1. Sample pretreatment
1.1 Fresh vegetables and fruits: Wash the sample with deionized water, and after drying, take the edible part and chop it to mix. The appropriate amount of chopped samples is taken by the quartile method, and made into a homogenate with a food grinder for later use. If you need to add water, record the amount of water added.
1.2 Meat, eggs, aquatic products and their products: use the quartile method to take the appropriate amount or all, and use a food grinder to make a homogenate for use.
1.3 Milk powder, soy milk powder, infant formula powder and other solid dairy products (excluding cheese): put the sample into a container with a lid that can hold 2 times the volume of the sample, and mix the sample thoroughly by repeatedly shaking and inverting the container until Make the sample uniform.
1.4 Fermented milk, milk, condensed milk and other liquid dairy products: Mix the sample thoroughly by stirring or repeatedly shaking and inverting the container.
1.5 Cheese: Take an appropriate amount of sample and grind it into a uniform slurry. To avoid water loss, excessive heat should be avoided during grinding.
2. Extraction
2.1 Fruits, vegetables, fish, meat, eggs and their products, etc .: Weigh 5 g of the sample homogenate (accurate to 0.01 g, the sample volume of the sample can be adjusted appropriately, the same below), wash it in 80 mL of water In a 100 mL volumetric flask, ultrasonically extract for 30 min and shake once every 5 min to keep the solid phase completely dispersed. Place it in a water bath at 75 ℃ for 5 min, take it to room temperature, and dilute it to the mark with water. After the solution was filtered through filter paper, a part of the solution was centrifuged at 10 000 rpm for 15 min, and the supernatant was set aside.
2.2 Marinated fish, cured meat and other preserved products: Weigh 2 g of the sample homogenate (accurate to 0.01 g), wash it into a 100 mL volumetric flask with 80 mL of water, and extract ultrasonically for 30 min, shaking every 5 min Once, keep the solid phase completely dispersed. Place it in a water bath at 75 ℃ for 5 min, take it to room temperature, and dilute it to the mark with water. After the solution was filtered through filter paper, a part of the solution was centrifuged at 10 000 rpm for 15 min, and the supernatant was set aside.
2.3 Milk: Weigh 10 g (accurate to 0.01 g) of the sample, place it in a 100 mL volumetric flask, add 80 mL of water, shake well, sonicate for 30 min, add 2 mL of 3% acetic acid solution, and place at 4 ℃ for 20 min, Remove to room temperature, dilute to the mark with water. The solution was filtered through filter paper, and the supernatant was taken for use.
2.4 Milk powder: Weigh 2.5 g (accurate to 0.01 g) of the sample, place it in a 100 mL volumetric flask, add 80 mL of water, shake well, sonicate for 30 min, add 2 mL of 3% acetic acid solution, and place at 4 ℃ for 20 min , Remove and leave to room temperature, add water to dilute to the mark. The solution was filtered through filter paper, and the supernatant was taken for use.
2.5 Take about 15 mL of the above-mentioned spare supernatant, pass through a 0.22 μm aqueous filter needle filter, C18 column, and discard the first 3 mL (if the chloride ion is greater than 100 mg / L, you need to pass through the needle filter, C18 column, Ag Column and Na column, discard the first 7 mL), collect the eluent to be tested later.
The solid phase extraction column needs to be activated before use. For example, when using Cleanert® IC-RP column (1.0 mL), Cleanert® IC-Ag column (1.0 mL) and Cleanert® IC-Na column (1.0 mL), the activation process is: The Cleanert® IC-RP column (1.0 mL) was passed through 10 mL of methanol and 15 mL of water in sequence before use, and was left to activate for 30 min. The Cleanert® IC-Ag column (1.0 mL) and the Cleanert® IC-Na column (1.0 mL) were passed through with 10 mL of water and left to activate for 30 min.
Attachment: GB 5009.33-2010 National Food Safety Standard Determination of Nitrite and Nitrate in Food
Sample preparation of National Food Safety Standard "Determination of Nitrite and Nitrate in Food"
Cleanert IC ion chromatography sample preparation series
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