- Email: [email protected]
Simultaneous determination of light rare earths in monazite sand by densitometry on thin-layer chromatograms
Tukmro. Vol. 33, No. 5. pp. 455-457. 1986 Prmted in Great Britain. All rights reserved
Copynghk
0039.9140!‘86 $3.00 + 0.00 (‘ 1986 Pergamon Press Ltd
SIMULTANEOUS DETERMINATION OF LIGHT RARE EARTHS IN MONAZITE SAND BY DENSITOMETRY ON THIN-LAYER CHROMATOGRAMS Hsu ZHANG-FA, JIA XI-PIK and Hu CHAO-SNENC Department of Chemistry, East China Normal University, 3663 Chung Shan Road (N), Shanghai, People’s Republic of China (Received 27 June 198.5. Revised 28 Seprember 1985. Accepted 23 Decenther 1985) Summary--The determination of individual light rare-earth metals in monazite sand is described, based an TLC with a mixture of di-isopropyl ether, diethyl ether. di(2-ethylhexyl)phosphate and nitric acid (8:8:0.4:0.07 v/v) as eiuent. Linear densitometr~c calibration graphs are obtained for individual light rare-earths in the range 0.015-0.60 pg. The minimum detectable quantities of La. Ce. Pr. Nd and Sm are 9, 10, 20, 13 and 12 ng, respectively. The relative standard deviations for the determination of La, Ce, Pr, Nd and Sm in monazitc sand were 1.8, 1.1, 5.9. 1.9 and 6.5%. respectively. Results were in good agreement with those obtained by spectraphotometry. Chromogenic reagenl, analytica/ grade. Chiorophosphonazo-m-NO? (CPAmN)’ (100 mg) was dissolved in 95% ethanol in a 5OO-mlstandard flask, 1.3 ml of concentrated hydrochloric acid was added and the mixture was diluted to the mark with 95% ethanol. Rure-enrrA metal stock solutions (5 mg/mf). The appropriate amount of ignited rare-earth oxide (“Specpure’“, Johnson-Matthey)’ was dissolved in dilute hydrochloric acid, and the solution diluted to the required volume. Mixed rare -earrh metal sock solution (0. I5 mg/ml). Made by mixing I .5 mt each of the individual light rare-earth stock solutions and of a similar yttrium solution in a 50-ml standard flask and making up to the mark with 10% v/v hydrochloric acid.
The increased applications of the rare-earth elements in the metallurgical and optical glass industries and their utilization in ever increasing amount makes it worthwhile to develop a rapid, sensitive and accurate technique for their determination, but few such meth-
ods have so far been proposed. The high efficiency of thin-layer chromatography (TLC) has resulted in its wide application in the analysis of organic and inorganic materials, but difficulties have been encountered in the separation of the rare-earth elements because of their similar chemical properties. Specker and co-workers’ 4 and Chen et ~1.’ have described the separation and determination of rare earths by TLC. In some cases, silaned silica gel has also been used as adsorbent,6 but the procedures proposed were time-consuming and no results for the analysis of monazite sand were given. In the present work, the TLC behaviour of the complexes of rare-earth metals with di(2-ethyihexyl)phosphate (HDEHP) is investigated. For the determination of La, Ce, Pr, Nd and Sm in monazite sand, prior extraction and back-extraction are necessary. With a mixture of HDEHP, di-isopropyl ether, diethyl ether and nitric acid (0.4:8:8:0.07 v/v) as efuent, a TLC-densitometric method for the determination of La, Ce, Pr, Nd and Sm in monazite sand has been developed.
l-Phe~yl-3-me~h~l-4-ben~o~~-5-pyro~olo~e
EXPERIMENTAL Apparatus
A double-beam densitometer equipped with a TLC scanner, an integrator and a microcomputer was used for all measurements. Reagents Di(2-erhylhexyl)phasphate
grade was used in the eluent.
(HDEHP).
A chemically pure
(PMBP).
A
0. I M solution in chloroform. Dissolve a sample containing up to 12 mg of rare-earth metals in 3 ml of concentrated sulphuric acid, by heating gently for about 30 min. Cool, add 10 drops of hydrogen peroxide to reduce cerium(IY) and evaporate nearly to dryness, until the residue appears white. Cool, add water, transfer to a 2.5-m] standard Bask and make up to the mark with water. Filter through a dry paper, discarding the first portion of the filtrate, and collect the rest in a 25ml polyethylene bottle. Take an aliquot (containing _ 5 mg of rare-earth metals) in a 60-ml separatory funnel. Add 2 ml of 10% sodium potassium tartrate (Rochelle salt) solution, one drop of Methyl Orange indicator and sufficient concentrated ammonia solution (or 20% sodium hydroxide solution) to change the colour of the solution to orange. Add 4 ml of buffer solution, pH 5.5 (0.2M sodium acetate--acetic acid), adjust the volume to 15 ml, add an equal volume of O.IM chloroform solution of PMBP, shake for 2 min and allow the layers to separate. Repeat the extraction with fresh PMBP solution twice more and strip each organic extract with three I S-ml portions of formic acid (pH t .9). Combine the aqueous extracts in a 250-ml beaker, add several drops of concentrated hydrochloric acid. evaporate almost to dryness, cool and moisten the residue with concentrated hydrochloric acid. Add a little water, transfer to a IO-ml standard flask and make up to the mark with OS!! vfv hydrochloric acid. Filter through a dry paper, discarding the first few drops of the filtrate, and collect the remainder in a IO-ml polyethylene bottle.
455
456
SHORT
Table
HN03, ml
HDEHP, ml
1. Rf
values of rare-earth metals with different eluents
iPr,O/Et,O,
ml
0.05
0.07 0.09 0.11
0.40
0.07
0.25 0.30 0.50
0.07
0.40
COMMUNICATIONS
8/S
O/IS
-___-..---...
R, x 100*
La
Ce
Pr
.~ Nd
Sm
Y
12,l llji 712 0 513 7+1 13&2 3+1 4+1 9*1 13&l 2014
32+5 35+4 30+4 21+2 27&3 29+3 39+2 11+2 i6&2 2821 35+2 46+5
55k2 51+1 49If:l 47_+1 42+2 45&I .%+I 17&l 30&L 47f2 54+3 58+3
66f2 63rtl 6121 5Ok2 52+3 55 * 1 69& 1 26 +2 46k 1 56 +2 67+ 3 68f3
X8+1 86fl 78f3 6855 75+4 78 + I 90&3 60+ 1 60): I 60& 1 98 52 98&Z
98F2 9852 98 f 2 98 + 2 98 + 2 98 & 2 98 2 2 98 & 2 98 & 2 98k2 98&2 9812
----
,...... --
*Mean and range of 3 runs.
Coat TLC plates (20 x 20 cm) with a 0.25 mm thickness of silica gel H slurried in 4% ammonium nitrate solution containing 1% sodium carboxymethyi~eilu~ose (CMC). Dry the plates at 120” for 90 min and store in a desiccator. Apply 0.2-4.0 1.11of mixed standard rare-earth metal solution at one end of the start line on the plate for reference purposes, and I &2.0 ~1 of the sample solution at the other, keeping the spot diameter at 64 mm by drying under an infrared lamp and controlling the spotting. Develop in a solvent-saturated atmosphere in a conventional tank by the ascending front technique until the solvent front has travelled at least 10 cm. Dry the plate at ‘70”for 15 min and spray it with 0.02% CPAmN solution while it is still hot. Dry for a further IO min at 70” to develop the spots (which begin to fade after 12 hr). Scan the plate with a densitometer in the double-beam (sample at 665 nm, background at 430 nm) and reflectance modes. Two ways of scanning are possible, linear or zigzag (9.9 x 1.0 mm and 1.25 x 1.25 mm, respectively). Scan each spot on the same plate in the direction of development at a rate of 20 cm/min (for both scanning modes). The linear scatter parameter (SX) chosen is 3.’ RESULTS
AND DISCUSSION
E@ct of foreign ions The effect, on the TLC separation of the rare earths, of common ions normally present in a solution of monazite sand was examined, and it was found that phosphate present in the sample interfered by precipitating some of the rare-earth content. The extraction and stripping procedures were necessary for the removal of phosphate in the analysis of monazite sand. For other samples, such as cerium-based alloys or fission products, these steps may not be necessary. Choice of efue~~ The Rf values obtained for La, Ce, Pr, Nd, Sm and Y with different eluents are listed in Table 1. The HDEHP-di-isopropyl ether-ðyl ether-nitric acid (0.4:8:8:0.07 v/v) eluent, was found best in terms of spot size, intensity and Rf values of light and heavy rare-earth metals. Alteration in the concentration of HDEHP or nitric acid affects the separation of light and heavy rare-earth metals, the RF values increasing with decreasing acidity and increasing volume of HDEHP. With the selected eluent, the heavy rare-
earth metals (represented by yttrium) migrated with the solvent front. Either di-isopropyl ether or diethyl ether can be used as diluent for the HDEHP, but though use of diethyi ether alone shortens the time of development, the spot-size is unsatisfactory, and when di-isopropyf ether alone is used, the R, values of Sm and the Y sub-group are nearly equal to 1.0 and although the spots are sharp, the development time is lengthened and the difference in R, values for adjacent elements is insufficient for scanning purposes (especially for Pr and Nd). For these reasons, a I:1 v/v ratio of the two ethers is used. Pr and Nd, which have proved very difficult to separate by TLC, are separated satisfactorily with this eluent. The TLC place Since CPAmN is also a chromogenic agent for calcium, calcium sulphate cannot be used as binder or substrate, so silica gel H is used with 1% CMC solution as binder. To improve the shape and size of the spots, 4% ammonium nitrate is also present in the 1% CMC solution. If the spot is not dried before development, the water present has a considerable effect on the RI values. For successful separation, this water is removed by drying at 70” for 1.5min. An alternative is to put the samples on an unactivated TLC plate and then dry it at 120” for 90 min before development; the composition of the sample does not undergo any chemical change and any errors are insignificant. Choice of scanning linear scatter parameter In the analysis of the TLC plate with a densitometer, there is no linear relationship between absorbance and concentration, owing to scattering of the monochromatic light beam by the adsorbent on the plate. Errors can arise from heterogeneity of the coloured spot and use of too large a light-beam area, so a small beam was used (1.25 x 1.25 mm for zigzag scanning and 0.9 x 10 mm for linear scanning) to minimize determination errors. The non-linear relation between absorbance and concentration was processed by microcomputer according to the
457
SHORT COMMUNICATIONS
Table 2. Results for determination of individual light rare-earth metal oxides (%) in monazite sand Sample
I
2
Element
Present method*
Spectrophotometric method (I)?
Spectrophotometric method (II)5
La(II1) Ce(IV) Pr(II1) Nd(III) SmfIII) Total
14.4 ;f; 0.3 21.5 k0.2 3.4 & 0.2 12.0 * 0.2 2.1 _cO.l 53.4
14.3 20.9 3.5 2.2 52.7
53.0
La(IH) Ce(IV) Pr(II1) Nd(If1) Sm(III) Total
10.I * 0.2 18.5 + 0.2 4.0 i. 0.2 IO.9 * 0.2 1.9io.i 45.4
IO.2 18.3 4.0 10.7 2.0 45.2
45.2
Il.8
*Mean (k standard deviation) of 6 determinations. tTLC plate developed as described, spots scraped off. rare-earth complex eluted and determined by spectrophotometry. @ample solution determined by spectrophotometry* to give total rareearth content.
Kubelka-Munk theory of light scattering”. A linear scatter parameter (SX) of 3 was chosen for calibration purposes. ~a~ibrut~on detection
curl’es,
reprod~c~bi~it~
and
~~rnits of
The integrated intensity of the spots was found to be a linear function of the rare-earth metal concentration (over the range 0.015-0.60 pg). All the light rare-earth metals gave similar calibration graphs. The results for samples can easily be obtained by scanning the spots for mixed rare-earth metal standards, and for the samples, processed on the same plate, and analysing the integrator output by microcomputer. The reproducibility was established by measurement of 6 spots each containing 0.3 pg of each light rare-earth metal, processed on the same plate. The relative standard deviations were 1.8, 1.2, 5.1, 1.6 and 4.8% for La, Ce, Pr, Nd and Sm, respectively. When the experiment was repeated on three different plates (total of 18 spots), the corresponding values were 2.3, 1S, 5.9, 2.5 and 5.7%. The minimum detectable quantity. defined as that quantity of individual light rare-earth metal giving a signal equal to twice the fluctuation of the blank value, and located on the linear portion of the calibration graphs was 9, 10, 20, 13 and 12 ng for La, Ce, Pr, Nd and Sm, respectively.
Determination of ~ndil~idu~l li& monazite sand
rare -earth metals in
To demonstrate the effectiveness of the method, two l-p1 samples of solution prepared from monazite sand were spiked with 1 ~1 of mixed standard rareearth metal solution and analysed. The recoveries for duplicate samples were 93-108% and the results shown in Table 2 are in reasonable agreement with those obtained by gravimetry and spectrophotometry. REFERENCES
1. K. Jungand H. Specker, Z. Anal. C&m., I977,288,28. 2. K. Jung, J. Maurer. J. Urlichs and H. Specker, ibid., 1978, 291, 328. 3. H. Specker and A. Hufnagel, ibid., 1984, 318, 198. 4. K. Jung and H. Specker, ibid., 1980, -300, 15. 5 Y. Chen, K. Zheng, H. Luo and J. Cheng, Fenxi Huaxue, 1983, 11, 101; Chem. Abstr., 1983, 99,472Ola.
6. H. Specker and W. Herrmann, Chem. Lab. Be&r., 1981, 32, 519. 7. C. G. Hsu, C. S. Hue, X. P. Chim. Am, 1981, 124, 177.
Jia and J. M. Pan, Anal.
8. G. F. Cheng, H. X. Huang, 2. S. Hu and X. P. Jia, J. East China Norm& Unicersiry (Nat. Sci. Ed.), 1983, 2, 73. 9. I-I. Yamamoto, T. Kurita, J. Suzuki, R. Him. K. Nakano, H. Makabe and K. Shibata, J. Chr~~~~~~., 1976, 116, 29.
Copynghk
0039.9140!‘86 $3.00 + 0.00 (‘ 1986 Pergamon Press Ltd
SIMULTANEOUS DETERMINATION OF LIGHT RARE EARTHS IN MONAZITE SAND BY DENSITOMETRY ON THIN-LAYER CHROMATOGRAMS Hsu ZHANG-FA, JIA XI-PIK and Hu CHAO-SNENC Department of Chemistry, East China Normal University, 3663 Chung Shan Road (N), Shanghai, People’s Republic of China (Received 27 June 198.5. Revised 28 Seprember 1985. Accepted 23 Decenther 1985) Summary--The determination of individual light rare-earth metals in monazite sand is described, based an TLC with a mixture of di-isopropyl ether, diethyl ether. di(2-ethylhexyl)phosphate and nitric acid (8:8:0.4:0.07 v/v) as eiuent. Linear densitometr~c calibration graphs are obtained for individual light rare-earths in the range 0.015-0.60 pg. The minimum detectable quantities of La. Ce. Pr. Nd and Sm are 9, 10, 20, 13 and 12 ng, respectively. The relative standard deviations for the determination of La, Ce, Pr, Nd and Sm in monazitc sand were 1.8, 1.1, 5.9. 1.9 and 6.5%. respectively. Results were in good agreement with those obtained by spectraphotometry. Chromogenic reagenl, analytica/ grade. Chiorophosphonazo-m-NO? (CPAmN)’ (100 mg) was dissolved in 95% ethanol in a 5OO-mlstandard flask, 1.3 ml of concentrated hydrochloric acid was added and the mixture was diluted to the mark with 95% ethanol. Rure-enrrA metal stock solutions (5 mg/mf). The appropriate amount of ignited rare-earth oxide (“Specpure’“, Johnson-Matthey)’ was dissolved in dilute hydrochloric acid, and the solution diluted to the required volume. Mixed rare -earrh metal sock solution (0. I5 mg/ml). Made by mixing I .5 mt each of the individual light rare-earth stock solutions and of a similar yttrium solution in a 50-ml standard flask and making up to the mark with 10% v/v hydrochloric acid.
The increased applications of the rare-earth elements in the metallurgical and optical glass industries and their utilization in ever increasing amount makes it worthwhile to develop a rapid, sensitive and accurate technique for their determination, but few such meth-
ods have so far been proposed. The high efficiency of thin-layer chromatography (TLC) has resulted in its wide application in the analysis of organic and inorganic materials, but difficulties have been encountered in the separation of the rare-earth elements because of their similar chemical properties. Specker and co-workers’ 4 and Chen et ~1.’ have described the separation and determination of rare earths by TLC. In some cases, silaned silica gel has also been used as adsorbent,6 but the procedures proposed were time-consuming and no results for the analysis of monazite sand were given. In the present work, the TLC behaviour of the complexes of rare-earth metals with di(2-ethyihexyl)phosphate (HDEHP) is investigated. For the determination of La, Ce, Pr, Nd and Sm in monazite sand, prior extraction and back-extraction are necessary. With a mixture of HDEHP, di-isopropyl ether, diethyl ether and nitric acid (0.4:8:8:0.07 v/v) as efuent, a TLC-densitometric method for the determination of La, Ce, Pr, Nd and Sm in monazite sand has been developed.
l-Phe~yl-3-me~h~l-4-ben~o~~-5-pyro~olo~e
EXPERIMENTAL Apparatus
A double-beam densitometer equipped with a TLC scanner, an integrator and a microcomputer was used for all measurements. Reagents Di(2-erhylhexyl)phasphate
grade was used in the eluent.
(HDEHP).
A chemically pure
(PMBP).
A
0. I M solution in chloroform. Dissolve a sample containing up to 12 mg of rare-earth metals in 3 ml of concentrated sulphuric acid, by heating gently for about 30 min. Cool, add 10 drops of hydrogen peroxide to reduce cerium(IY) and evaporate nearly to dryness, until the residue appears white. Cool, add water, transfer to a 2.5-m] standard Bask and make up to the mark with water. Filter through a dry paper, discarding the first portion of the filtrate, and collect the rest in a 25ml polyethylene bottle. Take an aliquot (containing _ 5 mg of rare-earth metals) in a 60-ml separatory funnel. Add 2 ml of 10% sodium potassium tartrate (Rochelle salt) solution, one drop of Methyl Orange indicator and sufficient concentrated ammonia solution (or 20% sodium hydroxide solution) to change the colour of the solution to orange. Add 4 ml of buffer solution, pH 5.5 (0.2M sodium acetate--acetic acid), adjust the volume to 15 ml, add an equal volume of O.IM chloroform solution of PMBP, shake for 2 min and allow the layers to separate. Repeat the extraction with fresh PMBP solution twice more and strip each organic extract with three I S-ml portions of formic acid (pH t .9). Combine the aqueous extracts in a 250-ml beaker, add several drops of concentrated hydrochloric acid. evaporate almost to dryness, cool and moisten the residue with concentrated hydrochloric acid. Add a little water, transfer to a IO-ml standard flask and make up to the mark with OS!! vfv hydrochloric acid. Filter through a dry paper, discarding the first few drops of the filtrate, and collect the remainder in a IO-ml polyethylene bottle.
455
456
SHORT
Table
HN03, ml
HDEHP, ml
1. Rf
values of rare-earth metals with different eluents
iPr,O/Et,O,
ml
0.05
0.07 0.09 0.11
0.40
0.07
0.25 0.30 0.50
0.07
0.40
COMMUNICATIONS
8/S
O/IS
-___-..---...
R, x 100*
La
Ce
Pr
.~ Nd
Sm
Y
12,l llji 712 0 513 7+1 13&2 3+1 4+1 9*1 13&l 2014
32+5 35+4 30+4 21+2 27&3 29+3 39+2 11+2 i6&2 2821 35+2 46+5
55k2 51+1 49If:l 47_+1 42+2 45&I .%+I 17&l 30&L 47f2 54+3 58+3
66f2 63rtl 6121 5Ok2 52+3 55 * 1 69& 1 26 +2 46k 1 56 +2 67+ 3 68f3
X8+1 86fl 78f3 6855 75+4 78 + I 90&3 60+ 1 60): I 60& 1 98 52 98&Z
98F2 9852 98 f 2 98 + 2 98 + 2 98 & 2 98 2 2 98 & 2 98 & 2 98k2 98&2 9812
----
,...... --
*Mean and range of 3 runs.
Coat TLC plates (20 x 20 cm) with a 0.25 mm thickness of silica gel H slurried in 4% ammonium nitrate solution containing 1% sodium carboxymethyi~eilu~ose (CMC). Dry the plates at 120” for 90 min and store in a desiccator. Apply 0.2-4.0 1.11of mixed standard rare-earth metal solution at one end of the start line on the plate for reference purposes, and I &2.0 ~1 of the sample solution at the other, keeping the spot diameter at 64 mm by drying under an infrared lamp and controlling the spotting. Develop in a solvent-saturated atmosphere in a conventional tank by the ascending front technique until the solvent front has travelled at least 10 cm. Dry the plate at ‘70”for 15 min and spray it with 0.02% CPAmN solution while it is still hot. Dry for a further IO min at 70” to develop the spots (which begin to fade after 12 hr). Scan the plate with a densitometer in the double-beam (sample at 665 nm, background at 430 nm) and reflectance modes. Two ways of scanning are possible, linear or zigzag (9.9 x 1.0 mm and 1.25 x 1.25 mm, respectively). Scan each spot on the same plate in the direction of development at a rate of 20 cm/min (for both scanning modes). The linear scatter parameter (SX) chosen is 3.’ RESULTS
AND DISCUSSION
E@ct of foreign ions The effect, on the TLC separation of the rare earths, of common ions normally present in a solution of monazite sand was examined, and it was found that phosphate present in the sample interfered by precipitating some of the rare-earth content. The extraction and stripping procedures were necessary for the removal of phosphate in the analysis of monazite sand. For other samples, such as cerium-based alloys or fission products, these steps may not be necessary. Choice of efue~~ The Rf values obtained for La, Ce, Pr, Nd, Sm and Y with different eluents are listed in Table 1. The HDEHP-di-isopropyl ether-ðyl ether-nitric acid (0.4:8:8:0.07 v/v) eluent, was found best in terms of spot size, intensity and Rf values of light and heavy rare-earth metals. Alteration in the concentration of HDEHP or nitric acid affects the separation of light and heavy rare-earth metals, the RF values increasing with decreasing acidity and increasing volume of HDEHP. With the selected eluent, the heavy rare-
earth metals (represented by yttrium) migrated with the solvent front. Either di-isopropyl ether or diethyl ether can be used as diluent for the HDEHP, but though use of diethyi ether alone shortens the time of development, the spot-size is unsatisfactory, and when di-isopropyf ether alone is used, the R, values of Sm and the Y sub-group are nearly equal to 1.0 and although the spots are sharp, the development time is lengthened and the difference in R, values for adjacent elements is insufficient for scanning purposes (especially for Pr and Nd). For these reasons, a I:1 v/v ratio of the two ethers is used. Pr and Nd, which have proved very difficult to separate by TLC, are separated satisfactorily with this eluent. The TLC place Since CPAmN is also a chromogenic agent for calcium, calcium sulphate cannot be used as binder or substrate, so silica gel H is used with 1% CMC solution as binder. To improve the shape and size of the spots, 4% ammonium nitrate is also present in the 1% CMC solution. If the spot is not dried before development, the water present has a considerable effect on the RI values. For successful separation, this water is removed by drying at 70” for 1.5min. An alternative is to put the samples on an unactivated TLC plate and then dry it at 120” for 90 min before development; the composition of the sample does not undergo any chemical change and any errors are insignificant. Choice of scanning linear scatter parameter In the analysis of the TLC plate with a densitometer, there is no linear relationship between absorbance and concentration, owing to scattering of the monochromatic light beam by the adsorbent on the plate. Errors can arise from heterogeneity of the coloured spot and use of too large a light-beam area, so a small beam was used (1.25 x 1.25 mm for zigzag scanning and 0.9 x 10 mm for linear scanning) to minimize determination errors. The non-linear relation between absorbance and concentration was processed by microcomputer according to the
457
SHORT COMMUNICATIONS
Table 2. Results for determination of individual light rare-earth metal oxides (%) in monazite sand Sample
I
2
Element
Present method*
Spectrophotometric method (I)?
Spectrophotometric method (II)5
La(II1) Ce(IV) Pr(II1) Nd(III) SmfIII) Total
14.4 ;f; 0.3 21.5 k0.2 3.4 & 0.2 12.0 * 0.2 2.1 _cO.l 53.4
14.3 20.9 3.5 2.2 52.7
53.0
La(IH) Ce(IV) Pr(II1) Nd(If1) Sm(III) Total
10.I * 0.2 18.5 + 0.2 4.0 i. 0.2 IO.9 * 0.2 1.9io.i 45.4
IO.2 18.3 4.0 10.7 2.0 45.2
45.2
Il.8
*Mean (k standard deviation) of 6 determinations. tTLC plate developed as described, spots scraped off. rare-earth complex eluted and determined by spectrophotometry. @ample solution determined by spectrophotometry* to give total rareearth content.
Kubelka-Munk theory of light scattering”. A linear scatter parameter (SX) of 3 was chosen for calibration purposes. ~a~ibrut~on detection
curl’es,
reprod~c~bi~it~
and
~~rnits of
The integrated intensity of the spots was found to be a linear function of the rare-earth metal concentration (over the range 0.015-0.60 pg). All the light rare-earth metals gave similar calibration graphs. The results for samples can easily be obtained by scanning the spots for mixed rare-earth metal standards, and for the samples, processed on the same plate, and analysing the integrator output by microcomputer. The reproducibility was established by measurement of 6 spots each containing 0.3 pg of each light rare-earth metal, processed on the same plate. The relative standard deviations were 1.8, 1.2, 5.1, 1.6 and 4.8% for La, Ce, Pr, Nd and Sm, respectively. When the experiment was repeated on three different plates (total of 18 spots), the corresponding values were 2.3, 1S, 5.9, 2.5 and 5.7%. The minimum detectable quantity. defined as that quantity of individual light rare-earth metal giving a signal equal to twice the fluctuation of the blank value, and located on the linear portion of the calibration graphs was 9, 10, 20, 13 and 12 ng for La, Ce, Pr, Nd and Sm, respectively.
Determination of ~ndil~idu~l li& monazite sand
rare -earth metals in
To demonstrate the effectiveness of the method, two l-p1 samples of solution prepared from monazite sand were spiked with 1 ~1 of mixed standard rareearth metal solution and analysed. The recoveries for duplicate samples were 93-108% and the results shown in Table 2 are in reasonable agreement with those obtained by gravimetry and spectrophotometry. REFERENCES
1. K. Jungand H. Specker, Z. Anal. C&m., I977,288,28. 2. K. Jung, J. Maurer. J. Urlichs and H. Specker, ibid., 1978, 291, 328. 3. H. Specker and A. Hufnagel, ibid., 1984, 318, 198. 4. K. Jung and H. Specker, ibid., 1980, -300, 15. 5 Y. Chen, K. Zheng, H. Luo and J. Cheng, Fenxi Huaxue, 1983, 11, 101; Chem. Abstr., 1983, 99,472Ola.
6. H. Specker and W. Herrmann, Chem. Lab. Be&r., 1981, 32, 519. 7. C. G. Hsu, C. S. Hue, X. P. Chim. Am, 1981, 124, 177.
Jia and J. M. Pan, Anal.
8. G. F. Cheng, H. X. Huang, 2. S. Hu and X. P. Jia, J. East China Norm& Unicersiry (Nat. Sci. Ed.), 1983, 2, 73. 9. I-I. Yamamoto, T. Kurita, J. Suzuki, R. Him. K. Nakano, H. Makabe and K. Shibata, J. Chr~~~~~~., 1976, 116, 29.