Total dissolved solids (TDS) is a measure of all organic and inorganic compounds dissolved in a liquid, showing the different ratios of solids. There are a number of uses for determining TDS: measuring pollution levels in rivers or lakes, or mineral levels in drinking water for example, as well as in agriculture in terms of irrigation. To calculate the TDS in a given liquid, follow these steps.
Step
Method 1 of 2: Using an Electrical Conductivity Meter
Step 1. Prepare your equipment
Before attempting to measure the TDS in your sample, be sure to prepare a clean and empty area suitable for the test kit and equipment used. If you don't have the equipment needed for this method, you can easily buy it online. You need:
- The beaker glass is clean, free of dust and other particles and has been pre-sterilized.
- The water sample that you are going to analyze is put into a sterile beaker. Ideally, the sample temperature should be 25°C at the time of analysis.
- Electrical conductivity meter - an instrument used to measure the ability of a solution to conduct electricity. This tool works by releasing an electric current into the solution, then measuring its resistance.
Step 2. Measure the conductivity of the sample
Make sure the beaker containing the sample is placed on a flat and stable surface. Turn on the conductivity meter, then insert the measuring rod into the sample. Wait for the reading shown in the instrument to stabilize before stating the result.
- You may need to wait a few seconds before the reading stabilizes, but it's important to wait for the numbers shown in the display to stop changing.
- The measure shown on the display of the conductivity meter is the purity of the water, which is expressed in S (micro-Siemens). The lower the S value, the purer your water sample will be, with a value of 0 S representing pure, pollution-free H20.
Step 3. Enter the data you got into the TDS formula
The basic formula for calculating total dissolved solids is the same as shown in the figure. In the formula, TDS is expressed in mg/L, EC is the conductivity of your sample (the reading from a conductivity meter), and ke is the correlation factor. The correlation factor depends on the solution you are using as a sample, and is also affected by the air conditions. The values are in the range of 0.55 to 0.8.
- In the example above, let's say the correlation factor at the current temperature and in the current pressure is 0.67. Plug the values you get into the formula. Thus the TDS value of your sample is 288.1 mg/L.
- Water with a TDS value of less than 500 mg/L meets the requirements of the Environmental Protectino Agency for drinking water.
- A high TDS value does not necessarily mean that the water is not safe for consumption; it simply states that the water has poor visual qualities, such as in terms of color, taste, smell, etc. If you doubt the safety of your drinking water, have it checked by a professional analyst.
Method 2 of 2: Using Filter Paper and Balance
Step 1. Prepare your equipment
Prepare a clean and empty area for the test kits and equipment needed. If you don't have the equipment needed for this test, you can easily purchase it online. You need:
- Clean beakers are free of dust and other particles and have been pre-sterilized.
- Water sample, pour into a beaker.
- Filter paper.
- Porcelain bowl.
- Stirring rod.
- A pipette large enough to collect a 50 ml sample.
- balance sheet.
Step 2. Weigh the porcelain bowl in milligrams (mg)
Make sure that it is completely dry and free of other particles.
Step 3. Stir the water sample in the beaker with a stirring rod
Stir vigorously enough to mix the solution. This is done to ensure that the particles in the solution are evenly distributed in the sample.
Step 4. Take 50 ml of sample with a pipette
Make sure you keep stirring the solution in the beaker while taking the sample - don't let the solids in the solution settle before you take a smaller sample. If you have trouble doing this, ask a friend to help you pipet the sample while you stir the solution.
Step 5. Strain the precipitate
Pass 50 ml of the sample in the pipette through the filter paper three times to ensure that all particles are collected in the paper.
Step 6. Weigh the porcelain bowl along with the precipitate
Transfer the precipitate from the previous step to the porcelain bowl you weighed in step 2, and wait for the precipitate to dry completely. After the bowl and the sediment in it are dry, re-weigh in milligrams (mg).
Step 7. Enter the data you obtained into the formula
Use this formula to calculate the TDS of your solution: TDS=[(A-B) * 1000]/ml sample
- In this formula, A represents the weight of the porcelain bowl + sediment, and B represents the weight of the porcelain bowl itself.
- Since you pipetted 50 ml of water, the number of "ml sample" in this example is 50.
- The final value of total dissolved solids is expressed in units of mg/L.
- Water with a TDS of less than 500 mg/L meets the Environmental Protectino Agency's requirements for drinking water.
- A high TDS value does not necessarily mean that the water is not safe for consumption; it simply states that the water has poor visual qualities, such as in terms of color, taste, smell, etc. If you doubt the safety of your drinking water, have it checked by a professional analyst.
Tips
- Water with a TDS of less than 1000 mg/L is considered fresh water.
- You can understand conductivity as the inverse of the electrical resistance of a liquid to an electric current.
- Siemens is the unit of conductivity. This unit is usually expressed in the letter S.
- If you have any doubts about the safety of drinking water, have it checked by a professional analyst.
