SOPH-1 and PACS-2: Sediment certified reference materials for the determination of tributyltin and dibutyltin

PDF version

This suite of certified reference materials are intended for the calibration of instruments and evaluation of methods for the determination of (C₄H₉)₃Sn⁺ (tributyltin, TBT) and (C₄H₉)₂Sn²⁺ (dibutyltin, DBT) in sediments or materials of a similar matrix.

Table 1: Certified Quantity Values

	Mass fraction - ng/g (as Sn)
Butyltin	SOPH-1	PACS-2
TBT	125 ± 7	832 ± 95
DBT	174 ± 9	1100 ± 135

Due to a lack of independent methods only an information value of 7 x 10² ng/g for MBT in PACS-2 is provided. Care should be taken not to attribute more reliability to this number than is warranted.

The certified values are based on the unweighted mean of results from data submitted by laboratories participating in several recent Comité Consultatif pour la Quantité de Matière (CCQM) comparisons. The expanded uncertainty (U_CRM) in the certified value is equal to U = ku_c where u_c is the combined standard uncertainty calculated according to the ISO Guide ^{Footnote 1} and k is the coverage factor. The value of u_c is determined from the combined uncertainties associated with the various methods (u_char) as well as uncertainties associated with homogeneity (u_hom) and stability (u_stab). It is intended that U_CRM encompasses every aspect that reasonably contributes to the uncertainty of the measurand ^{Footnote 2 Footnote 3}. A coverage factor (k) of 2 was applied.

Background

CCQM-P18, CCQM-P43 and CCQM-K28 were undertaken in 2002 and 2003 to assess the current capabilities of interested National Metrology Institutes (those which are members of the Consultative Committee for Amount of Substance) and selected outside 'expert' laboratories to quantitate tributyltin and dibutyltin in a prepared marine sediment. These exercises were sanctioned by the CCQM as an activity of the Inorganic Analysis Working Group, and were jointly piloted by the National Research Council Canada (NRC) and LGC Ltd (UK).

A detailed report addressing CCQM-P18 is published in Metrologia ^{Footnote 4}.

Preparation of material

SOPH-1 was prepared in-house at NRC following gravimetric blending of two NRC CRM marine sediments, PACS-2 and HISS-1, the latter containing negligible concentrations of TBT and thus serving as a solid, inert diluent.

HISS-1 was collected from the Hibernia Shelf, off the coast of Newfoundland. PACS-2 was collected in the harbour of Esquimalt, B.C. Both sediments were freeze dried and screened to pass a No. 120 (125 μm) screen and blended by Institute staff using the facilities of CANMET, Mining and Mineral Sciences Laboratories, a division of Natural Resources Canada, in Ottawa.

Table 2: Particle size, μm

	SOPH-1	PACS-2
Median	12.0	12.9
Mean	13.8	19.2
Mode	18.3	14.2

Storage and sampling

To ensure the stability of the organotin species it is necessary to store these materials at a temperature of -20 °C. Prior to use, the bottle should be well mixed by rotation, shaken and tightly closed immediately thereafter.

Characterization

Mean values submitted by selected laboratories participating in CCQM P-18, CCQM P-43 and CCQM K-28 were used to calculate the original certified value and the uncertainty of characterization (u_char) ^{Footnote 5}.

Homogeneity

These materials were tested for homogeneity at NRC. Also, randomly bottles were selected for the analysis by the participating laboratories. The homogeneity is warranted for samples of 500 mg and above.

Stability

An uncertainty component associated with the short term stability (transport) was evaluated but considered insignificant. Measurements were conducted on samples stored for one month at -20 °C, +4 °C and 22 °C. Based on a 10 year study of the stability of tributyltin in PACS-2, a constant degradation (1% per year) of the TBT has been observed. The values listed in this certificate account for this change.

Instructions for drying

A separate aliquot of the sediment should be used to obtain a dry weight correction factor. Drying for two hours at 105 °C has proved to be a relatively simple method to achieve a dry weight.

Expiration of certification

The certified values stated for SOPH-1 and PACS-2 are valid until December 2014 within the measurement uncertainty specified, provided the CRM is handled and stored in accordance with instructions herein. The stability of these CRMs will continue to be monitored.

Metrological traceability

Results presented in this certificate are traceable to the SI through gravimetrically prepared standards of established purity and international measurement intercomparisons. As such, they serve as suitable reference materials for laboratory quality assurance programs, as outlined in ISO/IEC 17025. This CRM is registered at the Bureau International des Poids et Mesures (BIPM) in Appendix C of the Comité International des Poids et Mesures database listing Calibration and Measurement Capabilities accepted by signatories to the Mutual Recognition Arrangement of the Metre Convention.

Accreditation

The Chemical Metrology laboratory is compliant to ISO 17025 and ISO Guide 34, with approval by The Inter-American Metrology System (SIM). The certificate of approval is available upon request.

Updates

Users should ensure that the certificate they have is current. The NRC web site will contain any new information.

Acknowledgements

The following staff members of the Measurement Science and Standards portfolio at the NRC contributed to the production and certification of SOPH-1 and PACS-2: V.J. Boyko, V.P. Clancy, J. Lam, P. Maxwell, Z. Mester, R.E. Sturgeon, S.N. Willie and L. Yang.

LGC Ltd., Teddington, Middlesex, UK, B. Fairman, C. Wolf-Briche, R. Wahlen and M. Sargent.

The cooperation of the following is gratefully acknowledged:

Crompton GmbH Research Analytic, Germany, P. Schultze.

Federal Institute for Materials Research and Testing (BAM), Berlin, Germany, T. Win, A. Liebich and R. Philipp.

European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, Belgium.

H. Schimmel, B. Sejerøe-Olsen and P. Konieczka.

Laboratoire National d'Essais (LNE), France, B. Lalere.

National Analytical Reference Laboratory (NARL), Pymble, Australia, P. Taylor, R. Hearn, L. Mackay and R. Myors.

National Institute for Standards and Technology Gaithersburg, MD, USA , M. Schantz.

National Metrology Institute of Japan (NMIJ), Tsukuba, Ibaraki, Japan, K. Inagaki and A. Takatsu.

University of Oviedo, Dept. of Chemistry, Spain, J.I. Garcia Alonso, P. Rodriguez González, J. Ruiz Encinar and A. Sanz-Medel.

Université de Pau et des Pays de l'Adour, Lab. de Chimie Analytique, Pau, France. M. Monperrus, O. Zuloaga, E. Krupp, D. Amouroux, and O. Donard.

University of Umeå, Sweden, W. Frech.

Korean Research Institute of Standard and Science, E. Hwang.

Date of issue: August 2004
Revised Oct 2009
Revised December 2011

Approved by:

Zoltan Mester, Ph. D.
Group Leader, Chemical Metrology
Measurement Science and Standards

Comments, information and inquiries should be addressed to:

National Research Council of Canada
Measurement Science and Standards
1200 Montreal Road
Building M-12
Ottawa, Ontario K1A 0R6

Telephone: 613-993-2359
Fax: 613-993-2451
Email: CRM-MRCInorganic-Inorganiques@nrc-cnrc.gc.ca