BS EN ISO 12193:2004 – Animal and vegetable fats and oils — Determination of lead by direct graphite furnace atomic absorption spectroscopy
1 Scope
This International Standard specifies a method for the determination of trace amounts (> 0,001 mg/kg) of lead in all types of crude or refined edible oils and fats.
2 Principle
The oil or fat is atomized in a graphite furnace, with or without a platform, connected to an atomic absorption spectrometer which has been previously calibrated using standard solutions of an organo compound of lead.
The metal content is measured from the observed absorbance at a wavelength of 283,3 nm.
3 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity.
3.1 Cyclohexane, analytical grade.
3.2 Lecithin, containing 2 % phosphorus.
3.3 Matrix modifier: 2 % (by mass/volume) lecithin solution prepared by dissolving 2 g of lecithin (3.2) in 1 00 ml of cyclohexane (3.1 ).
3.4 Blank oil, refined.
Any edible oil is suitable, stored in a metal-free polyethylene bottle. The lead content of the oil shall not be greater than 0,001 mg/kg.
3.5 Lead standard stock solution, c(Pb) = 1 0 mg/kg.
This is prepared by appropriate dilution of an organometallic standard with the blank oil (3.4).
NOTE A suitable standard is available from the following companies: 1)
Continental Oil Company, Ponca City, Oklahoma, USA (Conostan, 5 000 mg/kg);
Merck KGaA, Darmstadt, Germany [Certipur 1 1 5051 , lead standard dissolved in oil, c(Pb) = 1 g/kg] in standard oil;
VWR International [Certipur 1 .1 5051 , lead standard dissolved in oil, c(Pb) = 1 g/kg] in standard oil;
VWR International [Specpure ALFA01 9527.AD, lead, Organic AAS standard solution, Specpure, c(Pb) = 1 000 mg/g].
3.6 Lead standard working solutions: c(Pb) = 0,02 mg/kg, 0,05 mg/kg and 0,1 00 mg/kg, prepared daily by diluting the 1 0 mg/kg stock solution (3.5) with blank oil (3.4).
3.7 Argon, of minimum purity 99,99 %.
4 Apparatus
4.1 Polyethylene or polypropylene capped bottles, 20 ml, metal free.
The polyethylene or polypropylene capped bottles are made metal free in the following way. Clean the bottles thoroughly with warm nitric acid, rinse with distilled water and dry the bottles in a drying oven at about 80 °C.
4.2 Micropipettor, 20 µl.
4.3 Pipettor tips.
4.4 Electric oven, regulated at 60 °C ± 2 °C.
4.5 Atomic absorption spectrometer, equipped with either “peak height” mode and printer, or “area” mode and pen-recorder (full-scale response in 0,2 s), together with the appropriate electrode-less discharge lamp (or hollow cathode lamp) and deuterium or Zeeman background corrector.
4.6 Graphite furnace atomizer, placed in the atomic absorption spectrometer (4.5), equipped with a control unit for temperature programming.
4.7 Graphite tube, normal (uncoated) or coated (pyrolytic).
4.8 Pyrolytic platform, in combination with uncoated or pyrolytically coated graphite tube.
Both atomization with and without the platform may be used. The accuracy and the sensitivity with the platform is twice as good as without the platform.
5 Sampling
Laboratory samples of at least 1 ,5 g shall be stored in metal-free bottles (4.1).
It is important that the laboratory receive a sample that is truly representative and has not been damaged or changed during transport or storage.
Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 5555.
BS EN ISO 12193:2004 – Animal and vegetable fats and oils — Determination of lead by direct graphite furnace atomic absorption spectroscopy