Ferric pyrophosphate, as a food nutritional fortifier, has relevant quality standards and testing methods. The specific introduction is as follows:

I. Quality Standards

Appearance: Generally, it is a brownish-black or yellowish-white powder.

Content: Calculated based on iron (Fe), the content is usually required to be within the specified range. For example, for ferric pyrophosphate as a food additive, the iron content is required to be between 24.0% and 30.0%.

Heavy Metal Content: The contents of heavy metals such as lead (Pb) and arsenic (As) need to meet strict limit standards. For example, the lead content generally should not exceed 2mg/kg, and the arsenic content should not exceed 3mg/kg.

Loss on Drying: It is usually specified that the loss on drying does not exceed a certain proportion, such as not exceeding 1.0%, to ensure the stability and quality of the product.

Residue on Ignition: There is generally a corresponding limit requirement, for example, not exceeding 4.0%, to ensure that the content of inorganic impurities in the product is within a controllable range.

II. Testing Methods

1. Determination of Iron Content

Principle: Usually, ferric pyrophosphate is first dissolved to release iron ions, then a suitable oxidant is used to oxidize the iron ions to a higher valence state, and finally the iron content is determined by complexometric titration or redox titration. For example, ferric pyrophosphate is dissolved with hydrochloric acid, using sulfosalicylic acid as an indicator, and titrated with a standard disodium ethylenediaminetetraacetate (EDTA) solution.

Procedure: Weigh a certain amount of ferric pyrophosphate sample accurately to 0.0001g, place it in a conical flask, add an appropriate amount of hydrochloric acid solution, heat to dissolve it, and then cool it to room temperature. Add a certain amount of sulfosalicylic acid indicator, and titrate with the standard disodium ethylenediaminetetraacetate solution until the solution changes from purplish red to bright yellow, which is the end point. Calculate the iron content according to the volume of the standard titrant consumed.

2. Detection of Heavy Metal Content

Determination of Lead: Atomic absorption spectrometry or inductively coupled plasma mass spectrometry (ICP-MS) is commonly used. Taking atomic absorption spectrometry as an example, after digesting the sample, prepare the sample solution, introduce it into the atomic absorption spectrometer, measure its absorbance at the characteristic absorption wavelength of lead, and quantify it by comparing with the standard curve.

Determination of Arsenic: Hydride generation-atomic fluorescence spectrometry or the silver salt method can be used. In hydride generation-atomic fluorescence spectrometry, after digesting the sample, under acidic conditions, arsenic is converted into arsine gas, which is carried into the atomic fluorescence spectrometer by the carrier gas for determination.

3. Determination of Loss on Drying

Principle: Dry the sample under the specified temperature and time conditions, and calculate the percentage of loss on drying by weighing the mass difference of the sample before and after drying.

Procedure: Weigh a certain amount of the sample accurately to 0.0001g and place it in a weighing bottle that has been weighed to a constant mass. Put the weighing bottle into an oven and dry it to a constant mass at the specified temperature (such as 105°C). Take out the weighing bottle, place it in a desiccator, cool it to room temperature, and weigh it. Calculate the loss on drying according to the mass of the sample before and after drying.

4. Determination of Residue on Ignition

Principle: Ignite the sample at a high temperature to volatilize the organic matter and convert the inorganic impurities into corresponding oxides or salts. Calculate the content of the residue on ignition by weighing the mass of the residue after ignition.

Procedure: Weigh a certain amount of the sample accurately to 0.0001g and place it in a crucible that has been weighed to a constant mass. First, char it gently on an electric stove until there is no smoke, then put it into a high-temperature furnace and ignite it to a constant mass at the specified temperature (such as 800°C). Take out the crucible, place it in a desiccator, cool it to room temperature, and weigh it. Calculate the content of the residue on ignition according to the mass of the residue after ignition.