Common sense of water quality testing(3)

- Dec 13, 2019-

Multi-parameter detection

How can I dilute the test sample to the test range?

 

Q & A:

The simplest dilution method is the 1: 1 dilution method or the double dilution method, that is, 1 volume of deionized water or distilled water is added to 1 volume of the sample to be tested. This method can halve the concentration of the sample. Test the diluted sample according to the usual measurement procedure, and then multiply the result by 2 to get the concentration of the sample before dilution.

 

Example: A sample is being tested and the out of range is displayed on the test kit or test instrument. At this time, 5 mL of deionized water was added to the 5 mL sample, and the measurement was performed again. The measurement result obtained with the diluted sample is 1.9 mg / L, and the concentration of the sample before dilution is 3.8 mg / L.

 

If the sample concentration after double dilution still exceeds the range, you need to increase the dilution factor. For example, add 2 volumes of deionized water to 1 volume of sample and make a three-fold dilution (determination result multiplied by 3), or add 3 volumes of deionized water to 1 volume of sample and make a four-fold dilution (multiply the measurement result by 4 ), And so on. If you want to use the test sample as a blank in your test, then use the diluted sample as a blank.

 

When diluting, it is important to accurately measure the volume of the sample and deionized water. An incorrect measurement will result in an incorrect measurement result, and this incorrect result will be multiplied by the dilution factor. Therefore, according to the minimum requirements, use a graduated cylinder to take samples and deionized water. For better results, use a pipette to transfer the sample to a volumetric flask (Grade A) and add deionized water to the calibration line. Mix thoroughly before testing.

 

The tester can use a suitable pipette and volumetric flask to prepare a certain volume of diluted solution as needed. For example, when making a 20-fold dilution, you can transfer 1 mL of sample to 19 mL of deionized water, or 5 mL of sample to 95 mL of deionized water (or dilute to the score line in a 100 mL volumetric flask), so the dilution factor of the resulting solution is identical. If only 10 mL of the diluted sample is required for the test, use 10 mL for the measurement. The remaining diluted solution can be used as a blank sample or repeated measurement as required by the tester.

 

 

The simplest dilution method is the 1: 1 dilution method or the double dilution method, that is, 1 volume of deionized water or distilled water is added to 1 volume of the sample to be tested. This method can halve the concentration of the sample. Test the diluted sample according to the usual measurement procedure, and then multiply the result by 2 to get the concentration of the sample before dilution.

 

Example: A sample is being tested and the out of range is displayed on the test kit or test instrument. At this time, 5 mL of deionized water was added to the 5 mL sample, and the measurement was performed again. The measurement result obtained with the diluted sample is 1.9 mg / L, and the concentration of the sample before dilution is 3.8 mg / L.

 

If the sample concentration after double dilution still exceeds the range, you need to increase the dilution factor. For example, add 2 volumes of deionized water to a volume of sample and make a three-fold dilution (determination result multiplied by 3), or add 3 volumes of deionized water to a volume of sample and make a four-fold dilution (measurement result multiplied by 4) ), And so on. If you want to use the test sample as a blank in your test, then use the diluted sample as a blank.

 

When diluting, it is important to accurately measure the volume of the sample and deionized water. An incorrect measurement will result in an incorrect measurement result, and this incorrect result will be multiplied by the dilution factor. Therefore, according to the minimum requirements, use a graduated cylinder to take samples and deionized water. For better results, use a pipette to transfer the sample to a volumetric flask (Grade A) and add deionized water to the calibration line. Mix thoroughly before testing.

 

The tester can use a suitable pipette and volumetric flask to prepare a certain volume of diluted solution as needed. For example, when making a 20-fold dilution, you can transfer 1 mL of sample to 19 mL of deionized water, or 5 mL of sample to 95 mL of deionized water (or dilute to the score line in a 100 mL volumetric flask), so the dilution factor of the resulting solution is identical. If only 10 mL of the diluted sample is required for the test, use 10 mL for the measurement. The remaining diluted solution can be used as a blank sample or repeated measurement as required by the tester.

 

 

 

What's wrong with testing "overrange"?

 

Q & A:

When a test shows an "over-range" result, the measured concentration is above the upper limit of the test specification. That is, the color that appears after adding the reagent is darker than the color that the test tool box or test instrument can normally read the data, so that it cannot be read.

 

When the concentration of the sample to be measured exceeds the stated test range, some freshly taken samples can be diluted with deionized or distilled water. Measure the concentration of the diluted sample, and then multiply the measurement result by the dilution factor to obtain the actual concentration of the sample.

 

 digital refractormeter

 

I need to determine a sample with a concentration greater than the upper limit of the test specified by the instrument. What should I do?

 

Q & A:

Add deionized or distilled water to the sample and dilute it to a measurable concentration range. First measure the diluted sample, then multiply the obtained measurement result by the dilution factor to obtain the original sample concentration (before dilution). It must be ensured that sufficient test reagent is added to the diluted sample so that it can fully react with the parameters to be measured.

 

For some parameters, such as ozone (O3), sulfide (S2-), ferrous ion (Fe2 +), and deoxidizer, etc., it is not appropriate to use the dilution method for determination. Because some of these substances may be consumed by reacting with oxygen, or they may escape directly into the air. In this case, it is best to use a measurement method with a larger range. If the diluted water contains impurities, disinfectants such as liquid chlorine will be consumed, resulting in lower than the actual measurement results.