JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 93 Determination of Scandium Yttrium and Eight Rare Earth Elements in Silicate Rocks and Six New Geological Reference Materials by Simultaneous Multi-element Electrothermal Atomic Absorption Spectrometry With Zeeman-effect Background Correction* Joy G. Sen Gupta Geological Survey of Canada Ottawa Ontario Canada K 1A OE8 A method was developed for the simultaneous determination of a group of four rare earth elements (REE) in one firing using a multi-element graphite furnace atomic absorption spectrometer. The instrument can be programmed for automatic determination of an additional four REE elements in a second group by two firings. The sensitivities with a pyrolytic graphite coated graphite tube furnace are sufficiently high to permit the determination of low-pg g-I amounts of Y Nd and Sm and ng g-I amounts of Sc Eu Dy Ho Er Tm and Yb in silicate rocks from as little as 0.1 g or less of sample concentrate in a 1 ml final volume.After dissolution of the sample in acids Sc Y and the REE were preconcentrated by cation-exchange chromatography or coprecipitation with calcium oxalate and hydrated iron oxide carriers and determined by the proposed method. The interferences due to the presence of trace amounts of common metals in the ion-exchange concentrates were corrected for with Zeeman-effect background correction. Inter-method correlation plots for electrothermal atomic absorption spectrometry (ETAAS) versus inductively-coupled plasma mass spectrometry (ICP-MS) values and for oxalate versus ion-exchange recovery results for REE showed good agreement. Satisfactory results were obtained for Sc Y and eight REE in three international reference rocks MRG-1 SY-2 and NIM-G.The method was applied to the determination of these elements in six new candidate reference rocks of the Canadian Certified Reference Materials Project. In most instances the ETAAS results compared satisfactorily with those obtained independently by inductively coupled plasma atomic emission spectrometry (ICP-AES) and Keywords Scandium yttrium and rare earth element determination; silicate rocks and ores; multi-element electrothermal atomic absorption spectrometry; Zeeman-effect background correction; geological reference materials ICP-MS. There is a continuous need for scientists at the Geological Survey of Canada (GSC) to know the concentrations of yttrium and the rare earth elements (REE) in igneous mafic ultramafic and carbonate rocks for petrogenetic modelling.In most instances the lanthanide concentrations in these samples are so low that use of a preconcentration method and application of a highly sensitive instrumental technique are required to determine them. Neutron activa- t i ~ n ' - ~ stable isotope dilution mass spectrometry,6-8 spark- source mass spectrometry9-I3 and more recently direct current plasma emission spectr~metry,~~J~ inductively coupled plasma atomic emission spectrometry (ICP- AES)16-23 and inductively coupled plasma mass spectrome- try (ICP-MS)24-26 have been used with varying degrees of success.Other work in this area has involved the develop- ment of preconcentration of Sc Y and the REE by cation- exchange ~hromatography~~9~~ or by coprecipitation with calcium oxalate and hydrated iron oxide carrier^^^-^^ followed by determination using flame emi~sion,~~q~' flame atomic absorption spectrometry (AAS),28-33 optical emis- sion,31*33 electrothermal AAS (ETAAS)20~30-32-35 and ICP- AES.20 In the determination of Sc Y and the REE by ETAAS determination of only one element at a time rendered the process very laborious and time consuming. Moreover incompletely separated matrix elements after preconcentra- tion by ion exchange interfered in the determination of some elements; ash temperatures up to 2000°C and dilution of the concentrates were therefore recommended to eliminate these interference^.^^ In the proposed ETAAS *Presented in part at 74th Canadian Chemical Conference Hamilton Ontario June 2-6 199 1 .Government of Canada copyright reserved. Geological Survey of Canada Contribution No. 19092 method not only could four elements be determined in one firing and the instrument be programmed for the automatic determination of eight elements in two firings but also the interferences caused by the presence of associated impuri- ties in the concentrates obtained after ion-exchange separa- tion could be corrected for by Zeeman-effect background correction. The precision accuracy and speed of analysis were therefore greatly improved. The developed method was tested using reference ma- terials viz. Canada Centre for Energy and Mineral Techno- logy (CANMET) MRG-1 (Gabbro Rock) and SY-2 (Syenite Rock) and South African Bureau of Standards (SASS) SARM 1 NIM-G Granite with established REE contents and was then applied to the determination of SC Y and eight REE in six new candidate reference rocks and ores issued by the Canadian Certified Reference Materials Project (CCRMP).The results were compared with those obtained by ICP-AES and ICP-MS. Experimental Apparatus A Hitachi 2-9000 simultaneous multi-element atomic absorption spectrometer fitted with a pyrolytic graphite coated graphite tube furnace (part No. 190-6003) argon gas (UHP 99.999% exit pressure regulated to 44 lb in-2 and pre-dried by passing it through a Matheson Model 6406 gas purifier) and water (flow rate controlled at 1.5 1 min-' by a regulator) cooled to room temperature by mixing cold and hot water at the supply lines were used in all measurements.The built-in plotter of the 2-9000 instrument and an IBM- compatible PC were used for data recording. Before use a series of 12 borosilictte ion-exchange columns2* (each 30 cm x 1.8 cm i.d.) packed to a height of 15 cm with Dowex 50W-X8 cation-exchange resin (50-10094 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 mesh) were washed with 4 moll-' hydrochloric acid to free them from cations and then made neutral by washing with water. Reagents and Standard Solutions Ultra-pure water (ASTM Type I) and ACS-grade reagents were used throughout. Hydrochloric acid 1.7 and 4 mol 1-I. Nitric acid 2% vlv. Nitric acid 10% v/v-hydrogen peroxide 5% mixture.Bromophenol blue indicator solution 0.04%. Dissolve 40 mg of bromophenol blue in 100 ml of 95% ethanol and store in a tightly capped Nalgene bottle. Ammonium oxalate solution 0.1% mlv. Dissolve 1 g of ammonium oxalate in 1 1 of water and store in a plastic wash-bottle. Ammonium nitrate solution 1% mlv. Dissolve 10 g of ammonium nitrate in 1 1 of water and store in a plastic wash-bottle. A m mon ium eth ylenediam inetetraaceta te solution 0.8%. Weigh 4 g of ethylenediaminetetraacetic acid in a borosili- cate beaker add 100 ml of water and stir with gradual addition of sufficient ammonia solution until the solution becomes clear. Dilute to 500 ml with water and store in a plastic bottle. Methyl oxalate solution 40%. Dry oxalic acid crystals (COOH)2.2H20 in an air oven at 110 "C for several hours turning and breaking the lumps from time to time with a glass rod and exposing the crystals to heat to convert them completely into the anhydrous form.Cool grind to a powder and store in a stoppered bottle. Transfer 80 g of anhydrous oxalic acid into a 400 ml borosilicate beaker add 200 ml of methanol place the beaker on a medium hot- plate and stir with a glass rod to dissolve. Remove from the heat as soon as the solution becomes clear cool to room temperature and transfer into a stoppered bottle. Standard solutions of Sc Y and the REE 100 pg ml-I. Prepare by diluting 1000 pg ml-' Spex Industries plasma standard solutions (Sc Y La Ce Nd Sm Eu Gd Dy and Yb) and Johnson Matthey Chemicals Specpure standard solutions (Pr Tb Ho ER Tm and Lu) with 5% nitric acid.Prepare 100 ml of a stock synthetic standard solution of Sc Y and the REE only corresponding to the composition of 1 g ml-* of CANMET reference sample MRG-1 (based on the recommended values of Gladney and Roelandtsj6) by mixing aliquots of 1000 or 100 pg ml-l of the elements and diluting to 100 ml with 5% nitric acid (see Table 1 for composition). Prepare four working standard solutions of synthetic MRG- 1 having concentrations of sample equivalent to 0.05 0.10 0.15 and 0.20 g ml-l in terms of Sc Y and the lanthanides only by diluting 1 g ml-l of the above stock synthetic MRG-1 solution to appropriate volumes with 2% nitric acid. Store all standard solutions in tightly stoppered Nalgene bottles.Procedure Sample decomposition Weigh 1 g of the finely powdered and homogenized sample (-200 mesh) into a 100 ml Teflon beaker add a few drops of water and stir with a Teflon rod to make a slurry. Cautiously add (a small volume at a time) 10 ml each of concentrated nitric and hydrofluoric acids stir and quickly place a Teflon cover on the beaker to prevent loss due to vigorous exothermic reaction for some samples. Transfer to the groove of an iron hot-plate (or sand-bath) and evaporate nearly to dryness. Remove the beaker cool to room temperature add 10 ml each of concentrated hydrochloric and hydrofluoric acids and 2 ml of 70% perchloric acid and again evaporate nearly to dryness (avoid baking of the residue to prevent the formation of insoluble oxides). Repeat the evaporation process with an additional 10 ml of concentrated hydro- chloric acid.After cooling add 10 ml of concentrated hydrochloric acid 50 ml of water 5 ml of 0.8% ammonium ethylenedi- aminetetraacetate solution and dissolve the salts by stirring and heating on a hot-plate (or sand-bath). Filter the hot solution through a 9 cm Whatman No. 40 filter-paper and wash with hot 1 mol 1-l hydrochloric acid followed by water. Transfer any insoluble residue quantita- tively to the filter-paper using a rubber 'policeman' and a jet of water. Reserve the solution (filtrate A) transfer the residue into a 20 ml platinum crucible bum the paper in a mume furnace at 400 "C and finally heat to 800 "C to convert the salts into oxides. Cool the crucible to room temperature grind the residue to a fine powder with a round-tipped glass rod add 0.5 g of sodium carbonate and 0.1 g sodium peroxide and mix well.Place the covered crucible over a triangle enclosed by a chimney and fuse the mixture over a MCker burner at 1000 "C for 3-5 min. Remove the cover hold the tip of the crucible with platinum-tipped tongs and swirl the molten mass over the hot flame for complete decomposition of the residue then cool to room temperature. Cautiously add drops of concentrated hydrochloric acid and water to the crucible stir with a glass rod and warm on a hot-plate to dissolve the salts and loosen the cake. Transfer into a 20 ml beaker add more drops of concen- trated hydrochloric acid if necessary and warm on a hot- plate until dissolution of the salts is complete. Combine the solution with filtrate A dilute to 100 ml in a calibrated flask and store in a Nalgene bottle.Carry a blank through the above procedure for sample decomposition using the same amounts of acids and other reagents as for the sample. Preconcentration of Sc Y and the REE by ion-exchange separation Pipette 50 ml of the sample solution into a 100 ml borosili- cate beaker dilute to 80 ml with water mix well and pour into the ion-exchange column (a small volume at a time) and adjust the flow rate to 3 ml min-l. After the sample solution has passed through the column wash the beaker and the resin column with a total of 500 ml of 1.7 moll-' hydrochloric acid maintaining the flow rate the same as above. Discard the effluent. Elute the REE from the columns by washing with 650 ml of 4 mol 1-l hydrochloric acid at a flow rate of 4 ml min-l Table 1 corresponding to 1 g ml-'* Composition of a stock standard solution of synthetic MRG-I containing Sc Y and the REE only in concentrations Element Sc Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Concentration/pg ml-' 55 14 10 26 4 20 5 1.4 4 0.5 3 0.5 1.2 0.15 0.6 0.12 *See 'Recommended concentration' in ref. 36.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 95 and collect the effluent in a clean 800 ml borosilicate beaker. Evaporate the solution to dryness overnight on a low hot- plate. Dissolve the REE salts by heating with 10 ml of concentrated hydrochloric acid and transfer into a 20 ml borosilicate beaker by rinsing with an additional 10 ml of hot concentrated hydrochloric acid.Evaporate the solution to dryness on a hot-plate. Dissolve the REE salts by briefly warming with 2 ml of 2% nitric acid transfer into a 5 ml calibrated flask by rinsing the beaker with the same acid and dilute to the mark. Transfer the solution into a 7 ml screw-capped plastic vial. Carry out a blank separation with 50ml of the blank solution using the same procedure as above. Preconcentration of Sc Y and the REE by coprecipitation with calcium oxalate and iron oxide carriers Transfer 1-5 g of the finely powdered and homogenized material (-200 mesh) into a 100 ml Teflon beaker and decompose the sample in the same way as above. (For a 3-5 g sample use 20 ml each of concentrated nitric and hydrofluoric acids for initial sample decomposition and subsequently evaporate with 5 ml of 70% perchloric acid for decomposition of fluorides and removal of hydrofluoric acid.) After evaporation with 70% perchloric acid dissolve the residue by heating with a mixture of 10% nitric acid and 5% hydrogen peroxide.When decomposition of the excess of hydrogen peroxide is completed allow any insoluble resi- due to settle and filter through an 11 cm Whatman No. 40 filter-paper collecting the filtrate in a 400 ml beaker. Wash the residue with hot 10% nitric acid-5% hydrogen peroxide mixture and then with water. Transfer the residue into a 30 ml platinum crucible ignite to oxide as usual in a muMe furnace and fuse with 1-3 g of sodium hydrogensulfate to a clear melt. After cooling dissolve the fused mass in hot water adding if necessary a few drops of 1 + 1 sulfuric acid to clear any turbidity.Combine this solution with the main solution add 200 mg of calcium (as nitrate) and a few drops of the bromophenol blue indicator and heat to boiling on a hot-plate. Cautiously add 15 ml of 40% methyl oxalate solution and neutralize with a freshly prepared concentrated ammonia solution until the colour changes from yellow to blue (pH 3.8-4.6) and a copious white oxalate precipitate separates out. Heat again to boiling on the hot-plate (unattended overheating in the presence of a substantial amount of the oxalate precipitate may cause bumping and loss of the material) transfer the covered beaker to a steam-bath and digest the solution for 2-3 h with occasional stirring and addition of a few drops of ammonia solution to restore the blue colour.Test the completeness of oxalate precipitation by adding a few drops of calcium nitrate solution (CaO approximately 100 mg ml-l). In the presence of an excess of methyl oxalate the immediate appearance of a white turbidity or precipitate is indicative of the completeness of precipita- tion. If the precipitate does not appear immediately add a further 1 ml of the same calcium nitrate solution and a few drops of ammonia solution to attain the blue colour stir well and allow the precipitate to settle overnight. Filter through a 9 cm Whatman No 40 filter-paper and wash the precipitate and the paper thoroughly with 0.1% ammonium oxalate solution. Transfer the paper with the precipitate to the original beaker cover and decompose by refluxing with 25 ml of concentrated nitric acid and 5 ml of 30% hydrogen peroxide.Evaporate the solution to dryness and repeat the refluxing with nitric acid and hydrogen Table 2 Instrumental parameters. Slit-width fixed at 0.8 nm in an Hitachi 2-9000 instrument Hollow cathode Wavelength/ lamp current/ Element nm mA sc Y Nd Sm Eu DY Ho Er Tm Yb 326.9 4 10.2 492.4 429.6 459.4 42 1.2 410.4 400.8 37 1.8 246.5 5.0 5.0 10.0 10.0 5.0 10.0 10.0 5.0 10.0 5.0 Table 3 Temperature programme for simultaneous determination of Nd Ho Er and Tm (group 1) and Y Sm and Eu (group 2) Temperature/"C No. Stage Start End Time/s 1 Dry 75 75 10 2 Dry 90 90 60 3 Dry 120 130 20 4 Ash 850 850 20 5 Ash 1400 1400 10 6 Atom 3000 3000 10 7 Clean 3000 3000 5 Monitoring stage 1-7 Carrier gas 200 ml min-l Interrupted gas 0 ml min-l Check stage 1-7 Table 4 Temperature programme for simultaneous determination of Sc Dy and Yb Temperature/"C No.Stage Start End Time/s 1 Dry 75 75 10 2 Dry 90 90 60 3 Dry 120 130 10 4 Ash 850 850 20 5 Ash 1400 1400 10 6 Atom 2600 2600 10 7 Clean 2800 2800 5 Monitoring stage 1-7 Carrier gas 200 ml min-l Interrupted gas 0 ml min-I Check stage 1-7 peroxide if necessary to remove any dark carbonaceous matter. Dissolve the residue in 1 mol 1-l nitric acid and reprecipitate the oxalates of Ca Sc Y and the REE by the same procedure as above. After filtration and destruction of the organic matter with nitric acid and hydrogen peroxide evaporate the solution to dryness. Dissolve the residue in 50 ml of 1 mol 1-1 nitric acid add 5 mg of iron as iron(iI1) nitrate and dilute to 100 ml.Add 1 g of hydroxylamine hydrochloride mix well heat to boiling and add freshly prepared ammonia solution until a brown iron(1rr) hydroxide precipitate separates out and the solu- tion smells of ammonia. Add a 10 ml excess of smmonia solution (pH> 10) and some analytical filter pulp then stir with a glass rod to disperse the pulp. Cover the beaker with a watch-glass and allow the precipitate and the pulp to settle for about 2 h with occasional stirring. Filter through an 11 cm Whatman No. 40 filter-paper and wash the precipitate and the paper thoroughly with 1%96 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 ammonium nitrate solution. Transfer the paper with the precipitate into the original beaker and destroy the organic matter by refluxing with concentrated nitric acid and 30% hydrogen peroxide as usual. Evaporate the solution to dryness dissolve the residue in hot dilute nitric acid transfer the solution quantitatively into a 20 ml borosilicate beaker and evaporate first on a hot- plate and then on a steam-bath to a moist residue. Add 2 ml of 2% nitric acid to the residue briefly warm the beaker on the steam-bath transfer the solution quanti- tatively into a 5 ml calibrated flask and dilute to volume with the rinsings of the same acid.Transfer the solution into a 7 ml screw-capped plastic vial. Determination of Sc Y Nd Sm EM Dy Ho Er Tm and Yb by mult i-elemen t E TAAS Determine these elements in a group of four or three from the ion-exchange concentrates and/or the concentrates obtained by coprecipitation with calcium oxalate and hydrated iron oxide carriers (final concentration of the sample solution=O.l g ml-I or less) by following the directions given under Instrumentation and Calibration.Instrumentation and Calibration The parameters used in this work to set up the instrument are given in Table 2. A temperature programme found satisfactory for Nd Ho Er and Tm (group 1) and Y Sm and Eu (group 2) is given in Table 3. An atomization tempera- ture of 2600 "C was used for simultaneous determination of Sc Dy and Yb (see Table 4). A tertiary wavelength (326.9 nm) and a secondary wavelength (246.5 nm) were chosen for Sc and Yb respectively because of the very high sensitivities of their primary lines with the pyrolytic graphite coated graphite furnace at the concentrations of solutions employed for preparing calibration graphs and for measuring most unknown samples.The determination of REE in most rock samples tested in this method worked satisfactorily with calibration graphs prepared from four synthetic MRG-1 solutions with con- centrations of 0.05-0.2 g ml-' as prepared above (see under Reagents and Standard Solutions). To prepare calibration graphs 30 pl each of four standard solutions of synthetic MRG- 1 with concentrations of 0.05-0.20 g ml-I (see Table 5 for concentrations of Nd Ho Er and Tm as Group 1 elements and Table 6 for concentrations of Y Sm and Eu as Group 2 elements) were transferred into the furnace by the autosampler (see Table 7 for the programme) and the elements were atomized using 0.40 0.30 0.20 0.10 0 0.801 (b' 1 o.20 L 4 0 1x103 2x103 3x103 4x103 0 60 120 180 240 a 2 0.40 < 0.30 0.20 0.10 0.55 0.45 0.35 0.25 0.15 0 25 50 75 100 0 7.5 15.0 22.5 30.0 Concentration/ng ml-' Fig.1 Calibration graphs for (a) Nd; (b) Er; (c) Ho; and (d) Tm at an atomization temperature of 3000 "C. Quadratic correlation Nd 0.9943; Er 0.9959; Ho 0.9970; and Tm 0.9975 the temperature programme in Table 3. From the calibra- tion graphs thus prepared (see Figs. 1 and 2) the concentra- tions of these elements in the unknown sample concentrate (final concentration 0.1 g ml-I or less) were determined by drying 10-40 pl of the solution followed by ashing and atomization using the temperature programme in Table 3.For the simultaneous determination of Sc Dy and Yb 20 pl of standard solutions (see Table 8) were transferred into the furnace by the autosampler and the elements were atomized using the temperature programme in Table 4. From the resulting calibration graphs (see Fig. 3) the concentrations of these elements in the unknown sample concentrate (0.1 g ml-I or less) were determined from 10-40 pl of solution. Results and Discussion Sensitivity The sensitivities for Sc Y Nd Sm Eu Dy Ho Er Tm and Yb as obtained at different temperatures using a pyrolytic graphite coated graphite tube furnace are given in Table 9. Previous valuesj5 for these elements determined using a similar type of furnace mostly at 2700 "C with a Varian single-element graphite tube atomizer (Model GTA-95) are also included in Table 9 for comparison.Table 9 shows that for some elements such as Sc Ho Er Tm and Yb the Hitachi 2-9000 multi-element instrument is either as sensitive as or more sensitive than the Varian GTA-95 instrument. The use of a higher temperature such as Table 5 Concentrations of Nd Ho Er and Tm (ng m1-I) in synthetic standard solutions for preparation of calibration graphs Element Standard 1* Standard 2 Standard 3 Standard 4 Standard 5 Nd 0 1000 2000 3000 4000 Ho 0 25 50 75 100 Er 0 60 120 180 240 Tm 0.0 7.5 15.0 22.5 30.0 *High-purity 2% nitric acid. Table 6 Concentrations of Y Sm and Eu (ng m1-I) in synthetic standard solutions for preparation of calibration graphs Element Standard 1* Standard 2 Standard 3 Standard 4 Standard 5 Y 0 700 1400 2100 2800 Sm 0 2 50 500 750 1000 Eu 0 70 140 210 280 *High-purity 2% nitric acid.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993.VOL. 8 97 Table 7 Autosampler programme Signal mode Measurement mode Standard replicate Sample replicate Sample volume Dilution Modifier add Cup position Cuvette Firings Result on record Chart speed Data communication Calculation (groups 1 and 2) Carrier gas interruption Optical temperature control Background corrected Calibration graph I or 2 1 o r 2 x pl* Off (sample) No 1 - Y t Pyro. 0 Yes (Concentration +Absorbance) 1 On Peak height for all elements Yes On *X= 30 pl for Nd Ho Er and Tm (group 1) and Y Sm and Eu t =Up to a maximum number of 72. (group 2); 20 pl for Sc Dy and Yb. 3000 "C is desirable in order to increase the sensitivities for the determination of Y and Nd to about 5 pg g-l and those of Sm Eu Ho Er and Tm to low-ng g-l levels in some rocks.The ability of the furnace in the 2-9000 instrument (a) 0.60 - 0.40 - 0 500 1000 1500 2000 0.25 - ( b ) 0.20 - 0 250 500 750 1000 0 50 100 150 Concentrationhg mi-' Fig. 2 Calibration graphs for (a) Y (b) Sm and (c) Eu at an atomization temperature of 3000 "C. Quadratic correlation Y 0.9926; Sm 0.9989; and Eu 0.9931 1.15 - (a) 0.92 - 0 5.5 11.00 0.15 - ( b ) 0.12 - I - I I I 0 0.20 0.40 0.60 0.75 - ( c ) 0.65 - 0.55 - 0.45 - 0 0.03 0.06 0.09 0.12 Concentrationhg mi-' Fig. 3 Calibration graphs for (a) Sc (b) Dy and (c) Yb at an atomization temperature of 2600 "C. Quadratic correlation Sc 0.9983; Dy 0.9991; Yb 0.9864 to tolerate continuously a high temperature of 3000 "C for 200 or more firings without change makes it ideally suitable for routine determinations of refractory elements such as Y and the REE.In previous s t u d i e ~ ~ ~ J ~ J ~ atomization tem- peratures of 2500-2700 "C were employed with pyrolytic graphite coated graphite tube furnaces to maintain their usefulness for longer periods as at repeated firings at higher temperatures they deteriorated rapidly. Applications The validity of the proposed multi-element ETAAS method was tested with three international reference rocks CANMET MRG-1 (Gabbro Rock) and SY-2 (Syenite Rock) and SARM 1 NIM-G (Granite) with established REE contents. The results in Table 10 show that in most instances the ETAAS values are either very close to or within the range of 'recommended' or 'usable' Fig.4 shows inter-method correlation plots for Nd Sm Ho Er and Tm comparing the ETAAS and ICP-MS results for some rock samples submitted by GSC scientists for petrogenetic modelling. In all five instances the data points fall near the 45" line demonstrating good agreement between the ETAAS and ICP-MS values. Using the autosampler the determination of four ele- values. 29,32,33,35-38 Table 8 Concentrations of Sc Dy and Yb (ng ml-I) in synthetic standard solutions for preparation of calibration graphs Element Standard I* Standard 2 Standard 3 Standard 4 Standard 5 sc 0.00 2.75 5.50 8.25 11.00 DY 0.00 0.15 0.30 0.45 0.60 Yb 0.00 0.03 0.06 0.09 0.12 *High-purity 2% nitric acid.98 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 ETAAS Fig. 4 Inter-method correlation plots for ETAAS versus ICP-MS (a) Nd; (6) Sm; (c) Er; (d) Ho; and (e) Tm. Analyte concentrations inpgg-l Table 9 Sensitivities of Sc Y and REE elements as obtained with a pyrolytic graphite coated graphite tube furnace using the Hitachi 2-9000 simultaneous multi-element atomic absorption spectro- meter and comparison with some previous values Sensitivity*/pg Atomization This work with Previous values Element temperature/"C Hitachi 2-9000 with Varian GTA-95t s c Y Nd Sm Eu DY Ho Er Tm Yb 2600 2700 3000 2700 2800 2900 3000 2700 3000 2700 2 800 3000 2600 2700 2800 2700 2800 2900 3000 2 700 2800 2900 3000 2600 2700 2 800 2900 3000 2200 2600 423$ 480 4160 1900 1300 330 51 18 195 255 130 70 32 136 67 32 20 15 10 6 - - - - - - - - 3.81 1111 *Defined as the mass of the element in picograms that produces a change in absorbance compared with a pure solvent or blank of 0.0044.tSee ref. 35. $At 326.9 nm. §At 391.2 nm. 1At 398.8 nm. \/At 246.5 nm. 30 25 20 15 10 5 0 5 10 15 20 25 30 6 5 4 P) CI 4 3 B 2 1 0 1 2 3 4 5 6 1.5 - 0 0.5 1.0 1.5 2.0 Ion exchange Fig. 5 Inter-method correlation plots for oxalate versus ion- exchange preconcentration of Y and REE from CCRMP reference materials TDB- 1 WGB- 1 UMT- 1 WPR- 1 WMG- 1 and WMS- 1. (a) 0 Y; 0 Nd; and A Sm. (b) 0 Dy; 0 Er; and A Yb. (c) 0 Eu; 0 Ho; and A Tm. Analyte concentrations in pg g-'JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 99 Table 10 Determination of Sc Y and eight RE€ in MRG- 1 SY-2 and NIM-G by multi-element ETAAS after preconcentration by cation- exchange chromatography (results in pg g-l) MRG-1 (Gabbro Rock) SY-2 (Syenite Rock) NIM-G (Granite) This work* 50 14 Other values? 5 5 k 5 1 4 k 5 This work* 7.3 120 Other work 7.0 k 0.6-f 128k 17t 1201 ( 1 I 7 i25)ll 7 3 k 1 lt (8 1,84)11 i 6 + i t 171 2.4 k 0.3t 2 .3 ~ lo** 2in,ii 1 8 k 3 t 3.8 k 0.6t This work* 1 .o 113 Other work 0.5 -2.8$ 1154 80-187$ Element sc Y Nd 23 19.2 k 2.2 83 75 70** 43-83-43 14.6-2 1.5$ 0.3-2.2$ 15.4-17.2$ 68?tt 0.44,tt Sm Eu 5 1.8 4.5 k0.5 1.4 k 0.1 17 2.4 15 0.4 DY 3.5 2.9 k 0.9 21 16 Ho Er Tm Yb 0.6 1.4 0.2 0.8 0.5k0.01 1.1 k0.3 0.1 1 k0.05 0.6 4.0 13 2 18 3.4 11 2 17 3-5$ 3 ? t t 9.6-13.5$ l W t t 1.6-2.5$ 2**,tt 7- 16$ * Mean of two values.t 'Recommended concentration' in a compilation of data in ref. 36. $ See ref. 37. 4 See ref. 33. ISee ref. 29. 11 See ref. 32. **See ref. 35. tt'Usable value' reported in a compilation of data in ref. 38. Table 11 2-9000 spectrometer and comparison of results with those obtained by ICP-AES and ICP-MS (results in pg g-l) Determination of Sc Y and eight RE€ in three new CCRMP candidate reference rocks by multi-element ETAAS using a Hitachi Sample Element ETAAS (n) ICP-AES (n) ICP-MS (n) TDB-1 (Diabase Rock) sc Y Nd Sm EU DY Ho Er Tm Yb 33 36 2 3 k 5 (4) 2 7 k 1.6 (6) 9.3 k 1.7 (6) 1.9k0.1 (8) 5.5 5.7 0.93 0.97 2.8 k 0.2 (6) 0.34k0.02 (10) 2.5 2.5 33 30 26 k 5 (6) 6.4k0.7 (6) 5.8k0.5 (7) 1.10k0.22 (6) 0.39 k 0.13 (6) 23 k 5.7 (6) 1.9k0.3 (6) 3.2 k 0.7 (6) 2.9 k 0.6 - 31 k4.5 (1 1) 6.8 k 0.4 (1 1) 1.9k0.1 (11) 6.4k0.4(11) 26k2.2 (9) - - 2.9k0.5 (1 1) WGB-1 (Gabbro Rock) sc Y Nd Sm EU DY Ho Er Tm Yb s c Y Nd Sm Eu DY Ho Er Tm Yb UMT-1 (Ultramafic Rock) 30 34 1 8 k 1.6 (4) 1 5 2 2 (6) 3.4k0.9 (6) 1.3k0.16 (4) 2.8k0.2 (4) 0.46 0.47 1.4k0.5 (3) 0.22k0.10 (5) 1.4k0.1 (4) - 14k3.3 1 3 k 1 2.7k0.2 (6) 1.3k0.10 (1 1) 2.8k0.2 (11) 30 33 14k3.5 11 k 3.4 2.6 k 0.7 (6) 1.3k0.50 (6) 2.6 k 0.5 (6) 0.5 1 k 0.09 (6) 0.20 k 0.02 (6) 1.5k0.3 (6) 1.5k0.3 (6) 14 18 3.3k 1.1 (6) 1.3k0.4 (6) 0.35 k 0.12 (4) 1.3k0.5 (6) 0.26 2 0.06 (6) 0.8k0.2 (6) 0.10+0.03 (6) 0.8 20.2 (6) 6.5k2.5 (6) - 1.4k0.1 (11) 14 16 9.5 k 1.6 (4) 1.3 k0.2 (6) 0.32 k 0.04 (6) 1.8 k 0.3 (4) 0.23 0.20 5 k0.8 (6) 0.8 k 0.2 (8) 0.9 k 0.2 (4) 0.10 k 0.02 (8) - 6.5k0.6 (1 1) 5k0.9 (1 1) 1.3k0.2 (11) 1.5k0.2 (11) 0.35 k 0.03 (1 1) - - 0.7kO.l (11) ments in approximately 100 or more sample solutions could be completed per day.1 (Diabase Rock) WGB- 1 (Gabbro Rock) UMT- 1 (Ultra- mafic Ore Tailings) WPR- 1 (Peridotite Rock) WMG- 1 (Mineralized Gabbro) and WMS- 1 (Massive Sulfide Min- eral) were carried out using the proposed multi-element ETAAS method and by ICP-AES and ICP-MS. Determination of Sc y and eight REE in Six new CcRMp reference materials Determinations of Sc Y Nd Sm Eu Dy Ho Er Tm and Yb in six CCRMP candidate reference materials viz. TDB- Before determination the preconcentration of Sc Y and the REE was done mostly from replicate sample solutions100 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 ~ Table 12 Determination of Sc Y and eight REE in three new CCRMP candidate reference rocks by multi-element ETAAS using a Hitachi 2-9000 spectrometer and comparison of results obtained by ICP-AES and ICP-MS (results in pg g-l) Sample Element ETAAS ( n ) ICP-AES (n) ICP-MS ( n ) WPR-1 (Peridotite) sc Y Nd Sm Eu DY Ho Er Tm Yb sc Y Nd Sm Eu DY Ho Er Tm Yb s c Y Nd Sm Eu DY Ho Er Tm Yb WMG-1 (Mineralized Gabbro) WMS-1 (Massive Sulfide Mineral) 10 6 9 8 5.5 f 3.7 (4) I .5 f 0.9 (4) 0.3 0.3 1.8 1.5 0.13 0.1 1 0.55 k 0.20 (4) 0.57 f 0.02 (6) 0.13 0.16 20 21 13 12 12k4.5 (6) 2.9 2.9 0.8 0.9 3.2 3.2 0.40 0.43 1.3f0.45 (5) 0.2 f 0.04 (5) 1.6k0.2 (4) 1.8 1.3 5.9 5.0 4.3f1.1 (7) 0.6 f 0.1 (4) 0.1 0.1 0.7 0.8 0.08 k 0.0 1 (5) 0.06 f 0.01 (4) 0.31 k0.03 (7) 0.30k0.04 (6) - 8.4 4.2 4.7 f 0.3 (9) 5.92 1.4 (7) 1 .o f 0.2 (9) 0.3 k 0.05 (9) 1.3 k 0.4 (9) 4.7f2.1 (4) 2.7k 1 (4) 1.0k0.3 (4) 0.28 f 0.14 (4) 1.2 2 0.9 (4) - 0.18 k 0.04 (4) - 0.54 k 0.17 (4) - 0.07 2 0.02 (4) 0.50k0.10 (9) 0.50+-0.20 (4) - 21,21 1 2 f 1 (9) 122 1.8 (8) 11 f 1 (7) 9k0.4 (7) 2.8f0.2 (10) 2.4 f 0.2 (8) 0.74 2 0.03 (9) 0.71 k0.03 (8) 2.3f0.1 (9) 2.3k0.13 (8) - 0.48 k 0.03 (8) - 0.2 k 0.02 (8) - 1.1 k0.3 (8) 1.1 k0.2 (9) 1.220.2 (8) - 1.4 1.0 2k0.2 (9) 3.82 1.1 (6) 1.9k0.3 (9) 0.6k0.1 (6) 0.5 kO.l (9) 0.14 f 0.04 (9) 0.44fO.l (9) 0.4k 0.1 (9) 2.1 k 0.6 (9) 0.1 1 k 0.02 (9) 0.08 k 0.0 1 (9) 0.24k0.04 (9) 0.03 2 0.0 1 (9) 0.25 f 0.07 (9) - - - 0.23 f 0.04 (9) using an ion-exchange separation procedure.Also from some duplicate sample solutions preconcentration of these elements was performed using the calcium oxalate and hydrated iron oxide coprecipitation technique.As observed previously with some USGS reference rocks and CCRMP iron-formation reference materials,** satisfactory agree- ment was also found in this work between the results of these two sets of concentrates for Y and REE in the six new CCRMP candidate reference rocks (see Fig. 5 for inter- method correlation plots for oxalate versus ion-exchange preconcentration where most of the data points fall near the 45" line). The results for Sc Y and eight REE in the six new CCRMP reference samples (with 95% confidence limits where sufficient data were available) as obtained by ETAAS ICP-AES and ICP-MS methods on the same solutions (ion-exchange and/or oxalate preconcentrates) by three independent operators at the GSC laboratories are given in Tables 11 and 12.If the differences in the analytical mode used are considered (e.g. preconcentration procedure sample volume dilution calibration graph interferences final measurement technique and indepen- dent operator) the differences in results for high Y Nd and Sm concentrations in some samples such as TDB-1 and WGB-1 by the three methods appear to be minor. In most other instances the results are found to be of similar magnitude. Conclusions The determination of Sc Y and eight REE in geological materials using a multi-element graphite furnace atomic absorption spectrometer equipped with a Zeeman-effect background corrector and a large autosampler disc (capa- city 72 samples per run) is faster and more accurate than with a conventional single-element instrument without such background correction.The results are comparable to those of other instrumental techniques such as ICP-AES and ICP-MS. As the method is highly sensitive and usable with as little as 10-40 pl sample solution it is ideally suited for samples with very low REE contents and/or available only in small amounts. The proposed method has been in use in the GSC for about 18 months as an inexpensive procedure for the determination not only of trace and ultra-trace amounts of Sc Y and REE in geological materials but also of groups of other elements such as noble metals in rocks and metallurgical samplesJ9 and Li Cd Pb and Sb in rocks and environmental samples.4o The author is indebted to the coordinator of CCRMP for supplying the six new candidate reference materials used in this work and to his colleagues R.A. Meeds and N. B. Bertrand for determining Y and REE in them by ICP-AES and ICP-MS respectively. References 1 Haskin L. A. Wildeman T. R. and Haskin M. A. J. Radioanal. Chem. 1968 1 337. 2 Rey P. Wakita H. and Schmitt R. A. Anal. Chim. Acta 1970 51 163. 3 Roelandts I. Geostand. Newsl. 1977 1 7. 4 Brunfelt A. O. Roelandts I. and Steinnes E. Analyst 1974 99 277. 5 Kantipuly C. J. and Westland A. D. 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Talanta in the press. 40 Sen Gupta J. G. in preparation. Paper 2/03805F Received July 16 I992 Accepted September 24 1992