% was obtained for solution B, which is recommended by the authors”. In response to this claim, we are enclosing two figures. Figure 1 shows that the reproducibility for nine replications was 2.7%. Figure 2 shows that the overall sample-to-sample reproducibility of six different samples of the same concentration of mercury, each run in duplicate, was 1.2%. Another claim raised by Owens and Gladney was that “Continuous recording of the output of the atomic absorption unit revealed the Hg was being released from the furnace during the drying cycle . . .”. We observed a small ANALYTICAL CHEMISTRY, VOL. 48, NO. 4, APRIL 1976
787
Figure 1. Reproducibility of Hg signal. Conditions as in Ref. ( 7)
'I 10
Figure 2. Sample-to-samplereproducibility of mercury. Conditions as in Ref. ( 7) shoulder and a very sharp peak at the beginning of the drying cycle, which we found to be an H202 peak and not an Hg peak. Moreover, a signal reading of 0.000 A was observed for approximately 35 of the 40 s used for drying (after the appearance of the H202 peak and prior to the appearance of the mercury peak). If Hg is released from the furnace during the drying cycle as claimed by Owens and Gladney, a broad peak and a signal greater than 0.000 A would have been obtained. This was not observed to be the case, and we stand by our results as published ( 1 ) .
788
ANALYTICAL CHEMISTRY, VOL. 48, NO. 4, APRIL 1976
LITERATURE CITED (1) H. J. lssaq and W. L. Zielinski, Jr., Anal. Chem., 46, 1436 (1974).
Haleem J. Issaq* Walter L. Zielinski, Jr. NCI Frederick Cancer Research Center P.O. Box B Frederick, Md. 21701
RECEIVEDfor review December 24, 1975. Accepted December 24,1976.
