Determination of Trace Moisture in Oil

Determination of Trace Moisture in Oil

The determination of trace moisture in oil is one of the key indicators for oil quality testing. Common methods include coulometric method, Karl Fischer titration, and thermogravimetric analysis. The specific operating procedures are as follows:

‌I. Common Determination Methods and Steps‌

‌Coulometric Method (Electrolytic Method)‌

‌Instrument Preparation‌: Assemble the electrolytic cell, inject the electrolyte (e.g., methanol solution containing potassium iodide), and connect the measuring electrode and drying tube.

‌Calibration‌: Calibrate the instrument with 0.1 microliter of pure water to ensure an error within ±10 micrograms.

‌Sample Testing‌: Use a 1-milliliter syringe to extract the oil sample and slowly inject it into the electrolytic cell. The instrument automatically calculates the moisture content.

‌Thermogravimetric Method‌

‌Operation‌: Place 3-5 grams of oil sample on a sample dish, heat at 105°C until constant weight, and calculate the moisture content based on the weight difference.

‌Applicability‌: Suitable for vegetable oils like rapeseed oil, complying with the GB1536-2004 standard (moisture ≤0.2%).

‌Distillation Method‌

‌Steps‌: Mix the oil sample with anhydrous solvent for distillation, collect the condensed water, and read the results from the receiver's scale.

‌II. Key Precautions‌

‌Environmental Control‌: Humidity should be below 90% RH, and temperature should be between 0-60°C to avoid external moisture interference.

‌Sample Handling‌: Liquid oil samples should be shaken before sampling, and stirring speed should be increased for highly viscous samples.

‌Reagent Management‌: Karl Fischer reagent should be replaced regularly, and the electrolyte becomes ineffective when its color fades (pale yellow).

‌III. Rapid Detection Methods‌

‌Microwave Method‌: A portable microwave moisture meter can be directly inserted into the oil to display the moisture content in real-time (0.00%~99%).

‌Water-Indicating Paste Method‌: Qualitatively detects moisture in light oils like gasoline by observing the color change of the water-indicating paste upon contact with water.

‌IV. Data Interpretation and Standards‌

‌Unit Conversion‌: 1% moisture = 1000 ppm = 1000 mg/L.

‌Industry Standards‌: The trace moisture content in insulating oil is typically required to be ≤20 mg/L, with transformer oil needing even stricter control.

ST129 grain moisture meter automatically measures moisture [can measure 20 varieties], automatic temperature compensation, empty machine to correct moisture, automatic shutdown, user can self-calibrate and correct error.