CACB-1: Calcium carbonate certified reference material for lead and cadmium

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The following table shows those elements for which certified values have been established for this calcium carbonate reference material (CACB-1).

Certified values are based on unweighted mean results from data generated by two independent methods. 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 JCGM Guide^{Footnote 1} and k is the coverage factor. The value of u_c is determined from the combined uncertainties of the various analytical methods (u_char) as well as uncertainties associated with homogeneity (u_hom).

It is intended that U_CRM encompasses every aspect that reasonably contributes to the uncertainty of the measurement^{Footnote 2}. A coverage factor of k=2 was applied for all elements.

The table below lists the property values certified in CACB-1.

Table 1: Certified Quantity Values for CACB-1

Element	Mass fraction, ng/g
Cd	7.6 ± 1.1
Pb	243 ± 14

Intended use

CACB-1 is intended for the calibration of instruments and evaluation of methods for the determination of Pb and Cd in calcium carbonate or materials of a similar matrix.

Storage and sampling

This material should be kept tightly closed in the original bottle and should be stored in a cool location. The contents should be well mixed by rotation and shaking prior of the bottle prior to use. The bottle should be tightly closed immediately after use.

Preparation

This material was obtained from a commercial producer. It was blended and bottled into precleaned glass bottles in a Class 100 clean room at NRC.

Certified value

All measurements contributing to this certificate were conducted at NRC Ottawa. The certified values were calculated from the unweighted means of results from isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and electrothermal vapourization atomic absorption spectrometry (ETAAS). Both employed a preconcentration step. A column of iminodiacetate resin was used with ICP-MS whereas immobilized 8-hydroxyquinoline was used with ETAAS.

Uncertainties

Guidelines for CRM producers suggest all sources relevant to the user of the material should contribute to the uncertainty of the certified value ^{Footnote2 Footnote3 Footnote 4 Footnote 5 Footnote 6}. Included in the overall uncertainty estimate are uncertainties in the characterisation (u_char), uncertainties related to possible between-bottle variation (u_hom) as well as instability derived from effects relating to long-term storage and transport (u_stab). Expressed as standard uncertainties, these components can be combined as:

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

Results for the various uncertainty components used to calculate the certified values are shown in Table 2.

Characterisation

The characterisation uncertainties (u_char) were calculated from the standard deviation of the laboratory means. The calculated uncertainty components related to the characterization of CACB-1 are reported in Table 2 ^{Footnote 3}.

Homogeneity

The homogeneity components of the uncertainty in the certified values were derived from duplicate sub-samples (0.150 g) from twelve bottles of CACB-1. The results were evaluated using ANOVA ^{Footnote 6}.

Stability

Instability is not expected in the Pb and Cd content of CACB-1 provided the CRM is handled and stored in accordance with the instructions. However, this CRM will continue to be monitored and users will be notified if any observed significant irregularity occurs prior to the expiry date.

Table 2: Uncertainty Components for CACB-1

Element	Uncertainty, ng/g
	uchar	uhom	uc	uCRM (k=2)
Cd	0.50	0.12	0.53	1.1
Pb	7.1	1.0	7.2	14

Information values

A lack of independent values precluded the certification of the elements listed in Table 3. Information values for these measurands are given below along with their associated standard deviations derived from duplicate results from twelve bottles of CACB-1.

Table 3: Information values for trace metals in CACB-1

Element	Mass fraction, μg/g
	Mean	S.D.
Ba	3.45	0.02
Sr	225	1
Ni	4.33	0.03
Cu	0.35	0.01
Zn	4.88	0.10
Mo	0.40	0.01

Expiration of certification

The certified values for CACB-1 are considered valid until April 2015, 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.

Acknowledgements

The following staff members of the Measurement Science and Standards portfolio at the NRC contributed to the production and certification of CACB-1: C. Brophy, S. Willie, L. Yang.

Date of issue: August 2005
Date of expiry: April 2015

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