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The determination of lead in air by flameless atomic absorption spectrophotometry
SHORT
COMMUNICATIONS
439
The determination of lead in air by flameless atomic absorption spectrophotometry
The determination of lead contents in atmospheric particulates by means of atomic absorption spectroscopy has been reported by several investigators’ - ‘. In the usual sampling technique for such inorganically bound lead, the atmosphere under test is allowed to pass through some sort of filter in order to collect all particles above a certain size. The filter types used comprise glass fibre4-6, filter paper’ and millipore filters ‘. After the abs&ption, the filters can either be treated directly with hydrochloric acid’ or nitric acid6 or they can be dry-ashed at 500° 4*7. These methods have stood the test of experience and are very useful. However, large volumes of air must be aspirated through the filters to obtain enough lead for a determination. This makes the sampling rather time-consuming or requires heavy high-capacity pumps. When peak values or instantaneous values are of interest, aspiration times of 10-15 min or shorter and much smaller equipment are desirable. The new graphite furnace technique introduced by L’Vova in 1963 and further developed by Massmanng, West and Williams”, Donega and Burgess” and Welz and Wiedeking’“, has recently been marketed as a commercially available unit. This offers a unique possibility of determining trace elements in extremely small volumes with a high degree of accuracy. Since many samples can be injected into the graphite tube without a prior digestion or preconcentration step, most of the usual contamination encountered in ordinary trace element*analysis is avoided. The present communication describes the use of this technique in a simple, rapid and extremely sensitive method, combined with collection of lead particulales on millipore filters from air volumes down to 10 dm3. Equipment anti reagents Air contaminants were collected on 37-mm diameter MF-Millipore filters AA (0.8 pm), made of mixed cellulose esters. These filters were connected to a small portable battery-operated pump (Casella, London), calibrated to 2.7 dm3 air per min. A Perkin-Elmer Model 303 Atomic Absorption Spectrophotometer equipped with a Perkin-Elmer (Bodenseewerk) Graphite Cell H’GA 70, an automatic recorder readout accessory and a Hitachi-Perkin-Elmer Recorder Model 159 was used. Small sample aliquots were injected into the graphite tube by means of Eppendorf Marburg micropipettes. Flame atomic absorption measurements were carried out on a PerkinElmer 403 Atomic Absorption Spectrophotometer with a Boling burner head. A lead Intensitron hollow-cathode lamp was used as light source in all measurements. The only chemical used, nitric acid, was of analytical-reagent grade quality. Lead solutions. A lOOO-p.p.m. stock solution was prepared from 1.OOOg of pure lead metal dissolved in 25 ml of nitric acid and diluted to 1 1 with distilled water. From this solution O.l-p.p.m. standard solutions containing 5 ml of nitric acid per 100 ml were prepared daily. Measurements conditions Before sample volumes are atomized in the graphite tube, any solvent, organic material or other unwanted components of the matrix must be removed. Smoke signals or false absorption will otherwise occur. Therefore, two separate heat treatment stages, drying and charring (“ashing”) must be carried out before the atomizaAncrl. Chim. Acta, 55 (1971) 439441
440
SHORT COMMUNICATIONS
tion step. For such treatment, the HGA 70 is equipped with seven fixed programmes for easy reproduction of selected temperatures between 60” and 1100” and three clocks for time adjustment. The final atomization temperature is determined by the voltage for the resistance heating of the tube. Since there is little available information about the settings of the instrument for each type of analysis, the optimal time and temperature of the various stages had to be determined. It was found suitable to dry the sample at lOO”, to char at 330° and to atomize at 19OOO.Program 4 and a transformer setting of 5 V (2.5 kW) takes care of this automatically. A period of 30 set for each sequence was found satisfactory. Procedure Collect particulate lead samples by aspirating air for 10 min through the millipore filters. Soak the filters in 2.0 ml of 1 + 1 nitric acid in a 50-ml beaker andapply gentle heat. After 5 min., decant into a lo-ml volumetric flask and wash the filters with successive 2-ml portions of warm distilled water. Finally dilute to volume with distilled water. Inject S-50 /rl of O.l-p.p.m. lead standard solution into the graphite tube and register the lead absorption peak at program 4 with a 5-V atomization voltage and a 30-see sequence time. Prepare a blank solution from a new millipore filter treated with nitric acid as described above and register a blank value. Prepare a calibration curve from the peak height measurements after converting percentage absorption to absorbance and subtracting the blank value. (A straight line is obtained up to 2 ng of lead.) Measure small sample volumes in the same way, convert the peak heights to absorbance, subtract the blank value for the same injection volume and evaluate the lead concentration from the calibration graph. Light scattering Light scattering, causing too high absorption readings, is well known in flame absorption measurements. Such interference can be corrected for by selecting a nonabsorbing line within 10 nm of the analytical line and subtracting the absorption signal from the analytical value. It was found necessary in the present work to examine the peaks for such unspecific absorption. The analytical line used was 217.0 nm and the non-absorbing line was 209.8 nm. In the regular sample and standard solutions, no absorption was recorded at 209.8 nm. In order to establish if the lead particles had been completely dissolved and washed out’ of the millipore filters, the filters were treated with 1 ml of hot nitric acid; the lilters dissolved completely and the solutions were diluted to 10 ml. For the same aliquot sizes (20 PI), the same signals (11 OA)were recorded at both lines. This was taken as evidence of light scattering and also of complete lead extraction when the millipore filters were leached as recommended in the procedure. Results atld discussion The proposed method was used in the analysis of a number of air particulate samples collected in Oslo city in November 1970,l m above street level. Some of the results obtained are shown in Table I. It is obvious from these data that the sampling and analytical methods used offer satisfactory sensitivity. With lo-min sampling times and 20-~1 injection volumes, the sensitivity obtained for 1% absorption is about 0.7 And. C/tint. Acta, 55 (1971) 439-441
441
SHORT COMMUNICATIONS TABLE
I
ANALYSISOFSTANDARDS
ANDSAMPLCSOFOSLOCITYAIR
(Scaleexpansion 1) Air volume
Sample
Aliyuot (d)
(dm’) 0.1 p.p.m. standard 0.1 p,p.m. standard 0.1 p.p.m. standard Blank Blank Air sample 1, rush hour Air sample 2, rush hour Air sample 3, rush hour Air sample 4, suburb . Corrected
-
5 10 20 20 100 20 20 20 100
27 27 27 54
Peuk height (% abs.)
Concentration in air (pg Pb m- ‘)
Total amount= (ng)
14.4 24.4 41.5 1.9 9.2 12.2 17.5 6.5 10.1
-
0.5 1.0 2.0 0.07 0.35 0.43 0.66 0.18 < 0.05
7.9 12.2 3.3 < 0.2
for blank lcad content.
pg of lead per m3 air. The injected volume can easily be increased to 100 ~1. This was done in air sample 4, but the high lead content in the analytical-grade nitric acid, determined to be 3.5 pg l- 1 makes it doubtful that a correspondingly better sensitivity can be assumed. For lead concentrations below 1 fig m- 3 of air, an increased sampling time or the use of less contaminated acid will give higher sensitivity. The small sample volumes made it impossible to check the accuracy of the obtained analysis by preconcentration techniques and regular atomic absorption spectrophotometry. However, some sort of comparison was possible since the two solutions with the highest lead concentrations, sample 1 (22 p-16 1-r) and sample 2 (33 pg 1-l) could be measured directly on the Model 403 with maximum scale expansion. The measured values of 26 and 37 pg Pb l- ‘, respectively, are in acceptable accordance, when the low accuracy of the direct flame method in this concentration range is taken into consideration. Ccntrul Institute for Industriul Blindern, Oslo 3 (Norwuy)
Sverre H. Omang
Research,
C. L. CHAKRADARTI, J.W. ROIUNSON AND P. W. Wwr, Anal. Chim. Acrcr. 34 (1966) 269. G. TIIILLI~Z,Anal. Chcm., 39 (1967) 427. .I. CHOLAK, L. J. SCHAFER AND D. YEAGER. J. Amer. Id. Hyg. Assoc.. 29 (1968) 562. C. D. BURNIXAM,C. E. MOORE, T. KOWALSKI AND J. KRASNI~WSKI, Appl. Spcctrosc., 24 (1970)411. M. BEYER. Atomic Absorption ffewsletter, 8 (1969) 23. R. Moss AND E. V. BKOWI?IT, Analyst, 91 (1966) 428. V. SMOLCIC, Arhiv Hig. RU&I Toksikol., 17 (1966) 309; Awl. Ahstr.. 14 (1967) 5775. B. V. L'VOV, Spectrochim. Acta. 24B (1969) 53. H. MASSMANN, Spectrochim. Actu. 23B (1968) 215. T. S. WEST AND X. K. WILLIAMS, And. Chitn. Acta, 45 (1969) 27. 11 H. M. DONEGA AND T. E. BURGESS, And. Chem., 42 (1970) 1521. 12 B. WIZLZ AND E. WIEDBKING, 2. And. Chenl., 252 (1970) 111. 1 2 3 4 5 6 7 8 9 10
(Received 19th March 1971) And.
Chbn. Acta.
55 (197 1) 43944
1
COMMUNICATIONS
439
The determination of lead in air by flameless atomic absorption spectrophotometry
The determination of lead contents in atmospheric particulates by means of atomic absorption spectroscopy has been reported by several investigators’ - ‘. In the usual sampling technique for such inorganically bound lead, the atmosphere under test is allowed to pass through some sort of filter in order to collect all particles above a certain size. The filter types used comprise glass fibre4-6, filter paper’ and millipore filters ‘. After the abs&ption, the filters can either be treated directly with hydrochloric acid’ or nitric acid6 or they can be dry-ashed at 500° 4*7. These methods have stood the test of experience and are very useful. However, large volumes of air must be aspirated through the filters to obtain enough lead for a determination. This makes the sampling rather time-consuming or requires heavy high-capacity pumps. When peak values or instantaneous values are of interest, aspiration times of 10-15 min or shorter and much smaller equipment are desirable. The new graphite furnace technique introduced by L’Vova in 1963 and further developed by Massmanng, West and Williams”, Donega and Burgess” and Welz and Wiedeking’“, has recently been marketed as a commercially available unit. This offers a unique possibility of determining trace elements in extremely small volumes with a high degree of accuracy. Since many samples can be injected into the graphite tube without a prior digestion or preconcentration step, most of the usual contamination encountered in ordinary trace element*analysis is avoided. The present communication describes the use of this technique in a simple, rapid and extremely sensitive method, combined with collection of lead particulales on millipore filters from air volumes down to 10 dm3. Equipment anti reagents Air contaminants were collected on 37-mm diameter MF-Millipore filters AA (0.8 pm), made of mixed cellulose esters. These filters were connected to a small portable battery-operated pump (Casella, London), calibrated to 2.7 dm3 air per min. A Perkin-Elmer Model 303 Atomic Absorption Spectrophotometer equipped with a Perkin-Elmer (Bodenseewerk) Graphite Cell H’GA 70, an automatic recorder readout accessory and a Hitachi-Perkin-Elmer Recorder Model 159 was used. Small sample aliquots were injected into the graphite tube by means of Eppendorf Marburg micropipettes. Flame atomic absorption measurements were carried out on a PerkinElmer 403 Atomic Absorption Spectrophotometer with a Boling burner head. A lead Intensitron hollow-cathode lamp was used as light source in all measurements. The only chemical used, nitric acid, was of analytical-reagent grade quality. Lead solutions. A lOOO-p.p.m. stock solution was prepared from 1.OOOg of pure lead metal dissolved in 25 ml of nitric acid and diluted to 1 1 with distilled water. From this solution O.l-p.p.m. standard solutions containing 5 ml of nitric acid per 100 ml were prepared daily. Measurements conditions Before sample volumes are atomized in the graphite tube, any solvent, organic material or other unwanted components of the matrix must be removed. Smoke signals or false absorption will otherwise occur. Therefore, two separate heat treatment stages, drying and charring (“ashing”) must be carried out before the atomizaAncrl. Chim. Acta, 55 (1971) 439441
440
SHORT COMMUNICATIONS
tion step. For such treatment, the HGA 70 is equipped with seven fixed programmes for easy reproduction of selected temperatures between 60” and 1100” and three clocks for time adjustment. The final atomization temperature is determined by the voltage for the resistance heating of the tube. Since there is little available information about the settings of the instrument for each type of analysis, the optimal time and temperature of the various stages had to be determined. It was found suitable to dry the sample at lOO”, to char at 330° and to atomize at 19OOO.Program 4 and a transformer setting of 5 V (2.5 kW) takes care of this automatically. A period of 30 set for each sequence was found satisfactory. Procedure Collect particulate lead samples by aspirating air for 10 min through the millipore filters. Soak the filters in 2.0 ml of 1 + 1 nitric acid in a 50-ml beaker andapply gentle heat. After 5 min., decant into a lo-ml volumetric flask and wash the filters with successive 2-ml portions of warm distilled water. Finally dilute to volume with distilled water. Inject S-50 /rl of O.l-p.p.m. lead standard solution into the graphite tube and register the lead absorption peak at program 4 with a 5-V atomization voltage and a 30-see sequence time. Prepare a blank solution from a new millipore filter treated with nitric acid as described above and register a blank value. Prepare a calibration curve from the peak height measurements after converting percentage absorption to absorbance and subtracting the blank value. (A straight line is obtained up to 2 ng of lead.) Measure small sample volumes in the same way, convert the peak heights to absorbance, subtract the blank value for the same injection volume and evaluate the lead concentration from the calibration graph. Light scattering Light scattering, causing too high absorption readings, is well known in flame absorption measurements. Such interference can be corrected for by selecting a nonabsorbing line within 10 nm of the analytical line and subtracting the absorption signal from the analytical value. It was found necessary in the present work to examine the peaks for such unspecific absorption. The analytical line used was 217.0 nm and the non-absorbing line was 209.8 nm. In the regular sample and standard solutions, no absorption was recorded at 209.8 nm. In order to establish if the lead particles had been completely dissolved and washed out’ of the millipore filters, the filters were treated with 1 ml of hot nitric acid; the lilters dissolved completely and the solutions were diluted to 10 ml. For the same aliquot sizes (20 PI), the same signals (11 OA)were recorded at both lines. This was taken as evidence of light scattering and also of complete lead extraction when the millipore filters were leached as recommended in the procedure. Results atld discussion The proposed method was used in the analysis of a number of air particulate samples collected in Oslo city in November 1970,l m above street level. Some of the results obtained are shown in Table I. It is obvious from these data that the sampling and analytical methods used offer satisfactory sensitivity. With lo-min sampling times and 20-~1 injection volumes, the sensitivity obtained for 1% absorption is about 0.7 And. C/tint. Acta, 55 (1971) 439-441
441
SHORT COMMUNICATIONS TABLE
I
ANALYSISOFSTANDARDS
ANDSAMPLCSOFOSLOCITYAIR
(Scaleexpansion 1) Air volume
Sample
Aliyuot (d)
(dm’) 0.1 p.p.m. standard 0.1 p,p.m. standard 0.1 p.p.m. standard Blank Blank Air sample 1, rush hour Air sample 2, rush hour Air sample 3, rush hour Air sample 4, suburb . Corrected
-
5 10 20 20 100 20 20 20 100
27 27 27 54
Peuk height (% abs.)
Concentration in air (pg Pb m- ‘)
Total amount= (ng)
14.4 24.4 41.5 1.9 9.2 12.2 17.5 6.5 10.1
-
0.5 1.0 2.0 0.07 0.35 0.43 0.66 0.18 < 0.05
7.9 12.2 3.3 < 0.2
for blank lcad content.
pg of lead per m3 air. The injected volume can easily be increased to 100 ~1. This was done in air sample 4, but the high lead content in the analytical-grade nitric acid, determined to be 3.5 pg l- 1 makes it doubtful that a correspondingly better sensitivity can be assumed. For lead concentrations below 1 fig m- 3 of air, an increased sampling time or the use of less contaminated acid will give higher sensitivity. The small sample volumes made it impossible to check the accuracy of the obtained analysis by preconcentration techniques and regular atomic absorption spectrophotometry. However, some sort of comparison was possible since the two solutions with the highest lead concentrations, sample 1 (22 p-16 1-r) and sample 2 (33 pg 1-l) could be measured directly on the Model 403 with maximum scale expansion. The measured values of 26 and 37 pg Pb l- ‘, respectively, are in acceptable accordance, when the low accuracy of the direct flame method in this concentration range is taken into consideration. Ccntrul Institute for Industriul Blindern, Oslo 3 (Norwuy)
Sverre H. Omang
Research,
C. L. CHAKRADARTI, J.W. ROIUNSON AND P. W. Wwr, Anal. Chim. Acrcr. 34 (1966) 269. G. TIIILLI~Z,Anal. Chcm., 39 (1967) 427. .I. CHOLAK, L. J. SCHAFER AND D. YEAGER. J. Amer. Id. Hyg. Assoc.. 29 (1968) 562. C. D. BURNIXAM,C. E. MOORE, T. KOWALSKI AND J. KRASNI~WSKI, Appl. Spcctrosc., 24 (1970)411. M. BEYER. Atomic Absorption ffewsletter, 8 (1969) 23. R. Moss AND E. V. BKOWI?IT, Analyst, 91 (1966) 428. V. SMOLCIC, Arhiv Hig. RU&I Toksikol., 17 (1966) 309; Awl. Ahstr.. 14 (1967) 5775. B. V. L'VOV, Spectrochim. Acta. 24B (1969) 53. H. MASSMANN, Spectrochim. Actu. 23B (1968) 215. T. S. WEST AND X. K. WILLIAMS, And. Chitn. Acta, 45 (1969) 27. 11 H. M. DONEGA AND T. E. BURGESS, And. Chem., 42 (1970) 1521. 12 B. WIZLZ AND E. WIEDBKING, 2. And. Chenl., 252 (1970) 111. 1 2 3 4 5 6 7 8 9 10
(Received 19th March 1971) And.
Chbn. Acta.
55 (197 1) 43944
1