Six, analysis and testing
(1) Instrument calibration
Knowing the conductivity cell constant of the electrode, adjust the instrument according to the instruction manual of the conductivity meter, and calibrate the instrument with a potassium chloride standard solution whose conductivity is similar to that of the sample extract
Rinse the electrode several times with water, and then rinse the electrode with the extraction solution to be tested
Insert the electrode into the extraction solution to be tested, and correct the temperature to 25℃±1℃ in accordance with the requirements of the instruction manual of the conductivity meter, and measure the conductivity of the soil extraction solution
Read the conductivity value directly from the conductivity meter, and record the temperature of the extract at the same time
Seven, calculation and presentation of results
Obtain the conductivity value of the extract directly from the reading on the instrument, and the unit is expressed in mS/m
When the measurement result is greater than or equal to 100mS/m, three significant digits are retained; when the measurement result is less than 100mS/m, it is retained to one decimal place
Quality Assurance and Quality Control
(1) A laboratory blank should be measured for each batch of samples, and the blank conductivity value should not exceed 1mS/m
Otherwise, you should find the reason and re-determine
(2) Before each batch of samples is measured (or every month), the instrument needs to be calibrated with potassium chloride standard solution.
The average value of the conductivity of the three repeated measurements is compared with the conductivity of the standard solution of known mass concentration.
The relative error should not be More than 5%
Otherwise, the electrode should be cleaned or replaced
(3) One parallel sample should be made for every 10 samples or every batch (less than 10 samples/batch)
The allowable error of the parallel sample test results is shown in Table 9-2 .
Table 9-2 Repeatability of conductivity value
Nine, matters needing attention
(1) The potassium chloride standard solution should be transferred to a sealed polyethylene bottle for storage.
The sealed polyethylene bottle should not contain alkaline ions or alkaline metal cations
It is recommended to use plastic bottles
(2) When there are small bubbles on the electrode surface, tap the vibrating container to remove them to avoid measurement errors
(3) When extracting samples, avoid violent shaking
(4) After the sample is extracted, it should be determined in time
Related Links: Electrode Method for Measuring Soil Conductivity (1)