Determination of Arsenic in Food Additives by Atomic Fluorescence Spectrometry
GB 5009.76-2014 National Food Safety Standard Determination of arsenic in food additives Instead of GB/T 5009.76-2003 Determination of arsenic in food additives will be officially implemented on March 21, 2016. Atomic fluorescence spectrometry is one of the methods for the determination of arsenic in food additives. As a routine analytical instrument for detecting heavy metals such as arsenic, mercury and lead, atomic fluorescence has the characteristics of high sensitivity and easy operation. The atomic fluorescence spectrophotometer of hydrogenation atomic fluorescence spectrometry has four characteristics: “multiple, fast, good and economicalâ€. The following is a laboratory test to share how to use the atomic fluorescence spectrometer to test the arsenic in food additives.
According to the new standard, the use of atomic fluorescence spectrometer to test arsenic in food additives requires the preparation of the following reagents: sodium hydroxide (NaOH) (excellent grade), borohydride or borohydride (NaBH 4 or KBH 4 ), sulfur Urea (CH 4 N 2 S), nitric acid (HNO 3 ) (excellent grade pure), sulfuric acid (H 2 SO 4 ) (excellent grade pure), perchloric acid (HCIO 4 ) (excellent grade pure), hydrochloric acid (HCl) (excellent grade pure), magnesium nitrate [Mg(N0 3 ) 2 .6H 2 O], magnesium oxide (MgO), hydrogen peroxide (H 2 O 2 ).
Preparation of reagents
1. Sodium hydroxide solution (2 g/L): Weigh 2.0 g of sodium hydroxide, dissolve in 1 000 mL of water, and mix.
2. Hydroboric acid Na solution (10 g/L): Weigh 10.0 g of sodium borohydride, dissolve it in 1 000 mL of sodium hydroxide solution, and mix. It is ready for use (it can also weigh 14 g of borohydride K instead of borohydride Na).
3. Thiourea solution (50 g/L): Weigh 50 g of thiourea, dissolve it in 1 000 mL of water, and mix.
4. Sulfuric acid solution (1+9): Measure 100 mL of sulfuric acid and carefully pour 900 ml of water. Mix and mix.
5. Sodium hydroxide solution (100 g/L): Weigh 1.0 g of sodium hydroxide and dissolve in 10 mL of water.
6. Hydrochloric acid solution (1+1): Measure 100 mL of hydrochloric acid and slowly pour into 100 mL of water, mix and cool.
7. Magnesium nitrate solution (150 g/L): Weigh 150 g of magnesium nitrate, dissolve it in 1 000 mL of water, and mix.
Preparation of standard solution
1. Arsenic standard stock solution (0.1 mg/mL.): accurately weigh 0.1320 g of 2,3,3,3,3,3,3,3,3,3,3,3 In a mL volumetric flask, add 25 mL of sulfuric acid solution (1+9) to the mark.
2. Arsenic standard use solution (1/μg/mL): Pipette 1.00 mL of arsenic stock standard solution into a 100 mL volumetric flask and dilute to the mark with water.
Analysis step
Taking wet digestion as an example
Weigh solid sample 1 g ~ 2.5 g (accurate to 0.001 g), liquid sample 5 g ~ 10 g (accurate to 0.001 g), placed in a 100 mL Erlenmeyer flask, add 20 mL ~ 40 mL of nitric acid, sulfuric acid 1.25 mL, left overnight. The next day, it was placed on a hot plate and heated to digest (<220 ° C). If the digested solution is treated to about 10 mL, there will still be undecomposed substances or the color will become darker. Remove and cool, add 5 mL to 10 mL of nitric acid, and digest to about 10 mL for observation. Repeat this two or three times to avoid carbonization. If it is still not completely resolved, add 1 mL to 2 mL of perchloric acid, continue heating until the digestion is complete, and then continue to heat until the white smoke of perchloric acid is exhausted, and the white smoke of sulfuric acid begins to emerge. Remove the cooling, add 25 mL of water, and then heat to produce white sulfuric acid. Remove the cooling, transfer the digested solution into a 25 mL volumetric flask or a colorimetric tube with water, add 2.5 mL of thiourea solution (50 g/L), and finally bring up to volume with water and mix for testing. At the same time, do a blank test.
Standard series solution preparation
Accurately add 1 μg/mL arsenic standard solution 0 mL, 0.05 mL, 0.20 mL, 0.50 mL, 1.00 mL, 2.00 mL, sulfuric acid solution (1+9) 12.5 mL, 50 g/L thiourea in a 25 mL volumetric flask. 2.5 mL, add water to volume, equivalent to arsenic concentration 0 ng / mL, 2 ng / mL, 8 ng / mL, 20 ng / mL, 40 ng / mL, 80 ng / mL, mix and prepare.
Instrument reference conditions (the following conditions take the SK-Lee Atomic Fluorescence Spectrometer as an example)
Light source: hollow core cathode lamp, lamp current 60 ~ 80mA
Negative high pressure: -300 ~ -350V
Main gas flow rate: fixed value, about 500mL/min
Auxiliary gas flow rate: 800 ~ 1000mL / min
Pump speed: 70 ~ 80 rev / min
Detection limit (reference value): 0.01 ng / mL
Precautions:
(1) A certain amount of As is generally present in hydrochloric acid, so the use of superior grade HCL can reduce the blank. However, there are also some cases where the analysis of pure As content is lower than that of superior grade, and the content of As in different production plants or different production batches is also very different. Therefore, it is recommended to prepare 10% (V/V) with a small amount of HCl before use. Under the conditions of the comparison test.
(2) The various utensils before use must be soaked with (1+1) HNO 3 for 24 hours, and then carefully cleaned to prevent contamination of As.
(3) The standard stock solution of arsenic prepared in this specification is trivalent. In order to prevent arsenic from being oxidized during storage, it is recommended to add thiourea + ascorbic acid, and potassium iodide to pre-restore As (V) to As (III). Temperature effects, room temperature below or less than 15 ° C, should be placed for at least 30 minutes, the sample must also be pre-reduced.
(4) The volumetric flask with the standard solution must be fixed for a long time and cannot be changed arbitrarily.
(5) When preparing the standard solution, a fixed 5mL graduated pipette should be used, which can be directly used to prepare all standard series.
(6) The concentration of borohydride K solution has a great influence on the determination of As.
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