This certified reference material (CRM) is prepared for use in evaluation of accuracy of methylmercury and selected heavy metals analysis of human hair and other samples with similar matrices. Each bottle contains approximately 3 g of homogeneous human hair powder.
Preparation of Material
The male scalp hair of Japanese was collected in 3 barbershops located in Tokyo and Tsukuba in 1980. It was washed with non-ionic detergent, pulverized, sieved and blended. Approximately 3 g of the hair powder (<100 μm) was individually packed in acid-washed borosilicate bottles. The materials have been stored at -20 ℃ in the dark immediately after bottling.
The homogeneity of this CRM was evaluated by analyzing 5 subsamples from 5 randomly selected bottles for total Hg and other elements contents. Analysis of variance indicated no variability in Hg content of this CRM at 20-30 mg and in other elements. (e.g., Cu and Zn) at 120 mg aliquot.
Certified Values and Reference Values
Certified values for methylmercury, total Hg, Cd, Cu, Pb, Sb, Se and Zn are shown in Table 1. Certified values were determined by extensive collaboration analyses and were derived from at least 4 independent analytical methods specified in the table.
Reference values shown in Table 2 are given for information only. Note that certified and reference values are expressed on dry weight basis. For drying instruction, see Use below.
Table 1, Certified Values
Certified value±uncertainty expressed as μg/g dry weight.Samples should be dried at 85 ℃ for 4 hrs in a conventional electric oven and then cooled in a silicagel dessicator at room temperature before weighting.For detail see text.
|1:||Atomic absorption spectrometry (AAS)|
|2:||Cold vapor AAS|
|4:||Cold vapor atomic fluorescence spectrometry (CVAFS)|
|5:||Instrumental neutron activation analysis|
|6:||Radioactive neutron activation analysis|
|7:||Inductively coupled plasma atomic emission spectrometry|
|8:||Inductively coupled plasme mass spectrometry(ICP-MS)|
|9:||Nitrogen microwave induced plasma mass spectrometry (MIP-MS)|
|10:||Isotope dilution ICP-MS|
|11:||Isotope dilution MIP-MS|
|12:||X-ray fluorescence spectrometry|
|13:||Gas chromatography (GC)-electron capture detection|
Table 2, Reference Values
Note: Reference values are not certified and given only for information.Content*1
μg/g dry weight unless otherwise indicated.
This CRM should be storaged in its original bottle at -20 ℃ immediately after being received. Exposure to sunlight or UV radiation should be avoided because of possible methylmercury decomposition. Storage in a dark-colored polyethylene bag or container is recommended.
- This CRM was not sterilized because the procedure may decompose mehtylmercury. Handle as if it transmits diseases.
- The content of the bottle should be mixed well before each use to ensure homogeneity.
- The bottle should be left at room temperature for at least 30 min before weighing samples.The minimum sample of 120 mg of the material should be used.
- This CRM contains approximately 9 % moisture at the time of the preparation. The moisture content of the sample should be measured at the time of each use in order to correct the analytical value to dry weight basis value. Moisture content of this CRM is to be measured by the following procedure:
(1) Weigh accurately aliquot (>100 mg) of the material.
(2) Dry at 85 ℃ for 4 hrs in a conventional electric oven followed by cooling for 30 min in a silicagel dessicator at room temperature.
(3) Weigh again.
(4) The difference in the two weight measurements is assigned as moisture content.
In order to avoid possible loss/degradation of analytes by heating, use separate aliquot for moisture measurement from aliquots for analyte determination.
- This CRM contains small amount of silicious material. Addition of hydrofluoric acid to digesting acids is essential for a complete decomposition.
|1||New human hair certified reference material for methylmercury and trace elements|
|Frasenius J. Anal. Chem., 357:279-283 (1997)|
|Jun Yoshinaga, Masatoshi Morita, Kensaku Okamoto|
|2||Mercury speciation by liquid chromatography coupled with on-line chemical vapour generation and atomic fluorescence spectrometric detection (LC-CVGAFS)|
|Talanta, 66: 762-768(2005)|
|Emilia Bramanti, Cristina Lomonte, Massimo Onor, Roberto Zamboni, Alessandro D’Ulivo, Giorgio Raspi|
|3||Hair mercury levels, fish consumption, and cognitive development in preschool children from Granada, Spain|
|Environ. Res., 110: 96-104(2010)|
|Carmen Freire, Rosa Ramos, Maria-Jose Lopez-Espinosa, Sergi Diez, Jesus Vioque, Ferran Ballester, Mariana-Fatima Fernandez|
The isotopic composition of the mercury (Hg) in human hair is a useful tool for determining the routes of exposure to mercury. The isotopic composition of Hg in NIES CRM No.13, Human Hair has been determined and included in the certificate as additional information.
Within- and between-bottle variations in Hg isotopic measurements for NIES CRM No. 13 were found to be sufficiently small for the CRM to be used for its intended purpose (Table 1). The CRM can be used to confirm analytical results and for the precision management of analytical data. Further experimental details are given in A. Yamakawa et al., Accred. Qual. Assur. (2016) DOI 10.1007/s00769-016- 1196-x.
Table 1 Hg isotopic composition of NIES CRM No.13, Human Hair
Because mass independent fractionation in human hair varies with the type and quantity of the food, particularly seafood consumed, it can be used to estimate the sources of exposure. In addition, absorption of mercury, mostly in the form of methylmercury, by the human organism was shown to induce mass dependent fractionation of +2 % for δ202Hg, implying that the isotopic composition of Hg in human hair is as expected following its ingestion and distribution in the body (e.g., Yamakawa et al., 2016).
Isotopic compositions are reported in the delta (δ) notation relative to NIST SRM 3133:
δ***Hg (‰) = ([((***Hg/198Hg))sample/(***Hg/198Hg)NIST SRM 3133] – 1) × 1000
(***：mass of the Hg isotopes: 199, 200, 201, 202, and 204)
Mass-independent fractionation (MIF) is reported in capital delta (Δ) notation as the difference between the measured and the theoretical δ***Hg value:
Δ***Hg (‰) = δ***Hg − (β x δ202Hg),
(β：the kinetic or equilibrium fractionation factor appropriate for the particular isotope: δ199Hg/δ202Hg＝0.252, δ200Hg/δ202Hg＝0.502, δ201Hg/δ202Hg＝0.752, δ204Hg/δ202Hg＝1.492 (Bergquist and Blum, 2007)).
B. A. Bergquist, J. D. Blum : Science, 318, 417 (2007).
A. Yamakawa, A. Takeuchi, Y. Shibata, S. Berail, and O. F. X. Donard : Accred. Qual. Assur. (2016) DOI 10.1007/s00769-016-1196-x.
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