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Heavy metals referred to in this law refer to metal impurities that can react with thioacetamide or sodium sulfide to develop color under specified experimental conditions
Preparation of standard lead solutions
Weigh 0.
Precisely measure 10ml of the stock solution, put it in a 100ml measuring bottle, add water to dilute to the mark, and shake well to obtain (each 1ml is equivalent to 10μg of Pb)
Glass containers for preparation and storage shall not contain lead
first law
Unless otherwise specified, take three 25ml Nessler colorimetric tubes, add a certain amount of standard lead solution and 2ml acetate buffer (pH3.
If the dilute caramel solution or other non-interfering colored solution is added dropwise to the nail tube, if the color cannot be made consistent, the sample should be checked according to the second method
If the test product contains high iron salt which affects the inspection of heavy metals, the same amount of vitamin C 0.
When preparing the test solution, if more than 1ml of hydrochloric acid is used, more than 2ml of ammonia test solution is used, or other reagents are added for processing, unless otherwise specified, the same amount of reagents should be taken from the first tube solution and placed in a porcelain dish and evaporated to dryness.
second method
Unless otherwise specified, when it is necessary to use the second method for inspection, take the specified amount of the test sample under each category, carry out the incandescent treatment according to the inspection method for residue on ignition (General Rule 0841), and then take the remaining residue; or Directly take the residue left under the item of residue on ignition; if the test product is a solution, take the specified amount of solution under each category, evaporate to dryness, and then take the remaining residue after processing according to the above method; add 0.
third law
Unless otherwise specified, take an appropriate amount of the test sample, dissolve it in 5ml of sodium hydroxide test solution and 20ml of water, put it in a Nessler colorimetric tube, add 5 drops of sodium sulfide test solution, shake well, mix it with a certain amount of standard lead The color of the solution after the same treatment should not be darker
