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The analysis of silver by x-ray fluorescence spectrometry
Analytica
Chimica Acta,
97 (1978)
275-281
OE;lsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
THE ANALYSIS OF SILVER BY X-RAY SPECTROMETRY
F. T. WYBENGA
FLUORESCENCE
and L. R P. BUTLER*
National Physical Research Laboratory, P-0. Box 395, Pretoria (South Africa)
Council for Scientific
and Industrial
Research,
(Received 4th October 1977)
An x-ray fluorescence method is described for the analysis of silver alloys. The major e!ement silver as we!1 as the impurities are determined. Corrections are made for interelement. and line overlap effects. The results obtained compare favourably with wet chemical and emission spectrometric values. The method is rapid and reliable.
The value of silver has increased significantly in recent years, because of its increasingly wide usage and its relative scarcity. As with the precious metals, its assay, with regard both to purity and to the type and concen-
trations of impurity elements, requires the highest degree of accuracy and precision. Assay methods based on gravimetric techniques meet these requirements, but a total chemical analysis demands several techniques and is accordingly time-consuming, especially when the precious metals need to be determined. X-ray fluorescence spectroscopy is well known for its high degree of precision
and this, together with the fact that the method is non-destructive, suggested its use for the rapid analysis of silver alloys. Various alloys of silver, where the impurities included precious metals and totalled between 1 and 5%, were obtained. A method of analysis was developed which enabled the silver and other elements to be determined with a high degree of accuracy and precision. Line overlap and interelement effects
were present at the levels of impurities in the samples, and the correction methods of Lucas-Tooth and Pyne [ 11, Stephenson [ 21 and Kodama et al. [3] had to be applied. This paper describes the method and presents the results obtained on the range of alloys available. EXPERIMENTAL
Sample
prepamtion
The silver samples were prepared by melting in graphite crucibles at llOO°C in an induction furnace. They were vertically cast in a special mould (Fig. 1)
276 .
Fig. 1. Mould used for casting silversamples. to obtain discs of 40-mm diameter and Y-mm thickness. This procedure ensured that all samples were treated in the same way, thus removing the possibility that metallurgical history would affect results. It was established by means of a scanning electron microscope that these samples were homogeneous_ Smoothing of the surfaces of the sample was done on a water-covered surfacing disc with 180 and then 800 silicon carbide paper.
Appcra tus A Philips PW 122OC sequential x-ray fluorescence spectrometer with a molybdenum anode tube was used for all the measurements_ An 8K Honeywell computer was coupled to this instrument and was used to control the spectrometer as well as the automatic sample changer.
Selection of instrumental conditions Preliminary wavelength scans of some of the samples were made to establish optimum conditions (Fig. 2). LiF (200) as well as LiF (220) crystals were tried as analysing crystals. The resolution of the instrument was improved by
Fig. 2. Typical spectrum of silver sample. Sample S-11. Analysing crystal, MO anode, 80 kV, 50 mk Full scale, 4000 cps. x Spurious reflections_
LiF (220).
277 introducing an additional auxiliary soller collimator (150~,em spacing, 100 mm long) in front of ihe scintillation detector. Tine following results were obtained in these experiments. (i) Tine Pd KY and Ag &Y lines were inadequately separated with the LiF (200) crystal and the auxiliary collimator_ The LiF (220) crystal was therefore used. The loss in intensity was approximately 30% (ii) The LiF (200) analysing crystal gave adequate resolution for the separation of the Au La and Pt La lines, with the auxiliary colhmator. (iii) Spurious reflections do occur with the LiF (220) crystal, but fortunately not in positions where they affect the measurements. (iv) By using the long auxiliary collimator, the intensity is reduced by a factor of six for the Ag KCY and Pd KCY lines. This is not serious as adequate intensity is available for:these lines. The experimental conditions for individual elements are given in Table 1. All measurements were done in air with a fine primary soiler collimator (150~pm spacing), an auxiliary soller collimator in front of the detector (15O+m spacing, 100 mm long) and a scintillation detector_ Samples were loaded into the spectrometer by means of a sample changer controlled by the computer_
Correction procedure One in every four measurements was done on a single reference standard and all values were ratioed to these reference measurements to enable corr-
ection
for possible
by direct
drift. -Ail measurements
subtraction
dead-time
of a measurement
were corrected
for background
taken close to the peak and also for
losses.
TABLE1 Measuring Element
conditions line
Ag Km Background Pd Ka Background MO KCY Mo I& (Compton) Au La Background Pt La Background cu Klx Background Pb La Background Bi Lp Background
crystal
O2e
kV
mA
Counting
La? (220)
22.72 18.00 23.79 18.00 28.87 30.00 36.97 35.80 38.05 39.50
60 60 80 80 80 80 80 80 80 80
20 20 30 30 30 30 30 30 30 30
100 100 100 100 100 100 100 100 200 200
45.03
80
30
100
47.00 33.92 35.80 39.06 42.00
80 80 80 80 80
30 30 30 30 30
100 200 200 100 100
LiF LiF LiF LiF LiF LiF LIF LiF LiF LiF LiF LiF LiF LiF LiF
!220: (220) (220) (200) (200) (200) (200) (200) (200) (ZOO) (200) (200) (200) (220) (220)
time (s)
278
The equation used in the correction procedure is ci = Ao -I- AiRi + 2 AjRj + 5 14, RiRj j=l i= 1
whereCi is the concentration, and Ri is the intensity of the analytical element; Rf is the intensity of the interfering element: and Ao, A,,.A, and A, are constants. This equation differs from the normal Lucas-Tooth equation [I] in that the term AjRi isintroduced to correct for line overlap and po&ziblebackground effects. In the ideal case where no interference is present, the last two terms in the equation fall away. Under normal circumstances only some of the elements in a specific matrix have an appreciable effect on the determination of a concentration. The stepwise muhiregressional program [4] suggested by Stephenson [Z] was used to establish the regression constants. In this program it is possible to specify F-levels for the inclusion or deletion of variates. Non-significant variates are not inch~ded in the model_ A practical F-level is determined by the degrees of freedom. In the case of these analyses the F-level for inch&on and deletion was chosen as 2.0. The exact forms of the regression formulae had to be determined before any analyses were attempted. A number of standards had therefore to be ’ measured for ah the elements of interest mder the conditions given in Table 1. The regression equations given in Table 2 were obtained following the multiple regression method described. TABLE
2
Regressionequations &
C=36.30043RAg-1.82587 RAfo-0.66108RcuRA, i 62.60551
0.57374 RAu-
Standarderrorofestir;late= O.O773;r= AU
0.22638&
0.9982.
0.03075 R,0.60284 Rnlo i 0.04073 Rp, 0.63012 Standarderrorofestimate= 0.0052;r= 1.0000. C
=
2.88256 R,,
-
i- 0.07722 RX,+
cu
C= 1.256X&,-00.?04967&-00.09904 Standarderrorofestimate= O.O309;r= 0.9984.
Pd
C=0.80353Rpd-O.O0341Rpt-0.01062 Rpb+ 0.03386 RF,., x Rpd - 0.09389 Standard errorofestimate= O.OOlO;r= 0.9999.
Pt
C=O.10894 RPt-0.000129RAU i- 0.01041EC,+ Standarderrorofestimate= 0.0007;r=0.9998.
0.45910 R_+ X Rpd
0.000989 Rp,x
I&.,--
0.0155E
9 10 11 13 10 17 18 19 20 21 22 23 27 31 3G
I
Snmpll!
98.76 98.77 98.78 08.08 08.03 D8.54 08.01 9G.Gl 98.71 D8.GG 98.74 06.10 9G.09 96.23 DO.90 96.96 96.75 90.70 9G.G7 97.G4 97.37 97.40 96.98 07.03 0'7.14 97.18 07.10 OB.GO !lG.GG 06.136 9847 96.Gtj 94.9G DG.02 95.03 OG.33 06.41 96.69 96.73 9G.GO 06.20 9G.09 9G.06
0.019 0.192 O.lB4 0.081 2.644 2.109 1.495 1.743 29Gl 3.GO 0.806 0.908
0.023 0.193 0.151 0.08G 2691 2.025 21Gl 1.G29 1.846 1.073 2.024 2.884 3.48 2521 0.890 0.903
G.d.
Chcm
X.r.f.
Chem
G-d.
Gold (lb)
Silver (‘lo)
Aualylicnl results
TABLE 3
0.020 O.lDl O.lG3 0.083 2.GG2 1.070 2.106 1.499 1.7G2 1.735 1.773 2.97 3.687 2G4G 0.896 0.909
X.&f. 1.21 1.14 1.19 1.20 1.11 0.95 1.03 0.05 0.96 0.94 1.03 1.11 1.07 0.99 2.09 2.62
1.18 1.17 1.21 1.23 1.06 0.02 0.97 0.04 0.9G 0.03 1.17 1.18 LOG 1.00 1.99 2.G7
1.20 L17 1.20 1.18 1.08 0.98 1.02 0.84 0.98 0.94 1.03 1.10 1.12 0,97 2007 2067
0.001 0.0100 0.0136 0.0068 0.034 0.03B 0.039 0.043 0.077 0.088 0.113 0.238 0.22G 0.026 0.013 0.026 0.0108 0.0151 0.0072 0.037 0.037 0.042 O.OGl o.oaz O.OBG 0.118 0.240 0.216 0.027 0.012 0.022
G.d.
Pallndium (%)
Chem G.d. X.r.1. Chem
Copper(%)
0.009G 0.0146 0,0073 0.036 0.033 0.041 0,046 0.078 0.000 0.112 0.238 0.228 0.02G 0.013 0.026
X.r.f.
G 30 95 24 130 290 330 430 GGO GGO 98G 870 700 90 17 26
Chcm
26 94 23 127 202 326 482 cIG8 541 983 8OG GO6 15 18 19
GA.
27 92 21 144 287 322 440 GG3 842 982 871 700 78 -
X.cf.
Pliitinum (1w.m.)
280 RESULTS
Accuracy Standard values (them), glow discharge values (g-d.) and x-r-f. values are cold, copper, palladium and platinum in compared for the efements, silver, D Table 3. The chemical values were used in the multiple regression analysis. The accuracy of the method depends largely on the accuracy of the chemical values. Good agreement is found for ah the elements. The x.r_f_ method lends itself very well to silver determination at these high concentration levels. It is also very accurate for the minor and trace elements. The standard errors of estimate and the regression coefficients, r, shown in Table 2 are also measures of the accuracy. Compared to the other elements, copper has the lowest relative accuracy_ Although bismuth and lead were detectable on some of the samples, and could be measured, reliable values
for regression analysis on these two elements were not available. Precision Ten individual determinations were done on 6 samples to establish the precision of the method. The results are given in Table 4. Sensitivity and de tee tion limits Values for the sensitivities and detection limits of the elements gold, palladium and platinum, are given in Table 5. The lower limit of detection(s) is defined [5] as (3/m) (R,/T)“* 75, where R,is the counting rate on the background, ‘I’the counting time, and m the slope factor or sensitivity which is expressed in counts per second/%. In the case of palladium the background count is strongly influenced by the closeness of the very intense _4g Kol peak, which is responsible for the relatively poor detection limit. CONCLUSION
The x-ray fkrorescence method is well suited for the analysis of silver samples. A sophisticated computer is needed to obtain the correction parameters, but once these are available, calculations with a small on-line computer of 8K capacity is possible on routine samples, On a sequential x-ray spectrometer the time for an analysis is of the order of 30 mm.
281 TABLE 4 Precision of x-ray results (N = IO)=
- Ag(%) R-l
M
Cu (a)
Pb (p.p.m.)
11 7 65
12 8 71
1.2132 0.0063 0.52
107 3 2.9
98.68 0.049 0.05
0.1891 0.0020 1.1
30 4 14
94 8 8.6
1.1424 0.0029 0.25
78 4 4.6
(%I
98.59 0.046 0.05
0.1531 0.0018 1.2
96 4 4.4
140 7 5.0
1.2139 0.0048 0.39
65 3 4.1
Sr (%I
96.92 0.028 0.03
1.971 0.0052 0.27
286 6 2.2
345 13 3.7
0.9 546 0.0023 0.24
119 4 3.4
97.11 0.038 0.04
1.747 0.0058 0.33
549 8 1.5
908 10 1.1
0.9229 0.0038 0.41
264 6 2.4
96.81 0.035 0.04
1.776 0.0050 0.28
983
1113 10 0.9
1.0278 0.0043 0.41
216 5 2.3
(%)
S SE. (WI
R-12 M S S,
M S
M S Sr
S-10
Pd (p.p.m.)
0.0195 0.0024 12.1
R-11 IM
S-9
Pt (p.p.m.)
98.76 0.057 0.06
;
s-5
Au (%)
Fb)
M s sr (%)
10
1.1
aM = Mean. s = Standard deviation. sr = Relative standard deviation. T-ABLE 5 Sensitivity and detection limits of x-ray measurements
Sensitivity (cps/%) Counting time (sj Background count (cps) Detection limit (p.p.m.)
Gold
Palladium
Platinum
1115
2100
1160
100 35 16
100 315 25
200 29 10
REFERENCES 1 2 3 4
J. Lucas-Tooth and C. Pyne, Adv. X-ray Anal., 7 (1964) 523. D. A_ Stephenson, Anal. Chem., 43 (1971) 310. H. Kodama, J. E. Brydon and 3. C. Stone, Geochim. Cosmochim. Acta, 31 (1967) 649_ W. J. Dixon, BlMDOZR - Stepwise Regression, University of California Publications in Automatic Computation, No. 2, Biomedical Computer Programme, Univ. CaLif. Press, 1967. 5 R. Jenkins and J. L. de Vries, practical X-ray Spectrometry, 2nd. edn., Macmillan, 1970. p. 167.
Chimica Acta,
97 (1978)
275-281
OE;lsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
THE ANALYSIS OF SILVER BY X-RAY SPECTROMETRY
F. T. WYBENGA
FLUORESCENCE
and L. R P. BUTLER*
National Physical Research Laboratory, P-0. Box 395, Pretoria (South Africa)
Council for Scientific
and Industrial
Research,
(Received 4th October 1977)
An x-ray fluorescence method is described for the analysis of silver alloys. The major e!ement silver as we!1 as the impurities are determined. Corrections are made for interelement. and line overlap effects. The results obtained compare favourably with wet chemical and emission spectrometric values. The method is rapid and reliable.
The value of silver has increased significantly in recent years, because of its increasingly wide usage and its relative scarcity. As with the precious metals, its assay, with regard both to purity and to the type and concen-
trations of impurity elements, requires the highest degree of accuracy and precision. Assay methods based on gravimetric techniques meet these requirements, but a total chemical analysis demands several techniques and is accordingly time-consuming, especially when the precious metals need to be determined. X-ray fluorescence spectroscopy is well known for its high degree of precision
and this, together with the fact that the method is non-destructive, suggested its use for the rapid analysis of silver alloys. Various alloys of silver, where the impurities included precious metals and totalled between 1 and 5%, were obtained. A method of analysis was developed which enabled the silver and other elements to be determined with a high degree of accuracy and precision. Line overlap and interelement effects
were present at the levels of impurities in the samples, and the correction methods of Lucas-Tooth and Pyne [ 11, Stephenson [ 21 and Kodama et al. [3] had to be applied. This paper describes the method and presents the results obtained on the range of alloys available. EXPERIMENTAL
Sample
prepamtion
The silver samples were prepared by melting in graphite crucibles at llOO°C in an induction furnace. They were vertically cast in a special mould (Fig. 1)
276 .
Fig. 1. Mould used for casting silversamples. to obtain discs of 40-mm diameter and Y-mm thickness. This procedure ensured that all samples were treated in the same way, thus removing the possibility that metallurgical history would affect results. It was established by means of a scanning electron microscope that these samples were homogeneous_ Smoothing of the surfaces of the sample was done on a water-covered surfacing disc with 180 and then 800 silicon carbide paper.
Appcra tus A Philips PW 122OC sequential x-ray fluorescence spectrometer with a molybdenum anode tube was used for all the measurements_ An 8K Honeywell computer was coupled to this instrument and was used to control the spectrometer as well as the automatic sample changer.
Selection of instrumental conditions Preliminary wavelength scans of some of the samples were made to establish optimum conditions (Fig. 2). LiF (200) as well as LiF (220) crystals were tried as analysing crystals. The resolution of the instrument was improved by
Fig. 2. Typical spectrum of silver sample. Sample S-11. Analysing crystal, MO anode, 80 kV, 50 mk Full scale, 4000 cps. x Spurious reflections_
LiF (220).
277 introducing an additional auxiliary soller collimator (150~,em spacing, 100 mm long) in front of ihe scintillation detector. Tine following results were obtained in these experiments. (i) Tine Pd KY and Ag &Y lines were inadequately separated with the LiF (200) crystal and the auxiliary collimator_ The LiF (220) crystal was therefore used. The loss in intensity was approximately 30% (ii) The LiF (200) analysing crystal gave adequate resolution for the separation of the Au La and Pt La lines, with the auxiliary colhmator. (iii) Spurious reflections do occur with the LiF (220) crystal, but fortunately not in positions where they affect the measurements. (iv) By using the long auxiliary collimator, the intensity is reduced by a factor of six for the Ag KCY and Pd KCY lines. This is not serious as adequate intensity is available for:these lines. The experimental conditions for individual elements are given in Table 1. All measurements were done in air with a fine primary soiler collimator (150~pm spacing), an auxiliary soller collimator in front of the detector (15O+m spacing, 100 mm long) and a scintillation detector_ Samples were loaded into the spectrometer by means of a sample changer controlled by the computer_
Correction procedure One in every four measurements was done on a single reference standard and all values were ratioed to these reference measurements to enable corr-
ection
for possible
by direct
drift. -Ail measurements
subtraction
dead-time
of a measurement
were corrected
for background
taken close to the peak and also for
losses.
TABLE1 Measuring Element
conditions line
Ag Km Background Pd Ka Background MO KCY Mo I& (Compton) Au La Background Pt La Background cu Klx Background Pb La Background Bi Lp Background
crystal
O2e
kV
mA
Counting
La? (220)
22.72 18.00 23.79 18.00 28.87 30.00 36.97 35.80 38.05 39.50
60 60 80 80 80 80 80 80 80 80
20 20 30 30 30 30 30 30 30 30
100 100 100 100 100 100 100 100 200 200
45.03
80
30
100
47.00 33.92 35.80 39.06 42.00
80 80 80 80 80
30 30 30 30 30
100 200 200 100 100
LiF LiF LiF LiF LiF LiF LIF LiF LiF LiF LiF LiF LiF LiF LiF
!220: (220) (220) (200) (200) (200) (200) (200) (200) (ZOO) (200) (200) (200) (220) (220)
time (s)
278
The equation used in the correction procedure is ci = Ao -I- AiRi + 2 AjRj + 5 14, RiRj j=l i= 1
whereCi is the concentration, and Ri is the intensity of the analytical element; Rf is the intensity of the interfering element: and Ao, A,,.A, and A, are constants. This equation differs from the normal Lucas-Tooth equation [I] in that the term AjRi isintroduced to correct for line overlap and po&ziblebackground effects. In the ideal case where no interference is present, the last two terms in the equation fall away. Under normal circumstances only some of the elements in a specific matrix have an appreciable effect on the determination of a concentration. The stepwise muhiregressional program [4] suggested by Stephenson [Z] was used to establish the regression constants. In this program it is possible to specify F-levels for the inclusion or deletion of variates. Non-significant variates are not inch~ded in the model_ A practical F-level is determined by the degrees of freedom. In the case of these analyses the F-level for inch&on and deletion was chosen as 2.0. The exact forms of the regression formulae had to be determined before any analyses were attempted. A number of standards had therefore to be ’ measured for ah the elements of interest mder the conditions given in Table 1. The regression equations given in Table 2 were obtained following the multiple regression method described. TABLE
2
Regressionequations &
C=36.30043RAg-1.82587 RAfo-0.66108RcuRA, i 62.60551
0.57374 RAu-
Standarderrorofestir;late= O.O773;r= AU
0.22638&
0.9982.
0.03075 R,0.60284 Rnlo i 0.04073 Rp, 0.63012 Standarderrorofestimate= 0.0052;r= 1.0000. C
=
2.88256 R,,
-
i- 0.07722 RX,+
cu
C= 1.256X&,-00.?04967&-00.09904 Standarderrorofestimate= O.O309;r= 0.9984.
Pd
C=0.80353Rpd-O.O0341Rpt-0.01062 Rpb+ 0.03386 RF,., x Rpd - 0.09389 Standard errorofestimate= O.OOlO;r= 0.9999.
Pt
C=O.10894 RPt-0.000129RAU i- 0.01041EC,+ Standarderrorofestimate= 0.0007;r=0.9998.
0.45910 R_+ X Rpd
0.000989 Rp,x
I&.,--
0.0155E
9 10 11 13 10 17 18 19 20 21 22 23 27 31 3G
I
Snmpll!
98.76 98.77 98.78 08.08 08.03 D8.54 08.01 9G.Gl 98.71 D8.GG 98.74 06.10 9G.09 96.23 DO.90 96.96 96.75 90.70 9G.G7 97.G4 97.37 97.40 96.98 07.03 0'7.14 97.18 07.10 OB.GO !lG.GG 06.136 9847 96.Gtj 94.9G DG.02 95.03 OG.33 06.41 96.69 96.73 9G.GO 06.20 9G.09 9G.06
0.019 0.192 O.lB4 0.081 2.644 2.109 1.495 1.743 29Gl 3.GO 0.806 0.908
0.023 0.193 0.151 0.08G 2691 2.025 21Gl 1.G29 1.846 1.073 2.024 2.884 3.48 2521 0.890 0.903
G.d.
Chcm
X.r.f.
Chem
G-d.
Gold (lb)
Silver (‘lo)
Aualylicnl results
TABLE 3
0.020 O.lDl O.lG3 0.083 2.GG2 1.070 2.106 1.499 1.7G2 1.735 1.773 2.97 3.687 2G4G 0.896 0.909
X.&f. 1.21 1.14 1.19 1.20 1.11 0.95 1.03 0.05 0.96 0.94 1.03 1.11 1.07 0.99 2.09 2.62
1.18 1.17 1.21 1.23 1.06 0.02 0.97 0.04 0.9G 0.03 1.17 1.18 LOG 1.00 1.99 2.G7
1.20 L17 1.20 1.18 1.08 0.98 1.02 0.84 0.98 0.94 1.03 1.10 1.12 0,97 2007 2067
0.001 0.0100 0.0136 0.0068 0.034 0.03B 0.039 0.043 0.077 0.088 0.113 0.238 0.22G 0.026 0.013 0.026 0.0108 0.0151 0.0072 0.037 0.037 0.042 O.OGl o.oaz O.OBG 0.118 0.240 0.216 0.027 0.012 0.022
G.d.
Pallndium (%)
Chem G.d. X.r.1. Chem
Copper(%)
0.009G 0.0146 0,0073 0.036 0.033 0.041 0,046 0.078 0.000 0.112 0.238 0.228 0.02G 0.013 0.026
X.r.f.
G 30 95 24 130 290 330 430 GGO GGO 98G 870 700 90 17 26
Chcm
26 94 23 127 202 326 482 cIG8 541 983 8OG GO6 15 18 19
GA.
27 92 21 144 287 322 440 GG3 842 982 871 700 78 -
X.cf.
Pliitinum (1w.m.)
280 RESULTS
Accuracy Standard values (them), glow discharge values (g-d.) and x-r-f. values are cold, copper, palladium and platinum in compared for the efements, silver, D Table 3. The chemical values were used in the multiple regression analysis. The accuracy of the method depends largely on the accuracy of the chemical values. Good agreement is found for ah the elements. The x.r_f_ method lends itself very well to silver determination at these high concentration levels. It is also very accurate for the minor and trace elements. The standard errors of estimate and the regression coefficients, r, shown in Table 2 are also measures of the accuracy. Compared to the other elements, copper has the lowest relative accuracy_ Although bismuth and lead were detectable on some of the samples, and could be measured, reliable values
for regression analysis on these two elements were not available. Precision Ten individual determinations were done on 6 samples to establish the precision of the method. The results are given in Table 4. Sensitivity and de tee tion limits Values for the sensitivities and detection limits of the elements gold, palladium and platinum, are given in Table 5. The lower limit of detection(s) is defined [5] as (3/m) (R,/T)“* 75, where R,is the counting rate on the background, ‘I’the counting time, and m the slope factor or sensitivity which is expressed in counts per second/%. In the case of palladium the background count is strongly influenced by the closeness of the very intense _4g Kol peak, which is responsible for the relatively poor detection limit. CONCLUSION
The x-ray fkrorescence method is well suited for the analysis of silver samples. A sophisticated computer is needed to obtain the correction parameters, but once these are available, calculations with a small on-line computer of 8K capacity is possible on routine samples, On a sequential x-ray spectrometer the time for an analysis is of the order of 30 mm.
281 TABLE 4 Precision of x-ray results (N = IO)=
- Ag(%) R-l
M
Cu (a)
Pb (p.p.m.)
11 7 65
12 8 71
1.2132 0.0063 0.52
107 3 2.9
98.68 0.049 0.05
0.1891 0.0020 1.1
30 4 14
94 8 8.6
1.1424 0.0029 0.25
78 4 4.6
(%I
98.59 0.046 0.05
0.1531 0.0018 1.2
96 4 4.4
140 7 5.0
1.2139 0.0048 0.39
65 3 4.1
Sr (%I
96.92 0.028 0.03
1.971 0.0052 0.27
286 6 2.2
345 13 3.7
0.9 546 0.0023 0.24
119 4 3.4
97.11 0.038 0.04
1.747 0.0058 0.33
549 8 1.5
908 10 1.1
0.9229 0.0038 0.41
264 6 2.4
96.81 0.035 0.04
1.776 0.0050 0.28
983
1113 10 0.9
1.0278 0.0043 0.41
216 5 2.3
(%)
S SE. (WI
R-12 M S S,
M S
M S Sr
S-10
Pd (p.p.m.)
0.0195 0.0024 12.1
R-11 IM
S-9
Pt (p.p.m.)
98.76 0.057 0.06
;
s-5
Au (%)
Fb)
M s sr (%)
10
1.1
aM = Mean. s = Standard deviation. sr = Relative standard deviation. T-ABLE 5 Sensitivity and detection limits of x-ray measurements
Sensitivity (cps/%) Counting time (sj Background count (cps) Detection limit (p.p.m.)
Gold
Palladium
Platinum
1115
2100
1160
100 35 16
100 315 25
200 29 10
REFERENCES 1 2 3 4
J. Lucas-Tooth and C. Pyne, Adv. X-ray Anal., 7 (1964) 523. D. A_ Stephenson, Anal. Chem., 43 (1971) 310. H. Kodama, J. E. Brydon and 3. C. Stone, Geochim. Cosmochim. Acta, 31 (1967) 649_ W. J. Dixon, BlMDOZR - Stepwise Regression, University of California Publications in Automatic Computation, No. 2, Biomedical Computer Programme, Univ. CaLif. Press, 1967. 5 R. Jenkins and J. L. de Vries, practical X-ray Spectrometry, 2nd. edn., Macmillan, 1970. p. 167.