20th Australian Total Diet Survey
SUPPLEMENTARY INFORMATION - PART 4
Analytical Quality Assurance
Contaminants
A sample batch consists of approximately 60 samples. Within the batch, samples of the same matrix are grouped together, usually in sub-batches of 7 samples of the same matrix. Within each subgroup, one duplicate and one sample spike were analysed.
Where possible Certified Reference Materials (CRMs) are used to monitor recovery, eg NIST (National Institute of Science and Technology, USA) Bovine Liver, AGAL20 Bovine Liver. It is not possible to use CRMs for each matrix as they are not always available. Acceptance criteria had to be met for all sample spikes, duplicates and CRMs.
With every batch, analytical standards were run at the beginning and end of the run and acceptance criteria had to be met for the results to be accepted. 3 reagent blanks were analysed. All abnormally high concentrations (e.g. ,lead) samples were re-analysed to check reproducibility.
Pesticides
A sample batch consists of 10 samples of the same matrix. With every batch:
• Analytical standards were run at the beginning and end of the batch. Acceptance criteria had to be met for these standards;
• A solvent blank was analysed, made by running the solvent used for extraction through the entire analysis procedure;
• A spike was run and recoveries were checked against performance criteria;
• All positive samples were re-extracted and re-analysed to check reproducibility; and
• The identity of all positives found was confirmed by full scan gas chromatography/ mass spectrometry.
Summary of analytical methods used and limits of reporting achieved in the survey
Analytical methods used in the 20th ATDS
Chemical tests
Procedure and limit of reporting
Metal screen (antimony, arsenic, cadmium, copper, lead and mercury, selenium, tin, zinc)
Microwave digestion, with re-distilled nitric acid and determined using ICP–MS. Limits of reporting were 0.01 mg/kg except for antimony (0.002 mg/kg), cadmium (0.005 mg/kg), and mercury (0.002 mg/kg).
Inorganic arsenic
Perchloric acid digestion at 80° C for 1 hr, filtered, reduced with HBr and hydrazine sulphate to As 3+ . Hydride form generated with NaBH4and quantified by ICP-AES. Limit of reporting 0.05 mg/kg.
Organic Mercury
Extraction into acidified ethanol, centrifugation followed by ethylation, hexane extraction and analysis by GC/AED. Limit of reporting 0.5 m g/kg.
Organochlorine pesticides, Organophosphorus pesticides, Synthetic pyrethroid pesticides, Fungicide residues and PCBs
Acetone extraction and partition into dichloromethane/hexane. Extraction, evaporation and clean-up by GPC. GC determination with nitrogen/phosphorus detector for organophosphorus pesticides and fungicides; further clean up of extract using florisil chromatography followed by GC/ECD for organochlorine compounds, pyrethroids and fungicides; additional clean up using silica mini columns followed by GC/ECD for PCBs. Limit of reporting is 0.01 mg/kg.
Aflatoxins
Extraction into methanol/water. Purified using affinity chromatography. Determined using HPLC. Limit of reporting is 0.001 mg/kg.
Ochratoxins
Extraction into methanol/water. Purified using affinity chromatography. Determined using HPLC. Limit of reporting is 0.001 mg/kg.
Inhibitory Substances
Liquid from the sample is absorbed into paper discs which are used in a 3-plate microbial growth inhibition test. The limits of detection are 0.025 Units/mL org for penicillin, 0.2 Units/mL org for streptomycin, and 0.2 m g/mL org for oxytetracycline
AED Atomic Emission Detector
AES Atomic Emission Spectroscopy
GC Gas Chromatography
GPC Gel Permeation Chromatography
HPLC High Performance Liquid Chromatography
ICP Inductively Coupled Plasma
MS Mass Spectroscopy