What makes your moisture analyzer inaccurate?

2021/08/16


moisture analyzer

DSH Moisture Analyzer

The moisture analyzer is widely used because of its simple operation, high accuracy, fast titration speed and other advantages. However, this measurement process is affected by many factors, such as the electrode of the instrument, the nature of the sample, and the measurement environment. Inadequate consideration or improper selection will make the measurement result inaccurate.


 

1. The influence of electrodes

Titration is to determine the end of the reaction by the signal transmitted by the electrode. Therefore, the sensitivity of the electrode directly affects the measurement result. Many factors can cause the sensitivity of the electrode to decrease. For example, impurities adhering to the surface of the electrode can reduce the sensitivity of the electrode and cause the measurement result to be higher; if the electrode is used for too long, the sensitivity of the electrode will also decrease. Therefore, the electrode should be inspected and maintained in time before use.

 

2. The influence of electrolyte

In the normal measurement process, every 100mL of electrolyte can react with not less than 1g of water. In the actual measurement, if the measurement time is too long, the moisture in the air will affect the KF reagent. The stability of the A and B solution will decrease rapidly after mixing, and these factors will cause the sensitivity of the electrolyte to decrease. During the electrolysis process, if it is found that the electrolyte in the cathode chamber releases strong bubbles or has been contaminated to light reddish brown, the titration endpoint time will be lengthened. If these phenomena occur, the electrolyte should be replaced as soon as possible.

 

3. The influence of sample injection requirements and sample volume

When injecting the sample into the electrolyte, it should be noted that the needle needs to be inserted below the liquid surface and avoid contact with the wall of the electrolytic cell or the electrode to prevent sample loss. However, ordinary injection needles cannot meet the above requirements due to their short and thick needle tips. When choosing an injection needle, try to choose an injection needle with a tip length of about 15 cm. This injection needle can effectively avoid the above phenomenon.

In order to obtain accurate measurement results, the injection volume should be consistent with its water content. However, if the sampling speed is slow, the sample will volatilize or absorb moisture in the air, which will affect the measurement results. In order to weigh the quality of the sample and inject it in a short time, an electronic balance with a minimum division of 0.01mg can be arranged next to the moisture analyzer. The quality of the injection needle can be weighed immediately after sampling, and the sample can be injected, thereby reducing the possibility of error.

 

4. The impact of side reactions

The solution B of the KF reagent contains iodine, and mercaptans and hydrogen sulfide can consume iodine just like water, resulting in high water content determination results. Therefore, samples containing mercaptans or hydrogen sulfide are not suitable for Karl Fischer titration. Also not suitable for titration by the Karl Fischer method are samples of aldehydes and ketones. Commonly used Karl Fischer reagents generally use methanol as a solvent, and aldehydes and ketones will react with methanol to form acetals or ketals and water. Therefore, other reagents that do not contain methanol and are suitable for aldehydes and ketones should be used for the determination.

 

5. The influence of instrument conditions

(1) Electrolysis end parameter: Generally, whether the electrolysis process is over is controlled by the set maximum time or drift end point.

(2) Stirring speed: Stirring should be sufficient and uniform during titration. Properly adjust the stirring speed to ensure that the electrolyte is fully mixed. And the stir bar can't jump to prevent it from touching the electrode.

(3) The rate of iodine generation: The rate of iodine generation is related to the moisture content in the sample. The lower the moisture content, the slower the set rate of iodine generation. This can ensure that the moisture in the sample is completely electrolyzed.

 

6. The influence of drift value

If the instrument is not well sealed or the humidity in the measuring environment is high, the moisture in the air will slowly penetrate into the reaction system. During the measurement process, side reactions such as ketal or esterification reactions will generate water. Use Kafka's reagent that has exceeded the time limit and so on. These factors can cause the drift value to change. If the above situation is found, it should be resolved in time to ensure the accuracy and reliability of the measurement result.

 

What to do to ensure accuracy

In order to ensure the accuracy of the measurement of the trace moisture analyzer, the electrode should be cleaned and the electrolyte should be replaced in time before the measurement

When measuring, select a needle with a tip length of about 15cm for injection, and equip an electronic balance next to the moisture analyzer to facilitate timely weighing;

Choose the electrolyte according to the nature of the sample;

Adjust the rotating speed of the stirrer, control the iodine generation speed, and accurately determine the end point of the titration;

Fully understand the factors that may cause instrument drift and eliminate them in time.

 

 


In the measurement process, as long as you carefully observe, fully analyze, constantly explore, control and eliminate various unfavorable factors that affect the measurement, accurate measurement results can be obtained. In addition, we are a Moisture Analyzer Manufacturer. Please contact us if you need them.