DOLT-4: Dogfish liver certified reference material for trace metals

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Elements for which certified values have been established for this dogfish (Squalus acanthias) liver CRM, along with their expanded uncertainty (U_CRM = ku_c, where u_c is the combined standard uncertainty calculated according to the JCGM Guide ^Footnote1 and k is the coverage factor) are listed below. It is intended that U_CRM encompasses every aspect that reasonably contributes to the uncertainty of the certified mass fraction ^Footnote2. Values are based on dry mass.

Table 1: Certified quantity values for DOLT-4

Element	Mass fraction, (mg/kg)
Arsenic (d,e,h)	9.66 ± 0.62
Cadmium (d,e,i,p)	24.3 ± 0.8
Copper (d,e,i,p)	31.2 ± 1.1
Iron (d,i)	1833 ± 75
Lead (d,e,p)	0.16 ± 0.04
Mercury (c,d,p)	2.58 ± 0.22
Nickel (d,e,i,p)	0.97 ± 0.11
Selenium (e,h)	8.3 ± 1.3
Silver (d,e,p)	0.93 ± 0.07
Zinc (d,i,p)	116 ± 6
CH3Hg (as Hg) (g,s,t)	1.33 ± 0.12

Coding

The coding refers only to the instrumental method of determination of the measurand.

• c - Cold vapour atomic absorption spectrometry
• d - Inductively coupled plasma mass spectrometry
• e - Electrothermal vaporization atomic absorption spectrometry (ETAAS)
• g - Solid phase microextraction (SPME) isotope dilution gas chromatography mass spectrometry
• h - Hydride generation atomic absorption spectrometry
• i - Inductively coupled plasma atomic emission spectrometry
• p - Isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS)
• s - SPME isotope dilution gas chromatography ICPMS
• t - Ethylation cold vapor atomic fluorescence spectrometry.

Intended use

This reference material is primarily intended for use in the calibration of procedures and the development of methods for the determination of trace metals in marine fauna and materials of similar matrix.

Storage and sampling

This material should be stored in a cool and dark location. Prior to use, the bottle should be rotated and shaken to ensure the contents are well mixed. The bottle should be tightly closed thereafter. Certified values are based on a minimum 0.250 g sub-sample from the bottle.

Instructions for drying

Determination of dry mass should be performed on a separate sample to avoid contamination. DOLT-4 can be dried to constant mass by: (1) drying at reduced pressure (e.g., 50 mm Hg) at room temperature in a vacuum desiccator over magnesium perchlorate for 24 hours; (2) vacuum drying (about 0.5 mm Hg) at room temperature for 24 hours.

Information values

The following table presents information values for elements which could not be certified because of insufficient information to accurately assess uncertainties.

Table 2: Information values for DOLT-4

Element	Mass fraction, (mg/kg)
Na	6800
Mg	1500
Al	6800
K	9800
Ca	680
Cr	1.4
Co	0.25
Sr	5.5
Mo	1
Sn	0.17

Preparation of DOLT-4

This reference material was processed at the Guelph Food Technology Center, Guelph Ontario. The preparation sequence is illustrated on the following page. The final product was sterilized by gamma irradiation (minimum dose of 25 kGy) at the Canadian Irradiation Centre, Laval, Quebec.

Certified values

DOLT-4 was provided as an unknown sample to a group of laboratories participating in an annual intercomparison for trace metals in marine samples coordinated by NRC ^Footnote3. Data generated by NRC were also included in the pool of intercomparison results. Laboratories were requested to provide triplicate results using an analytical method of choice based on total digestion of the sample. DOLT-3 was provided as a quality control sample.

Data were returned to NRC for evaluation. Results from a select sub-group of participants were used for the certification of DOLT-4. Such laboratories were selected based on their performance history in previous intercomparisons.

Included in the overall uncertainty estimate are uncertainties in the batch characterization (u_char) and uncertainties related to possible between-bottle variation (u_hom). Expressed as standard uncertainties these components can be combined as:

Equation 1:  $u_{\mathrm{c(CRM)}}^2=u_{\mathrm{char}}^2+u_{\mathrm{hom}}^2+u_{\mathrm{stab}}^2$

Based on NRC's experience with similar materials, uncertainty components for long and short term stability were considered negligible and are thus not included in the uncertainty budget.

Expiration of certificate

A predecessor CRM, DOLT-2, has been periodically analyzed for more than nine years and found to be both physically and chemically stable over this time interval. We expect similar characteristics from DOLT-4. The certified values for DOLT-4 are considered valid until April 2014, provided the CRM is handled and stored in accordance with instructions herein.

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.

Date of issue: May 2008
Date of expiry: April 2014

Acknowledgements

The following staff members of the Measurement Science and Standards portfolio at the NRC contributed to the production and certification of DOLT-4: C. Brophy, P. Maxwell, L. Yang and S. Willie.

The cooperation of I. Britt and A. Mannen of the Guelph Food Technology Centre, Guelph, ON, Canada in the preparation of this material is gratefully acknowledged.

The following laboratories participated in the certification of DOLT-4:

ALS Environmental Vancouver, B.C.

Australian Institute of Marine Sciences, Queensland, 4810, Australia

Australian Nuclear Science and Technology, Organizastion, Environmental Science Program Menai, N.S.W., Australia

Battelle Pacific Northwest, Sequim Bay Road, Sequim, WA

Massachusetts Water Resources Authority, Central Laboratory, Winthrop, MA

NOAA, National Ocean Service, Hollings Marine Laboratory, Charleston, SC

San Francisco Public Utilities Commission, Southeast Laboratory, San Francisco, CA

Texas A. & M. College of Veterinary Medicine, Trace Element Research Laboratory, College Station, TX

Texas Parks and Wildlife Environmental Contaminants Laboratory San Marcos, TX

U.S. Customs Laboratory, Savannah, GA

USGS-WRD, 3039 Amwiler Road, Atlanta, GA

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