JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL. 6 Determination of Minor and Trace Elements in Ferrochromium and Ferromanganese by Inductively Coupled Plasma Atomic Emission Spectrometry* 535 Ivan HlavaCek and lrena HlavaCkova Chemical Laboratories of Poldi United Steelworks CS-272 62 Kladno Czechoslovakia A procedure using inductively coupled plasma atomic emission spectrometry (ICP-AES) has been developed for the analysis of ferrochromium and ferromanganese i.e. for the determination of aluminium cobalt chromium copper manganese molybdenum nickel silicon titanium and vanadium. The sample is dissolved with a mixture of phosphoric and sulphuric acids in a polytetrafluoroethylene vessel without the application of hydrofluoric acid. In this way both ferrochromium and ferromanganese samples are quantitatively converted into a soluble form. No separation of the analyte elements from the matrix is required.The sample dissolution procedure the instrumental conditions for ICP-AES some important spectral interferences the precision of determination and detection and determination limits are given. The detection limits were 12 ng ml-I for Co Cu and V; 60 ng ml-l for Mn Mo Ni Si and Ti; 120 ng ml-I for Al and Cr. The precision of determination characterized by ten standard deviations was 20-40 ng ml-l for Co Cu and V; 200-400 ng ml-l for Al Cr Mn Mo Ni Si and Ti. The sample dissolution was also performed in a microwave oven. The analytical procedures were verified by means of Czechoslovak British and German ferrochromium and ferromanganese certified reference materials.The silicon content in the ferroalloys was also verified by a gravimetric method For comparison the samples were analysed by flame atomic absorption spectrometry. Keywords Inductively coupled plasma atomic emission spectrometry; ferrochromium and ferromanganese; multi-element analysis; phosphoric acid and silicon; microwave digestion The steel producing industry requires rapid and reliable analysis of ferroalloys such as ferrochromium and ferro- manganese. Inductively coupled plasma atomic emission spectrometry (ICP-AES) enables complex routine chemical analyses to be performed which were previously carried out by a combination of classical and instrumental analytical procedures. The main interest is focused on the multi- element analysis of ferrochromium (carbon content 0.0 1 - 1 0%) and ferromanganese by ICP-AES.Scott et a!. analysed ferromanganese for aluminium boron cobalt chromium copper molybdenum nickel titanium and vanadium in the presence of the matrix elements e.g. iron and manganese. They found that the effects of the matrix elements on the detection limits were insignificant. The effect of the ferromanganese matrix on the intensities of the spectral lines for the analyte elements was negligible. Kanaev and Trofimov2 have reviewed the flame atomic absorption spectrometry (FAAS) procedures used for the analysis of various ferroalloys including ferrochromium and ferromanganese. Foster and Garden3 determined the silicon content in ferromanganese samples after dissolution with hydrofluoric hydrochloric and nitric acids.For ferrotungsten analysis using ICP-AES the solid sample (including silicon) was dissolved using phosphoric acid4 in a polytetrafluoroethylene (PTFE) vessel provided that the silicon is bonded as silicotungstic acid. The sample decomposition with phosphoric acid was used for both low- and high-alloy steels e.g. corrosion-resistant and high- speed and nickel-base alloys (Nim~nic).~i~ Experimental Instrumentation All measurements were made by means of an ARL 33000 LA sequential emission spectrometer with an inductively coupled argon plasma. The spectrometer is equipped with a Commodore 64 computer connected on-line. A Henry *Presented in part at the VII Polish Spectroanalytical Confer- ence and X CANAS (Conference on Analytical Spectroscopy) Torun Poland 1988.radiofrequency generator with an operating power of 1250 W an operating frequency of 27.12 MHz and a maximum reflected power of 10 W was employed. A Fassel-type quartz plasma torch was used. The pneu- matic concentric glass nebulizer (Meinhard type) operated under a pressure of 0.3 MPa. The argon carrier gas of flow rate 1.15 1 min-l passed through the nebulizer after being moistened by means of a bubbler. The sample uptake was by means of the Venturi effect without the use of a peristaltic pump. The sample uptake rate was 1.5-1.8 ml min-l for water and depended on the nebulizer used. The spectrometer consisted of a monochromator with a 1 m radius concave grating ( 1440 lines mm-l) in a Paschen- Runge mounting with fixed secondary slits which were sequentially opened and shut as required.The reciprocal dispersion was 0.695 nm mm-l in the first order. The observation height was 14 18 22 or 26 mm. A Perkin-Elmer 503 atomic absorption spectrometer equipped with an electrodeless discharge lamp source was used for comparative analysis by FAAS. A commerical domestic microwave oven Philips M 704 with a timer and variable power settings equivalent to outputs of 210 330 450 and 600 W was used. Reagents and Solutions All of the chemicals used were of analytical-reagent grade and solutions were prepared with de-ionized water. All stock solutions of metals were prepared from high-purity metals (99.9% or higher) and stored in polyethylene bottles. The detailed preparation of the element stock solutions has been described previ~usly.~ Hydrochloric acid (36% m/m) nitric acid (65% m/m) sulphuric acid (98% m/m) phosphoric acid (85% m/m) and hydrogen peroxide (30% m/m) were also used.Instrumental Conditions for ICP-AES The instrumental conditions for ICP-AES are given in Table 1. All of the measurements were performed using the spectral lines recommended by the manufacturer except for536 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 199 1 VOL. 6 Table 1 Analyte elements and instrumental conditions for ICP-AES Secondary Observation Element Wavelength/ slit-width/ height/ and line nm Pm mm A1 I c o I Cr I c u I Mn I1 Mo I Ni I1 Si I Ti I v I1 394.401 350.228 360.533 324.754 257.610 3 17.035 23 1.604 251.61 1 363.546 31 1.071 75 75 75 75 75 75 75 75 75 75 22 26 22 22 18 22 18 18 22 18 cobalt where the Co I 350.228 nm line was used instead of the original Co I1 238.892 nm line.The original cobalt line at 238.892 nm was severely affected by the iron spectra. The choice of observation height for the analyte elements had been made previ~usly.~ Table 2 shows a summary of spectral interferences of accompanying elements when measuring at the instru- mental conditions chosen. The linearity of the measure- ments was confirmed by analyses of prepared sample solutions; the analyte elements were added within the expected concentration range of the real ferroalloy samples. Instrumental Conditions for FAAS For verification of the accuracy of the results the determi- nation of the elements was carried out by FAAS using the same sample solutions as for ICP-AES and from a sulphuric acid medium for ferrochromium samples and a hydrochloric and nitric acid medium for ferromanganese samples.For the determination of elements in sample solutions containing phosphoric acid depression of the signals was found. The effect of silicon on the determina- tion of manganese' in ferrochromium was almost elimi- nated using a dinitrogen oxide-acetylene flame. Sample Preparation ICP-AES Ferrochromiurn. Weigh 0.500 g of sample in the fine powder form into a PTFE beaker (it is important for the so-called 'hard ferrochromium' i. e. ferrochromium con- taining more than 2% of carbon to be ground to a particle size of less than 0.15 mm without separating the various size fractions.) Add 10 ml of sulphuric acid (1 + 1) and 25 ml of concentrated phosphoric acid.Dissolve under a PTFE deckel (the water must not be evaporated from the acid mixture too quickly) by heating at about 150 "C. After sample dissolution remove the deckel and then evaporate the solution until white fumes of sulphur trioxide appear at a temperature of between 180 and 220 "C for about 10 min cool and dilute immediately to 250 ml with water in a glass calibrated flask. Ferrornanganese. Weigh 0.500 g of the sample in a fine powder form into a PTFE beaker. Add 10 ml of sulphuric acid (1 + l) 25 ml of concentrated phosphoric acid and 10 ml of concentrated nitric acid. Dissolve under a PTFE deckel by heating at about 100 "C. After sample dissolution remove the deckel and then evaporate the solution until white fumes of sulphur trioxide appear at a temperature of between 180 and 220 "C for about 10 min cool add a few drops of hydrogen peroxide until the solution is colourless and dilute immediately to 250 ml with water in a glass calibrated flask.The sample solutions obtained by this process were clear and stable for long periods and accurate analytical results were obtained with the same sample solutions 3 months later. Microwave digestion For sample preparation using the microwave oven weigh 0.500 g of sample (ferrochromium or ferromanganese) into a PTFE beaker. Add the same amounts of acids as before (see procedure for ferrochromium or ferromanganese) to the samples. Leave the ferromanganese samples for 3 min. Place the PTFE beaker with sample in the microwave oven heat for about 10 min at 330 W cool and dilute imme- diately (after adding a few drops of hydrogen peroxide for ferromanganese) to 250 ml in a glass calibrated flask.FAAS Ferrochromium. Weigh 0.500 g of sample into a glass beaker add 20 ml of sulphuric acid (1 + 1) and dissolve by heating at about 100 "C. After sample dissolution evapo- rate the solution until white fumes of sulphur trioxide appear cool and dilute to approximately 50 ml. Add 5 ml of concentrated nitric acid heat to boiling cool dilute to 100 ml with water in a glass calibrated flask and filter. When determining silicon it is necessary to use the sample decomposition procedure as described under ICP-AES. Ferromanganese. Weigh 0.500 g of sample into a glass beaker add 10 ml of nitric acid (1 + 1) and 10 ml of hydrochloric acid (1 + 1) and dissolve by heating at about Table 2 Interferences from added elements of 1 % concentration (ICP-AES) Background equivalent concentration (Oh) Interfering element A1 c o Cr c u Mn Mo Ni Si Al c o Cr c u Fe Mn Mo Ni Si Ti V - t O .O O 1 0.0002 <0.0001 <0.0001 0.0001 0.0003 0.001 1 0.0002 0.000 1 5 <0.0001 <o.oooo 1 0.0001 3 0.0000 1 0.00004 0.0000 1 0.0004 0.0004 0.0001 0.00025 0.000 1 2 - tO.OOO 1 0.025 (0.00 1 0.0045 <0.00001 0.000 1 0.00004 0.0007 0.0002 0.0003 - <0.0000 1 < 0.00002 0.00003 <0.00001 tO.OOOO 1 -0.00035 <0.00001 <o.ooo 1 0.00006 <0.00001 - <0.00002 <o.oooo 1 t0.00002 (0.001 t0.00005 - <0.00003 <0.00001 <o.ooo 1 <0.00005 0.00005 0.00005 0.0003 <0.0002 <0.0001 0.001 0.0002 t0.00005 <0.0001 0.00 12 (0.001 - t0.00005 (0.005 t 0.0005 t0.00 1 0.000 1 0.0002 0.0002 <o.ooo 1 0.0002 0.00005 - t 0.00005 <0.0002 0.000 1 t0.00003 <0.0005 <0.0004 0.0075 <0.00006 <0.0003 t0.0003 - Ti 0.000 1 0.0006 0.0005 0.0004 0.0005 <0.0002 0.08 0.0001 5 0.001 0.0007 - V < 0.00005 ~0.00015 0.0003 0.00005 0.00006 t0.0005 0.00 1 5 <0.00001 <0.0001 0.01 1JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL.6 537 100 "C. After sample dissolution heat to boiling cool then dilute to 100 ml in a glass calibrated flask and filter. When determining chromium it is necessary to use the sample decomposition procedure described under ICP-AES because chromium might not otherwise be quantitatively converted into a soluble form.A11 of the sample solutions analysed by ICP-AES or FAAS contained the same amounts of acid so that undesirable effects of for example viscosity and density could be avoided. A blank and synthetic samples were used for calibration and were prepared by the same procedure as for the real ferrochromium or ferromanganese samples. The matrix element composition was simulated using high-purity metals. For example both the blank and synthetic calibra- tion samples contained 0.15 g of iron metal and 0.35 g of chromium metal for the ferrochromium samples containing 30 k 5% of iron and 70 f 5% of chromium. Similarly the blank sample and synthetic calibration samples contained 0.05 g of iron metal and 0.40 g of manganese metal for the ferromanganese samples containing 10 -t 5% of iron and 80 t 5% of manganese.The synthetic calibration samples also contained known additions of the analyte elements in the concentration range to be considered. For practical purposes the matrix composition of the calibration samples can also be timulated using the Czecho- slovakian Analytical Normal (CSAN) Certified Reference Materials (CRM) 4-2-0 1 ferrochromium and CSAN CRM 4-3-0 1 ferromanganese with known additions of some analyte elements. Results and Discussion The dissolution of the ferrochromium and ferromanganese samples using hydrochloric nitric or sulphuric acid is sometimes unsuitable because of the precipitation of silicic acid from sample solutions of high silicon content. Further- more some analyte elements can be adsorbed by the precipitated silicic acid causing a loss of analyte elements from the sample solution after filtration.In addition sample dissolution can often be incomplete. Dissolution of ferrochromium especially of 'hard ferrochromium' is 100 ' 50 .$ 0 I C 0) w .- PB - A' / 50 /+ - /* 2 0 - * /* c 0) 0 2 4 6 8 1 0 0 2 4 6 8 1 0 0 .- Q) tT ; 100 - v - 50 - 0 - + 0 2 4 6 8 1 0 t 1 I " " 0 2 4 6 8 1 0 very difficult; it is possible with repeated applications of sulphuric acid but it is time consuming. Chromium(mr) sulphate precipitates from ferrochromium sample solutions in the presence of sulphuric acid particularly after evapora- ting to white fumes of sulphur trioxide. Application of hydrofluoric acid is also unsuitable because the nebulizing system consists of a glass nebulizer a glass chamber and a quartz plasma t o r ~ h .~ Unfortunately in this work the spectrometer was not equipped with an HF resistant nebulizing system. Furthermore the sample dissolution with hydrofluoric acid or various acid mixtures was also incomplete. Fusion of the ferrochromium samples with sodium peroxide contaminates the final sample solutions with alkali salts and crucible material e.g. iron and nickel. Also nebulizer clogging ionization interferences and sample contamination by analyte elements can occur. For this reason an alternative procedure for sample dissolution was investigated. The potential problems were solved by the application of phosphoric acid which gave good results. For example a ferrochromium sample con- taining up to about 10% of carbon was dissolved and analysed without any problems.It has been found that phosphoric acid with the potential addition of sulphuric acid can dissolve all analyte and matrix elements including silicon. However it is necessary to perform the sample dissolution in PTFE vessels because both glass and quartz vessels are corroded during the procedure thereby contami- nating the sample solutions with silicon. It is presumed that SiP207 is formed during the dissolu- tion process.8 Silicon is determined together with the other analyte elements thereby eliminating the need for a separate gravimetric determination of silicon. The use of a microwave oven for sample dissolution was also examined using the same procedure as in the PTFE beakers under atmospheric pressure.The digestion time was reduced from 2-3 h to about 10 min for both ferrochromium and ferromanganese samples. The spectral interferences (ICP-AES) of the matrix elements on the intensities of the spectral lines of the analyte elements were investigated. Table 2 shows the effects of the interfering elements for the chosen instrumen- tal conditions. A substantial interference effect was found 0 1 2 3 4 5 Mo /' +/+ 1 1 1 1 1 0 2 4 6 8 1 0 0 4 8 12 16 20 0 4 8 12 16 20 Concentration/pg mi-' Fig. 1 Calibration graphs (background corrected) for A pure aqueous acid solutions; and B synthetic ferrochromium solutions538 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 199 1 VOL. 6 ~~ Table 3 Comparison of results (O/O) for ferrochromium reference materials CSAN CRMs 4-2-01 and 4-2-02 British Chemical Standard (BCS) CRM 203/2 and Bundensanstalt fur Materialforschung und -prufurg (BAM) Euronorm CRM (ECRM) 533-1 are low carbon content; CSAN CRM 4-2-03 is of mid-range carbon content; and CSAN CRM 4-2-04 BCS-CRM 204/1 and BAM ECRM 530-1 are high carbon content Sample Method/source A1 Co c u Mn Mo Ni Si Ti V &AN CRM 4-2-01 (0.073% C 70.36% Cr) CSAN CRM 4-2-02 (0.01 1% c 84.70% Cr) (1.27% C 66.86% Cr) (6.18% C 70.27% Cr) (0.027% C 7 1.7% Cr) (4.56% C 66.3% Cr) (6.46% C 64.9 Cr) (0.008~/0 c CSAN CRM 4-2-03 CSAN CRM 4-2-04 BCS-CRM 203/2 BCS-CRM 2041 1 BAM ECRM 530-1 BAM ECRM 533-1 66.2% Cr) * Informative value.Certificate FAAS Certificate FAAS Certificate FAAS Certificate FAAS Certificate FAAS Certificate FAAS Certificate ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES Certificate ICP-AES - (0.02 (0.02 (0.02 < 0.02 (0.02 (0.02 (0.02 (0.02 - - - - - (0.02 (0.02 (0.02 0.56 0.615 0.008 - (0.02 - 0.04 0.040 0.015 0.013 0.04 0.040 0.03 0.033 0.044 0.045 0.045 0.055 0.053 0.038 0.036 0.053 0.053 - - - - - 0.016 0.0 1 5 0.014 0.013 0.022 0.02 1 0.015 0.0 12 0.010 0.010 0.013 0.01 1 0.007 0.006 - - - - - - 0.009 - 0.30 0.31 0.27 0.275 0.27 0.27 0.08 0.07 0.30 0.315 0.19* 0.165 0.16 0.16 0.155 0.18 0.165 - - - - - (0.0 1 (0.01 (0.01 (0.01 (0.0 1 (0.01 (0.01 (0.0 1 (0.01 (0.01 (0.01 (0.01 (0.01 - - - - - - - (0.01 - 0.33 0.34 0.105 0.1 1 0.36 0.37 0.28 0.27 0.22 0.24 0.40* 0.38 0.40 0.19 0.19 0.31 0.305 - - - - 1.96 2.00 1.98 0.20 0.18 1.58 1.65 1.59 0.73 0.75 0.72 0.67 0.67 1.53* 1.55 1.52 0.49 0.52 0.09 0.09 5 - - - t0.005 (0.01 - - (0.01 - - tO.O1 - - (0.01 (0.005 (0.01 - - - 0.015 0.05 0.045 - t o .0 1 - 0.088 0.089 0.04 1 0.042 0.064 0.064 0.12 0.115 0.180 0.178 0.185 0.105 0.103 0.23 0.24 0.023 0.023 - - - - Table 4 Comparison of results (O/O) for real ferrochromium samples Sample (7.1 7% c 69.10% Cr) (6.18% C 70.55% Cr) (0.145% C 70.00% Cr) (0.067% C 70.00% Cr) (0.25°/o C 70.50% Cr) (1.66% C 68.65% Cr) (0.42% C 70.00% Cr) (6.92% C 69.65% Cr) A1 A2 A3 A4 A5 A6 A7 A8 Method/source Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravime tric FAAS ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES c o 0.04 I 0.04 1 0.036 0.038 0.04 1 0.040 0.040 0.038 0.040 0.039 0.04 1 0.040 0.040 0.041 0.035 0.035 - - - - - - - - at the Cr I 360.533 nm spectral line for samples containing cobalt and high iron contents.The interfering spectral lines are Co I 360.536 nm and Fe 1360.546 nm. In practice the spectral matrix interference was eliminated using a blank and calibration samples that contained almost iden- tical amounts of the matrix elements such as iron and chromium for ferrochromium or iron and manganese for ferromanganese (described under Sample Preparation). The possible interferences (see Table 2) were corrected if necessary for the increase or decrease in the spectral background due to differences in the sample matrix c u 0.027 0.026 0.029 0.029 0.026 0.027 0.032 0.033 0.022 0.023 0.032 0.032 0.026 0.027 0.035 0.034 - - - - - - - - Mn Ni 0.47 0.38 0.45 0.36 0.86 0.34 0.84 0.32 0.2 1 0.33 0.20 0.32 0.2 1 0.31 0.2 1 0.30 0.18 0.35 0.195 0.33 0.40 0.36 0.4 1 0.35 0.38 0.35 0.4 1 0.36 0.47 0.31 0.47 0.32 - - - - - - - - - - - - - - - - Si 0.90 0.9 1 1.41 1.40 1.34 1.34 1 .oo 0.98 0.345 0.34 0.63 0.62 1.45 1.44 1.05 1.05 - - - - - - - - composition.(The chromium or manganese contents of the matrix in real ferrochromium and ferromanganese samples were determined by titrimetric methods because of the greater precision of determination.) The influence of the sample matrix on the slopes of the calibration graphs for the analyte elements was also investigated. The calibration graphs for some analyte elements in ferrochromium are shown in Fig. 1.These graphs were measured for both pure aqueous acid solutions of the elements and synthetic ferrochromium solutions containing 0.6 mg ml-l of iron and 1.4 mg ml-l ofJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL. 6 539 Table 5 Comparison of results (Yo) for reference materials ferromanganese. CSAN CRM 4-3-01 and BCS-CRM 280/1 are of low carbon content; and CSAN CRM 4-3-02 and BCS-CRM 208/1 of high carbon content Sample (1.03% C 90.62% Mn) CSAN CRM 4-3-01 CSAN CRM 4-3-02 (6.74% C 77.56% Mn) Methodlsource Certificate NAA FAAS Certificate NAA FAAS ICP-AES ICP-AES ICP-AES Certificate FAAS ICP-AES ICP-AES Certificate FAAS ICP-AES ICP-AES A1 c o 0.038 0.034 0.035 0.066 0.072 0.070 - - Cr 0.39 0.35 0.37 0.053 0.06 0.06 0.16* 0.155 0.56* 0.53 0.55 - - - - - - cu 0.060 0.066 0.063 0.I 1 0.155 0.150 0.04* 0.041 0.038 0.04* 0.039 0.037 - - - - - Mo 0.01 3 0.01 5 0.01 5 0.027 0.03 0.025 - - Ni Si 0.69 Ti V - (0.005 (0.02 - 0.023 0.023 - - 0.042 0.043 - - 0.046 0.043 - - 0.045 0.044 - 0.05 0.05 0.005 (0.01 - 0.70 0.03* - 0.005 (0.01 - 0.08* 0.06 0.07 - - 0.01 0.01 5 - (0.005 (0.02 0.14 0.145 - 0.02 0.01 0.98 0.89 0.07 2.01 - Insoluble residue (6.80% C 76.4% Mn) Insoluble residue (0.47% C 80.4% Mn) Insoluble residue BCS-CRM 208/1 BCS-CRM 280 0.04 0.05 0.036 0.036 0.01 5 0.01 5 0.075 0.07 - 0.008 (0.02 - - 0.04 5 0.045 - - 0.02 5 0.02 - - 0.1 1 0.10 - 1.97 0.025 * Informative value not certified. Table 6 Comparison of results (To) for real ferromanganese samples Sample Method/source Co c u Ni Si - 0.535 0.16 - 0.165 0.535 - 0.47 0.165 0.49 - 0.50 0.16 - 0.17 0.525 - 2.50 0.04 - 0.035 2.46 - 0.13 0.12 - 0.12 0.13 - 2.47 0.04 - 0.04 2.42 0.155 - B1 (6.45% C 79.55% Mn) (6.64% C 79.30% Mn) (6.54% C 80.50% Mn) (5.68% C 77.50% Mn) (6.50% C 79.25% Mn) (5.67% C 69.25% Mn) B2 B3 B4 B5 B6 Gravimetric FAAS Gravimetric FAAS Gravimetric FAAS Gravime tric FAAS Gravime tric FAAS Gravime tric FAAS ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES - 0.099 0.098 0.099 0.097 0.099 0.099 0.018 0.015 0.077 0.078 - - - - - 0.09 0.09 0.09 0.085 0.09 0.09 0.02 0.015 0.06 0.06 - - - - 0.024 0.020 0.05 0.04 Table 7 Precision of determination of analyte elements (Yo) Sample Parameter A1 c o Cr Cu Mn Mo Ni Si Ti V &AN CRM 4-2-0 1 Average ( n = 1 2) ferrochromium t0.02 0.040 - 0.015 0.31 (0.01 0.34 1.98 t0.01 0.089 0.0023 SD* - 0.0007 - 0.0013 0.008 - 0.016 0.022 - RSDT - 1.9 - 8.7 2.5 - 4.7 1.1 - 2.6 Average ( n = 6) SD - 0.0013 0.012 0.0010 - 0.005 0.008 0.018 - 0.0010 RSD - 3.6 3.1 1.5 - 33.3 15.7 2.5 - 4.3 &AN CRM 4-3-0 1 ferromanganese t 0 .0 2 0.035 0.37 0.063 - 0.015 0.05 0.70 (0.01 0.023 * SD Standard deviation. t RSD Relative standard deviation. chromium. Corrections (see Table 2) were applied for the increase in the spectral background caused by the presence of the sample matrix elements. The slopes of the two calibration graphs for every analyte element were almost identical the relative differences were found to be <lo/o. No significant matrix effect occurred for these elements. A small but detectable difference in the slopes of the calibra- tion graphs for aluminium was observed. Similar results were obtained for ferromanganese in both the pure aqueous acid solutions of the analyte elements and the synthetic ferromanganese solutions containing 0.2 mg ml-I of iron and 1.6 mg ml-l of manganese.The matrix effect was eliminated by simulating the matrix composition in both the blank and calibration samples. The effect of sodium salts which contaminated the synthetic calibration samples taken from the silicon stock540 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL. 6 solution has been described previ~usly.~ By using suitable standard ferrochromium and ferromanganese samples for calibration i.e. CRMs the sodium effect was eliminated. The accuracy of ICP-AES was verified by means of the Czechoslovak British and German reference materials and real ferrochromium and ferromanganese samples.For comparison some samples were analysed by FAAS. In some instances the silicon content was also verified by a gravimet ric met hod. The certified values and the analytical results for the reference materials and real ferrochromium samples obtained using FAAS and ICP-AES are summarized in Tables 3 (reference materials) and 4 (real samples) includ- ing the matrix composition. For silicon the results of the gravimetric analysis are given in Table 4. Special emphasis was given to the silicon determination and therefore the correlation of results obtained using ICP-AES and a gravimetric method was studied over a long period. Altogether 100 ‘soft’ (<2% of carbon) and 100 ‘hard‘ (2- 10% of carbon) ferrochromium samples were analysed by both methods.An evaluation of the results obtained was carried out by the method of linear regression. The correlation coefficients for soft and hard ferrochromium were found to be 0.997 and 0.988 respectively. The certified values and results for the reference ma- terials and real ferromanganese samples obtained using FAAS and ICP-AES are summarized in Tables 5 (reference materials) and 6 (real samples) including _the matrix composition For the ferromanganese samples CSAN CRM 4-3-01 and CSAN CRM 4-3-02 the results obtained using neutron activation analysis (NAA) are also shown in Table 5 . The results of gravimetric analysis for silicon are given in Table 6 . A difference between the certified value and the value obtained using ICP-AES for Si in the ferromanganese sample BCS-CRM 208/1 was also found (Table 5).The insoluble non-metallic residue that remained after sample dissolution was analysed using ICP-AES after separation by membrane filtration and fusion with a mixture of sodium carbonate and sodium tetraborate (1+1) in a platinum crucible. The residue contained nearly 100% silicon dioxide. The same analysis was carried oyt for the ferromanganese reference materials samples CSAN CRM 4-3-02 and BCS-CRM 280. The results obtained for insoluble silicon are also included in Table 5. Both the ferrochromium and the ferromanganese samples are quantitatively dissolved using the described decomposi- tion procedures except when aluminium and silicon (bonded as oxides) are pre~ent.~ If the ferroalloy sample contains a non-metallic component e.g.as in a slag it is necessary to analyse an insoluble residue after fusing. Therefore it is necessary to check visually the final sample solutions. The precision cf the analytical method using ICP-AES yas studied for CSAN CRM 4-2-01 ferrochromium and CSAN CRM 4-3-0 1 ferromanganese. The statistical data are presented in Table 7. The limits of detection defined as three times the standard deviation of the background noise and determi- nation defined as ten times the standard deviation of the Table 8 Limits of detection and determination Limit of detection Limit of determination Element O/o ng ml-I Oh ng ml-‘ A1 0.006 Co 0.0006 Cr 0.006 Cu 0.0006 Mn 0.003 Mo 0.003 Ni 0.003 Si 0.003 Ti 0.003 V 0.0006 20 12 20 12 60 60 60 60 60 12 0.02 0.002 0.02 0.002 0.0 1 0.0 1 0.0 1 0.0 1 0.0 1 0.002 400 40 400 40 200 200 200 200 200 40 background noise for all the analyte elements in the presence of the matrix elements are reported in Table 8 for the wavelengths listed in Table 1.Conclusion The ICP atomic emission spectrometric procedure can be applied effectively to the multi-element analysis of ferro- chromium and ferromanganese. The described procedure is reliable and relatively simple. Silicon can be determined together with the other analyte elements. The application of hydrofluoric acid is not required and therefore a quartz plasma torch and a glass nebulizer can be used because they are not corroded. The sample solutions obtained are clear and stable for long periods. If a microwave oven is used for the sample dissolution the digestion time is substantially reduced. The results obtained using ICP-AES are in good agreement with the certified FAAS and gravimetric values. The proposed dissolution procedure with phosphoric acid is widely applicable and has already been used for various other types of alloys and steels. References Scott R. H. Strasheim A. and Oakes A. R. ZCP Inf Newsl. 1978 3 448. Kanaev N. A. and Trofimov N. V. Atomno-Absorbcionnyi i Plamennofotometricheskii Analizy Splavov Metallurgiya Mos- cow 1983 pp. 101 and 146. Foster P. and Garden J. Analusis 1973-1974 2 675. HlavaEek I. and HlavaEkova I. J. Anal. At. Spectrom. 1986 1 331. HlavaEkova I. and HlavaEek I. Hutn. Listy 1984 39 890. HlavaEek I. and HlavaEkova I. Czechoslovakian Patent No. A 0 231 522 1985. Begak 0. Yu. Zh. Anal. Khim. 1975 30 2269. Philbrick F. A. Holmyard E. J. and Palmer W. G. A . Text Book of Theoretical and Inorganic Chemistry J. M. Dent and Sons London 1949 p. 587. Talvitie N. A. Anal. Chem. 1951 23 623. Paper 0/010 74J Received March 12th I990 Accepted May 9th 1991