Analysis of copper in ethanol. Final Report

Transcription

1 Key comparison CCQM-K100 Analysis of copper in ethanol Final Report Authors: Tao ZHOU () 1, Elias Kakoulides () 2, Yanbei ZHU () 3, Reinhard Jaehrling, Olaf Rienitz () 4, David Saxby () 5, Pranee Phukphatthanachai, Charun Yafa () 6, Guillaume Labarraque () 7, Oktay Cankur, Süleyman Z. Can ( ) 8, Leonid A. Konopelko, Yu, A, Kustikov () 9, Rodrigo Caciano de Sena, Janaina Marques Rodrigues, Gabriel Fonseca Sarmanho, Werickson Fortunato de Carvalho Rocha, Lindomar Augusto dos Reis () 10 1 National Institute of Metrology () - China 2 Hellenic Metrology Institute () - Greece 3 National Metrology Institute of Japan () -Japan 4 Physikalisch-Technische Bundesanstalt () Germany 5 National Measurement Institute Australia () Australia 6 National Institute of Metrology (Thailand) () - Thailand 7 Laboratorie National de Metrologie et d essais () - France 8 National Metrology Institute of Turkey ( ) - Turkey 9 D.I. Mendeleyev Institute of Metrology () - Russia 10 National Institute of Metrology, Quality and Technology ( ) - Brazil July 2014

2 Abstract The key comparison CCQM-K100 was organized by the Inorganic Analysis Working Group of CCQM to assess the capability of the national metrology institutes (NMI) to measure the mass fraction of copper in fuel ethanol produced from sugar cane. The National Institute of Metrology, Quality and Technology () acted as the coordinating laboratory. Ten NMI took part in the comparison and most of them used inductively coupled plasma mass spectrometry (ICP-MS) and ID-ICP-MS for measuring the copper content. In parallel to this key comparison, the pilot study CCQM-P127 was organized in order to give less experienced institutes the opportunity to participate. 1. Introduction The increment of renewable sources in the energy matrix of the countries is an effort to reduce dependence on crude oil and the environmental impacts associated with its use. Fuels derived from biomass (ethanol, biodiesel, etc) plays an important role as source of alternative energy and are an important way to minimize the greenhouse gas emissions. In order to help overcome the lack of widely accepted quality standards for fuel ethanol and to guarantee its competitive in the international trade market, the NMIs have been working to develop certified reference materials for bio-fuels and measurement methods. Inorganic impurities such as Cu, Na and Fe can be present in fuel ethanol and it is associated to corrosion and the formation of oxides deposits in some engine parts [1]. Considering the emerging importance of bio-fuels and the need to harmonize the quality standards, proposed a Key Comparison (KC) of Analysis of copper in ethanol and the proposal was agreed as CCQM-K100 with the parallel pilot study CCQM-P127. The KC servers to facilitate claims by participants on the Calibration and Measurement Capabilities (CMC) as listed in Appendix C of the Key Comparison Database (KCDB) under the Mutual Recognition Arrangement of the International Committee for Weights and Measures (CPIM MRA). 2

3 2. List of Participants Table 1 summarizes all participating NMIs. Table 1. List of participating NMIs No. Participant Country Contact 1 National Institute of Metrology, Quality and Technology Brazil Dr. Rodrigo Caciano de Sena 2 Physikalisch-Technische Bundesanstalt 3 National Measurement Institute Australia 4 Laboratoire national de métrologie et d'essais 5 National Institute of Metrology 6 National Metrology Institute of Japan 7 National Metrology Institute of Turkey 8 Hellenic Metrology Institute -National Reference Laboratory for Chemical Metrology 9 D.I. Mendeleyev Institute for Metrology 10 National Institute of Metrology (Thailand) 3. Samples Germany Australia France China Japan Turkey Greece Russia Thailand Dr.-Ing. Olaf Rienitz David Saxby Dr. Guillaume LABARRAQUE Tao ZHOU Yanbei ZHU Dr. Oktay CANKUR Dr. Elias Kakoulides Prof. Leonid A. Konopelko Pranee Phukphatthanachai; Dr. Charun Yafa The fuel ethanol used to produce the samples was obtained from the fermentation of extract of sugar cane. The material was provided by a Brazilian producer and used without pretreatment. The sample was homogenized and bottled in amber glass ampoules of 10 ml subjected prior to blanketing with argon and then flame sealed. Fourteen ampoules of the testing material were randomly selected from the lot and then analyzed by ICP OES coupled to an ultrasonic nebulizer with a membrane for desolvation [1]. One-way ANOVA method was used for evaluating the results and the homogeneity of the batch was expressed as the between bottles heterogeneity (u bb ) of the mass fraction of Cu [2]. The relative standard u bb was 0.20 %. Long-term and short-term stability studies were carried out for the testing material using the same analytical procedures used to the homogeneity study. The long-term stability was conducted at 20 ºC during six months and additionally the study was extended until the deadline for submission of the results. The short-term stability was conducted at 40 ºC over a four weeks period. The stability was evaluated according to the ISO GUIDE 35 criterions and the trendanalysis of results was performed [2]. The basic model for the stability study is expressed as: Y 1 = b0 + b X + ε (1) where b0 and b1 are the regression coefficients, and ε denotes the random error component. The significance of b 1 was tested comparing the b1 value with the product of the b1 uncertainty s( b1 ) and the Student s t-factor for n-2 degrees of freedom and p = 0.05 (95 % level of confidence).since b 1 < t( 0.95,n-2) s(b 1 ), the slope was insignificant and, as a consequence, no instability was observed for the test material at 20º C and 40º C during the testing period. Based on these results, the testing material was considered fit for the purpose of the comparison. 3

4 4. Technical Protocol The technical protocol, attached as Annex A, instructed participants concerning treatment of the samples, methods of measurement, reporting of results and the time schedule. The deadline for the reporting of results was originally intended to be February 29, 2012 in the protocol; it was, however, postponed to March 10, Methods of Measurement The summary of the reported technical details of the methods of measurements are listed in Table 2. Participants were allowed to use any suitable method(s) of measurements or sample preparation. Table 2. Summary of measurements methods and sample preparation used by the participants Institute Sample preparation/ Digestion Instrumental Method Analytical Method Calibration Standard (Source of Samples were evaporated to near dryness. The residues were treated with nitric acid (65 %) and evaporated. The final residue was diluted using nitric acid 0.15 mol/kg Dilution with nitric acid (1.4 % w/w). Concentration of ethanol in the samples analyzed was about 2%. Around 1.5 g of sample had been up taken from the ampoules and directly diluted with spike 65 Cu (1) (2)* Samples were evaporated to near dryness and after treated with concentrated nitric acid Sample dilution with nitric acid (1 mol/l). Concentration of ethanol in the samples analyzed was about 1 %. 0.5 ml of the samples was diluted to ca. 50 ml of 1 mol L -1 HNO 3. Concentration of ethanol in the samples analyzed was about 1 %. Co was used as internal standard. Samples were gravimetrically diluted using 2 % (w/w) HNO 3 (Initially 5-times diluted solutions were further diluted with the same solution before introduction into the ICP-MS to decrease the alcohol content to ~2 % level). HR-ICP-MS HR-ICP-MS ICP-MS HR-ICP-MS ICP-MS ICP-MS HR-ICP-MS Double Isotopic Dilution Double Isotopic Dilution Double Isotopic Dilution Isotopic Dilution Isotopic Dilution Gravimetric Standard Addition with Internal Standard Internal Standard Traceability BAM-A-primary-Cu- 1 (BAM-Germany) and 65 Cu-enriched from Chemotrade/Germany NIST SRM 3114 and 65 Cu enriched from ORNL 65 Cu enriched. Calibrant in house prepared calibration solution based on high-purity Cu CRM:GBW08615 and 65 Cu enriched (ERM-AE633) Cu standard (JCSS) and 65 Cu enriched (Oak Ridge National Laboratory) Cu and Co standards (JCSS) NIST SRM 3114 and Co as internal standard 4

5 Table 2. (continuation) Institute Sample preparation/ Digestion Instrumental Method Microwave assisted digestion (HNO 3 /H 2 O 2 ) Sample was diluted in pure deionized water. Concentration of ethanol in the samples analyzed was about 10 %. Sample preparation was carried out by making dilution with nitric acid Sample was diluted with nitric acid 2 % (v/v). Concentration of ethanol in the samples analyzed was about 2 %. HR-ICP-MS ET-AAS ICP-QMS ICP-MS Analytical Method Double Isotopic Dilution External Standard calibration Isotopic Dilution External Standard calibration Calibration Standard (Source of Traceability NIST SRM 3114 and 65 Cu enriched (EURISO-TOP) Cu solution (GSO ) NIST SRM 3114 NIST SRM 3114 Note: * submitted two results using different methods. Only the ID-ICP-MS was considered to calculate the Key Comparison Reference Value (KCRV). 6. Results and Discussion The participant s results of CCQM-K100 comparison are summarized in Table 3, as well as in Figure 1. Table 3. Results reported by individual NMIs for Cu in CCQM-K100. Institute Mass fraction U* u* k** (µg g -1 ) (µg g -1 ) (µg g -1 ) (1) (2) *U = expanded uncertainty and u = standard uncertainty **k = coverage factor Note: 1 The results submitted by, and were not included in the calculation of the key comparison reference value (KCRV). 2 submitted two results using different methods. Only the ID-ICP-MS was considered to calculate the KCRV. 5

6 (1) (2) Mass fraction (µg g -1 ) Figure 1: Results for Cu of CCQM-K100. Error bar representing the standard uncertainty (u), as reported Key Comparison Reference Value (KCRV) and associated uncertainties Screening data for consistency and anomalous values Following a systematic approach proposed in the CCQM Guidance note [3], first the data sets were checked for outliers. The Grubbs one, Dixon, Chi-square, Box-plot tests were chosen. The tests were carried out considering an interval of 95% of confidence. The outlier testing results are summarized in Table 4. Table 4. Summary of outlier testing for data set of CCQM-K100. Test Grubbs one Dixon Chi-square Box-plot Outlier In order to establish the degree of equivalence among results from participants of the CCQM-K100, a reference value was estimated according to the CCQM Guidance note [3]. During the CCQM/IAWG meeting held on the 15 and 16 April 2013, BIPM Sévres, the Draft A of the CCQM-K100 was presented. After the initial discussions it was decided that the median of results should be used as the KCRV. Additionally, it was observed that some results appear to be outliers. The participants were requested to review their results and inform the coordinating 6

7 laboratory on a technical basis if any measurement problems were identified. It was agreed that the results of participants, that reported any measurement problem, should be removed of the KCRV estimation. After the CCQM IAWG meeting, (Russia) and (France) sent to the coordinator technical explanations about their results. The technical reasons are stated as follow: has reported that the possible reasons for their bias in the results of the CCQM- K100. We noticed some little differences in our sample preparation with respect to the others partners, in particular our dilution rate of the ethanol sample was lower than that applied by the others. This could have interfered with the ICPMS measurements. Hence, we suggest not to take into account the value for the calculation of the KCRV. However, we would like to confirm this hypothesis, repeating the experiments. Do you still have some sample used during the comparison that we could use for that? asked about the possibility of Inmetro send additional samples used in the CCQM- K100 comparison. Inmetro sent five ampoules, used in the CCQM-K100, for. has reported that carried out measurements using 2 methods: ET-AAS (the main set of results) and ICP-AES (additional measurements). We sent to the pilot laboratory the result, obtained by ET-AAS ( ± ) mg/kg, which turned out to be 17 % lower than median. The result obtained by ICP-AES was ( ± ) mg/kg, and is much higher and closer to median. We think now that the reason of significant deviation of AAS result from KCRV is that AAS did not provide high enough temperature for complete atomization of Cu. ICP-AES turned out to be more appropriate for the purpose. tried to repeat the measurements for verifying if the discrepancy of their results is attributed to technical reasons. The NMI reported that had some technical problems with their ICP-MS and was not possible to carry out the measurements. The NMI suggested not includes their results in the KCRV estimation. asked Inmetro about the possibility to send new samples for repeat the measurements. In March 2014 reported the results and has identified the reason for s low result. There was one detail of the subsampling procedure that caused Cu to be lost from the sample. This was fairly reproducible at 5% of the copper content. The same problem did not affect any of the QC we did for CCQM-K100 so the mistake didn t get identified. After the problem was identified and fixed, measurements gave ng/g. In this regard, the measurements results reported by, and were not included in the estimation of KCRV. 7

8 Calculation of the KCRV Table 5 shows the mean, median and Mixture model median (MM-Median) of results with associated uncertainties. Table 5. Results of calculation Estimators Value (µg g -1 ) Standard uncertainty (µg g -1 ) Degrees of freedom Mean Median MM-estimate As can be seen, there is a good agreement among the consensus values calculated. After discussion at the IAWG meeting held in April 2012, it was agreed to use the median as the KCRV. The median is a simple and robust estimator of KCRV and does not require the participants uncertainty for calculation of the u (KCRV) [3]. The measurement results of the CCQM-K100 with the KCRV (median) and u (KCRV) are shown in the Figure 2. The solid horizontal line in red is the KCRV and the dotted lines show its respective standard uncertainty. The error bar line of each result represents the combined standard uncertainty. k Mass fraction (µg g -1 ) (1) Figure 2: Results reported by the CCQM-K100 participants. Error bar denotes the standard uncertainty. The solid line shows the KCRV median ( µg g -1 ) and the dotted lines are standard uncertainty of KCRV. (2) 6.2. Equivalence statements 8

9 The degree of equivalence (DoE) and its uncertainty between the participant results and the KCRV was calculated according the following equations [3]: d i = ( x KCRV ) i (2) U ( d KCRV 2 2 i ) = 2 u( xi ) + u( ) (3) di DoE = U d ) ( i (4) Where x i is the reported value of the participants of CCQM-K100; d i is the difference between the reported value and the KCRV and U (d i ) is the expanded uncertainty (k=2) of the difference d i at 95 % level of confidence. The equivalence statements for CCQM-K100 are presented in the Table 6 and are shown graphically (Figures 3 and 4). NMI x i (µg g -1 ) Table 6. Equivalence statement for CCQM-K100 KCRV d i U (d i ) (µg g -1 ) (µg g -1 ) (µg g -1 ) d i relative* (%) U (d i ) relative* (%) DoE (1) (2) * Relative to the KCRV 9

10 (1) (2) d i (µg g -1 ) Figure 3: Equivalence statement for CCQM-K100 based on the KCRV (median). The error bar denotes the U (d i ) (1) (2) d i relative (%) Figure 4: Equivalence statement for CCQM-K100 based on the KCRV (median). The error bar denotes the U (d i ) relative value (%). 8. Demonstration of Core Capabilities As agreed by the CCQM Inorganic Analysis Working Group (IAWG), the Core- Capilities (CC) system will be employed to improve the efficiency and effectiveness of key comparisons to support CMC claims. With the use of this system, new CMC claims can be 10

11 supported by describing CC are required to provide the claimed measurement service and then referecing CC that were successfully demonstrated by participation in key comparison. In this connection, all participants were requested to submit their Inorganic CC Tables to the coordinator for compilation and are summarized in the Annex B. 9. Conclusion The results of the CCQM-K100 were discussed at the IAWG meetings held at Paris and Turkey in After the initial discussion, the median was chosen by the IAWG as the KCRV. The discussion of the results of CCQM-K100 continued during the IAWG meeting held at Paris (April, 2013) and was suggested not include in the KCRV the results of participants that report any technical problems with their results. 10. Acknowledgement The coordinating laboratory would like to thank the contributions from the contract persons and/or analysts of participating NMIs and Dr. Mike Sargent by the supporting during the course of this KC and Dr. David Lee Duewer from NIST by the supporting at the data analysis. 11. References 1. Rocha, M.S., Mesko, M.F., Silva, F.F., Sena, R.C., Quaresma, M.C.B., Araújo, T.O., Reis, L.A. Determination of Cu and Fe in fuel ethanol by ICP OES using direct sample introduction by an ultrasonic nebulizer and membrane desolvator. Journal of Analytical Atomic Spectrometry, 26, , International Organisation for Standardization, ISO Guide 35: Reference materials General and statistical principles for certification, Geneva, Switzerland, CCQM Guidance Note: Estimation of a consensus KCRV and associated degrees of equivalence, Version 6,

12 Annex A - Technical Protocol Key Comparison CCQM-K100 Analysis of Cu in Ethanol Introduction The limited supply of non-renewable forms of energy and its contribution to global warming has increased the interest in renewable energy sources such as bioethanol. The use of bioethanol as a fuel requires its regulation and quality control. Inorganic impurities are present on bioethanol at low concentrations and its analysis requires the development and validation of new methodologies. No specific study has been carried out for content of copper in ethanol. This study will investigate the core competences of participants to assessment the content of copper in ethanol. Participants are request to complete the Inorganic Core Capabilities Tables as a means of providing evidence for their CMC claims. Time schedule Deadline for registration: 07 October 2011 Dispatch of the samples: October, 2011 Deadline for receipt of the result report: 29 February 2012 Presentation of results at the CCQM/IAWG Meeting: April, 2012 Draft report: October, 2012 Samples Samples Preparation: The bioethanol used to produce the samples was obtained from the fermentation of extract of sugar cane. The material was provided by a Brazilian producer and used without pretreatment. The sample was homogenized and bottled in amber glass ampoules of 10 ml subjected prior to blanketing with argon and then flame sealed. Homogeneity and stability testing Homogeneity of testing material was evaluated by analyzing of 15 samples for Cu, chosen from the whole batch using a random stratified sample picking scheme. The cooper content was determinate by ICP-OES coupled to ultrasonic nebulizer and membrane desolvator. There is no evidence that the material is not homogeneous. A four week isochronous study was performed to evaluate stability of bioethanol during transport. Further, a long term stability study (12 months) has been done to confirm the stability of the material for the time of the study. There was no significant instability noted for these samples. The stability of material will be continued during the next few months. Distribution Each participant will receive 5 numbered ampoules. The participants will be informed of the date of dispatching of samples. Participants are required to confirm the receipt of the ampoules, and send the return receipt to us by . If there is any damage, please contact us immediately and will send others samples. 12

13 Measurands The samples of CCQM-K100 and CCQM-P127 are the same. The expected mass fraction is mg/kg. Handling and storing instructions: To avoid evaporation and contamination, the samples should be kept sealed until use, stored at 20 C and not exposed to intense direct light and ultraviolet radiation. The samples should be open carefully and the measurement should be carried out immediately after the sample opened. Choice of method/procedure. All participants are encouraged to use their most sensitive and accurate methods. Please include a full description of your method of analysis when reporting the results. If IDMS method is used, please report the source of isotopically labeled spike material used. Analysis Participants are requested to perform at least 3 independent measurements. Participants should report the mean value of the measurements and its associated uncertainty. Report of results The report should be sent to the coordinating laboratory by before 29 February will confirm the receipt of each report. If the confirmation does not arrive within 10 days, please contact us. The report must include: Result should be reported as a value of 3 independent measurements with corresponding standard uncertainty. The value of the results and their associated standard uncertainties must be expressed in mg/kg. If the final result has been calculated from more than one method, the individual results from the contributing methods must also be reported. A detailed description of the applied analytical procedure including the sample preparation and calibration methods. Participants are asked to provide information about their metrological traceability. Each participant should make an assessment of the experimental uncertainty (according to ISO/GUM or the Eurachem/CITAC Guide). Each variable contribution to the uncertainty of the result should be identified and quantified in order to be included in the combined standard uncertainty of the results. A full uncertainty budget must be reported, as part of the results. Participants Participation is open to all interested CCQM members. Participants are allowed to choose the elements of their interest and all participants must identify which comparison who wants to participate. 13

14 Registration Please register on line no later than 07 October, 2011 using attached form. Coordinating laboratory and contact person Rodrigo Caciano de Sena National Institute of Metrology, Quality and Technology () Av. Nossa Senhora da Gracas, 50, Xerém Duque de Caxias/Rio de Janeiro Brazil Tel./: Fax: Valnei Smarçaro da Cunha National Institute of Metrology, Quality and Technology () 14

15 Annex B Inorganic Core Capabilities Table Key Comparison CCQM-K100 Analyte: Cu Method: ID-ICP-MS Participating Institutes:,,,,,, Capabilities/Challenges Contamination control and correction All techniques and procedures employed to reduce potential contamination of samples as well as blank correction procedures. The level of difficulty is greatest for analytes that are environmentally ubiquitous and also present at very low concentrations in the sample. Digestion/dissolution of organic matrices All techniques and procedures used to bring a sample that is primarily organic in nature into solution suitable for liquid sample introduction to the ICP. Digestion/dissolution of inorganic matrices All techniques and procedures used to bring a sample that is primarily inorganic in nature into solution suitable for liquid sample introduction to the ICP. Volatile element containment All techniques and procedures used to prevent the loss of potentially volatile analyte elements during sample treatment and storage. Pre-concentration Techniques and procedures used to increase the concentration of the analyte introduced to the ICP. Includes evaporation, ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Vapor generation Techniques such as hydride generation and cold vapor generation used to remove the analyte from the sample as a gas for introduction into the ICP. Matrix separation Techniques and procedures used to isolate the analyte(s) from the sample matrix to avoid or reduce interferences caused by the matrix. Includes ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Techniques and procedures used to isolate the analyte(s) from the sample matrix to avoid or reduce interferences caused by the matrix. Includes ionexchange, extraction, precipitation procedures, but not vapor generation procedures. Spike equilibration with sample The mixing and equilibration of the enriched isotopic Not tested Tested Specific challenges encountered The contamination of sample preparation procedure is not ignorable. Considerably high efforts to control and check blank level. Essential for accurate IDMS 15

16 spike with the sample. Capabilities/Challenges Signal detection The detection and recording of the analyte isotope signals. The degree of difficulty increases for analytes present at low concentrations, of low isotopic abundance, or that are poorly ionized. Not tested Tested Specific challenges encountered Good signal intensity is required to improve isotope ratio. Memory effect Any techniques used to avoid, remove or reduce the carry-over of analyte between consecutively measured standards and/or samples. Correction or removal of isobaric/polyatomic interferences Any techniques used to remove, reduce, or mathematically correct for interferences caused by mass overlap of analyte isotopes with isobaric or polyatomic species. Includes collision cell techniques, high resolution mass spectrometry, or chemical separations. The relative concentrations and sensitivities of the analyte isotopes and the interfering species will affect the degree of difficulty. Detector deadtime correction Measurement of, and correction for, ion detector deadtime. Importance increases in situations where high ion count rates are encountered. Only e reported that applied correction for the detector deadtime. Mass bias/fractionation control and correction Techniques used to determine, monitor, and correct for mass bias/fractionation. Mass bias is necessary for IDMS method. Mass bias is corrected by using natural isotope ratio standard solution. Approximate ratio matching used to minimize effect of mass bias. Spike calibration Techniques used to determine the analyte concentration in the enriched isotopic spike solution. Most participantes used double IDMS and combined the method with Matrix matching 16

17 Key Comparison CCQM-K100 Analyte: Cu Method: ETA-AAS (or GF-AAS) Participating Institutes: Capabilities/Challenges Not tested Tested Specific challenges encountered Cu was not detected in the pure deionized water after system Millipore and blank (~10% EtOH) Contamination control and correction All techniques and procedures employed to reduce potential contamination of samples as well as blank correction procedures. The level of difficulty is greatest for analytes that are environmentally ubiquitous and also present at very low concentrations in the sample. Digestion/dissolution of organic matrices All techniques and procedures used to bring a sample that is primarily organic in nature into solution suitable for liquid sample introduction to the ETA-AAS. Digestion/dissolution of inorganic matrices All techniques and procedures used to bring a sample that is primarily inorganic in nature into solution suitable for liquid sample introduction to the ETA-AAS. Volatile element containment All techniques and procedures used to prevent the loss of potentially volatile analyte elements during sample treatment and storage. Pre-concentration Techniques and procedures used to increase the concentration of the analyte introduced to the ETA-AAS. Includes evaporation, ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Matrix separation Techniques and procedures used to isolate the analyte(s) from the sample matrix to avoid or reduce interferences caused by the matrix. Includes ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Hydride preconcentration/matrix separation of volatile species. Coupling of a hydride system to the ETA-AAS and optimization of conditions. Calibration of analyte concentration The preparation of calibration standards and the strategy for instrument calibration. Includes external calibration and standard additions procedures. Also use of matrix-matched standards to minimize effect of interferences. The sample from ampoule is diluted in the pure deionized water by gravimetric method (dilution factor of ten) Effect of the EtOH-matrix is minimized by diluting the sample with deionized water External calibration is carried out by four Cu standard solutions, prepared with using ethanol matrix (~10% EtOH). So calibration solutions matrix corresponds to the matrix of sample Signal detection The detection and recording of the absorption signals of analytes. The degree of difficulty increases for analytes present at low concentrations, of low atomic absorption coefficient. Requires selection of operating conditions such as light source, absorption line, Zeeman background correction conditions. Includes selection of signal processing conditions (peak area or height). Selection of D2-correction signal, processing conditions (peak height) 17

18 Capabilities/Challenges Not tested Tested Specific challenges encountered Memory effect Any techniques used to avoid, remove or reduce the carry-over of analyte between consecutively measured standards and/or samples. Optimization of the furnace temperature program Optimization of temperature and duration of steps for sample drying, pyrolysis to remove (residual) organics, and atomization. Furnace temperature program to minimize analyte loss in the drying/pyrolysis steps, while maximizing analyte vaporization in the atomization step. Correction or removal of matrix effects or interferences Chemical or instrumental procedures used to avoid or correct for spectral and non-spectral interferences. Includes effects of differences in viscosity and chemical equilibrium states of analyte between the standard and sample. Selection of matrix modifier to adjust volatility of analyte and/or matrix to eliminate these effects is also included. Addition of reactive gases (eg oxygen) to the carrier gas to improve matrix separation. Also included is Zeeman or other background correction techniques to remove interference due to absorption and scattering from coexisting molecules/atoms in the sample. VM Furnace temperature program consist of 7 steps. Furnace with pyrolytic surface is used. Calibration of the equipment is carried with using Cu standard solutions+ ethanol matrix (~10% EtOH. D2- signal correction is used. 18

19 Key Comparison CCQM-K100 Analyte: Cu Method: ICP MS Participating Institutes:, Capabilities/Challenges Not tested Tested Specific challenges encountered Efforts to control and check blank level. Contamination control and correction All techniques and procedures employed to reduce potential contamination of samples as well as blank correction procedures. The level of difficulty is greatest for analytes that are environmentally ubiquitous and also present at very low concentrations in the sample. Digestion/dissolution of organic matrices All techniques and procedures used to bring a sample that is primarily organic in nature into solution suitable for liquid sample introduction to the ICP. Digestion/dissolution of inorganic matrices All techniques and procedures used to bring a sample that is primarily inorganic in nature into solution suitable for liquid sample introduction to the ICP. Volatile element containment All techniques and procedures used to prevent the loss of potentially volatile analyte elements during sample treatment and storage. Pre-concentration Techniques and procedures used to increase the concentration of the analyte introduced to the ICP. Includes evaporation, ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Vapor generation Techniques such as hydride generation and cold vapor generation used to remove the analyte from the sample as a gas for introduction into the ICP. Matrix separation Techniques and procedures used to isolate the analyte(s) from the sample matrix to avoid or reduce interferences caused by the matrix. Includes ion-exchange, extraction, precipitation procedures, but not vapor generation procedures. Techniques and procedures used to isolate the analyte(s) from the sample matrix to avoid or reduce interferences caused by the matrix. Includes ionexchange, extraction, precipitation procedures, but not vapor generation procedures. Calibration of analyte concentration The preparation of calibration standards and the strategy for instrument calibration. Includes external calibration and standard additions procedures. Signal detection The detection and recording of the analyte signals. The degree of difficulty increases for analytes present at low concentrations, or that are have weak emission lines.. Memory effect Any techniques used to avoid, remove or reduce the carry-over of analyte between consecutively measured standards and/or samples. Complex spectral backgrounds Any techniques used to remove, reduce, or mathematically correct for interferences caused by the overlap of analyte emission lines with atomic, ionic, or molecular emission from matrix components. The relative concentrations and sensitivities of the analyte and the interfering species will affect the degree of Matrix matching standard addition method was applied to have matrix matched standards and samples. 19

20 Capabilities/Challenges Not tested Tested Specific challenges encountered difficulty. Samples containing high concentration matrix components with large numbers of emission lines or molecular bands may increase the measurement challenge. Correction or removal of matrix-induced signal suppression or enhancement Chemical or instrumental procedures used to avoid or correct for matrix-induced signal suppression or enhancement. High concentrations of acids, dissolved solids, or easily ionized elements will increase the degree of difficulty. Cu-free ethanol is required to prepare the standard solution for matrix matching. 20