Detection of chlorophyll copper in food additives

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A. General regulations

The reagents and water used in this standard, unless otherwise specified, refer to analytical pure reagents and Grade III water specified in GB/T6682-2008. The standard titration solution, impurity determination standard solution, formulation, and product used in the experiment shall be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603 unless other requirements are specified. The solution used in the experiment refers to aqueous solution when no specific solvent is specified for preparation

A.2 Identification Test

A.2.1 Physical Properties

Easily soluble in water, almost insoluble in low alcohols, and insoluble in chloroform.

. The aqueous solution is transparent and free from precipitation. In acidic conditions (below pH 6.5) or in the presence of calcium ions, precipitation occurs

A.2.2 Determination of absorption peak

Take the sample solution from A.4.3.1 absorbance measurement, and the sample solution has the maximum absorption peak within the two wavelength ranges of 405nm ± 3nm and 630nm ± 3nm.

A.2.3 Copper sodium ion test

Weigh 1g of the sample and place it in a crucible that has been burned to constant weight at 800 ℃± 25 ℃. Slowly heat until the sample is completely carbonized.

. Cool the carbonized sample, wet the residue with 0.5mL~1mL sulfuric acid, continue heating until the sulfuric acid vapor escapes, and burn the residue to constant weight in a high-temperature furnace at 800 ℃± 25 ℃. Add 10mL of hydrochloric acid solution (1+3) to the residue, heat and dissolve it in a water bath, filter and add water to 10mL, and use this as the test solution for the following tests:

a) Take the test solution for flame color test. Initially green, then yellow

b) Take 5mL of the test solution and add 0.5mL of 0.1% sodium diethyldithiocarbamate solution (1g dissolved in 1000mL of water) to produce a brownish red precipitate

A.3 Determination of pH

Prepare a sample solution with a concentration of 1% (1g of the sample is dissolved in 100mL of water), and measure its pH using a pH meter.

A.4 Determination of absorbance and absorbance ratio

A.4.1 Reagents and materials

A.4.1.1 0.15mol/L disodium hydrogen phosphate solution: Weigh 53.7g of disodium hydrogen phosphate (Na2HPO4 · 12H2O), dissolve with water, dilute and dilute to 1000mL

A.4.1.2 0.15mol/L potassium dihydrogen phosphate solution: Weigh 20.4g of potassium dihydrogen phosphate (KH2PO4), dissolve in water, dilute, and bring to a constant volume of 1000mL

A.4.1.3; Phosphate buffer solution (pH 7.5): Mix 21 parts of 0.15mol/L disodium hydrogen phosphate solution with 4 parts of 0.15mol/L potassium dihydrogen phosphate solution

A.4.2 Instruments and Equipment

Spectrophotometer

A.4.3 Analysis Steps

A.4.3.1 Sample Solution Preparation

Accurately weigh 0.1g of the sample to the nearest 0.0002g, dissolve with water, transfer to a 100mL volumetric flask, add to the mark, and shake well. Take 1mL of the above aqueous solution, dilute with phosphate buffer (pH7.5) and bring to a constant volume of 100mL, which is the sample solution

A.4.3.2 Determination

Take the sample solution and place it in a 1cm colorimetric dish. Use phosphate buffer (pH7.5) as the blank control, and use a spectrophotometer to measure the absorbance at the maximum absorption wavelength within the two wavelength ranges of 405nm ± 3nm and 630nm ± 3nm.

. (The absorbance should be controlled between 0.3 and 0.7, otherwise the sample solution concentration should be adjusted and the absorbance should be re measured.)

A.4.4 Result calculation

A.4.4.1 The sample solution concentration is 1%, and the absorbance measured at the maximum absorption wavelength within the range of 405nm ± 3nm using a 1cm colorimetric dish is calculated as (405nm ± 3nm). Calculate according to formula (A.1):

Where:

A1- the actual absorbance of the sample solution measured

C1- The concentration value of the tested sample solution (converted to concentration on a dry basis based on the measured sample's drying weight loss), in grams per milliliter (g/mL)

A.4.4.2 The absorbance ratio is calculated as w1 according to formula (A.2):

In the formula:

(405nm ± 3nm) - The absorbance measured at the maximum absorption wavelength within the range of 405nm ± 3nm using a 1cm colorimetric dish with a sample solution concentration of 1%

(630nm ± 3nm) - The absorbance measured at the maximum absorption wavelength within the range of 630nm ± 3nm using a 1cm colorimetric dish with a sample solution concentration of 1%, using the same method as (405nm ± 3nm)

The experimental results shall be based on the arithmetic mean of the parallel measurement results. The absolute difference between two independent measurement results obtained under repeatability conditions shall not exceed 2% of the arithmetic mean

A.5 Total Copper Content

A.5.1 Sample Treatment

Accurately weigh 0.1g of the sample to the nearest 0.0002g, place it in a silicon dish, burn it at no more than 500 ℃ until carbon free, wet it with 1-2 drops of sulfuric acid, and ash it again. Boil and dissolve the ash in a 10% hydrochloric acid solution three times (5mL each time), and filter it into a 100mL volumetric flask. After cooling, bring to volume with water to the mark. This is the sample solution

A.5.2 Determination

Except for sample treatment, other steps shall be measured according to the method specified in GB/T5009.13.

A.6 Free Copper Content

A.6.1 Sample Treatment

Accurately weigh 0.1g of the sample, dissolve it in about 50mL of water, adjust the pH to 4.0 with 1mol/L hydrochloric acid, bring to a constant volume of 100mL, filter, and this is the sample solution

A.6.2 Determination

Except for sample treatment, other steps shall be measured according to the method specified in GB/T5009.13.

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