液样处理：简谈稀释液的确定和稀释因子的计算方法

In practical terms, diluting the liquid sample will definitely cause secondary pollution and amplify the incorrect counting results of the liquid particle counter. Therefore, when measuring the particle contamination level, it is advisable not to dilute it. However, if the liquid sample shows the following three situations, it needs to be diluted:

The particle concentration of the liquid sample is higher than the coincidence error limit of the particle sensor;
The color of the liquid sample is too dark, which affects the particle counting results;
The viscosity of the liquid sample is too high, and the particle counter sampling device cannot guarantee that the liquid sample passes through the particle sensor at the working flow rate.

When the viscosity of the liquid sample is too high, the first consideration should be to use heating to reduce the viscosity of the liquid sample, but the heating temperature should not exceed 60 ℃. If the liquid sample cannot be guaranteed to pass through the sensor at the working flow rate after being heated to 60 ℃, dilution should be used.

Determination of diluent

Before diluting the liquid sample, it is necessary to first confirm which diluent and dilution factor to use. The diluent should preferably be a clean liquid that is the same as the liquid sample. If it is necessary to reduce the viscosity of the liquid sample or increase its transparency, a low viscosity clean solvent compatible with the liquid sample and sampling container should be selected. The commonly used diluents are as follows:

10th, 12th, and 15th aviation hydraulic oils;
MIL-PRF-5606 (Mineral Oil)
Toluene;
Analytical grade isopropanol;
HL-XX mineral oil (classified according to GB/T 7631.2)
Softened water, deionized water (for water-based liquids);
Analytical grade petroleum ether, with a boiling range of (90-120) ℃ (solvents with low boiling ranges are prone to producing bubbles during measurement, which can affect particle counting)

Method for calculating dilution factor

The dilution factor refers to the ratio of the total volume (the sum of the volume of the liquid sample and the volume of the diluent) to the volume of the liquid sample. The number and concentration of particles measured after dilution multiplied by the dilution factor is the original number and concentration of particles in the liquid sample.

（典型的稀释比和稀释因子对应关系表）

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Liquid sample processing: a brief discussion on the determination of diluent and the calculation method of dilution factor