Fresenius Z. Anal. Chem. 302, 278-280 (1980) [.rl~lllhl$ Zeitrdlhl'iIl fiir

�9 by Springer-Verlag 1980

Direct Spectrographic Analysis of Trace Elements in Soil Samples

V. P. Bellary and Y. A n a n t h a r a m a Sarma*

Spectroscopy Division, Bhabha Atomic Research Centre, Trombay, Bombay-400085, India

Direkte spektrographischc Analyse von Elementspuren in Bodenproben

Zusammenfassung. Eine direkte emissionsspektrogra- phische Methode zur Best immung von Ba, Co, Cr, Cu, Mn, Ni, Pb, V und Zn in Bodenproben wird beschrie- ben. Die yon organischen Substanzen freie Probe wird mit einem Gemisch yon Graphi t und innerem Standard vermischt und mit Hilfe yon 15 A Gleichstrom in einer Elektrode vom Typ U C C 1989 angeregt. Die Spektren werden in einem 3,4 m Jarrel-Ash Git terspektrograph auf SA-1 Platten aufgenommen. Zur Aufstellung der Eichkurven werden synthetische Standards verwendet. Die Genauigkeit (Variationskoeffizient) betrfigt +_1~%.

Summary. A direct emission spectrographic method for the estimation o f Ba, Co, Cr, Cu, Mn, Ni, Pb, V and Zn in soil samples is described. The sample, free f rom organic matter is thoroughly mixed with graphite- internal s tandard mixture and excited in U C C 1989 type electrode using 15 A d.c. A 3.4 m Jarrel-Ash grating spectrograph is employed to pho tograph the spectra on SA-1 photographic plates. Synthetic stan- dards are used for establishing working curves. The precision of the method, expressed as coefficient of variation is + 11%.

Key words: Analyse yon Boden; Spektrographie; Elementspuren

1. Introduction

Informat ion on the composi t ion of soil, particularly its trace element content is o f interest to investigators in various fields of research. In addit ion to agricultural

* Address for Correspondence

chemists and soil scientists, environmentalists, nutri- tionists and others are also interested in these data. The presence of certain toxic elements in nature which affect animals and man has led to intensified studies o f not only atmosphere and water but also soil. In this study, a direct emission spectrographic method is described for the determination o f Ba, Co, Cr, Cu, Mn, Ni, Pb, V and Zn in soil samples. There are a few direct spectro- graphic methods [5, 6, 8, 10] where some of these above elements have been analysed in soils. Other methods [1, 2, 7, 9] are also given literature, but adequate details are not available. Cruft [3] has used the Stal lwood jet with argon-oxygen mixture to improve the sensitivity for some of the above elements. In the present method, the d. c. arc in air is used for excitation and the desired limits o f determination are reached.

2. Experimental

2.1. Summary of the Method. The soil sample, free from organic matter, is thoroughly mixed with graphite-internal standard mixture in the ratio 1 : 5 by weight and 40 mg of the mixture is loaded in UCC 1989 type preformed electrode. The sample is excited in a d.c. arc at 15 A and the resulting spectra are recorded on SA-1 photographic plates employing a 3.4 m Jarrel-Ash grating spectrograph. The optical densities of the analysis lines are measured and intensity ratios obtained using standard procedures. The elemental concentrations are found from these intensity ratios using working curves.

2.2. Preparation o f Base Mixture. The constituents which occur in soils at 1% level or above seldom vary for more than five-fold from soil to soil, while trace constituents vary by a factor of 1000 in different soils. Therefore, to match with the average composition of soil, a base mixture was prepared using different major element compounds of Analar grade purity: 61.5 % SiOz, 20 % A1203, 5 % F%O3, 3.5% CaCO3, 2% MgO, 3.5% Na2CO 3, 3.5% K2CO 3 and 1% TiO2. This mixture is ground in an agate mortar and sintered for 24h at 900~ in a muffle furnace. After sintering, the base material becomes very hard. It is again ground in an agate mortar to 100 mesh size.

2.3. Preparation of Standards. Using the above base mixture, a master standard is prepared by dry-mixing spec-pure compounds of the

0016-1152/80/0302/0278/$01.00

V. P. Bellary and Y. A. Sarma: Spectrographic Analysis of Trace Elements in Soil Samples 279

Table 1. Experimental parameters

Lower electrode : Upper electrode:

Charge : Spectrograph:

Grating :

Wavelength range:

Reciprocal linear dispersion:

Slit width: Optical system:

Excitation source: Voltage : Current: Analytical gap: Diaphragm:

Emulsion: Exposure: Emulsion calibration:

Photographic processing:

Microphotometer: Calculator:

Anode UCC 1/4" neck type, 1989 Cathode UCC 1/8" graphite rod, ta- pered to a point 40 mg 3.4m Jarrell-Ash grating spectro- graph in Ebert mount 30,000 lines/inch plane grating blazed at 3300 A in the first order 2280 ~ to 3480 ~ in the first order recorded on two plates

2.5 A/mm 10 pm Image of the arc focussed on the slit using a cylindrical lens of 10 cm focal length Jarrell-Ash Custom Vari Source 230 V 15 A d.c. 3 mm An aperture at mirror to cut off glowing electrode tips Kodak Spectrum Analysis SA-I 15s Rotating sector having eight steps with a log ratio of 0.2 between two consecutive steps

Developed in Kodak D-19 developer for 3 rain at 20~ and fixed in F-5 fixer for 10min, washed in distilled water and dried Hilger, non-recording Respectra calculator (Dennert and Pepe, Federal Republic of Germany)

Table 2. Analysis lines

Element Analysis line Int. Std. line Determination Std. (/~) (A) range Dev.

(ppm) Z

Ba 2335.27 Sn 2785.03 4 0 - 800 12 Co 2521.36 Sn 2785.03 5 - 500 15 Pb 2663.17 Sn 2785.03 1 0 - 500 8 Mn 2799.84 Sn 2785.03 40--2000 8 Cu 2824.44 Sn 2785.03 4 0 - 2000 10 Cr 3014.92 Pd 2922.49 5 - 500 13 Ni 3050.82 Pd 2922.49 15 500 10 V 3183.41 Pd 2922.49 5 - 500 9 Zn 3345.02 Pd 2922.49 40-2000 12

elements of interest. The successive step dilution with base mixture gives a set of standards. The concentration values are 5, 10, 20, 50, 100, 200 and 500 ppm for Co, Cr, Ni, Pb and V; and 20, 40, 80, 200, 400, 800 and 2000 ppm for Ba, Cu, Mn and Zn. Pd is used as an internal standard for Cr, Ni, V and Zn; and Sn is used as an internal standard for Ba, Co, Cu, Mn and Pb. The required amounts of Pd and SnO 2 are mixed with spec-pure graphite powder to get Pd and SnO/

10.C

O <~1C 0s

Z kH

~_ 01

C o CF ~-nMn

Ni P d / n ~-n ~ - / o / /o

o.ol ~ lb lbo ]o'oo ~ooo CONCENTRATION IN PPM

Fig. 1. Working curves for Ni, Cr, Co, Mn and Zn in Soil. (10 ppm residual correction applied to Ni)

10,0

(2_ <~1.0 CK

>-

Z LU

z_ o,7

0.0"

Pb V - -

- - Sn Cu a "

lb l&0 1060 2'00o CONCENTRATION IN PPM

Fig. 2. Working curves for V, Pb, Ba and Cu in Soil

at 500 ppm concentration of each. Finally, all the standards are mixed with graphite-internal standard mixture in the ratio 1 : 5.

2.4. Preparation of Samples. One gram of soil sample is dried in the oven at I05~ and then ignited in a furnace at 450~ for I h to destroy most of the organic matter. The percentage reduction in weight is noted for correction of analytical values which are reported on sample basis. After furnace heating, the sample is ground and mixed thoroughly in an agate mortar with graphite-internal standard mixture (0.05 ~ Pd and 0.05 % SnO2 on graphite) in the ratio 1:5.

2.5. Choice of Carriers and Buffers. To improve the detection limits of the elements in soil, different carriers like NazCO 3 at 2 %; NaF at 1 ~ ; AgCI, Ge metal and Sb20 3 at 6 and 12 % were tried, but suitable carrier action was not found. Since the base composition of soil is very complex and varies considerably from soil to soil, graphite as a buffer-diluent is necessary to reduce effects due to matrix variation on the analysis. Soil base with graphite mixed in the ratio of 3 : 2 to 1 : 8 were tried. Different mixing ratios were not having marked differ- ences on the sensitivity of trace elements. Therefore, the ratio 1 : 5 is selected to have sufficient dilution of the sample without undue loss of sensitivity.

280 Fresenius Z. Anal. Chem., Band 302 (1980)

Table 3. Results of USGS: AGV-1 and GSP-1 samples

Element AGV-I GSP-I

Recom- Values Recom- Values mended determined mended determined values [41 by us values [4] by us

Values in ppm on sample basis

Ba 1208.0 1270.0 1300.0 1000.0 Co 14.1 10.5 6.4 7.0 Cr 12.2 12.8 12.5 19.5 Cu 59.7 53.0 33.3 39.0 Mn 763.0 760.0 331.0 275.0 Ni 18.5 19.5 12.5 12.6 Pb 35.1 46.0 51.3 67.0

3. Discussion

3.1. Experimental Parameters. The optimized experi- mental parameters are given in Table 1.

3.2. Selection of Analysis Lines. Analysis lines used are free from interference from emission lines of other expected elements and molecular b a n d components like SiO. In the case of nickel, a b lank correction of 10 ppm was found necessary. The list of the analysis lines and de terminat ion range is given in Table 2. The typical working curves drawn on log-log scale are shown in Figs. 1 and 2.

3.3. Precision and Accuracy. The precision of the method has been assessed by calculating the coefficient of var ia t ion from 12 determinat ions from spectra taken on six plates. The average percent s tandard deviat ion for each element is tabula ted in the last co lumn of Table 2. To assess the accuracy of the method, USGS standards AGV-1 and GSP-I were analysed for the elements Ba, Co, Cr, Cu, Mn, Ni and Pb and the results are given in Table 3.

Acknowledgement. The authors are grateful to Dr. N. A. Narasimham, Head, Spectroscopy Division for his keen interest and to Dr. P. S. Murty and Dr. R. M. Dixit for useful discussions.

References

1. Belitsina, G. D., Zyrin, N. G.: Tr. Vtorogo Mezhvux. Sovesch. Po Mikroelementum 1961, 285-92.

2. Chesnokov, O. F. : Spektrosk. Tr. Sob. Sovesch. 4th, 1965 (Publ. 1969), 297-8.

3. Cruft, E. F.: Econ. Geology 49, 458 (1964) 4. Flanagan, F. J. : Geochim. Cosmochim. Acta 37, 1189 (1973) 5. Glinski, J. : Trans. 8th Int_ Cong. Soil. Sci. Bucharest, 1964, 3,

19-24 (PUN. 1967). 6. Kashun, S.M.: Biol. Zh. Arm. 22, 115 (1969) 7. Kvetkina, A. A., Shlavitskaya, Z. I. : Tr. Inst. Poehvoved., Akad.

Nauk Kaz. SSR 14, 188 (1963) 8. MacLean, K. S., Byers, D. L., Brown, M. H. : Anal. Chem. 50,

1366 (1967) 9. Michajluk, L., Borowiez, A.: Rocz. Glebozn. 18, 19 (1967)

10. Seeley, J. L., Dick, D., Arvik, J. H., ZimdahI, R. L., Skogerboe, R. K. : Appl. Spectrosc. 26, 456 (1972)

Received January 11, 1980