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A new premixed chemical burner for emission and absorption spectroscopy with separated fuel and sample introduction
0584-8547183 13.00+.00 ,(3 1983. Pergamon Press Ltd.
Specfrochimica Acta.Vol. 388.No. S/6.pp.937-943.1983. Pr~nled in Greal B&din.
A new premixed chemical burner for emission and absorption spectroscopy with separated fuel and sample introduction P. B. ZEEMAN,C.
MULLER
and W. H.
GUNTER
Merensky Institute for Physics, University of Stellenbosch, Stellenbosch 7600, Republic of South Africa
(Received 23 December 1982) Abstract--A new version of the Babington nebulizer is described where dry aerosols from solutions and powder samples can be introduced into air-acetylene and nitrous oxide-acetylene flames, as well as ICP torches. A special burner is described in which the premixed burner gasesare completely separated from the sample introduction into the flame plasma. The powder samplescould also be successfullyintroduced into a 9.2 MHz high power ICP, as well as 28 and 50 MHz low power ICP sources.The investigations show that a powder leafsample behavessimilarly to an aqueous solution in the plasmas of a nitrous oxide-acetylene flame and the ICP sources.
1. INTRODUCTION PREMIXED FLAMES using air-acetylene or nitrous oxide-acetlene as burner gases in conjunction with pneumatic nebulizers are well established in modern practice. When diluted solutions are aspirated no difficulties are encountered, but when high concentration samples are to be introduced into the flame, clogging of the burner slit may occur. When powder samples are introduced by means of a Babington [I] type nebulizer the use of the ordinary slot type burner head becomes impracticable due to blocking of the slot by solid particles. In view of the need for a nebulizer and burner which can accommodate samples in powder form and operate carefree, but renders reproducible and accurate results, a version of the Babington type nebulizer was constructed together with a burner having the unique feature that sample introduction is completely separated from the premixed burner gases. Details of this burner, hereafter called the Merensky burner, and results obtained from pure chemicals and leaf samples are given below.
2.
CONSTRUCTIONAL
DETAILS
OF THE MERENSKY
NEBULIZER
AND BURNER
The Merensky nebulizer and burner are shown in Figs 1(ak(c). The nebulizer (1) is made from a stainless steel cylinder with i.d. 1Omm having a fine hole (2) with diameter 0.3 or 0.4 mm. It fits into a stainless steel cylinder (3) into which passes the sample introducing tube (4). The end (5) of this tube is sliced as is shown in Fig. 1(a). This sliced end portion is located symmetrically above the fine hole (2) by means ofa brass block (6) and a centering pin (7). The latter prevents rotation and sideways movement of the tip (5). The nebulizer assembly is drained through the side tube (8). Distilled water can be introduced through the tube (9) to wash the nebulizer (2) and the tip (5) of the sample introducing tube in order to minimize memory effects. The aerosol from the nebulizer rises into the spray chamber (9a), Fig. l(b), made from Perspex and having an i.d. of 46 mm and overall length 170 mm. Airtight introduction of air and transport of aerosol is accomplished by means of O-ring seals, as shown. Condensed droplets are drained through the tube (lo), while additional air or other gases can be introduced through tube (11) to facilitate faster upwards movement of the aerosol. The aerosol is dried and heated to approximately 300°C by means of the furnace (12) which was made by winding resistance wire over asbestos sheet wrapped around a Pyrex or quartz tube (13) with i.d. 25 mm. The dried and heated aerosol is transferred by means of a conical brass piece (14), Fig. 1(c), with a cylindrical tip (15) into the centre of the burner head (16). The conical brass aerosol conveyer is insulated thermally from the burner body (17) by means of boron nitride rings (18) and (19). The burner body is water-cooled by means of the tube (20). [l]
R. C.
FRY
and M. B. DENTON, Anal. Chem. 49, 1413 (1977). 937
938
P. B. ZEEMAN et al.
The thermal insulation at (18) and (19) prevents condensation of the heated aerosol and thus no blocking of the outlet (15), which has an i.d. of 3.3 mm, occurs. The furnace tube (13), conical portion (14) and cylindrical tip (15) can be made from quartz, in which case the boron nitride rings can be omitted.
n
Fig. l(a). Merensky nebulizer and sample introducing tube.
Fig. 1(b). Pyrex spray chamber.
Chemical burner for emission and absorption spectroscopy
Fig. l(c). Burner head with separated central aerosol tube.
The fuel and support gases are introduced into the burner by means of the tubes (21). The burner chamber is completely sealed from the sample introducing system so that the latter can be removed or replaced without disturbing the burning flame whether the latter was fed by air-acetylene or nitrous oxide-acetylene. The burner head consists of three rows of concentric holes (22), as shown in Fig. l(c), 0.8 mm in diameter in the case of a burner head for nitrous oxide-acetylene use and 1.0 mm diameter for air-acetylene. In the Merensky burner the aerosol is thus introduced centrally into the flame and pierces the flame gas in the same manner as in an inductively-coupled plasma when the latter operates properly. At the lower end of the flame, radiation from the sample is constricted to a narrow region, while it spreads to cover the full flame diameter higher up after experiencing a long enough residence time in the flame. The best height above the burner block for optimum radiance from the sample can thus be selected. This optimum height can be varied by introducing additional air through the side tube (11). The aspirator and burner assembly is remarkably free from memory effects. Solutions or powder mixtures were always aspirated from lower to higher concentrations. Occasionally pure water was squirted over the nebulizer assembly (2) and (5) to remove slurry that might have accumulated there. These “severe” influxes of water aerosol had no effect on chemical flames, but may extinguish an ICP.
3. APPARATUSAND EXPERIMENTALPROCEDURES 3.1. Excitation sources and standards used
The properties of the Merensky nebulizer were investigated by using an air-acetylene flame, a nitrous oxide-acetylene flame, a 9.2 MHz high-power ICP, as well as a 28 MHz Arlabs and a 50 MHz Philips low-power ICP.
940
P. B. i&MAN
et al.
These experiments were carried out by first using a series of standard solutions made from spectroscopy-pure chemicals, the object being to determine the reproducibility of the nebulizer and compare its performance with that of well-founded pneumatic ones. However, further investigations were carried out to determine the feasibility of using this nebulizer to aspirate samples in the form of slurries as well. For this purpose a sample of fruit tree leaves granted to us by Fruit and Fruit Technology Institute was grounded in a ball mill and then sieved through a 50 micron mesh. To this fine powder pure water was added and “solutions” were made containing 0.125, 0.25, . . ., 8g leaf powder per lOOm1 of water. The feasibility of the Merensky nebulizer as a practical instrument or not, will in the first instance be judged from the results obtained for the experiments carried out on standard solutions aspirated into the various excitation sources and dispersed by the spectrometers used. If its operation is satisfactory with these ordinary solutions, it would be an advantage in general because it is inexpensive and simple to make. It would be an interesting additional advantage if it gives accurate and reproducible spectral radiances for samples in powder form. This aspect of its acceptability will be judged from the results obtained with the fruit leaf samples. 3.2. Sample introduction into chemical flame and ICP sources The samples in the form of slurries were activated by means of a magnetic stirrer to ensure even distribution of powder in the water mixture. All samples were introduced into the flame or ICP sources by means of a peristaltic pump having 16 rollers and a variable speed of rotation. After preliminary experiments a speed of 3 revolutions per second was adopted for all measurements. It then delivered 0.05 ml of sample per second. This delivery is much less than that of commercial pneumatic nebulizers. Market pulsations in aerosol generation were observed at the nebulizer tip due to the action of the peristaltic pump. These, however, eased out in the aerosol chamber and the heated quartz tube leading to the flame or ICP source and good reproducibility in signal strength was obtained as is shown in the results. When powders are transported, it is important to avoid sharp bends in the tubing through which the powder is passed. Also only dry powders can be transported through medium-sized and small bore tubing or else severe clogging will occur. For this reason the aspirated wet powder was rapidly dried on leaving the spray chamber. Also the dried powder should be delivered hot to the excitation source to prevent the formation of drops due to condensation. The samples were introduced into the Merensky burner via the electrical heater (12) and the insulated tapered brass piece (14) shown in Figs. 1(b) and (c). In the case of ICP sources the samples entered through a central opening in the Teflon bases [2] of our ICP “burner” assemblies. Another type of heater tube was used with a spherical ball joint at the top which joined the furnace to the sample introducing tube of the ICP. The results obtained with the Merensky nebulizer and ICP sources were compared with those obtained from other aerosol generator techniques, for example those described by JONESet al. [3], the sample elevator described by SOMMERand OHLS [4]; aerosol generation along the lines of flameless AA, developed by us, etc. Details of these results will be described in a future publication. When the Merensky nebulizer was attached to an ICP source, argon was used as the compressed gas. The aspirated particles were carried upwards through the spray chamber and furnace tube by this emerging gas stream, but-when necessary-additional argon could be introduced into the spray chamber through the side tube (1 l), shown in Fig. 1, to facilitate proper piercing of the ICP plasma. 3.3. Spectrometer and measuring device used The radiation from the Merensky burner was measured on a commercial Techtron AA5 spectrometer. A slit width of 1OOpm was used. The anode current from the photomultiplier was digitized by means of AFCs [5]. The resultant pulses were counted on a special electronic [2] W. H.
GUNTER. M.Sc. thesis. University of Stellenbosch (1980). [3] J. L. JONES, R. L. DAHLQUIST and R. E. HOYT, Appl. Specrros. 25,628 [4] D. SOMMER and K. 0~~s Frvsenius Z. Anal. Chem. 304, 97 (1980). [S] F. M. HAMM and P. B. ZEEMAN, Appl. Speccrosc. 30, 70 (1976).
(1971).
Chemicalburner for emissionand absorptionspectroscopy
941
unit, designed and built by us. This unit can be set for various integration times and can simultaneously receive the signals from six spectral lines. The results from the various channels were visually displayed to check any erroneous operations while the measurements were in progress, but could also simultaneously be paper-punched or printed out by means of a Axiom IMP mini-printer. For these investigations an integration time of 4s was used throughout and ten sequential readings were recorded for statistical analysis. 4. DISCUSSION OF RESULTS 4.1. General When the direct analysis of powder samples is attempted, the question of reliable standards becomes very important. It seems highly unlikely that a powder sample will behave similar to a solution in a particular excitation source due to the vast difference in chemical composition. Severe systematic errors can be expected when chemical solutions are used as standards for the direct quantitative characterization of elements in powder samples. For this reason a special leave sample prepared by the Research Institute for Fruit and Fruit Technology, on which hundreds of determinations were already made, was adopted as our powder standard for the present investigation. The next question is whether this powder sample will behave similarly to a chemical solution in a particular source in that a straight calibration curve is obtained when a series of standards, prepared by treating the powder as though it was an ordinary chemical from the shelf, is aspirated into the excitation source. To investigate this possibility a series of “standard solutions” containing 0.125,0.25, 0.5, . . . , up to 8g of powder per 100 ml pure water, was introduced into the Merensky burner and the various ICP sources. The object was to see whether the measured radiances fall on a straight line, as is ordinarily observed with standard chemical solutions. 4.2. Calibration curves and results obtained with Merensky burner Experiments on the air-acetylene flame using high grade chemicals were confined to solutions of Na and Ca, using the Na I 589 nm and the Ca I 422.6 nm lines. With the nitrous oxide-acetylene flame experiments were conducted using the Ca I 422.6nm and Ca II 393.3 nm lines. The performance of the Merensky nebulizer was compared under the same experimental conditions with a commercial Techtron nitrous-oxide burner, with the latter parallel to the optic axis and also perpendicular to it. The results are shown in Fig. 2. The Merensky burner should resemble more closely the Techtron burner in the perpendicular than in the parallel mode. This is clearly shown in the figure, with the Techtron burner slightly more sensitive, but it used about ten times as much sample per second. The difference in signal strength could easily be wiped out by a higher speed of rotation of the peristaltic pump or perhaps by using another portion of the flame. The relative standard deviation (RSD) for the Merensky burner was approximately 1 “/ofor the higher concentrations, but that of the Techtron burner and pneumatic nebulizer was definitely better. It would be interesting to determine this figure for the Techtron burner when the same peristaltic pump is used. According to the results one may, no doubt, conclude that the performance of the Merensky burner and nebulizer is at par with commercial ones. As regards the acceptance of powder samples the commercial nebulizers of the pneumatic type fall away completely. With the Merensky system using nitrous oxide-acetylene as fuel, good results for Ca 422.6, Na 589.0 and Mg 285.2 nm were obtained as is shown in Fig. 3. These experiments were carried out by introducing the leaf “solutions” into the nitrous-oxide acetylene flame in the manner described above. The curve for Ca I shows the ordinary trend of calibration curves for standard solutions and commercial burners. The same applies to a somewhat lesser degree for the Na and Mg lines in so far that a higher standard deviation is obtained as is also indicated by the error bars. The RSD for Ca was 3.0’;/,;for the three higher concentration points of Na and Mg it was 5 “/ and 3 “/, respectively. In considering these results one must bear in mind that for example 500mg leaves “dissolved” in 1OOml water represents approximate concentrations of 5Opg ml- ’ Ca, 5pgml-’ Naand 25pgml-’ Mg. It is thus natural to expect higher standard deviations for the latter two elements. In reviewing
P. B. ZEEMAN et al.
942
SOLUTIONS
,/
lo6 7 ln E
---
PARALLEL - . - . - - PERPENDICULAR MERENSKY
i
1
1
2
1
I
1
I
I
I
8
16
32
64
1
1
I
I
IO00
128 250 wm
Fig. 2. Calibration curves for standard solutions in nitrous oxide flame obtained with Merensky and Techtron nebulizcrs.
LEAF
SAMPLES
counts
,
I
,
I
2DO0 .125 .250 .500 gm / 100 1 water Fig. 3. Calibration curves for leaf “solutions” in nitrous oxide flame using Merensky nebulizer.
Chemical burner for emission and absorption spectroscopy
943
these results, it thus seems reasonable to conclude that the leaf “solutions” behave like ordinary stock solutions. These results open up a possible new approach to the routine analyses of at least some elements in plant material. Acknowledgements-The authors wish to thank the University of Stellenbosch for financial and other support as well as the Council for Scientific and Industrial Research for bursar& and grants in aid of the research.
SA(B)38/5-6-S
Specfrochimica Acta.Vol. 388.No. S/6.pp.937-943.1983. Pr~nled in Greal B&din.
A new premixed chemical burner for emission and absorption spectroscopy with separated fuel and sample introduction P. B. ZEEMAN,C.
MULLER
and W. H.
GUNTER
Merensky Institute for Physics, University of Stellenbosch, Stellenbosch 7600, Republic of South Africa
(Received 23 December 1982) Abstract--A new version of the Babington nebulizer is described where dry aerosols from solutions and powder samples can be introduced into air-acetylene and nitrous oxide-acetylene flames, as well as ICP torches. A special burner is described in which the premixed burner gasesare completely separated from the sample introduction into the flame plasma. The powder samplescould also be successfullyintroduced into a 9.2 MHz high power ICP, as well as 28 and 50 MHz low power ICP sources.The investigations show that a powder leafsample behavessimilarly to an aqueous solution in the plasmas of a nitrous oxide-acetylene flame and the ICP sources.
1. INTRODUCTION PREMIXED FLAMES using air-acetylene or nitrous oxide-acetlene as burner gases in conjunction with pneumatic nebulizers are well established in modern practice. When diluted solutions are aspirated no difficulties are encountered, but when high concentration samples are to be introduced into the flame, clogging of the burner slit may occur. When powder samples are introduced by means of a Babington [I] type nebulizer the use of the ordinary slot type burner head becomes impracticable due to blocking of the slot by solid particles. In view of the need for a nebulizer and burner which can accommodate samples in powder form and operate carefree, but renders reproducible and accurate results, a version of the Babington type nebulizer was constructed together with a burner having the unique feature that sample introduction is completely separated from the premixed burner gases. Details of this burner, hereafter called the Merensky burner, and results obtained from pure chemicals and leaf samples are given below.
2.
CONSTRUCTIONAL
DETAILS
OF THE MERENSKY
NEBULIZER
AND BURNER
The Merensky nebulizer and burner are shown in Figs 1(ak(c). The nebulizer (1) is made from a stainless steel cylinder with i.d. 1Omm having a fine hole (2) with diameter 0.3 or 0.4 mm. It fits into a stainless steel cylinder (3) into which passes the sample introducing tube (4). The end (5) of this tube is sliced as is shown in Fig. 1(a). This sliced end portion is located symmetrically above the fine hole (2) by means ofa brass block (6) and a centering pin (7). The latter prevents rotation and sideways movement of the tip (5). The nebulizer assembly is drained through the side tube (8). Distilled water can be introduced through the tube (9) to wash the nebulizer (2) and the tip (5) of the sample introducing tube in order to minimize memory effects. The aerosol from the nebulizer rises into the spray chamber (9a), Fig. l(b), made from Perspex and having an i.d. of 46 mm and overall length 170 mm. Airtight introduction of air and transport of aerosol is accomplished by means of O-ring seals, as shown. Condensed droplets are drained through the tube (lo), while additional air or other gases can be introduced through tube (11) to facilitate faster upwards movement of the aerosol. The aerosol is dried and heated to approximately 300°C by means of the furnace (12) which was made by winding resistance wire over asbestos sheet wrapped around a Pyrex or quartz tube (13) with i.d. 25 mm. The dried and heated aerosol is transferred by means of a conical brass piece (14), Fig. 1(c), with a cylindrical tip (15) into the centre of the burner head (16). The conical brass aerosol conveyer is insulated thermally from the burner body (17) by means of boron nitride rings (18) and (19). The burner body is water-cooled by means of the tube (20). [l]
R. C.
FRY
and M. B. DENTON, Anal. Chem. 49, 1413 (1977). 937
938
P. B. ZEEMAN et al.
The thermal insulation at (18) and (19) prevents condensation of the heated aerosol and thus no blocking of the outlet (15), which has an i.d. of 3.3 mm, occurs. The furnace tube (13), conical portion (14) and cylindrical tip (15) can be made from quartz, in which case the boron nitride rings can be omitted.
n
Fig. l(a). Merensky nebulizer and sample introducing tube.
Fig. 1(b). Pyrex spray chamber.
Chemical burner for emission and absorption spectroscopy
Fig. l(c). Burner head with separated central aerosol tube.
The fuel and support gases are introduced into the burner by means of the tubes (21). The burner chamber is completely sealed from the sample introducing system so that the latter can be removed or replaced without disturbing the burning flame whether the latter was fed by air-acetylene or nitrous oxide-acetylene. The burner head consists of three rows of concentric holes (22), as shown in Fig. l(c), 0.8 mm in diameter in the case of a burner head for nitrous oxide-acetylene use and 1.0 mm diameter for air-acetylene. In the Merensky burner the aerosol is thus introduced centrally into the flame and pierces the flame gas in the same manner as in an inductively-coupled plasma when the latter operates properly. At the lower end of the flame, radiation from the sample is constricted to a narrow region, while it spreads to cover the full flame diameter higher up after experiencing a long enough residence time in the flame. The best height above the burner block for optimum radiance from the sample can thus be selected. This optimum height can be varied by introducing additional air through the side tube (11). The aspirator and burner assembly is remarkably free from memory effects. Solutions or powder mixtures were always aspirated from lower to higher concentrations. Occasionally pure water was squirted over the nebulizer assembly (2) and (5) to remove slurry that might have accumulated there. These “severe” influxes of water aerosol had no effect on chemical flames, but may extinguish an ICP.
3. APPARATUSAND EXPERIMENTALPROCEDURES 3.1. Excitation sources and standards used
The properties of the Merensky nebulizer were investigated by using an air-acetylene flame, a nitrous oxide-acetylene flame, a 9.2 MHz high-power ICP, as well as a 28 MHz Arlabs and a 50 MHz Philips low-power ICP.
940
P. B. i&MAN
et al.
These experiments were carried out by first using a series of standard solutions made from spectroscopy-pure chemicals, the object being to determine the reproducibility of the nebulizer and compare its performance with that of well-founded pneumatic ones. However, further investigations were carried out to determine the feasibility of using this nebulizer to aspirate samples in the form of slurries as well. For this purpose a sample of fruit tree leaves granted to us by Fruit and Fruit Technology Institute was grounded in a ball mill and then sieved through a 50 micron mesh. To this fine powder pure water was added and “solutions” were made containing 0.125, 0.25, . . ., 8g leaf powder per lOOm1 of water. The feasibility of the Merensky nebulizer as a practical instrument or not, will in the first instance be judged from the results obtained for the experiments carried out on standard solutions aspirated into the various excitation sources and dispersed by the spectrometers used. If its operation is satisfactory with these ordinary solutions, it would be an advantage in general because it is inexpensive and simple to make. It would be an interesting additional advantage if it gives accurate and reproducible spectral radiances for samples in powder form. This aspect of its acceptability will be judged from the results obtained with the fruit leaf samples. 3.2. Sample introduction into chemical flame and ICP sources The samples in the form of slurries were activated by means of a magnetic stirrer to ensure even distribution of powder in the water mixture. All samples were introduced into the flame or ICP sources by means of a peristaltic pump having 16 rollers and a variable speed of rotation. After preliminary experiments a speed of 3 revolutions per second was adopted for all measurements. It then delivered 0.05 ml of sample per second. This delivery is much less than that of commercial pneumatic nebulizers. Market pulsations in aerosol generation were observed at the nebulizer tip due to the action of the peristaltic pump. These, however, eased out in the aerosol chamber and the heated quartz tube leading to the flame or ICP source and good reproducibility in signal strength was obtained as is shown in the results. When powders are transported, it is important to avoid sharp bends in the tubing through which the powder is passed. Also only dry powders can be transported through medium-sized and small bore tubing or else severe clogging will occur. For this reason the aspirated wet powder was rapidly dried on leaving the spray chamber. Also the dried powder should be delivered hot to the excitation source to prevent the formation of drops due to condensation. The samples were introduced into the Merensky burner via the electrical heater (12) and the insulated tapered brass piece (14) shown in Figs. 1(b) and (c). In the case of ICP sources the samples entered through a central opening in the Teflon bases [2] of our ICP “burner” assemblies. Another type of heater tube was used with a spherical ball joint at the top which joined the furnace to the sample introducing tube of the ICP. The results obtained with the Merensky nebulizer and ICP sources were compared with those obtained from other aerosol generator techniques, for example those described by JONESet al. [3], the sample elevator described by SOMMERand OHLS [4]; aerosol generation along the lines of flameless AA, developed by us, etc. Details of these results will be described in a future publication. When the Merensky nebulizer was attached to an ICP source, argon was used as the compressed gas. The aspirated particles were carried upwards through the spray chamber and furnace tube by this emerging gas stream, but-when necessary-additional argon could be introduced into the spray chamber through the side tube (1 l), shown in Fig. 1, to facilitate proper piercing of the ICP plasma. 3.3. Spectrometer and measuring device used The radiation from the Merensky burner was measured on a commercial Techtron AA5 spectrometer. A slit width of 1OOpm was used. The anode current from the photomultiplier was digitized by means of AFCs [5]. The resultant pulses were counted on a special electronic [2] W. H.
GUNTER. M.Sc. thesis. University of Stellenbosch (1980). [3] J. L. JONES, R. L. DAHLQUIST and R. E. HOYT, Appl. Specrros. 25,628 [4] D. SOMMER and K. 0~~s Frvsenius Z. Anal. Chem. 304, 97 (1980). [S] F. M. HAMM and P. B. ZEEMAN, Appl. Speccrosc. 30, 70 (1976).
(1971).
Chemicalburner for emissionand absorptionspectroscopy
941
unit, designed and built by us. This unit can be set for various integration times and can simultaneously receive the signals from six spectral lines. The results from the various channels were visually displayed to check any erroneous operations while the measurements were in progress, but could also simultaneously be paper-punched or printed out by means of a Axiom IMP mini-printer. For these investigations an integration time of 4s was used throughout and ten sequential readings were recorded for statistical analysis. 4. DISCUSSION OF RESULTS 4.1. General When the direct analysis of powder samples is attempted, the question of reliable standards becomes very important. It seems highly unlikely that a powder sample will behave similar to a solution in a particular excitation source due to the vast difference in chemical composition. Severe systematic errors can be expected when chemical solutions are used as standards for the direct quantitative characterization of elements in powder samples. For this reason a special leave sample prepared by the Research Institute for Fruit and Fruit Technology, on which hundreds of determinations were already made, was adopted as our powder standard for the present investigation. The next question is whether this powder sample will behave similarly to a chemical solution in a particular source in that a straight calibration curve is obtained when a series of standards, prepared by treating the powder as though it was an ordinary chemical from the shelf, is aspirated into the excitation source. To investigate this possibility a series of “standard solutions” containing 0.125,0.25, 0.5, . . . , up to 8g of powder per 100 ml pure water, was introduced into the Merensky burner and the various ICP sources. The object was to see whether the measured radiances fall on a straight line, as is ordinarily observed with standard chemical solutions. 4.2. Calibration curves and results obtained with Merensky burner Experiments on the air-acetylene flame using high grade chemicals were confined to solutions of Na and Ca, using the Na I 589 nm and the Ca I 422.6 nm lines. With the nitrous oxide-acetylene flame experiments were conducted using the Ca I 422.6nm and Ca II 393.3 nm lines. The performance of the Merensky nebulizer was compared under the same experimental conditions with a commercial Techtron nitrous-oxide burner, with the latter parallel to the optic axis and also perpendicular to it. The results are shown in Fig. 2. The Merensky burner should resemble more closely the Techtron burner in the perpendicular than in the parallel mode. This is clearly shown in the figure, with the Techtron burner slightly more sensitive, but it used about ten times as much sample per second. The difference in signal strength could easily be wiped out by a higher speed of rotation of the peristaltic pump or perhaps by using another portion of the flame. The relative standard deviation (RSD) for the Merensky burner was approximately 1 “/ofor the higher concentrations, but that of the Techtron burner and pneumatic nebulizer was definitely better. It would be interesting to determine this figure for the Techtron burner when the same peristaltic pump is used. According to the results one may, no doubt, conclude that the performance of the Merensky burner and nebulizer is at par with commercial ones. As regards the acceptance of powder samples the commercial nebulizers of the pneumatic type fall away completely. With the Merensky system using nitrous oxide-acetylene as fuel, good results for Ca 422.6, Na 589.0 and Mg 285.2 nm were obtained as is shown in Fig. 3. These experiments were carried out by introducing the leaf “solutions” into the nitrous-oxide acetylene flame in the manner described above. The curve for Ca I shows the ordinary trend of calibration curves for standard solutions and commercial burners. The same applies to a somewhat lesser degree for the Na and Mg lines in so far that a higher standard deviation is obtained as is also indicated by the error bars. The RSD for Ca was 3.0’;/,;for the three higher concentration points of Na and Mg it was 5 “/ and 3 “/, respectively. In considering these results one must bear in mind that for example 500mg leaves “dissolved” in 1OOml water represents approximate concentrations of 5Opg ml- ’ Ca, 5pgml-’ Naand 25pgml-’ Mg. It is thus natural to expect higher standard deviations for the latter two elements. In reviewing
P. B. ZEEMAN et al.
942
SOLUTIONS
,/
lo6 7 ln E
---
PARALLEL - . - . - - PERPENDICULAR MERENSKY
i
1
1
2
1
I
1
I
I
I
8
16
32
64
1
1
I
I
IO00
128 250 wm
Fig. 2. Calibration curves for standard solutions in nitrous oxide flame obtained with Merensky and Techtron nebulizcrs.
LEAF
SAMPLES
counts
,
I
,
I
2DO0 .125 .250 .500 gm / 100 1 water Fig. 3. Calibration curves for leaf “solutions” in nitrous oxide flame using Merensky nebulizer.
Chemical burner for emission and absorption spectroscopy
943
these results, it thus seems reasonable to conclude that the leaf “solutions” behave like ordinary stock solutions. These results open up a possible new approach to the routine analyses of at least some elements in plant material. Acknowledgements-The authors wish to thank the University of Stellenbosch for financial and other support as well as the Council for Scientific and Industrial Research for bursar& and grants in aid of the research.
SA(B)38/5-6-S