1 Scope
This standard specifies the determination method of pH in meat and meat products, aquatic products including ostracean (oyster and ostrica) and canned food.
It is applicable to pH testing of homogenization product in meat and meat products, pH nondestructive testing of carcass, dressed carcass and lean meat, pH determination of aquatic products including ostracean (oyster, ostrica) and the pH determination of canned food.
2 Principle
Glass electrode is used as indicator electrode and calomel electrode or silver-silver chloride electrode is used as reference electrode; if the hydrogen ion concentration in specimen or specimen solution is changed, the electromotive force between indicator electrode and reference electrode will be changed and DC potential (namely potential difference) will be generated; the DC potential will be input to A/D converter via pre-amplifier and the pH may be measured.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class-III water (defined in GB/T 6682) are adopted for the purpose of this method. Water used for preparing buffer solution shall be newly-boiled, or CO2-free (the carbon dioxide is eliminated with nitrogen free from carbon dioxide).
3.1 Reagent
3.1.1 Potassium hydrogen phthalate [KHC6H4(COO)2].
3.1.2 Potassium dihydrogen phosphate (KH2PO4).
3.1.3 Disodium hydrogen phosphate (Na2HPO4).
3.1.4 Potassium bitartrate (KHC4H4O6).
3.1.5 Diammonium hydrogen citrate (Na2HC6H5O7).
3.1.6 Citric acid monohydrate (C5H8O7•H2O).
3.1.7 Sodium hydroxide (NaOH).
3.1.8 Potassium chloride (KCl).
3.1.9 Iodoacetic acid (C2H3IO2).
3.1.10 Ethyl ether (C4H10O).
3.1.11 Ethanol (C2H6O).
3.2 Reagent preparation
3.2.1 Buffer solution with pH of 3.57 (20℃): saturated water solution prepared with potassium bitartrate at 25℃ and the pH of this solution is 3.56 at 25℃ and 3.55 at 30℃. Or standard solution approved and awarded with reference material certificate by the nation shall be adopted.
3.2.2 Buffer solution with pH of 4.00 (20℃): dry potassium hydrogen phthalate to constant weight at 110℃~130℃ and cool to room temperature in dryer. Add 10.211g (to the nearest 0.001g) of potassium hydrogen phthalate into 800ml water, dissolve it, and then scale the volume with water to 1 000mL. The pH of this solution is 4.00 at 0℃~10℃ and 4.01 at 30℃. Or standard solution approved and awarded with reference material certificate by the nation shall be adopted.
Foreword i
1 Scope
2 Principle
3 Reagents and Materials
4 Apparatuses
5 Analysis Procedures
6 Expression of Analysis Results
7 Precision