National Food Safety Standard
Determination of Iron in Foods
食品安全国家标准
食品中铁的测定
1 Scope
This standard specifies flame atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry for the determination of iron content in foods.
This standard is applicable to the determination of iron content in foods.
Method I Flame Atomic Absorption Spectrometry
2 Principle
After the digestion of specimen, and the atomic absorption flame atomization, the absorbance value is determined at 248.3nm. Within the range of certain concentration, the absorbance value of iron is in direct proportion to the iron content and quantitation is realized by comparing with standard series.
3 Reagents and Materials
Unless otherwise specified, guaranteed reagents and Grade II water (defined in GB/T 6682) are adopted for the purposes of this method.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Sulfuric acid (H2SO4).
3.2 Reagents preparation
3.2.1 Nitric acid solution (5+95): measure 500mL of nitric acid, pour it into 950mL of water and mix well.
3.2.2 Nitric acid solution (1+1): measure 250mL of nitric acid, pour it into 250mL of water and mix well.
3.2.3 Sulfuric acid solution (1+3): measure 50mL of sulfuric acid, slowly pour it into 150mL of water and mix well.
3.3 Standards
Ammonium ferric sulfate [NH4Fe(SO4)2·12H2O, CAS No.7783-83-7]: purity>99.99% or the standard iron solution (in certain concentration) that is approved and awarded with reference material certificate by the nation.
3.4 Preparation of standard solution
3.4.1 Iron standard stock solution (1 000mg/L): accurately weigh 0.863 1g (accurate to 0.000 1g) of ammonium ferric sulfate, dissolve it with water, add into 1.00mL of sulfuric acid solution (1+3), then transfer the solution into a 100mL volumetric flask, bring the volume to the scale with water and mix well. The mass concentration of this iron solution is 1 000mg/L.
3.4.2 Standard intermediate solution of iron (100mg/L): accurately pipet 10mL of iron standard stock solution (1 000mg/L) to a 100mL volumetric flask, bring the volume to the scale with nitric acid solution (5+95) and then mix well. The mass concentration of this iron solution is 100mg/L.
3.4.3 Standard series solution of iron: respectively pipet 0mL, 0.500mL, 1.00mL, 2.00mL, 4.00mL and 6.00mL of standard intermediate solution of iron (100mg/L) into 100mL volumetric flasks, add into nitric acid solution (5+95) to bring the volumes to the scale and mix well. The mass concentration of iron in standard series solution is 0mg/L, 0.500mg/L, 1.00mg/L, 2.00mg/L, 4.00mg/L and 6.00mg/L respectively.
Note: The specific concentration of iron in standard solution series may be determined according to the sensitivity of apparatus and the actual iron content in the sample.
4 Apparatuses
Note: All the glassware and polytetrafluoroethylene digestion inner tanks shall be soaked in nitric acid solution (1+5) over night, flushed with tap water repeatedly and finally washed clean with water.
4.1 Atomic absorption spectrometer: equipped with flame atomizer and iron hollow cathode lamp.
4.2 Analytical balance: with sensitivity of 0.1mg and 1mg.
4.3 Microwave digestion instrument: equipped with polytetrafluoroethylene digestion inner tank.
4.4 Adjustable electrothermal furnace.
4.5 Adjustable electric hot plate.
4.6 Pressure digestion tank: equipped with polytetrafluoroethylene digestion inner tank.
4.7 Thermostatic dry oven.
4.8 Muffle furnace.
5 Analysis Procedures
5.1 Specimen preparation
Note: Specimen shall not be contaminated during the sampling and preparation processes.
5.1.1 Grain and beans samples
Pulverize the sample and store it in plastic bottle after foreign substances are removed from it.
5.1.2 Vegetables, fruits, fish and meat samples
Clean the sample with water, dry it in the air, take the edible part to make into homogenate and store the homogenate in the plastic bottle.
5.1.3 Shake such liquid samples as beverage, liquor, vinegar, soy sauce, edible oils and liquid milk well.
5.2 Specimen digestion
5.2.1 Wet digestion
Accurately weigh 0.5g~3g (accurate to 0.001g) of solid specimen or accurately transfer 1.00mL~5.00mL of liquid specimen to the digestion pipe with scale, add into 10mL of nitric acid and 0.5mL of perchloric acid, digest them on adjustable electrothermal furnace (reference conditions: 120℃/0.5h~1h, temperature rising to 180℃/2h~4h and temperature rising to 200℃~220℃). If the digestive solution is sepia, add into nitric acid again, digest until white smoke is emitted and digestive solution is colorless and transparent or slightly yellow; take out the digestion pipe and after cooling, transfer the digestive solution to a 25mL volumetric flask, wash for 2~3 times with a small amount of water, combine the washing solution into the volumetric flask, bring the volume to the scale with water and then mix well for future use. Carry out the specimen blank test simultaneously. Wet digestion can also be carried out on adjustable electric hot plate with conical flask according to the above-mentioned operating methods.
5.2.2 Microwave digestion
Accurately weigh 0.2g~0.8g (accurate to 0.001g) of solid specimen or accurately transfer 1.00mL~3.00mL of liquid specimen into the microwave digestion tank, add into 5mL of nitric acid, and digest the specimen according to the operation procedures of microwave digestion (see Table A.1 for digestion conditions). After cooling, take out the digestion tank, and catch acid to about 1.0mL by placing it on 140℃~160℃ electric hot plate. After cooling down, transfer the digestive solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into volumetric flask, bring the volume to the scale with water and mix well for future use. Carry out the specimen blank test simultaneously.
5.2.3 Pressure tank digestion
Accurately weigh 0.3g~2g (accurate to 0.001g) of solid specimen or accurately transfer 2.00mL~5.00mL of liquid specimen into the digestion inner tank and add into 5mL of nitric acid. Cover up the inner cover, tighten the stainless steel enclosure, put the tank in thermostatic drying oven and maintain for 4h~5h at 140℃~160℃. After cooling, slowly loosen the outer tank, take out the digestion inner tank, catch acid to about 1.0mL on the adjustable electric hot plate at 140℃~ 160℃. After cooling down, transfer the digestive solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into volumetric flask, bring the volume to the scale with water and mix well for future use. Carry out the specimen blank test simultaneously.
5.2.4 Dry digestion
Accurately weigh 0.5g~3g (accurate to 0.001g) of solid specimen or accurately transfer 2.00mL~5.00mL of liquid specimen into the crucible, heat with soft fire, carbonize it to smokeless and transfer to the muffle furnace for ashing for 3h~4h at 550℃. Take it out after cooling; for the specimen not ashed completely, add into several drops of nitric acid, heat with soft fire, carefully evaporate to dryness, and transfer it to a 550℃ muffle furnace; continuously ash for 1h~2h until the specimen acts like lime; cool down, take it out, dissolve it with proper amount of nitric acid solution (1+1), transfer the solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into the volumetric flask and bring the volume to the scale with water. Carry out the specimen blank test simultaneously.
Contents
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Apparatuses
5 Analysis Procedures
6 Expression of Analysis Results
7 Accuracy
8 Others
Appendix A Temperature Programming of Microwave Digestion
Appendix B Reference Conditions of Flame Atomic Absorption Spectrometry
National Food Safety Standard
Determination of Iron in Foods
食品安全国家标准
食品中铁的测定
1 Scope
This standard specifies flame atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry for the determination of iron content in foods.
This standard is applicable to the determination of iron content in foods.
Method I Flame Atomic Absorption Spectrometry
2 Principle
After the digestion of specimen, and the atomic absorption flame atomization, the absorbance value is determined at 248.3nm. Within the range of certain concentration, the absorbance value of iron is in direct proportion to the iron content and quantitation is realized by comparing with standard series.
3 Reagents and Materials
Unless otherwise specified, guaranteed reagents and Grade II water (defined in GB/T 6682) are adopted for the purposes of this method.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Sulfuric acid (H2SO4).
3.2 Reagents preparation
3.2.1 Nitric acid solution (5+95): measure 500mL of nitric acid, pour it into 950mL of water and mix well.
3.2.2 Nitric acid solution (1+1): measure 250mL of nitric acid, pour it into 250mL of water and mix well.
3.2.3 Sulfuric acid solution (1+3): measure 50mL of sulfuric acid, slowly pour it into 150mL of water and mix well.
3.3 Standards
Ammonium ferric sulfate [NH4Fe(SO4)2·12H2O, CAS No.7783-83-7]: purity>99.99% or the standard iron solution (in certain concentration) that is approved and awarded with reference material certificate by the nation.
3.4 Preparation of standard solution
3.4.1 Iron standard stock solution (1 000mg/L): accurately weigh 0.863 1g (accurate to 0.000 1g) of ammonium ferric sulfate, dissolve it with water, add into 1.00mL of sulfuric acid solution (1+3), then transfer the solution into a 100mL volumetric flask, bring the volume to the scale with water and mix well. The mass concentration of this iron solution is 1 000mg/L.
3.4.2 Standard intermediate solution of iron (100mg/L): accurately pipet 10mL of iron standard stock solution (1 000mg/L) to a 100mL volumetric flask, bring the volume to the scale with nitric acid solution (5+95) and then mix well. The mass concentration of this iron solution is 100mg/L.
3.4.3 Standard series solution of iron: respectively pipet 0mL, 0.500mL, 1.00mL, 2.00mL, 4.00mL and 6.00mL of standard intermediate solution of iron (100mg/L) into 100mL volumetric flasks, add into nitric acid solution (5+95) to bring the volumes to the scale and mix well. The mass concentration of iron in standard series solution is 0mg/L, 0.500mg/L, 1.00mg/L, 2.00mg/L, 4.00mg/L and 6.00mg/L respectively.
Note: The specific concentration of iron in standard solution series may be determined according to the sensitivity of apparatus and the actual iron content in the sample.
4 Apparatuses
Note: All the glassware and polytetrafluoroethylene digestion inner tanks shall be soaked in nitric acid solution (1+5) over night, flushed with tap water repeatedly and finally washed clean with water.
4.1 Atomic absorption spectrometer: equipped with flame atomizer and iron hollow cathode lamp.
4.2 Analytical balance: with sensitivity of 0.1mg and 1mg.
4.3 Microwave digestion instrument: equipped with polytetrafluoroethylene digestion inner tank.
4.4 Adjustable electrothermal furnace.
4.5 Adjustable electric hot plate.
4.6 Pressure digestion tank: equipped with polytetrafluoroethylene digestion inner tank.
4.7 Thermostatic dry oven.
4.8 Muffle furnace.
5 Analysis Procedures
5.1 Specimen preparation
Note: Specimen shall not be contaminated during the sampling and preparation processes.
5.1.1 Grain and beans samples
Pulverize the sample and store it in plastic bottle after foreign substances are removed from it.
5.1.2 Vegetables, fruits, fish and meat samples
Clean the sample with water, dry it in the air, take the edible part to make into homogenate and store the homogenate in the plastic bottle.
5.1.3 Shake such liquid samples as beverage, liquor, vinegar, soy sauce, edible oils and liquid milk well.
5.2 Specimen digestion
5.2.1 Wet digestion
Accurately weigh 0.5g~3g (accurate to 0.001g) of solid specimen or accurately transfer 1.00mL~5.00mL of liquid specimen to the digestion pipe with scale, add into 10mL of nitric acid and 0.5mL of perchloric acid, digest them on adjustable electrothermal furnace (reference conditions: 120℃/0.5h~1h, temperature rising to 180℃/2h~4h and temperature rising to 200℃~220℃). If the digestive solution is sepia, add into nitric acid again, digest until white smoke is emitted and digestive solution is colorless and transparent or slightly yellow; take out the digestion pipe and after cooling, transfer the digestive solution to a 25mL volumetric flask, wash for 2~3 times with a small amount of water, combine the washing solution into the volumetric flask, bring the volume to the scale with water and then mix well for future use. Carry out the specimen blank test simultaneously. Wet digestion can also be carried out on adjustable electric hot plate with conical flask according to the above-mentioned operating methods.
5.2.2 Microwave digestion
Accurately weigh 0.2g~0.8g (accurate to 0.001g) of solid specimen or accurately transfer 1.00mL~3.00mL of liquid specimen into the microwave digestion tank, add into 5mL of nitric acid, and digest the specimen according to the operation procedures of microwave digestion (see Table A.1 for digestion conditions). After cooling, take out the digestion tank, and catch acid to about 1.0mL by placing it on 140℃~160℃ electric hot plate. After cooling down, transfer the digestive solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into volumetric flask, bring the volume to the scale with water and mix well for future use. Carry out the specimen blank test simultaneously.
5.2.3 Pressure tank digestion
Accurately weigh 0.3g~2g (accurate to 0.001g) of solid specimen or accurately transfer 2.00mL~5.00mL of liquid specimen into the digestion inner tank and add into 5mL of nitric acid. Cover up the inner cover, tighten the stainless steel enclosure, put the tank in thermostatic drying oven and maintain for 4h~5h at 140℃~160℃. After cooling, slowly loosen the outer tank, take out the digestion inner tank, catch acid to about 1.0mL on the adjustable electric hot plate at 140℃~ 160℃. After cooling down, transfer the digestive solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into volumetric flask, bring the volume to the scale with water and mix well for future use. Carry out the specimen blank test simultaneously.
5.2.4 Dry digestion
Accurately weigh 0.5g~3g (accurate to 0.001g) of solid specimen or accurately transfer 2.00mL~5.00mL of liquid specimen into the crucible, heat with soft fire, carbonize it to smokeless and transfer to the muffle furnace for ashing for 3h~4h at 550℃. Take it out after cooling; for the specimen not ashed completely, add into several drops of nitric acid, heat with soft fire, carefully evaporate to dryness, and transfer it to a 550℃ muffle furnace; continuously ash for 1h~2h until the specimen acts like lime; cool down, take it out, dissolve it with proper amount of nitric acid solution (1+1), transfer the solution to a 25mL volumetric flask, wash the inner tank and inner cover for 2~3 times with a small amount of water, combine the washing solution into the volumetric flask and bring the volume to the scale with water. Carry out the specimen blank test simultaneously.
Contents of GB 5009.90-2016
Contents
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Apparatuses
5 Analysis Procedures
6 Expression of Analysis Results
7 Accuracy
8 Others
Appendix A Temperature Programming of Microwave Digestion
Appendix B Reference Conditions of Flame Atomic Absorption Spectrometry