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Some observations on the atomization of lead with a metal micro-tube atomizer
Analytica
Chimica Acta,
83 (1976)
381-384
Printed in The Netherlands
OElsevier Scientific Publishing Company, Amsterdam -
Short
Communication
SOME OBSERVATIONS METAL MICRO-TUBE
ON THE ATOMIZATION ATOMIZER
KIYOHISA
OHTA and MASAMI
Deparlmenf
of
Chemistry,
Faculty
OF LEAD
WITH
A
SUZUKI* of Engineering,
Mie
Unicersity.
h-amihama-cho,
Tsu-shi,
Mie-ken 514 (Japan). (Received
25
July 1975)
Flameless atomic absorption spectrometry has often been applied to the determination of lead. Norval and Butler [l] described the effects of anions on the atomization of lead with the high-temperature graphite tube; they showed that sensitivities increased in the order SO’,- < NO; < Cl- and interpreted these results in terms of the heats of formation of the different molecules_ MatouGek and Brodie [2] reported that it was necessary to add an excess of phosphoric acid to samples of airborne particulates before flameless atomic absorption because of the presence of up to fourteen different lead compounds in atmospheric particulates. Kashiki and Yamazoe [ 31 reported that different alkyl-lead compounds in gasolines yield different responses in flameless atomic absorption spectrometry with a carbon rod atomizer, and avoided the difficulties involved by the addition of iodine. The present communication describes the behavior of various lead compounds and complexes in atomization with a metal micro-tube atomizer [4, 51 which can provide a uniform temperature rapidly. Experimental
Apparatus. A Nippon Jarrell-Ash 0.5-m Ebert-type monochromator with R 106 photomultiplier tube (Hamamatsu TV Co.) and JEOL AA-HMA signal control unit was used for atomic absorption measurements. The response of this detection system was faster by about two orders of magnitude than that of a conventional system for flame spectrometry. The output from the signal control unit was monitored by an Iwatsu DS 5016 dual-beam synchroscope with a time constant of 1 ps and by a Hitachi 056-1001 recorder (0.4 s full-scale deflection). The molybdenum micro-tube atomizer has been described previously [4] _ A lead hollow-cathode lamp (Hamamatsu TV Co_) was used; its unmodulated radiation was focussed into the microtube through the quartz window of the atomization chamber and refocussed on the slit of the monochromator. The lead absorption was measured at *To whom correspondenceshould be addressed.
382
217.0 nm. The tube temperature was measured as follows: the voltage signal from the atomizer and the absorption signal were recorded simultaneously with two beams of the synchroscope. Both signals were synchronized and the temperature was determined from the voltage signal which had previously been calibrated in terms of temperature with an optical pyrometer. Argon was used as purge gas at a flow-rate of 460 ml min-‘, with hydrogen at a flow-rate of 20 ml min-‘. All sample injections were made with a glass micro-pipet. Reagents. The following solutions were used: aqueous solutions of lead chloride, iodide, nitrate and sulfate; lead naphthenate in chloroform (or MIBK); and lead oxinate, diethyldithiocarbamate and iodide complexes in chloroform (or MIBK). All solutions of complexes were prepared by extraction. All chemicals were analytical-reagent grade.
Results and discussion The atomic absorption of lead from various compounds and complexes at different temperatures is shown in Fig. 1. Inorganic compounds were dried at 150 o C before atomization, and decomposition at 500 o C was Aso applied to organic complexes_ Each absorption was obtained by atomizing for 10 s. The temperature for mavimum absorption is lower for nitrate and carbamate. The curve for chloride was similar to that of nitrate. The curves for sulfate and iodide indicate the relative difficulty of atomization_ The need for
'SO-
40-
zo-
L
I
I
1000
1500
Tube
temperature
I
2000 “C
Fig. 1. Atomic absorption of lead from various compounds temperatures. (a) Nitrate (a); (b) sulfate (-x); (c) iodide (a); (0); (f) naphthenate (x )_
and complexes (d) carbamate
at different (0); (e) oxinate
383
a higher temperature for atomization from the oxinate complex may result from the production of a complex residue at the decomposition temperature. Sulfide was found in the residue from carbamate. GomiS‘Cek et al. [6] described the decomposition of lead tetramethylenedithiocarbamate to lead sulfide, which gives free lead atoms at the atomization temperature. The reproducibility of the absorption peak at 1960°C was good for oxinate, carbamate, chloride, and nitrate, but not for iodide and sulfate. Naphthenati showed somewhat poorer reproducibility of the absorption peak. In contrast to the present results, Aggett and West [7] reported that the behavior of organometallic systems in atomization with a carbon filament was virtually identical to that of aqueous solutions of the metals. The absorption signals were also monitored by feeding the output signals from the photomultiplier direct to the synchroscope. The micro-tube atomizer was heated for 1 s, reaching maximum temperature (2300 o C) about 0.6 s after the power had been switched on. The lead absorption from the osinate commenced 0.26 s after the power had been switched on, and 0.39-0.42 s was required for inorganic compounds. The temperature for masimum absorption and the absorption peak area for various compounds and complexes are summarized in Table 1 which shows that the atomization of lead is attained more satisfactorily from organic complexes than from inorganic compounds_ Incomplete atomization was shown for lead iodide and sulfate. Iodine or iodine monochloride is used in the determination of lead in gasoline to overcome the variation in atomic absorption response with the chemical form of lead. Atomization from the iodide is not recommended in the present work because of lower sensitivity and poor reproducibility of absorption signals. A very small peak appears before the main peak for osinate, and is believed to be caused by the decomposition of oxine. Although lead napthenate is frequently used as a standard in non-aqueous atomic absorption work, satisfactory atomization of lead from this compound was not expected_ Attempts to correlate the results with thermodynamic TABLE
1
Atomization Compound
Nitrate Chloride Iodide Sulfate Osinate Carbamate Naphthenate ---___
characteristics Temperature for maximum absorption signal (” C)
Absorption peak areas (ratio)
1590 1590 1590 15so 1180 1200 1300
1 1 0.8 0.4 1.4 1.2 0.i
384
data were unsuccessful. Hydrogen may make some contributions to atomization A popular hypothesis for atomization in the carbon atomizer is that the metal oxide is reduced by the carbon to the free metal. From the present work, it seems reasonable to assume that dissociation to the free metal was brought about, without the formation of oxide, for some compounds and complexes which were atomized at comparatively lower temperatures. REFERENCES 1 E. Norval and L. R. P. Butler, Anal. Chim. Acta, 58 (1972) 47. 2 J. P. MatouSek and K. G. Brodie, Anal. Chem., 45 (1973) 1606. 3 M. Kashiki and S. Yamazoe, Anal. Lett., 7 (1974) 53. 4 K. Ohta and M. Suzuki, Talanta, 22 (1975) 465. 5 K. Ohta and M. Suzuki, Anal. Chim. Acta, ‘77 (1975) 288. 6 S. GomEek, Z. Lengar, J. Cernetic and V. Hudnik, Anal. Chim. Acta, 73 (1974) 7 J. _4ggett and T. S. West, Anal. Chim. Acta, 57 (1971) 15.
97.
Chimica Acta,
83 (1976)
381-384
Printed in The Netherlands
OElsevier Scientific Publishing Company, Amsterdam -
Short
Communication
SOME OBSERVATIONS METAL MICRO-TUBE
ON THE ATOMIZATION ATOMIZER
KIYOHISA
OHTA and MASAMI
Deparlmenf
of
Chemistry,
Faculty
OF LEAD
WITH
A
SUZUKI* of Engineering,
Mie
Unicersity.
h-amihama-cho,
Tsu-shi,
Mie-ken 514 (Japan). (Received
25
July 1975)
Flameless atomic absorption spectrometry has often been applied to the determination of lead. Norval and Butler [l] described the effects of anions on the atomization of lead with the high-temperature graphite tube; they showed that sensitivities increased in the order SO’,- < NO; < Cl- and interpreted these results in terms of the heats of formation of the different molecules_ MatouGek and Brodie [2] reported that it was necessary to add an excess of phosphoric acid to samples of airborne particulates before flameless atomic absorption because of the presence of up to fourteen different lead compounds in atmospheric particulates. Kashiki and Yamazoe [ 31 reported that different alkyl-lead compounds in gasolines yield different responses in flameless atomic absorption spectrometry with a carbon rod atomizer, and avoided the difficulties involved by the addition of iodine. The present communication describes the behavior of various lead compounds and complexes in atomization with a metal micro-tube atomizer [4, 51 which can provide a uniform temperature rapidly. Experimental
Apparatus. A Nippon Jarrell-Ash 0.5-m Ebert-type monochromator with R 106 photomultiplier tube (Hamamatsu TV Co.) and JEOL AA-HMA signal control unit was used for atomic absorption measurements. The response of this detection system was faster by about two orders of magnitude than that of a conventional system for flame spectrometry. The output from the signal control unit was monitored by an Iwatsu DS 5016 dual-beam synchroscope with a time constant of 1 ps and by a Hitachi 056-1001 recorder (0.4 s full-scale deflection). The molybdenum micro-tube atomizer has been described previously [4] _ A lead hollow-cathode lamp (Hamamatsu TV Co_) was used; its unmodulated radiation was focussed into the microtube through the quartz window of the atomization chamber and refocussed on the slit of the monochromator. The lead absorption was measured at *To whom correspondenceshould be addressed.
382
217.0 nm. The tube temperature was measured as follows: the voltage signal from the atomizer and the absorption signal were recorded simultaneously with two beams of the synchroscope. Both signals were synchronized and the temperature was determined from the voltage signal which had previously been calibrated in terms of temperature with an optical pyrometer. Argon was used as purge gas at a flow-rate of 460 ml min-‘, with hydrogen at a flow-rate of 20 ml min-‘. All sample injections were made with a glass micro-pipet. Reagents. The following solutions were used: aqueous solutions of lead chloride, iodide, nitrate and sulfate; lead naphthenate in chloroform (or MIBK); and lead oxinate, diethyldithiocarbamate and iodide complexes in chloroform (or MIBK). All solutions of complexes were prepared by extraction. All chemicals were analytical-reagent grade.
Results and discussion The atomic absorption of lead from various compounds and complexes at different temperatures is shown in Fig. 1. Inorganic compounds were dried at 150 o C before atomization, and decomposition at 500 o C was Aso applied to organic complexes_ Each absorption was obtained by atomizing for 10 s. The temperature for mavimum absorption is lower for nitrate and carbamate. The curve for chloride was similar to that of nitrate. The curves for sulfate and iodide indicate the relative difficulty of atomization_ The need for
'SO-
40-
zo-
L
I
I
1000
1500
Tube
temperature
I
2000 “C
Fig. 1. Atomic absorption of lead from various compounds temperatures. (a) Nitrate (a); (b) sulfate (-x); (c) iodide (a); (0); (f) naphthenate (x )_
and complexes (d) carbamate
at different (0); (e) oxinate
383
a higher temperature for atomization from the oxinate complex may result from the production of a complex residue at the decomposition temperature. Sulfide was found in the residue from carbamate. GomiS‘Cek et al. [6] described the decomposition of lead tetramethylenedithiocarbamate to lead sulfide, which gives free lead atoms at the atomization temperature. The reproducibility of the absorption peak at 1960°C was good for oxinate, carbamate, chloride, and nitrate, but not for iodide and sulfate. Naphthenati showed somewhat poorer reproducibility of the absorption peak. In contrast to the present results, Aggett and West [7] reported that the behavior of organometallic systems in atomization with a carbon filament was virtually identical to that of aqueous solutions of the metals. The absorption signals were also monitored by feeding the output signals from the photomultiplier direct to the synchroscope. The micro-tube atomizer was heated for 1 s, reaching maximum temperature (2300 o C) about 0.6 s after the power had been switched on. The lead absorption from the osinate commenced 0.26 s after the power had been switched on, and 0.39-0.42 s was required for inorganic compounds. The temperature for masimum absorption and the absorption peak area for various compounds and complexes are summarized in Table 1 which shows that the atomization of lead is attained more satisfactorily from organic complexes than from inorganic compounds_ Incomplete atomization was shown for lead iodide and sulfate. Iodine or iodine monochloride is used in the determination of lead in gasoline to overcome the variation in atomic absorption response with the chemical form of lead. Atomization from the iodide is not recommended in the present work because of lower sensitivity and poor reproducibility of absorption signals. A very small peak appears before the main peak for osinate, and is believed to be caused by the decomposition of oxine. Although lead napthenate is frequently used as a standard in non-aqueous atomic absorption work, satisfactory atomization of lead from this compound was not expected_ Attempts to correlate the results with thermodynamic TABLE
1
Atomization Compound
Nitrate Chloride Iodide Sulfate Osinate Carbamate Naphthenate ---___
characteristics Temperature for maximum absorption signal (” C)
Absorption peak areas (ratio)
1590 1590 1590 15so 1180 1200 1300
1 1 0.8 0.4 1.4 1.2 0.i
384
data were unsuccessful. Hydrogen may make some contributions to atomization A popular hypothesis for atomization in the carbon atomizer is that the metal oxide is reduced by the carbon to the free metal. From the present work, it seems reasonable to assume that dissociation to the free metal was brought about, without the formation of oxide, for some compounds and complexes which were atomized at comparatively lower temperatures. REFERENCES 1 E. Norval and L. R. P. Butler, Anal. Chim. Acta, 58 (1972) 47. 2 J. P. MatouSek and K. G. Brodie, Anal. Chem., 45 (1973) 1606. 3 M. Kashiki and S. Yamazoe, Anal. Lett., 7 (1974) 53. 4 K. Ohta and M. Suzuki, Talanta, 22 (1975) 465. 5 K. Ohta and M. Suzuki, Anal. Chim. Acta, ‘77 (1975) 288. 6 S. GomEek, Z. Lengar, J. Cernetic and V. Hudnik, Anal. Chim. Acta, 73 (1974) 7 J. _4ggett and T. S. West, Anal. Chim. Acta, 57 (1971) 15.
97.