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The selenium content of U.S.G.S. standard rocks
Chemical Geology, 12 (1973) 77-80 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
Short Communication THE SELENIUM CONTENT OF U.S.G.S. STANDARD ROCKS*
M.M. SCHNEPFE and F.J. FLANAGAN U.S. Geological Survey, Washington, D. C. (U.S.A.)
(Accepted for publication July 10, 1973)
ABSTRACT Schnepfe, M.M. and Flanagan, F.J., 1973. The selenium content of U.S.G.S. standard rocks. Chem. Geol., 12: 77-80. Selenium was determined in duplicate portions from three bottles of six U.S.G.S. standard rocks by a spectrofluorimetric procedure. The following averages, as p.p.m. Se, were obtained: PCC-1, 0.031; GSP-1, 0.088; BCR-1, 0.12; SCo-1, 0.91 ; MAG-1, 1.3; and SGR-I, 3.7. One-way analysis of variance of the several sets of data showed no significant differences in the selenium content among bottles of any specific rock; these samples may be accepted as homogeneous for their selenium contents by this analytical method. METHOD, RESULTS AND DISCUSSION As part of a program t o acquire data on standard samples and to determine if selenium is distributed homogeneously among the samples, the selenium contents of six U.S.G.S. standards have been determined by a spectrofluorimetric procedure (Schnepfe, unpublished method, 1973). Three rock standards, GSP-1 (granodiorite), PCC-1 (peridotite), and BCR-1 (Columbia River Basalt), have been described previously and analytical data have been compiled (Flanagan, 1967, 1969). Two other samples, MAG-1, a marine mud from the Gulf of Maine, and SCo-1, a portion of the Cody Shale from Wyoming, have been described and some analytical data have been reported (Flanagan, 1973). The sixth sample, SGR-1, a portion of the Green River Formation, has been released without a descriptive paper, but some data are available (Flanagan, 1973). The analytical procedure involves an alkaline sintering o f a 1.0-g sample and the subsequent aqueous leaching o f the sinter. The selenium in the leachate is isolated by coprecipitation with tellurium. After dissolution of the s e l e n i u m - t e l l u r i u m precipitate, the selenium is reacted with 2,3-diaminonaphthalene to form 4,5-benzopiazselenol which is extracted into cyclohexane. The fluorescence of the cyclohexane extract is then measured, and the selenium content is calculated from a calibration line. The line is made by measuring the fluorescence o f known amounts of selenium which are coprecipitated with
*Publication authorized by the Director, U.S. Geological Survey.
78
M.M. SCHNEPFE AND F.J. FLANAGAN
TABLE I Determinations, conclusions from the analysis of variance, and summary of estimates of the selenium content of U.S.G.S. ~mples (p.p.m.)* Sample
PCC-1
GSP-1
BCR-1
SCo-I
MAG-1
SGR-1
Bottle
1 2 3 1 2 3 I 2 3 1 2 3 1 2 3 1 2 3
Se
Mean
a
b
0.034 0.035 0.034 0.090 0.079 0.089 0.120 0.120 0.110 1.04 0.93 0.89 1.29 1.36 1.30 3.75 3.70 3.30
0.034 0.020 0.029 0.072 0.100 0.100 0.120 0130 0.110 0.88 0.90 0.80 1.28 1.30 1.32 3.80 3.60 4.00
Stand. Dev.
C.V. error C:~)
Concl. (/~,. ~s)
bottles (2 d.f.)
error (3 d.f.)
0.031
neg.
0.006
19.4
n.s.
0.088
neg.
0.012
13.6
n.s.
0.118
0.007
0.004
3.4
n.s.
0.907
0.022
0.076
8.4
n.s.
1.308
0.013
0.026
2.0
n.s.
3.69
neg.
0.289
7.8
n.s.
*Stand. Dev. = standard deviation; d.f. = degrees of freedom; C.V. = coefficient of variation; Concl. = conclusion from the analysis of variance; neg. indicates a negative bottle variance that results when the mean sum of squares for within bottles is larger than that for between bottles; n.s. = not significant.
t e l l u r i u m a n d carried t h r o u g h t h e same p r o c e d u r e used for t h e samples. One h u n d r e d t h o f a m i c r o g r a m o f s e l e n i u m in pure s o l u t i o n is d e t e r m i n a b l e w i t h i n a relative s t a n d a r d d e v i a t i o n o f 25%, t h u s s e t t i n g t h e d e t e r m i n a t i o n limit at a p p r o x i m a t e l y 0.01 p.p.m. Se in a 1.0-g sample. W h e n t h e a m o u n t o f s e l e n i u m is greater t h a n 0.1 /Jg, a relative s t a n d a r d d e v i a t i o n o f 10% or less m a y be e x p e c t e d . A simple e x p e r i m e n t a l design w i t h a single variable o f classification (McNeal et al., 1 9 7 2 : F l a n a g a n , 1 9 7 3 ) was used t o e s t i m a t e t h e s e l e n i u m c o n t e n t s a n d t o d e t e r m i n e if s e l e n i u m is h o m o g e n e o u s l y d i s t r i b u t e d a m o n g b o t t l e s of samples. T h e design allows us t o e s t i m a t e a b e t w e e n - b o t t l e s t a n d a r d d e v i a t i o n in a b o u t h a l f of t h e tests, a n d t o e s t i m a t e a n a n a l y t i c a l error w h i c h m a y also include some s a m p l i n g a n d some r a n d o m errors. The usual h y p o t h e s i s , t h a t s e l e n i u m is d i s t r i b u t e d h e t e r o g e n e o u s l y a m o n g t h e b o t t l e s , was assumed. D u p l i c a t e 1.0-g p o r t i o n s were weighed f r o m e a c h o f t h r e e r a n d o m l y selected b o t t l e s o f t h e several s t a n d a r d s : t h e s e p o r t i o n s were r a n d o m l y o r d e r e d , a n d t h e s e l e n i u m c o n t e n t s were d e t e r m i n e d . T h e data, c o n c l u s i o n s f r o m t h e analysis o f variance, a n d a s u m m a r y o f the e s t i m a t e s are given in T a b l e I. Averages in this t a b l e are listed w i t h t h r e e significant figures a l t h o u g h
THE SELENIUM CONTENT OF U.S.G.S. STANDARD ROCKS
79
the analytical precision (the square root of the mean sum of squares for within bottles) may indicate that only two figures are justifiable. The analyses of variance for the several sets of data show that the mean sum of squares for the variation attributable to bottle means is not significantly greater (Fo.9s) than that for within b o t t l e s We must therefore reject our hypothesis that the selenium content differs among bottles, and we may consider the bottles of samples to be homogeneous for Se by this method. The coefficients of variation in the table generally decrease as the amount of the element determined increases. The coefficients for the two shales, SCo-1 and SGR-I, are exceptions to this trend, but it is not believed that these large coefficients are due to interferences from the relatively high organic content o f these samples, as the marine mud, MAG-1, has a low coefficient of variation although it contains almost 2% organic matter. Our averages for GSP-I, PCC-1, and BCR-1 agree reasonably with, but are higher than, selenium data first published by Brunfelt and Steinnes (1967). Laul et al. (1970) gave an upper limit of 0.04 p.p.m, for the Se content of GSP-1, whereas Brunfelt and Steinnes found 0.059 p.p.m. In contrast, Laul et al. gave only an upper limit o f 0 . 1 8 p.p.m, for PCC-1, a factor of six or more higher than values of 0.022 p.p.m, by Brunfelt and Steinnes and of 0.031 p.p.m, in the present study. The recent compilation of data (Flanagan, 1973) contains five quantitative averages, ranging from 0.092 to 0.121 p.p.m., for the Se content of BCR-1. If we form a confidence interval by using the average of our six determinations and one bottle standard deviation, the inequality thus obtained, 0.115 < 0.118 < 0.121, includes the averages of 0.121 p.p.m. reported by Brunfelt and Steinnes (1971) and of 0.116 p.p.m, by Brunfelt et al. (1971 ). If we expand the confidence interval by using two bottle standard deviations rather than one, the resulting interval, 0 . 1 1 2 - 0 . 1 2 4 , does not include the mean of 0.105 p.p.m. reported by Allen et al. (1970). Because of the close agreement of the three averages in the inequality formed with one standard deviation, our estimate of 0.118 p.p.m. Se may be considered as the best value for BCR-1. If we may assume that whatever accuracy contained in the data for BCR-1 is also applicable for the remaining samples, a reasonable assumption as the entire set of 36 determinations was randomized, our averages for the remaining samples in Table I may also be considered as best values.
REFERENCES Allen, R.O., Haskin, L.A., Anderson, M.R. and Muller, O., 1970. Neutron activation analysis for 39 elements in small or precious geologic samples. J. Radioanal. Chern., 6:115-137. Brunfelt, A.O. and Steinnes, E., 1967. Determination of selenium in standard rocks by neutron activation analysis. Geochim. Cosmochim. Acta, 31: 283-285. Brunfelt, A.O. and Steinnes, E., 1971. A neutron activation scheme developed for the determinations of 42 elements in lunar material. Talanta, 18:1197-1208. Brunfelt, A.O., Heier, K.S. and St einnes, E., 1971. Determination of 40 elements in Apollo 12 materials by neutron activation analysis. Proc. Lunar Sci. Conf., 2nd, Geochim. Coxmochim. A cta, Suppl. No.2, 2:1281-1290.
80
M.M. SCHNEPFE AND F.J. FLANAGAN
Flanagan, F.J., 1967. U.S. Geological Survey silicate rock standards. Geochim. Cosmochim. Acta, 31: 289-308. Flanagan, F.J., 1969. U.S. Geological Survey standards, 2. First compilation of data for the new U.S.G.S. rocks. C,eoehim. Cosmochim. Acta, 33: 81-120. Flanagan, F.J. (Compiler and Editor), 1973. Descriptions and analyses of seven new U.S.G.S. rock standards. U.S. Geol. Surv. Prof. Pap., No.840, in press. Laul, J.C., Case, D.R., Wechter, M., Schmidt-Bleek,~F. and Lipschutz, M.E., 1970. An activation analysis technique for determining groups of trace elements in rocks and chondrites. J. Radioanal. Chem., 4: 241-264. McNeal, J.M., Suhr, N.H. and Rose, A.W., 1972. Inhomogeneity of mercury in the U.S.G.S. rock standards. Chem. Geol., 10: 307-311.
Short Communication THE SELENIUM CONTENT OF U.S.G.S. STANDARD ROCKS*
M.M. SCHNEPFE and F.J. FLANAGAN U.S. Geological Survey, Washington, D. C. (U.S.A.)
(Accepted for publication July 10, 1973)
ABSTRACT Schnepfe, M.M. and Flanagan, F.J., 1973. The selenium content of U.S.G.S. standard rocks. Chem. Geol., 12: 77-80. Selenium was determined in duplicate portions from three bottles of six U.S.G.S. standard rocks by a spectrofluorimetric procedure. The following averages, as p.p.m. Se, were obtained: PCC-1, 0.031; GSP-1, 0.088; BCR-1, 0.12; SCo-1, 0.91 ; MAG-1, 1.3; and SGR-I, 3.7. One-way analysis of variance of the several sets of data showed no significant differences in the selenium content among bottles of any specific rock; these samples may be accepted as homogeneous for their selenium contents by this analytical method. METHOD, RESULTS AND DISCUSSION As part of a program t o acquire data on standard samples and to determine if selenium is distributed homogeneously among the samples, the selenium contents of six U.S.G.S. standards have been determined by a spectrofluorimetric procedure (Schnepfe, unpublished method, 1973). Three rock standards, GSP-1 (granodiorite), PCC-1 (peridotite), and BCR-1 (Columbia River Basalt), have been described previously and analytical data have been compiled (Flanagan, 1967, 1969). Two other samples, MAG-1, a marine mud from the Gulf of Maine, and SCo-1, a portion of the Cody Shale from Wyoming, have been described and some analytical data have been reported (Flanagan, 1973). The sixth sample, SGR-1, a portion of the Green River Formation, has been released without a descriptive paper, but some data are available (Flanagan, 1973). The analytical procedure involves an alkaline sintering o f a 1.0-g sample and the subsequent aqueous leaching o f the sinter. The selenium in the leachate is isolated by coprecipitation with tellurium. After dissolution of the s e l e n i u m - t e l l u r i u m precipitate, the selenium is reacted with 2,3-diaminonaphthalene to form 4,5-benzopiazselenol which is extracted into cyclohexane. The fluorescence of the cyclohexane extract is then measured, and the selenium content is calculated from a calibration line. The line is made by measuring the fluorescence o f known amounts of selenium which are coprecipitated with
*Publication authorized by the Director, U.S. Geological Survey.
78
M.M. SCHNEPFE AND F.J. FLANAGAN
TABLE I Determinations, conclusions from the analysis of variance, and summary of estimates of the selenium content of U.S.G.S. ~mples (p.p.m.)* Sample
PCC-1
GSP-1
BCR-1
SCo-I
MAG-1
SGR-1
Bottle
1 2 3 1 2 3 I 2 3 1 2 3 1 2 3 1 2 3
Se
Mean
a
b
0.034 0.035 0.034 0.090 0.079 0.089 0.120 0.120 0.110 1.04 0.93 0.89 1.29 1.36 1.30 3.75 3.70 3.30
0.034 0.020 0.029 0.072 0.100 0.100 0.120 0130 0.110 0.88 0.90 0.80 1.28 1.30 1.32 3.80 3.60 4.00
Stand. Dev.
C.V. error C:~)
Concl. (/~,. ~s)
bottles (2 d.f.)
error (3 d.f.)
0.031
neg.
0.006
19.4
n.s.
0.088
neg.
0.012
13.6
n.s.
0.118
0.007
0.004
3.4
n.s.
0.907
0.022
0.076
8.4
n.s.
1.308
0.013
0.026
2.0
n.s.
3.69
neg.
0.289
7.8
n.s.
*Stand. Dev. = standard deviation; d.f. = degrees of freedom; C.V. = coefficient of variation; Concl. = conclusion from the analysis of variance; neg. indicates a negative bottle variance that results when the mean sum of squares for within bottles is larger than that for between bottles; n.s. = not significant.
t e l l u r i u m a n d carried t h r o u g h t h e same p r o c e d u r e used for t h e samples. One h u n d r e d t h o f a m i c r o g r a m o f s e l e n i u m in pure s o l u t i o n is d e t e r m i n a b l e w i t h i n a relative s t a n d a r d d e v i a t i o n o f 25%, t h u s s e t t i n g t h e d e t e r m i n a t i o n limit at a p p r o x i m a t e l y 0.01 p.p.m. Se in a 1.0-g sample. W h e n t h e a m o u n t o f s e l e n i u m is greater t h a n 0.1 /Jg, a relative s t a n d a r d d e v i a t i o n o f 10% or less m a y be e x p e c t e d . A simple e x p e r i m e n t a l design w i t h a single variable o f classification (McNeal et al., 1 9 7 2 : F l a n a g a n , 1 9 7 3 ) was used t o e s t i m a t e t h e s e l e n i u m c o n t e n t s a n d t o d e t e r m i n e if s e l e n i u m is h o m o g e n e o u s l y d i s t r i b u t e d a m o n g b o t t l e s of samples. T h e design allows us t o e s t i m a t e a b e t w e e n - b o t t l e s t a n d a r d d e v i a t i o n in a b o u t h a l f of t h e tests, a n d t o e s t i m a t e a n a n a l y t i c a l error w h i c h m a y also include some s a m p l i n g a n d some r a n d o m errors. The usual h y p o t h e s i s , t h a t s e l e n i u m is d i s t r i b u t e d h e t e r o g e n e o u s l y a m o n g t h e b o t t l e s , was assumed. D u p l i c a t e 1.0-g p o r t i o n s were weighed f r o m e a c h o f t h r e e r a n d o m l y selected b o t t l e s o f t h e several s t a n d a r d s : t h e s e p o r t i o n s were r a n d o m l y o r d e r e d , a n d t h e s e l e n i u m c o n t e n t s were d e t e r m i n e d . T h e data, c o n c l u s i o n s f r o m t h e analysis o f variance, a n d a s u m m a r y o f the e s t i m a t e s are given in T a b l e I. Averages in this t a b l e are listed w i t h t h r e e significant figures a l t h o u g h
THE SELENIUM CONTENT OF U.S.G.S. STANDARD ROCKS
79
the analytical precision (the square root of the mean sum of squares for within bottles) may indicate that only two figures are justifiable. The analyses of variance for the several sets of data show that the mean sum of squares for the variation attributable to bottle means is not significantly greater (Fo.9s) than that for within b o t t l e s We must therefore reject our hypothesis that the selenium content differs among bottles, and we may consider the bottles of samples to be homogeneous for Se by this method. The coefficients of variation in the table generally decrease as the amount of the element determined increases. The coefficients for the two shales, SCo-1 and SGR-I, are exceptions to this trend, but it is not believed that these large coefficients are due to interferences from the relatively high organic content o f these samples, as the marine mud, MAG-1, has a low coefficient of variation although it contains almost 2% organic matter. Our averages for GSP-I, PCC-1, and BCR-1 agree reasonably with, but are higher than, selenium data first published by Brunfelt and Steinnes (1967). Laul et al. (1970) gave an upper limit of 0.04 p.p.m, for the Se content of GSP-1, whereas Brunfelt and Steinnes found 0.059 p.p.m. In contrast, Laul et al. gave only an upper limit o f 0 . 1 8 p.p.m, for PCC-1, a factor of six or more higher than values of 0.022 p.p.m, by Brunfelt and Steinnes and of 0.031 p.p.m, in the present study. The recent compilation of data (Flanagan, 1973) contains five quantitative averages, ranging from 0.092 to 0.121 p.p.m., for the Se content of BCR-1. If we form a confidence interval by using the average of our six determinations and one bottle standard deviation, the inequality thus obtained, 0.115 < 0.118 < 0.121, includes the averages of 0.121 p.p.m. reported by Brunfelt and Steinnes (1971) and of 0.116 p.p.m, by Brunfelt et al. (1971 ). If we expand the confidence interval by using two bottle standard deviations rather than one, the resulting interval, 0 . 1 1 2 - 0 . 1 2 4 , does not include the mean of 0.105 p.p.m. reported by Allen et al. (1970). Because of the close agreement of the three averages in the inequality formed with one standard deviation, our estimate of 0.118 p.p.m. Se may be considered as the best value for BCR-1. If we may assume that whatever accuracy contained in the data for BCR-1 is also applicable for the remaining samples, a reasonable assumption as the entire set of 36 determinations was randomized, our averages for the remaining samples in Table I may also be considered as best values.
REFERENCES Allen, R.O., Haskin, L.A., Anderson, M.R. and Muller, O., 1970. Neutron activation analysis for 39 elements in small or precious geologic samples. J. Radioanal. Chern., 6:115-137. Brunfelt, A.O. and Steinnes, E., 1967. Determination of selenium in standard rocks by neutron activation analysis. Geochim. Cosmochim. Acta, 31: 283-285. Brunfelt, A.O. and Steinnes, E., 1971. A neutron activation scheme developed for the determinations of 42 elements in lunar material. Talanta, 18:1197-1208. Brunfelt, A.O., Heier, K.S. and St einnes, E., 1971. Determination of 40 elements in Apollo 12 materials by neutron activation analysis. Proc. Lunar Sci. Conf., 2nd, Geochim. Coxmochim. A cta, Suppl. No.2, 2:1281-1290.
80
M.M. SCHNEPFE AND F.J. FLANAGAN
Flanagan, F.J., 1967. U.S. Geological Survey silicate rock standards. Geochim. Cosmochim. Acta, 31: 289-308. Flanagan, F.J., 1969. U.S. Geological Survey standards, 2. First compilation of data for the new U.S.G.S. rocks. C,eoehim. Cosmochim. Acta, 33: 81-120. Flanagan, F.J. (Compiler and Editor), 1973. Descriptions and analyses of seven new U.S.G.S. rock standards. U.S. Geol. Surv. Prof. Pap., No.840, in press. Laul, J.C., Case, D.R., Wechter, M., Schmidt-Bleek,~F. and Lipschutz, M.E., 1970. An activation analysis technique for determining groups of trace elements in rocks and chondrites. J. Radioanal. Chem., 4: 241-264. McNeal, J.M., Suhr, N.H. and Rose, A.W., 1972. Inhomogeneity of mercury in the U.S.G.S. rock standards. Chem. Geol., 10: 307-311.