1 Scope
This standard specifies the determination of chromium in foods by graphite furnace atomic absorption spectrometry and inductively coupled plasma/mass spectrometry.
This standard is applicable to the determination of chromium in foods.
Method I Graphite furnace atomic absorption spectrometry
2 Principle
Atomize the digested specimen in a graphite furnace, and determine the absorbance at 357.9nm. Within a certain concentration range, the absorbance of chromium is proportional to the content of chromium, which is quantified by comparing with the standard series.
3 Reagents and materials
Unless otherwise specified, guaranteed reagents and Class-II water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Ammonium dihydrogen phosphate (NH4H2PO4).
3.2 Reagent preparation
3.2.1 Nitric acid solution (5+95): measure 50mL nitric acid, and pour it slowly into 950mL water and mix well.
3.2.2 Nitric acid solution (1+1): measure 50mL nitric acid, and pour it slowly into 50mL water and mix well.
3.2.3 Ammonium dihydrogen phosphate solution (20g/L): weigh 2g ammonium dihydrogen phosphate, dissolve it with a small amount of nitric acid solution (5+95), and dilute it with nitric acid solution (5+95) to 100mL, and mix well.
3.3 Standard sample
Potassium dichromate (K2Cr2O7, CAS No. 7778-50-9): with a purity of >99.99%, or standard sample certified by the state and issued with the reference material certificate.
3.4 Preparation of standard solutions
3.4.1 Chromium standard stock solution (1,000mg/L): accurately weigh 0.2829g potassium dichromate (bake at 110℃ for 2h), dissolve in water, transfer into a 100mL volumetric flask, dilute with nitric acid solution (5 +95) to the scale, and mix well. The mass concentration of chromium in this solution is 1,000mg/L.
3.4.2 Chromium standard intermediate solution (1,000μg/L): accurately pipette 1.00mL chromium standard stock solution (1,000mg/L) into a 10mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well. Then accurately pipette 1.00mL the above solution into a 100mL volumetric flask, dilute it with nitric acid solution (5+95) to the scale, and mix well. The mass concentration of chromium in this solution is 1,000μg/L.
3.4.3 Chromium standard solution series: respectively pipette 0mL, 0.150mL, 0.400mL, 0.800mL, 1.20mL and 1.60mL chromium standard intermediate solution into 100mL volumetric flasks, dilute them with nitric acid solution (5+95) to the scale, and mix well. The mass concentrations of chromium in these solutions are 0μg/L, 1.50μg/L, 4.00μg/L, 8.00μg/L, 12.0μg/L and 16.0μg/L, respectively. Freshly prepare the solutions before use.
Note: The mass concentration of chromium in the standard solution series may be determined according to the instrument sensitivity and the actual content of chromium in the sample.
4 Instruments and equipment
Note: All glasswares and polytetrafluoroethylene digestion inner tanks shall be soaked in nitric acid solution (1+5) overnight, flushed with water repeatedly, and finally washed clean with water and dried.
4.1 Atomic absorption spectrometer: with graphite furnace atomizer and chromium hollow cathode lamp.
4.2 Electronic balance: with sensitivities of 0.1mg and 1mg respectively.
4.3 Adjustable electric heating plate or adjustable electric furnace.
4.4 Microwave digestion system: with a polytetrafluoroethylene digestion inner tank.
4.5 Pressure digestion tank: with a polytetrafluoroethylene digestion inner tank.
4.6 Thermostatic drying oven.
4.7 Muffle furnace.
4.8 Sample crushing equipment: homogenizer and high-speed pulverizer.
Foreword i
1 Scope
Method I Graphite furnace atomic absorption spectrometry
2 Principle
3 Reagents and materials
4 Instruments and equipment
5 Analysis steps
6 Expression of analysis results
7 Precision
8 Others
Method II Inductively coupled plasma/mass spectrometry
Annex A Temperature programming for microwave digestion and reference conditions for graphite furnace atomic absorption spectrometer
