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Estimate the salinity of water by Conductivity measurement (CAT#: STEM-PPA-0020-WXH)

Introduction

Salinity is a key parameter used to classify bodies of water as fresh, slightly saline, moderately saline, or highly saline. In freshwater systems, salt concentrations are usually less than 1,000 ppm (1 psu). Ocean water is highly saline, with salt concentrations averaging about 35,000 ppm (35 psu).




Principle

Conductivity is the measure of the ability of any solution to pass an electrical current. Conductivity is usually affected by free ions which are dissolved in any solution. The ions can be chloride, sulfate, nitrate, phosphate, sodium, magnesium, iron, calcium, or aluminum.

Applications

Quality control: Surveillance of feedwater purity, control of drinking water and process water quality, estimation of the total number of ions in a solution or direct measurement of components in process solutions.

Procedure

1. Use a conductivity standard solution (usually potassium chloride or sodium chloride) to calibrate the meter for the range that you will be measuring.
2. Rinse the probe with distilled or deionized water.
3. Select the appropriate range beginning with the highest range and working down. Read the conductivity of the water sample. If the reading is in the lower 10 percent of the range, switch to the next lower range. If the conductivity of the sample ex ceeds the range of the instrument, you may dilute the sample. Be sure to perform the dilution according to the manufacturer's directions because the dilution might not have a simple linear relationship to the conductivity.
4. Rinse the probe with distilled or deionized water and repeat step 3 until finished.

Materials

Conductivity Meters