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Symbols and units for integrated absorbance in electrothermal atomic absorption spectrometry (ET-AAS)
Spectrochrmico Am, Vol 47B. No. 8. pp. 104.%1044. Pnnted in GreatBntam.
1992 0
05&%8547/92 $5.00 + .OO 1992 Pergamon PressLtd
VIEWS AND CRITICISMS
Symbols and units for integrated absorbance in electrothermal atomic absorption spectrometry (ET-AAS) (Received 17 March 1992; accepted 19 March 1992)
L’vov, in his book Atomic Absorption Spectrochemical Analysis [l] pointed out that, “integration is not yet used enough in cuvette methods. There is, however, no doubt that it would make a decisive step towards the entire elimination of foreign-component effects on results of atomic absorption determination of elements in samples of whatever composition or state of aggregation”. It should be emphasized that this book was written well before the introduction of the first commercial electrothermal atomizer in 1970. In the same book, L’vov also made the statements that “. . . measures of QA (integrated absorbance) are on the whole less prone to random experimental error than measures of Apeak” and that, “. . . there are good prospects for developing an absolute method of analysis, based on cuvettes, with a calibration obtained once and for all time for each element”. L’vov also gave his opinion on “Massmann’s attempt at simplifying the procedure”. He predicted that, “the correctness of using the integration method of measuring absorption is dubious in this case, since the temperature of the cuvette is steadily rising while the measurements are being made, and TV,the time spent by atoms in the cuvette, is not constant” [l]. This may well be the explanation why peak height absorbance was used almost exclusively for signal evaluation during the first decade of ET-AAS as all commercial atomizers were based on Massmann’s simplified design. Another reason was certainly that the AA spectrometers at that time were not designed for ET-AAS and did not offer the possibility of using peak integration. In 1978 L’vov [2] repeated that “the integration method has a much greater potential for carrying out absolute measurements of absorption with furnaces since, unlike the amplitude method, it does not have any limitations as to the atomization conditions and as to the signal recording”. In the same paper L’vov raised the question of whether there are “. . . any prospects for the improvement of the now popular atomizers preserving at the same time the inherent simplicity of their analytical procedure” and, as an almost universal solution to the problem, he proposed that the sample be vaporized from a graphite platform installed inside the furnace instead of from the tube wall [3]. This finally led to the introduction of the Stabilized Temperature Platform Furnace (STPF) concept by SLAVIN et al. [4], the most important features of which included vaporization of the sample from a “L’vov platform” and integration of the absorbance over time. In the meantime, after another decade of experience in ET-AAS, it has more or less been accepted that atomization pulses should be evaluated using integrated absorbance, and it is the opinion of this author that papers dealing with mechanisms and interferences that are based on peak height absorbance should no longer be accepted for publication. In view of the increasing acceptance of signal integration in ET-AAS it appears important that a uniform terminology, unambiguous symbols and the appropriate units are used. L’vov used the symbol QA for the integrated absorbance [1,2]:
and he expressed the measured quantities in absorbance X seconds [l]. SLAVIN et al. [4] adopted the latter term with a minor modification to absorbance-seconds (abs-sec). In later work, SLAVIN et al. [5] further abbreviated that term or symbol to As and used it together with the numerical integrated absorbance value as if it were a unit. Many analysts followed this practice. It must be pointed out, however, that this is not in keeping with the recommendations of the International Union of Pure and Applied Chemistry (IUPAC) regarding quantities, units and symbols and their use in Physical Chemistry [6]. A (in italic) is the symbol for the (decadic) absorbance and is a dimensionless quantity. According to IUPAC [6], a clear distinction should be drawn between the names and symbols 1043
1044
Views and criticisms
for physical quantities and the names and symbols for units. In order to avoid confusion, symbols for physical quantities and symbols for units must not be combined. The risk for confusion is particularly marked if a roman A is used, as has been done in most publications. A (in roman) is the symbol for the unit ampere, the electric current, and the symbols for units are mandatory and must not be used for any quantity. As (ampere seconds) in terms of SI based units stands for coulomb, C, the electric charge. The unit for the integrated absorbance is simply seconds, s, because A is a dimensionless quantity as has already been pointed out. It might be worthwhile to consider the introduction of a separate unit for the integrated absorbance similar to Hertz for frequency (Hz = vibrations per second) or becquerel for radioactivity (Bq = decays per second) and it might be appropriate to use L’vov (Lv) as the symbol for that unit. In terms of SI base units, however, the only appropriate unit for the integrated absorbance is s. Finally, as symbols for physical quantities are only recommendations, the author would like to recommend the symbol A,,, or A, for integrated absorbance in analogy to Apeak used by L’vov [l] and others for peak absorbance.
SUMMARY The importance of using integrated absorbance for peak evaluation under thermal equilibrium conditions in ET-AAS has been reviewed. In view of the increasing acceptance of integrated absorbance it is important that a uniform terminology, accepted symbols and the appropriate units are used. The symbol As for the integrated absorbance is against the rules of IUPAC. The unit for the integrated absorbance is s (seconds). However, the introduction of a new unit such as Lv (L’vov) might be considered. The symbol A,,, or A, is proposed for integrated absorbance in analogy to Apeak or A, for peak absorbance. Department of Applied Research Bodenseewerk Perkin-Elmer GmbH D-7770 iiberlingen F.R.G.
B.
WELZ
REFERENCES [l] B. V. L’vov, Atomic Absorption Spectrochemicul Analysis. Hilger, London (1970). [2] B. V. L’vov, Spectrochim. Acta 33B, 153 (1978). [3] B. V. L’vov, L. A. Pelieva and A. I. Shamopolsky, Zh. Prikl. Spektrosk. 27, 395 (1977). [4] W. Slavin, D. C. Manning and G. R. Carnrick, At. Spectrosc. 2, 137 (1981). [5] W. Slavin, G. R. Carnrick, D. C. Manning and E. Pruszkowska, At. Spectrosc. 4, 69 (1983). [6] International Union of Pure and Applied Chemistry, Physical Chemistry Division: Quantities, Units and Symbols in Physical Chemistry, I. Mills, T. Cvitas, K. Homann, N. Kallay and K. Kuchitsu. Blackwell, Oxford, U.K. (1988).
1992 0
05&%8547/92 $5.00 + .OO 1992 Pergamon PressLtd
VIEWS AND CRITICISMS
Symbols and units for integrated absorbance in electrothermal atomic absorption spectrometry (ET-AAS) (Received 17 March 1992; accepted 19 March 1992)
L’vov, in his book Atomic Absorption Spectrochemical Analysis [l] pointed out that, “integration is not yet used enough in cuvette methods. There is, however, no doubt that it would make a decisive step towards the entire elimination of foreign-component effects on results of atomic absorption determination of elements in samples of whatever composition or state of aggregation”. It should be emphasized that this book was written well before the introduction of the first commercial electrothermal atomizer in 1970. In the same book, L’vov also made the statements that “. . . measures of QA (integrated absorbance) are on the whole less prone to random experimental error than measures of Apeak” and that, “. . . there are good prospects for developing an absolute method of analysis, based on cuvettes, with a calibration obtained once and for all time for each element”. L’vov also gave his opinion on “Massmann’s attempt at simplifying the procedure”. He predicted that, “the correctness of using the integration method of measuring absorption is dubious in this case, since the temperature of the cuvette is steadily rising while the measurements are being made, and TV,the time spent by atoms in the cuvette, is not constant” [l]. This may well be the explanation why peak height absorbance was used almost exclusively for signal evaluation during the first decade of ET-AAS as all commercial atomizers were based on Massmann’s simplified design. Another reason was certainly that the AA spectrometers at that time were not designed for ET-AAS and did not offer the possibility of using peak integration. In 1978 L’vov [2] repeated that “the integration method has a much greater potential for carrying out absolute measurements of absorption with furnaces since, unlike the amplitude method, it does not have any limitations as to the atomization conditions and as to the signal recording”. In the same paper L’vov raised the question of whether there are “. . . any prospects for the improvement of the now popular atomizers preserving at the same time the inherent simplicity of their analytical procedure” and, as an almost universal solution to the problem, he proposed that the sample be vaporized from a graphite platform installed inside the furnace instead of from the tube wall [3]. This finally led to the introduction of the Stabilized Temperature Platform Furnace (STPF) concept by SLAVIN et al. [4], the most important features of which included vaporization of the sample from a “L’vov platform” and integration of the absorbance over time. In the meantime, after another decade of experience in ET-AAS, it has more or less been accepted that atomization pulses should be evaluated using integrated absorbance, and it is the opinion of this author that papers dealing with mechanisms and interferences that are based on peak height absorbance should no longer be accepted for publication. In view of the increasing acceptance of signal integration in ET-AAS it appears important that a uniform terminology, unambiguous symbols and the appropriate units are used. L’vov used the symbol QA for the integrated absorbance [1,2]:
and he expressed the measured quantities in absorbance X seconds [l]. SLAVIN et al. [4] adopted the latter term with a minor modification to absorbance-seconds (abs-sec). In later work, SLAVIN et al. [5] further abbreviated that term or symbol to As and used it together with the numerical integrated absorbance value as if it were a unit. Many analysts followed this practice. It must be pointed out, however, that this is not in keeping with the recommendations of the International Union of Pure and Applied Chemistry (IUPAC) regarding quantities, units and symbols and their use in Physical Chemistry [6]. A (in italic) is the symbol for the (decadic) absorbance and is a dimensionless quantity. According to IUPAC [6], a clear distinction should be drawn between the names and symbols 1043
1044
Views and criticisms
for physical quantities and the names and symbols for units. In order to avoid confusion, symbols for physical quantities and symbols for units must not be combined. The risk for confusion is particularly marked if a roman A is used, as has been done in most publications. A (in roman) is the symbol for the unit ampere, the electric current, and the symbols for units are mandatory and must not be used for any quantity. As (ampere seconds) in terms of SI based units stands for coulomb, C, the electric charge. The unit for the integrated absorbance is simply seconds, s, because A is a dimensionless quantity as has already been pointed out. It might be worthwhile to consider the introduction of a separate unit for the integrated absorbance similar to Hertz for frequency (Hz = vibrations per second) or becquerel for radioactivity (Bq = decays per second) and it might be appropriate to use L’vov (Lv) as the symbol for that unit. In terms of SI base units, however, the only appropriate unit for the integrated absorbance is s. Finally, as symbols for physical quantities are only recommendations, the author would like to recommend the symbol A,,, or A, for integrated absorbance in analogy to Apeak used by L’vov [l] and others for peak absorbance.
SUMMARY The importance of using integrated absorbance for peak evaluation under thermal equilibrium conditions in ET-AAS has been reviewed. In view of the increasing acceptance of integrated absorbance it is important that a uniform terminology, accepted symbols and the appropriate units are used. The symbol As for the integrated absorbance is against the rules of IUPAC. The unit for the integrated absorbance is s (seconds). However, the introduction of a new unit such as Lv (L’vov) might be considered. The symbol A,,, or A, is proposed for integrated absorbance in analogy to Apeak or A, for peak absorbance. Department of Applied Research Bodenseewerk Perkin-Elmer GmbH D-7770 iiberlingen F.R.G.
B.
WELZ
REFERENCES [l] B. V. L’vov, Atomic Absorption Spectrochemicul Analysis. Hilger, London (1970). [2] B. V. L’vov, Spectrochim. Acta 33B, 153 (1978). [3] B. V. L’vov, L. A. Pelieva and A. I. Shamopolsky, Zh. Prikl. Spektrosk. 27, 395 (1977). [4] W. Slavin, D. C. Manning and G. R. Carnrick, At. Spectrosc. 2, 137 (1981). [5] W. Slavin, G. R. Carnrick, D. C. Manning and E. Pruszkowska, At. Spectrosc. 4, 69 (1983). [6] International Union of Pure and Applied Chemistry, Physical Chemistry Division: Quantities, Units and Symbols in Physical Chemistry, I. Mills, T. Cvitas, K. Homann, N. Kallay and K. Kuchitsu. Blackwell, Oxford, U.K. (1988).