1 scope of application

This method is suitable for the citric acid and potassium hydroxide or potassium carbonate as food additive potassium citrate prepared. The product as acidity regulator, stabilizer and coagulator and quality improver in food industry.

2 chemical name, molecular formula, structural formula, relative molecular mass

Chemical name: 2-, 2, 3, three,, carboxylic acid, potassium

Molecular formula: C6H5K3O7 and H2O

COOK - CH2

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Structural formula: C - COOK - HO - H2O

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COOK - CH2

Relative molecular weight: 324.41 (according to the 1989 international atomic weight)

3 technical requirements

3.1. appearance

White or slightly yellow crystalline or crystalline powder.

3.2. food additive potassium citrate should conform to the following table requirements:

Project

Index

Potassium citrate (dry) content (in C6H5K3O7),%

More than

Ninety-nine

alkalinity

Through experiment

Arsenic (in As),%

Less than or equal to

Zero Point Zero Zero Zero three

Heavy metal (in Pb),%

Less than or equal to

Zero point zero zero one

Dry weight loss,%

3 ~ 6

4 test methods

4.1. identification test

4.1.1. main reagents

Pyridine acetic anhydride solution: 3 + 1.

4.1.2. identification method

Identification of 4.1.2.1. citrate

Said take approximately 1 g of sample dissolved in 100ml water, shake, take 0.5ml placed in existing 20ml pyridine acetic anhydride solution tube, shake, the solution should be a magenta.

Identification of 4.1.2.2. potassium ion

Said to take about 5, G sample, dissolved in 100mL water, with platinum wire dipped in this solution, in the colorless flame burning, flame should be purple blue.

Determination of potassium citrate (C6H5K3O7) content in 4.2.

4.2.1. principle overview

Glacial acetic acid as solvent and crystal violet as the indicator, with perchloric acid standard solution titration to test solution from purple into blue as the end point, in the form of anhydrous calculated the content.

4.2.2. reagent

Glacial acetic acid;

Standard titration solution of perchlorate: C (HClO4) = 0.1mol / L;

Crystal violet indicator: 5g / L.

4.2.3. determination method

Said from 4.6 drying a 0.25g, accurate to 0.0002g, placed in a dry 250ml conical flask, plus 40ml glacial acetic acid, slightly heating, dissolving, cooling to room temperature, 2 drops of crystal violet instruction liquid, with perchloric acid titrant to the solution from purple variable blue as the end point. At the same time to do a blank test.

4.2.4. result calculation

The percentage of potassium citrate (C6H5K3O7) was calculated by the formula (X):

= X

(V1V0) c * 0.1021

X 100 =

(V1V0) c * 10.21

M

M

Formula: V1 - Sample titration consumes the volume of the standard solution of hydrochloric acid, mL;

V0 - Blank titration consumes the volume of the standard solution of hydrochloric acid, mL;

C -- the actual concentration of the standard titration solution of perchlorate, mol / L;

M - sample quality, g;

LG - and ~ perchloric acid standard titration solution [C (HClO4) = 1.000mol / l] quite, expressed in grams of potassium citrate.

The results should be expressed to 1 decimal places.

4.2.5. allowed difference

The arithmetic mean value of the two parallel test results was determined.

The difference between the two parallel test results shall be no more than 0.2%.

Determination of alkalinity of 4.3.

4.3.1. reagent

Hydrochloric acid standard titration solution: C (HCl) = 0.1mol / L;

Phenolphthalein solution: 10g / L.

4.3.2. analysis steps

Said from 1.0 g of sample, accurate to 0.01 g, dissolved in 20ml of carbon dioxide free water, add 1 drop of phenolphthalein indicator solution, the solution should be pink. Plus 0.4mL hydrochloric acid standard titration solution, pink should disappear.

Determination of arsenic (As) in 4.4.

Said from 1.0 g of sample, accurate to 0.01 g, dissolved in 25ml of water, as the sample solution, absorb arsenic (arsenic) 3 mu g of arsenic standard solution, solution are respectively arranged in the conical flask, add 5 ml of HCl (in the sample solution containing sulfuric acid or hydrochloric acid, minus the liquid samples contained acid number of ML), add water to 30ml, plus 5ml15% of potassium iodide solution and 5 drops 40% stannous chloride solution, mixing, placed at room temperature for 10min.

To the conical flask, the 3G without arsenic metal zinc, and immediately plug pre loaded with lead acetate cotton and bromide tribute test to determine the content of arsenic in tube, 25 placed 1H and remove arsenic spots were compared, samples of arsenic spot not deeper than the arsenic standard arsenic spots.

If the sample is treated, the standard of arsenic will be treated with the same method.

Determination of heavy metal (Pb) by 4.5.

4.5.1. sample treatment: 1.0g sample, accurate to 0.01g, dissolved in 25mL water, as a sample solution.

4.5.2. determination:

Absorb lead (PB) 10 mu g of lead standard solution in 50 ml of sodium's colorimetric tube a (such as sample treated, must also learn and equal to the number of sample liquid reagent blank solution), add water to 25 ml, mix, add 1 drop of phenolphthalein indicating liquid with dilute hydrochloric acid or dilute ammonia 6mol / L or 1mol / L adjusting pH to sex (phenolphthalein red just fade), add pH3.5 of acetate buffer 5ml, mixing, spare.

Take a and a tube supporting sodium's colorimetric tube, join (10 ~ 20) ml (or moderate) sample solution, and add water to 25ml, mix, add 1 drop of 1% phenolphthalein indicator solution, with dilute hydrochloric acid or dilute ammonia 6mol / L or 1mol / L to adjusting the pH to neutral (phenolphthalein red just fade). Addition of pH3.5 acetate buffer 5ml, mixing, stand-by.

After two tubes to add 10 ml of freshly prepared H2S saturated solution, and add water to 50 ml scale, mixing, placing the 5 min in the dark, observed in a white background, the pipe B color not deep in a tube of chroma.

Determination of dry weight loss of 4.6.

1.5g sample, accurate to 0.0002g, will be filled with a sample weighing bottle lid slightly open, placed in the oven of 180 + 2 degrees Celsius, weighing bottles should be placed around the thermometer mercury ball. After drying 2h, cover the lid tightly, remove the weighing bottle, put it in the dryer, cool to room temperature (not less than 3Omin)