Determination of total cadmium, lead, arsenic, mercury and inorganic arsenic in mushrooms: outcome of IMEP-116 and IMEP-39

Figures & data

Table 1. Analytical methods used by the expert laboratories.

Certifier	Sample treatment/digestion/analytical method	Technique
BAM	Total As, Cd and Pb: 0.25 g of sample. Microwave-assisted digestion. 6 ml of HNO3 (sub-boiling) in an Ultra Clave III. Power 1000 W, ramp 20 min. Hold 30 min. Digestion temperature 250°C at 100 bar. ICP equipped with a collision cell. Argon + helium as collision gas. Multi-point calibration from 0 to 10 µg l^−1 (five points) for total As and Pb, 0–25 µg l^−1 for Cd	ICP-MS
BAM	Total Hg: 0.25 g of sample. Microwave-assisted digestion. 6 ml of HNO3 (sub-boiling) in an Ultra Clave III. Power 1000 W, ramp 20 min. Hold 30 min. Digestion temperature: 250°C at 100 bar. CV-AFS, amalgamation mode (gold trap). Argon as gas. Multi-point calibration from 0 to 125 µg l^−1 (five points)	CV-AFS
BAM	Total Hg: 0.12 g of sample. Solid sampling cold-vapour AAS, combustion + amalgamation (gold trap). Advanced elementar Hg analyser (AMA-254) at the wavelength of 253.7 nm. Oxygen as gas mode. Multi-point calibration from 0.5 to 36 ng (nine points) and from 40 to 500 ng (nine points)	AMA-254
LSPA	Total As, Cd, Pb: the digestion of samples was carried out using a microwave digestion system, Ethos one (Milestone Inc., Shelton, CT, USA), equipped with the Q-20 Quartz Rotor Ultratrace Analysis (20 ml quartz tubes, 250ºC and 40 bars operating parameters). A unique sample digestion procedure was applied to all samples and analytes. 0.25 g of sample were weighted in quartz digestion vessels and 5 ml of HNO3:H2O 1:1 were added in a fume hood. The mixture was left to react over 1 h approximately until finishing the gas generation process. Analysis was performed on an ELAN DRC II ICP-MS (PerkinElmer) equipped with a perfluoroalcoxy standard nebuliser and a peltier cooled baffled glass cyclonic spray chamber (both Elemental Scientific, Omaha, NE, USA). Multi-element standard solutions were used for external calibration. Six standards in 2% (w/w) HNO3 matrix for As, Cd and Pb were prepared at levels ranging from 0.1 to 50 μg l^−1. The calibration curve was drawn from six points, including the calibration blank and a weighted linear regression approach with internal standardisation was applied	ICP-MS
LSPA	Total Hg: 40 mg of sample were weighted directly in quartz samples boats and placed in the Hg analyser. To prevent explosions inside the catalyser, 500 μl of ultra-pure water were added in the quartz boats together with the samples. At least two quality control samples (CRM) were analysed in each sequence	Elemental Hg analyser
KFUG	Total As: a portion of the powdered samples (about 250 mg weighed with a precision of 0.1 mg) was weighed directly into 12 ml quartz tubes and concentrated nitric acid (2 ml) and H2O (2 ml) were added. The tubes were transferred to a Teflon^® rack of the Ultraclave microwave system (MLS GmbH, Leutkirch, Germany) and covered with Teflon caps. After closing the system, an argon pressure of 4–106 Pa was applied and the mixture was heated to 250°C for 30 min before being allowed to cool to RT. After mineralisation, the samples were transferred to 15 ml polypropylene tubes (Greiner, Bio-one, Frickenhausen, Germany) and diluted with water to 9 ml (based on mass). Finally, 1 ml of a solution containing 50% methanol (to enhance the As response) and 100 μg l^−1 each of Ge and In as internal standards were added to all digested samples giving a final concentration of 5% methanol and 10 μg l^−1 of Ge and In. All standards for total As determinations were prepared with 20% (v/v) of concentrated nitric acid and also 5% methanol for matrix matching with the digested samples. The As concentrations in the digests were determined by ICP-MS using helium as the collision cell gas	ICP-MS
KFUG	iAs: about 0.5 g of powder were weighed with a precision of 0.1 mg into 50 ml polypropylene tubes and a solution (10 ml) of 20 mmol l^−1 trifluoracetic acid containing 50 μl of a 30% H2O2 solution was added. Samples were extracted with a GFL-1083 shaking water bath (Gesellschaft für Labortechnik, Burkwedel, Germany) at 95°C for 60 min. After cooling to RT the extracts were centrifuged for 15 min at 4700g. An aliquot of 1 ml was transferred to Eppendorf vials and centrifuged for 15 min at 8900g. The supernatant was used directly for HPLC-ICP-MS analysis	HPLC-ICP-MS
CSIC	iAs: 0.5–1 g of sample. Concentrated HCl is added and water. Reducing agent (2 ml of HBr and 1 ml of hydrazine sulphate) is added. 10 ml of CHCl3. Agitate and separate the phases. Repeat the extraction three times. iAs is back-extracted with 10 ml of HCl. 2.5 ml of ashing aid suspension (20% w/v Mg(NO3).6H2O and 2% w/v MgO) and 10 ml HNO3 are added. Evaporated to dryness in a sand bath and place at a muffle at 150°C. Increase the temperature to 425 ± 25°C for 12 h. The white ash is dissolved in 6 mol l^−1 HCl and reduced with pre-reducing solution (5% w/v KI and 5% w/v ascorbic acid). After 30 min, filter through Whatman No. 1 and dilute with 6 mol l^−1 HCl. Samples are analysed by flow injection-hydride generation AAS	FI-HG-AAS
UB	iAs: a microwave digestion system (Ethos Touch Control, Milestone, Gomensoro, Barcelona, Spain), with a microwave power of 1000 W and temperature control, was used for the extraction procedure. An Agilent 7500ce ICPMS was coupled to an Agilent 1200 LC quaternary pump to determine iAs content. The analytical column Hamilton PRP-X100 (250 × 4.1 mm, 10 µm; Hamilton, Reno, NV, USA) was protected by guard column filled with the corresponding stationary phase. The outlet of the LC column was connected via PEEK capillary tubing to the nebuliser (BURGENER Ari Mist HP type) of the ICP-MS system, which was the As-selective detector. 0.25 g aliquots of the test material and three CRMs, for internal quality control, were weighed in PTFE vessels and then extracted by adding 10 ml of 0.2% (w/v) HNO3 and 1% (w/v) H2O2 solution in a microwave digestion system. The temperature was raised first to 55°C (and held for 10 min) then to 75°C (and held for 10 min) and finally the digest was taken up to 95°C and maintained for 30 min. Samples were cooled to RT and centrifuged at 3500 rpm for 12 min. The supernatant was filtered through PET filters (pore size 0.45 μm) and analysed by HPLC-ICP-MS	HPLC-ICP-MS

Note: Certified reference materials (CRMs).

Table 2. Average measurements reported by the expert laboratories (X_n), their expanded measurement uncertainties (U_n), assigned values, standard uncertainty contributions (from characterisation, homogeneity and stability) and combined uncertainties (u_ref) and the standard deviation for the PTs assessment (mg kg⁻¹).

	Total As	Total Cd	Total Hg	Total Pb	iAs
Xn ± Un (k = 2)	0.638 ± 0.026	4.42 ± 0.19	0.0782 ± 0.0032	0.274 ± 0.019	0.330 ± 0.014
	0.61 ± 0.06	3.99 ± 0.44	0.0781 ± 0.007	0.260 ± 0.016	0.286 ± 0.037
	0.69 ± 0.05		0.072 ± 0.007		0.348 ± 0.026
Xref	0.646	4.21	0.076	0.267	0.321
uchar	0.017	0.15	0.002	0.008	0.010
ubb	0.007	0.04	0.002	0.009	0.004
ust	0.015	0.06	0.002	0.010	0.007
uref	0.024	0.17	0.004	0.016	0.013
Uref (k = 2)	0.048	0.33	0.007	0.031	0.026
σp	0.10	0.42	0.011	0.05	0.06
σp (%)	15%	10%	15%	20%	19%

Note: Experts do not necessarily correspond to the order in which they were presented.

Figure 1. (colour online) X_lab and U_lab as reported by the participants in IMEP-39 and IMEP-116 for the total mass fraction of Cd.

Figure 2. (colour online) X_lab and U_lab as reported by the participants in IMEP-39 and IMEP-116 for the total mass fraction of Pb.

Figure 3. (colour online) X_lab and U_lab as reported by the participants in IMEP-39 and IMEP-116 for the total mass fraction of As.

Figure 4. (colour online) X_lab and U_lab as reported by the participants in IMEP-39 and IMEP-116 for the total mass fraction of Hg.

Figure 5. (colour online) X_lab and U_lab as reported by the participants in IMEP-39 and IMEP-116 for the total mass fraction of iAs.

Figure 6. (colour online) Distribution of satisfactory, questionable and unsatisfactory (a) z- and (b) ζ-scores for IMEP-39 and IMEP-116.

Table 3. Uncertainty assessment. Proportion of participants in each study who received the ‘a’, ‘b’ or ‘c’ ratings (%).

	Case a		Case b		Case c
Measurand	IMEP-116	IMEP-39	IMEP-116	IMEP-39	IMEP-116	IMEP-39
Total As	69	57	9	37	22	6
Total Cd	54	34	16	47	30	19
Total Hg	58	44	12	36	30	20
Total Pb	67	52	18	40	15	8
iAs	63	55	6	27	31	18

Figure 7. (colour online) Chromatograms showing the distribution of As species in the test item, as obtained by two expert laboratories using anion exchange-ICP-MS.

Figure 8. (colour online) Distribution of results reported for the total mass fraction of As on the basis of the technique used.