CERTIFICATE OF ANALYSIS

Transcription

1 CERTIFICATE OF ANALYSIS Soft Drinking Water Metals Constituent 1,2 Number of laboratories Certified value 3,4 (µg/l) Uncertainty 5 (µg/l) k value 5 Aluminium Arsenic Barium Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc Number of laboratories Certified value 3,4 (mg/l) Uncertainty 5 (mg/l) k value 5 Calcium Magnesium Sodium ) Cadmium, iron and zinc were determined at LGC using Isotope Dilution ICP-MS (IDMS). These certified values were confirmed by the results of an interlaboratory comparison using different methods (see Table 1). 2) The remaining measurands were certified using the results of an interlaboratory comparison using different methods (see Table 1). 3) Unweighted median value of the concentration determined by participant laboratories. Each data set was obtained in a different laboratory and/or using a different method of measurement. For cadmium, iron and zinc, the unweighted mean of 6 replicate IDMS measurements was used. 4) The results are traceable to the SI through the physical and chemical standards used by LGC and the interlaboratory study participant laboratories. The certified values are reported to 3 significant figures. 5) The quoted uncertainty is the half-width of the expanded uncertainty interval calculated using a coverage factor (k), which gives a level of confidence of approximately 95 %. 6) Converted from a measurement made on a weight/weight basis using a measured density of kg/m 3. This certificate is valid for 12 months from the date of shipment provided the sample is stored under the recommended conditions. The minimum amount of sample to be used is 1 ml. European Reference Material ERM -CA022a was produced and certified under the responsibility of LGC according to the principles laid down in the Technical Guidelines of the European Reference Materials co-operation agreement between BAM-LGC-IRMM. Information on these guidelines is available on the Internet ( Accepted as an ERM, Teddington, November Signed: 4005 Dr Derek Craston, Government Chemist LGC Limited Queens Road Teddington Middlesex TW11 0LY, Page 1 of 6

2 Element Number of laboratories Indicative Values 1 Indicative value (µg/l) Concentration Uncertainty 2 (µg/l) k value 2 Boron Potassium Selenium ) These indicative values are derived from the interlaboratory study for this material. For these elements less than 10 laboratories submitted data for the interlaboratory study and the data were therefore not considered reliable enough to give certified values. These indicative values are supplied based on the data received, and may still be of use to laboratories assessing method performance for these analytes. 2) The quoted uncertainty is the half-width of the expanded uncertainty interval calculated using a coverage factor (k), which gives a level of confidence of approximately 95 %. Element Additional Material Information Number of laboratories Concentration Information value (µg/l) Antimony Information derived from the interlaboratory study. For this element the data were not considered reliable enough to provide an estimate of uncertainty. DESCRIPTION OF THE MATERIAL Soft drinking water was sourced from the Bury (Lancashire, ) potable mains supply. The water was then filtered through 0.2 µm cellulose filter paper and acidified to approximately ph 2 by addition of high purity nitric acid to give a final concentration of approximately 0.1 % nitric acid. This material was then analysed by ICP-MS and ICP-OES at LGC to establish the base levels of the elements of interest. High purity metal standards (QCD Analysts, Florida, USA) were used to spike the base material to levels as close to the drinking water regulation limits as possible (98/83/EC of 1998, enacted in Statutory Instrument 2000 No. 3184). The amount of each metal standard added to the material was calculated taking account of the base level of the respective element in the solution. The material was spiked using calibrated pipettes, and was stirred continuously during preparation. The material was then bottled in 250 ml screw cap HDPE bottles. The homogeneity of the material was assessed by analysis of thirty randomly selected units from across the fill run (except for Cd, Fe, Sb and Zn where ten units were used). The results were then analysed by oneway ANOVA, and the contribution to the combined uncertainty was calculated from the larger of the between unit standard deviation and the method standard deviation. INTENDED USE This material is intended for use in the development, validation or quality control of analytical methods for the determination of elements in soft drinking water. The material may also be applicable to other matrices where suitable reference materials are not available. Information on how to compare an analytical result with the certified value can be found in ERM Application Note 1; Page 2 of 6

3 CHARACTERISATION The material was characterised using a combination of IDMS analysis carried out at LGC and an interlaboratory study organised by LGC. IDMS characterisation was carried out for cadmium, iron and zinc. The participants of the interlaboratory study were asked to characterise aluminium, antimony, arsenic, barium, boron, cadmium, calcium, chromium, copper, iron, lead, magnesium, manganese, nickel, potassium, selenium, sodium and zinc. The IDMS values quoted were converted to µg/l using a measured density of kg/m 3. ANALYTICAL METHOD USED FOR CERTIFICATION IDMS Cadmium (Cd), iron (Fe) and zinc (Zn) were determined at LGC by exact matching double isotope dilution mass spectrometry (IDMS). The sample (6.8 g) was spiked with a solution containing enriched 106 Cd, 57 Fe and 67 Zn to give predicted 111 Cd: 106 Cd, 56 Fe: 57 Fe and 66 Zn: 67 Zn ratios of 1. For the characterisation of the material, 6 replicate measurements were made on a single bottle. For calibration, standards prepared from high purity metals were diluted to give similar concentrations to that of the sample. The cadmium standard was prepared from cadmium shot (Spex Certiprep, Metuchen, New Jersey, USA, % purity); the iron standard was prepared from iron wire (Alfa Aesar, Heysham,, % purity); the zinc standard was prepared from zinc rod (Johnson Matthey, Royston,, % purity). QC standards were prepared from Romil 1000 µg/ml standard solutions (Romil, Cambridgeshire, ), also at concentrations similar to that of the sample. All standard and QC solutions were spiked with the enriched 106 Cd, 57 Fe and 67 Zn to match the ratio of the sample blends. The measurements were performed using an Agilent 7500ce collision/reaction cell inductively coupled plasma mass spectrometer (CRC-ICP-MS) operating in standard mode for Cd, hydrogen (H 2 ) mode for Fe and helium (He) mode for Zn. The certified values were assigned as the mean of the 6 replicate measurements. Interlaboratory Study This material was sent out to interlaboratory study in February Participant laboratories chose suitable methods with which they were familiar. These methods included ICP-MS, ICP-OES and AAS/AES. The number of laboratories using each type of method is shown in Table 1. The data from the interlaboratory study were processed using a robust statistical approach, after screening laboratories based on their performance in analysing a separate QC sample. The certified value for each analyte was assigned as the median of medians of the accepted laboratory data. The characterisation uncertainty assigned was the robust standard error of the robust mean of the accepted laboratory data. Page 3 of 6

4 Table 1 Methods used by participant laboratories Analyte ICP-MS ICP-OES Ion Chromatography Photometric AAS/AES Total Aluminium Antimony Arsenic Barium Boron Cadmium Calcium Copper Chromium Iron Lead Magnesium Manganese Nickel Potassium Selenium Sodium Zinc Page 4 of 6

5 PARTICIPANTS The following laboratories participated in the interlaboratory study for this material. AMEC Earth & Environmental Analytical Data Services Ltd Analytical Services Laboratory Philippines Anglian Water Bodycote Laboratories Clydebank Bodycote Laboratories Greenock Bodycote Laboratories Runcorn British Geological Survey CEH Lancaster CSIR Water Laboratories Republic of South Africa Industrial Technology Institute Sri Lanka Instituto Nacional de Saude Portugal LATU - Atomic Spectrometry Department Uruguay Seychelles Bureau of Standards Seychelles Sutton and East Surrey Water Verein dt. Zementwerke e.v. Germany Wessex Water SAFETY INFORMATION Refer to Material Safety Data Sheet. INSTRUCTIONS FOR USE Before use the material should be thoroughly mixed by inversion, and allowed to equilibrate to room temperature. The minimum amount of sample to be used is 1 ml. STORAGE The material should be stored at (5 ± 4) C in its original packaging. After use the bottle should be securely sealed and returned to storage at (5 ± 4) C. Page 5 of 6

6 Unit Number: Shipment Date: LEGAL NOTICE The values quoted in this certificate are the best estimate of the true values within the stated uncertainties and based on the techniques described herein. No warranty or representation, express or implied, is made that the use of the product or any information, material, apparatus, method or process which is the subject of or referred to in this certificate does not infringe any third party rights. Further, save to the extent: (a) prohibited by law; or (b) caused by a party's negligence; no party shall be liable for the use made of the product, any information, material, apparatus, method or process which is the subject of or referred to in this certificate. In no event shall the liability of any party exceed whichever is the lower of: (i) the value of the product; or (ii) 500,000; and any liability for loss of profit, loss of business or revenue, loss of anticipated savings, depletion of goodwill, any thirdparty claims or any indirect or consequential loss or damage in connection herewith is expressly excluded. Production of this reference material and certificate was supported by the Department for Innovation, Universities & Skills as part of the National Measurement System Chemical & Biological Metrology Knowledge Base Programme. This certificate may not be published except in full, unless permission for the publication of an approved extract has been obtained in writing from LGC Limited. It does not of itself impute to the subject of measurement any attributes beyond those shown by the data contained herein. Page 6 of 6