Anal. Chem. 1982, 54, 136-137
136 P
320*257
322459
il
h
I
I
256
260
268
262
264
Figure 2. Schematic constant neutral spectrum for losses of C035CIin the 1st FFR.
scan corresponds to a section with a plane of constant p and to a horizontal line in Figure 1. The resultant profile should show two broad and possibly overlapping peaks, having heights in the ratio of the natural abundances of 37Cland 35Cl. Chess and Gross (4, 7) used a V,E scan (a linked scan of V and E at constant B with V I E held constant), which corresponds to a section of the ion current surface with a plane of constant p and to a vertical line in Figure 1. The profile obtained from a VJ3 scan at p = 0.803 (Figure 1) will be influenced by instrumental factors and by the distribution of kinetic energy released in the fragmentation, but given a small range of w , and peaks that are sufficiently broad and flat-topped in the p direction, it should approximate the profile from a constant neutral spectrum (8-11) for losses of C035Cl. from the isotopic M+. ions. Peak heights in this latter profile should correspond to the distribution of natural isotopes for CllH40C13,provided that there is no interference from other reactions such as loss of the elements of CHOCl from the M+. ions, from ion fragmentations of other components of the mixture, or from reactions occurring outside the 1st FFR. Our simulation of the constant neutral spectrum for losses of C035Cl., based on the same assumptions as for Figure 1,is shown in Figure 2. It agrees well with the profiles obtained by Chess and Gross over the range of p from 256.5 to 259.5 p for which comparison is possible ( 4 ) and with that
obtained for losses of C1- from M+. ions of 2,3,4,6-tetrachlorophenol (7). Note that the senses of the x axes of the figures of Chess and Gross and our Figure 2 are opposite. An ion current surface contains peaks for all the ion reactions in a mass spectrometer possessing tandem analyzers, whether the ion currents originate from a single compound or from a mixture in the ion source. High selectivity in MS/MS necessitates a judicious choice of those regions of the surface that contain peaks peculiar to the component or components of interest. Appropriate cross-sections through the distinctive peaks can then be used for multiple ion monitoring to validate an assignment and to increase the specificity of the analysis. The concept of an ion current surface facilitates the understanding and planning of MS/MS experiments.
LITERATURE CITED Kondrat, R. W.; Cooks, R. G. Anal. Chem. 1978, 50, 81 A-92 A. Yost, R. A.; Enke, C. G. Anal. Chem. 1979, 51, 1251 A-I264 A. McLafferty, F. W. Acc. Chem. Res. 1980, 13, 33-39. Chess, E. K.; Gross, M. L. Anal. Chem. 1980, 52, 2057-2061. Lacey, M. J.; Macdonald, C. G. Org. Mass Spectrom. 1977, 12,
587-594. Lacey, M. J.; Macdonaid, C. 0.; Donchl, K. F.; Derrick, P. J. Org. Mass Spectrom., in press. Gross, M. L. Unlversity of Nebraska, personal cornmunicatlon. Lacey, M. J.; Macdonald, C. G. Anal. Chem. 1979, 51, 691-695. Zakett, D.; Schoen, A. E.; Kondrat, R. W.; Cooks, R. G. J. Am. Chem. SOC. 1979, 101, 6781-6783. Haddon, W. F. Org. Mass Spectrom. 1980, 15, 539-543. Shushan, B.; Boyd, R. Anal. Chem. 1981, 53, 421-427.
Michael J. Lacey* Colin G . Macdonald CSIRO Division of Entomology P.O. Box 1700 Canberra City 2601, A.C.T. Australia RECEIVEDfor review June 16,1981. Accepted September 28, 1981.
Exchange of Comments on Matrix Interferences in Graphite Furnace Atomic Absorption Spectrometry by Capacitive Discharge Heating Sir: Chakrabarti et al. ( 1 ) have presented details of their promising new technique of graphite furnace atomic absorp-
tion by capacitive discharge heating. Particularly intriguing is the possibility of thereby developing an essentially
Table I. Reported Values for U.S. Geological Survey Marine Mud MAG-1 Ni
Pb
amt of Pb, PPm 28.0 27.2 26.2 23.8 20.4b
a
Key:
techniquea GFAA
Mass spec. GFAA FAA
Comp. spec.
ref 5 6 7 8 2
amt of Ni, Ppm 70.2 70 60 56 53.8 53.5 53 53 50.7 50 50 48.3 48 45 41 30
technique Comp. spec. XRF FAA FAA XRF FAA NAA NAA
Em. spec. Em. spec. NAA XRF
Em. spec. XRF
Em. spec. NAA
Mn
ref 2 9 10 11 12 8 13 14 15 9 16 10 17 18 9 19
amt of Mn, PPm 1020 880 850 850 770 770 770 7 15 695 690 670 660 610
technique Comp. spec. XRF XRF FAA
Color Em. spec. FAA FAA
Em. spec. NAA FAA FAA NAA
ref 2 12 9 20 15 9 9 21 17 19 8 11 22
Color, colorimetric; Comp. spec., computerized emission spectrometry; Em. spec., other emission spectrometry;
FAA, flame atomic absorption; GFAA, graphite furnace atomic absorption; Mass spec., mass spectrometry; NAA, neutron Values taken by Chakrabarti et al. (1)as “most probable”. activation analysis; XRF, X-ray fluorescence. 0003-2700/82/0354-0136$01.25/00 I981 American Chemical Society
137
Anal. Chem. 1982, 5 4 , 137-138
“matrix-independent” scheme of instrumental analysis. They reported excellent recoveries for selected elements in two National Bureau of Standards reference materials of biological origin and in six different synthetic solutions simulating seawaters, presumably prepared in theiir own laboratory. Data were also preseinted for lead, niclkel, and manganese in U.S. Geological Survey Marine Mud MAG-1. No information was given on the preparation of the sample solution, so neither the nature nor the magnitude of the matrix introduced in the graphite furnace is known. Further, no reference was given for the “most probable values” upon which ”recoveries” were based. MAG-1 was one of 11 group of eight proposed reference samples of rocks described in a report edited by Flanagan (2), including some 25 papers, each of which ]presented analytical results for some elements in some or all of the eight samples. The values considered “most probable” by Chakrabarti et al. are evidently those of Walthall et al. ( 3 ) ,the results of a computerized spectrographic method. The same report (2) included several other papers which listed data on MAG-1. Because the U.S. Geological Survey has not published consensus values for the compositions of the eight samples, Gladney and Goode ( 4 ) prepared an updated compilation of data in the literature, together with estimated “average”values for some constituents, where justified. Table I, which lists published values for lead, nickel, and manganese in MAG-1, is based on the work of‘Gladney and Goode, as well as some additional data gleaned from more recent literature. The mean of the five lead results is 25.1 ppm, the median 26.2 ppm (Chakrabarti et al. used 20.4 pprn). The 16 nickel results yield a mean of 52.0 ppm, median 51.8 ppm (Chakrabarti et al. used 70.2 ppm). For 13 manganese results, the mean is 765 ppm, the median 770 ppm (Clhakrabartiet al. used 1020 ppm). By using only the results reported by one laboratory as “most probable values”, Chakrabarti et al. based their “recoveries” on the lowest reported1 values for lead and the highest for nickel and manganese. Depending on whether the mean or median is taken as a more reatlistic “most probable value”, the actual recoveries amount to 77-80% for lead, 134-135% for nickel, ,and 127-128% for manganese. It is indeed puzzling that Chakrabarti et al. obtained such apparently ”good” recoveries when they compared their results with those of Walthall i?tal. (3),results which are far removed
Sir: Our paper ( I ) was primarily intended to report the development of an analytical technique which uses a proportionality constant (called the sensitivity constant) to determine the concentration of analytes in unknown samples and which does not require analytical Calibration curves nor background correction. Our papers ( I , 2) (the latter shown as ref 24 in the former) have emphasized freedom from the requirement of employing analytical calibration curves which is the unique aspect of’ our contribution. Abbey has ignored
from the general trend of others reported by a variety of analytical techniques. It can be argued that these discrepancies concern only one of the nine samples tested and are therefore irrelevant in terms of the potential of the proposed method. It can also be argued that the estimate of recoveries on the rock sample is excessively optimistic and hence that the claim of freedom from matrix interferences is open to question.
LITERATURE CITED (1) Chakrabarti, C. L.; Wan, C. C.; Hamed, H. A,; Berteis, P. C. Anal. Chem. 1981, 53, 444. (2) Fianagan, F. J., Ed. Geol. Sum. Prof. Pap. (US.)1976, No. 840. (3) Walthall, F. G.;Dorrzapf, A. J., Jr.; Flanagan, F. J. Geol. Surv. Prof. Pap. ( U . S . ) 1976, No. 840,99. (4) Gladney, E. S.;Goode, W. E. Geostandards Newsl. 1981, 5 , 31. (5) Rantala, R. 1’. T.; Lorlng, D. H. Geostandards Newsl. 1978, 2 , 125. (6) McLennan, S. M.; Taylor, S. R. Chem. Geol. 1980, 29,333. (7) Aruscavage, P. F.; Campbell, E. Y. Talanta 1979, 2 6 , 1052. (8) Tessier, A,; Campbell, P. G. C.: Bisson, M. Geostandards Newsl. 1980,
4, 145. (9) Geological Survey of Canada 1977,unpublished results. (IO) Quintin, M.; Martln, A,; de Kersabiec, A. M. Geostandards News/. 1978, 2 , 199. (11) Slnex, S.A.; Cantlllo, A. Y.; Helz, G. R. Anal. Chem. 1980, 52, 2342. (12) Fabbi, B. P.; Espos, L. F. Geol. Surv. Prof. Pap. ( U . S . ) 1976, No. 840,89. (13) Rowe, J. J.; Steinnes, E. J . Res. U.S.Geol. Sum. 1977, 5 , 397. (14) Rosenberg, R. J.; Zilllacus, R. Geostandards Newsl. 1960, 4 , 191. (15) Manhelm, F. T.; Hathaway, J. C.; Flanagan, F. J.; Fletcher, J. D. Geol. Surv. Prof. Pap. ( U S . ) 1978, No. 840, 25. (16) Baedecker, P. A.; Rowe, J. J.; Steinnes, E. J . Radioanal. Chem. 1977, 40, 115. (17) Govindaraju, K., Cent. Rech. PBtrog. Mochim., Nancy, France, private communicatlon, 1977. (18) Quiseflt, J. P.; deJean de la Batie, R.; Faucherre, J.; Malingre, G.: Vie le Sage, R. Geostandards Newsl. 1979, 3 , 181. (19) Stuart, D. C., Atom. Energ. Canada Ltd., Ottawa, private communlcation, 1981. (20) Clemency, C. V.; Borden, D. M. Geostandards News/. 1978, 2 , 147. (21) Thomas, J. A.; Mountjoy, W.; Huffman, C., Jr. Geol. Surv. Prof. Pap. ( U . S . )1978, No. 840,p 119. (22) Gordon, G. E.; Waiters, W. 6.; Zolier, W. H.; Anderson, D. L.; Failey, M. P. Tech. Report ORO-5173-008; Department of Chemistry, University of Maryland: College Park, MD, 1979.
Sydney Abbey Analytical Chemistry Section Geological Survey of Canada 601 Booth Street Ottawa, Ontario, Canada K1A OE8
RECEIVED for review May 18,1981.Accepted October 2,1981.
this fundamental point and has questioned the whole contribution on the basis of one table-Table 11. We are reproducing below Table 11-the % recovery values have been expanded to show the associated indeterminate errors. There was one typing error in Table 11 which has now been corrected-the recovered value shown as one standard deviation for Mn should read k0.021 instead of f0.21. The value quoted as “most probable value” was taken from Walthall et al. (3) and should have been referenced in our paper ( I ) ; also,
Table 11. Recoveries, Solution Sampling, United States Geological Survey Marine Mud, MAG-1 element analysis line, nm most probable value, kg/kg recovered value,a kg/kg Pb
Ni Mn
283.3 23 2.0 403.1
(2.04 (7.02 (1.02
i:
0.13) X IO-’ 0.66) X 0.04) x 10-3
I
(2.01 i: 0.13) x 10-5 (6.97 I0.23) X (0.98 i: 0.021) x 10-3
The i values represent one standard deviation of five successive replicate determinations. successive replicate determinations. a
0003-2700/82/0354-0137$01.25/0@ 1981 American Chemical Society
recoveries,b % 98.5 99.3 95.9
i:
8.9
* 9.9 * 4.3
Arithmetic means of five
