Difference Between Residual Chlorine and Total Residual Chlorine

In the chemical industry, residual chlorine (Residual Chlorine) and total Residual Chlorine (TRC) are two commonly referred terms, especially in scenarios involving chloride monitoring and management. Although they are both related to chlorine residues, there are significant differences in definition, measurement methods and application scenarios. This article will analyze the difference between the two in depth to help readers better understand their meaning and its application in practice.

1. Residual chlorine (Residual Chlorine) definition and measurement method

Residual chlorine is a measurement method commonly used in laboratories to evaluate the residual concentration of chlorine in liquids or gases. Through the chemical oxygen demand (COD) test, residual chlorine refers to the concentration of chloride in the solution that has not been consumed under standard experimental conditions. Specifically, the measurement method of residual chlorine includes the following steps:

1. Solution: The sample to be tested is diluted and a reagent is added, usually using a copper sulfate solution, to promote chloride precipitation.
2. Precipitation and Filtration Removal: Precipitated chlorides are removed by filtration, followed by washing of the filter paper to ensure that residual reagents do not interfere with subsequent testing.
3. Determination: Use the acidifying agent to acidify the filtrate, and then by colorimetry or other chemical methods to determine the remaining reagent concentration.

The measurement method of residual chlorine is simple and economical, and is suitable for preliminary monitoring of chloride concentration. Because of its direct measurement process, the residual chlorine value often ignores some complex reaction conditions.

2. Total residual chlorine (Total Res,Total Residual Chlorine) definition and measurement method

Total residual chlorine is a more accurate method of determination, which takes into account not only directly reacted chlorides, but also those that are not completely consumed under regular experimental conditions. The total residual chlorine determination method usually involves more complex chemical reactions to ensure that all possible chloride residues are accurately calculated.

Specifically, the total residual chlorine measurement process includes the following steps:

1. Solution: As with the residual chlorine measurement method, the sample is diluted and added to the copper sulfate solution.
2. Precipitation and Filtration: Remove the precipitate by filtration and washing.
3. Acidification and chemical reaction: under acidic conditions, by introducing additional reagents (such as potassium iodide) to promote unmeasured chloride further reaction.
4. Determination: by colorimetry or other precision chemical methods to determine the total residual chlorine concentration.

Since the total residual chlorine takes into account all possible chloride residues, its value is usually higher than the residual chlorine value. Therefore, the measurement of total residual chlorine is more appropriate in scenarios where high accuracy is required.

3. The difference between residual chlorine and total residual chlorine and influencing factors

Although both residual chlorine and total residual chlorine are used to measure chloride residues, the following significant differences exist between them:

• Definition: residual chlorine is directly through the chemical oxygen demand test measured value, while the total residual chlorine is in the same conditions, through a more complex chemical reaction value.
• Measurement method: the determination method of residual chlorine is relatively simple, and the total residual chlorine needs to introduce additional reagents and steps to ensure that all chlorides are accurately determined.
• Application: Residual chlorine is suitable for preliminary monitoring and simple process control, while total residual chlorine is suitable for high-precision environments, such as water quality analysis or industrial process control.

The difference between residual chlorine and total residual chlorine is also related to the measurement conditions. For example, the measurement of residual chlorine may be affected by factors such as solution pH, temperature and reagent concentration, while the determination of total residual chlorine is more comprehensive and better reflects the actual chloride residue.

4. Select residual chlorine or total residual chlorine basis

In practical applications, the choice of whether to use residual chlorine or total residual chlorine needs to be determined according to the specific situation:

• Preliminary monitoring: In the need to quickly obtain the chloride residue in the scene, the residual chlorine measurement is more economical and convenient, suitable for daily process monitoring.
• High precision: In water quality control, environmental monitoring or industrial production, total residual chlorine determination can provide more accurate data to help make more scientific decisions.

Differences in residual chlorine and total residual chlorine may also affect the results of data analysis. For example, if only the residual chlorine value is used to evaluate the chloride control effect of the system, some unmeasured chloride residues may be ignored, resulting in data bias.

5. Residual chlorine and total residual chlorine future trends

With the continuous progress of chemical technology, the method of determination of chloride residues is also constantly optimized. In the future, the determination of total residual chlorine may become more popular, especially in areas where high precision is required, such as environmental monitoring and industrial control. Residual chlorine still plays an important role in everyday applications, especially in terms of its economy and simplicity.

While there are differences in definitions and methods of measurement, both are important tools for understanding and managing chloride residues. Choosing the appropriate measurement method is helpful to improve the accuracy of the data, so as to better apply it in practical work.