SH/T 0086-1991 Determination of water content in engine coolant concentrate (Karl Fischer method)

Summary page. This page is a compiled excerpt/summary of the standard — it is not the full standard text and does not replace it. Verify every value against the official standard and the product certificate before use.

SH/T 0086-1991 is applicable to the determination of water content in glycol-type engine coolant concentrates by the Karl Fischer method.

Evidence note: the content of this page was compiled from the original text of this standard held in the Origin Standard library (entries marked “〔to be verified〕” indicate 〔source text unclear〕); for individual values and the current status of the standard, please refer to the original standard pages and the product certificate. Verification note: the marks 〔to be verified〕 and 〔source text unclear〕 identify specific points that still require checking against the original standard and do not mean that verification has been completed. Do not use these values or steps directly as a basis for work.

Scope: Applicable to glycol-type engine coolant concentrates. Not applicable: not provided in the available material.

Principle: A double platinum electrode is used as the indicator electrode, and an endpoint display unit assembled on the "dead-stop" principle indicates the endpoint of the reaction; the water content of the sample is calculated from the volume of Karl Fischer reagent consumed.

Apparatus: Endpoint display unit: its circuit principle is given in Annex A Automatic burette: 50 mL, minimum division 0.1 mL 〔source text unclear〕), with reservoir, drying tube and double-bulb hand pump Electromagnetic stirrer Titration vessel: 250 mL flat-bottomed three-necked flask Double platinum indicator electrode: for construction and maintenance see Annex B Syringes: 1, 5, 10 and 50 mL, fitted with 11.5 cm hypodermic needles Porcelain crucible: 400 mL Conical flask: 1000 mL

Reagents and reference materials: Self-indicating silica gel Molecular sieve: 3A or 5A Iodine: analytical grade Anhydrous methanol: analytical grade Pyridine: analytical grade 〔source text unclear〕) Ethylene glycol monomethyl ether: chemically pure Sulphuric acid: chemically pure Distilled water: meeting the grade 3 water requirements of GB/T 6682 Sulphur dioxide: purity above 99 %, in cylinders or prepared in-house Note: preparation of sulphur dioxide — place 240 g of sodium sulphite (sodium bisulphite) in a 2 L round-bottomed flask and add sulphuric acid dropwise to generate sulphur dioxide gas, which shall be dried with sulphuric acid before use. Caution: most of the reagents used in this standard are toxic and corrosive and are harmful to health if ingested; avoid direct contact and inhalation. In case of contact, rinse with plenty of water. Drying of reagents (7.1) Place 3A or 5A molecular sieve in a porcelain crucible and dry it at a constant temperature of 480 °C ± 20 °C in a high-temperature furnace for 4 h, then allow the molecular sieve to cool in the furnace to 200 °C to 300 °C. Through a suitable funnel, quickly add the molecular sieve to the reagents listed in 5.2 to 5.4, in an amount sufficient to give a molecular sieve layer about 3 mm thick, then immediately close the bottle cap tightly, invert the reagent bottle several times, and leave for 24 h before use. Caution: drying of reagents shall be carried out in a well-ventilated area with no open flames. Preparation of Karl Fischer reagent titrant (6 mg H₂O/mL) (7.2) In a clean, dry 1000 mL conical flask with a ground-glass stopper, add 133 g ± 1 g of iodine and dissolve in 425 mL ± 2 mL of pyridine, then add 425 mL ± 2 mL of anhydrous ethylene glycol monomethyl ether; cool the mixture in a cooling bath below 4 °C, then pass sulphur dioxide gas, dried with sulphuric acid, through a conduit into the mixture cooled in the cooling bath until the volume of the mixture has increased by 70 mL ± 1 mL, or until the mass of the sulphur dioxide cylinder has decreased by 102 g ± 1 g; shake the mixture well, leave it properly for 12 h, and it is then ready for use.

Key conditions: Instrument adjustment (7.3): 7.3.1 Assemble the burette, titration vessel, stirrer, indicator electrode and endpoint display unit as shown in the figure below. 7.3.2 With a clean, dry syringe, take 30 mL to 50 mL of anhydrous methanol and inject it into a titration vessel that has been washed and dried in advance, so that the liquid level is above the platinum wires of the double platinum indicator electrode. Start the stirrer and adjust it to stir evenly and smoothly. Turn on the endpoint display switch without inserting the electrode plug, adjust the potentiometer knob, and select a scale at which the microammeter pointer deflects between 10 μA and 30 μA as the endpoint indication position (the potentiometer knob shall not be turned during titration). Insert the electrode plug; the microammeter pointer should now return to near zero. Stir for 30 s, add Karl Fischer reagent titrant dropwise until the microammeter pointer deflects to the selected endpoint position and remains stable for 30 s; the titration endpoint is then considered reached and the instrument adjustment is complete. Standardization of the Karl Fischer reagent titrant (7.4): the Karl Fischer reagent titrant must be standardized before testing each day as described in 7.4.1 to 7.4.2. 7.4.1 Add 25 mL of ethylene glycol monomethyl ether and 30 mL to 50 mL of anhydrous methanol to the titration vessel respectively, and titrate to the endpoint as described in 7.3.2. Draw 0.15 mL to 0.18 mL of distilled water with a syringe, weigh to 0.0001 g, inject into the titration vessel that has reached the endpoint, stir for 30 s, add Karl Fischer reagent titrant dropwise until the solution in the titration vessel reaches the titration endpoint, and record the volume of Karl Fischer reagent titrant consumed, read to 0.1 mL. 7.4.2 The titre T (mg H₂O/mL) of the Karl Fischer reagent titrant is calculated according to equation (1): T = m₁ / V₁ where: m₁ — mass of water injected into the titration vessel, g; V₁ — volume of Karl Fischer reagent titrant consumed in the titration, mL. Titration apparatus diagram (as labelled in the source text): 1 — drying tube; 2 — burette; 3 — injection port; 4 — titration vessel; 5 — stirrer; 6 — stirrer bar; 7 — indicator electrode; 8 — endpoint display unit; 9 — reservoir.

Calculation and results: The water content X [% (m/m)] of the sample is calculated according to equation (2): X = (V₂ × T) / (10 × m₂) where: V₂ — volume of Karl Fischer reagent titrant consumed in the test, mL; T — titre of the Karl Fischer reagent titrant, mg H₂O/mL; m₂ — mass of sample injected, g.

Quality control: Judge the reliability of the determination results as follows (95 % confidence level). Repeatability: the difference between two results of repeated determination by the same operator shall not be greater than 0.5 mL of Karl Fischer reagent titrant. Reproducibility: the difference between the results submitted by two laboratories shall not be greater than the following values: Sample water content 0.1 % to 1.0 % (m/m): reproducibility 15 % of the arithmetic mean 〔source text unclear〕) Sample water content > 1.0 % to 10 % (m/m): reproducibility 5 % of the arithmetic mean

Normative references: GB/T 6682 Water for analytical laboratory use — specification and test methods SH/T 0065 Sampling of engine coolant or rust inhibitor test samples and preparation of their aqueous solutions Annex A Circuit and principle of the endpoint display unit (supplementary) Annex B Construction and maintenance of the double platinum indicator electrode (supplementary)

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