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游离氯（游离余氯、活性氯、余氯量）、总氯（总余氯）检测

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发布时间：2025-07-16 14:10:04 更新时间：2025-07-15 14:10:04

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作者：中科光析科学技术研究所检测中心

Introduction: Understanding Chlorine Detection in Water Quality Management

Chlorine is a widely used disinfectant in water treatment processes, playing a critical role in eliminating pathogens and ensuring the safety of drinking water, swimming pools, and industrial systems. The detection of chlorine residues, specifically free chlorine (also known as free residual chlorine, active chlorine, or residual chlorine) and total chlorine (total residual chlorine), is essential for maintaining optimal water quality. Free chlorine refers to the active, uncombined forms of chlorine, such as hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻), which provide effective disinfection by killing bacteria and viruses. In contrast, total chlorine encompasses both free chlorine and combined chlorine (e.g., chloramines formed when chlorine reacts with ammonia or organic matter), which are less effective for disinfection but still contribute to overall chlorine levels. Accurate detection is vital because insufficient chlorine can lead to microbial contamination and health risks, such as waterborne diseases, while excessive chlorine may cause adverse effects like skin irritation, respiratory issues, and the formation of harmful disinfection by-products (DBPs) like trihalomethanes. Regulations in many countries mandate regular monitoring, especially in public water supplies, where free chlorine levels typically need to be maintained at 0.2–2.0 mg/L to ensure safety without compromising taste or odor. This article delves into the key aspects of chlorine detection, including the specific projects, instruments, methods, and standards involved, to provide a comprehensive guide for professionals in environmental science, public health, and water treatment industries.

检测项目 (Detection Projects)

The primary detection projects focus on quantifying free chlorine and total chlorine in various aqueous environments. Free chlorine detection measures the concentration of active disinfectants like HOCl and OCl⁻, which directly indicate the disinfection power of the water. This is crucial for real-time monitoring in settings like drinking water distribution systems or swimming pools, where immediate disinfection capability must be assured. Total chlorine detection, on the other hand, assesses the sum of free chlorine and combined chlorine compounds (e.g., monochloramine or dichloramine), providing a broader picture of overall chlorine consumption and potential for by-product formation. Key differences lie in their applications: free chlorine is often prioritized for routine disinfection checks, while total chlorine is essential for evaluating treatment efficiency and compliance with regulatory limits. For instance, in wastewater treatment, high total chlorine might indicate incomplete disinfection or the presence of organic contaminants. Both projects require precise measurement to avoid errors; factors like pH, temperature, and interfering substances (e.g., organic matter or metals) must be considered during sampling to ensure representativeness. Typically, samples are collected in clean containers and tested immediately or preserved to prevent degradation, with target ranges varying by con—e.g., 1–3 mg/L free chlorine for pools versus 0.5–2 mg/L for drinking water per WHO guidelines.

检测仪器 (Detection Instruments)

Various instruments are employed for accurate chlorine detection, each offering specific advantages in sensitivity, portability, and ease of use. Common devices include colorimeters or spectrophotometers, which measure color changes in reagents to quantify chlorine concentrations; these are highly precise and suitable for laboratory settings. For field applications, portable digital chlorine meters (e.g., those from brands like Hach or Hanna Instruments) are popular, featuring probes that provide real-time readings via electrochemical sensors. These meters often include automatic temperature compensation and data logging capabilities. Additionally, DPD (N,N-diethyl-p-phenylenediamine) comparators offer a low-cost, user-friendly option for visual color matching, ideal for on-site testing by non-experts. Advanced instruments like ion-selective electrodes (ISEs) or amperometric sensors provide continuous monitoring in automated systems, such as municipal water plants. When selecting instruments, factors like detection range (typically 0–10 mg/L for chlorine), resolution, calibration requirements, and resistance to interference are critical. For example, spectrophotometers require regular calibration using standard solutions, while digital meters may need electrode maintenance to ensure longevity and accuracy across diverse water matrices.

检测方法 (Detection Methods)

Standardized methods for chlorine detection ensure reliability and reproducibility, with the DPD method being the most widely used for both free and total chlorine assays. In this method, DPD reagent reacts with free chlorine to form a pink or red complex, the intensity of which is measured colorimetrically at 515 nm; for total chlorine, potassium iodide is added to liberate iodine from combined chlorine, which then reacts with DPD. The procedure involves adding reagents to a water sample, incubating briefly, and reading absorbance with a spectrophotometer or comparator. Another common approach is the iodometric titration method, where chlorine oxidizes iodide to iodine, which is then titrated with sodium thiosulfate using starch as an indicator—this is highly accurate but time-consuming. Electrochemical methods, such as amperometry, use sensors to detect chlorine-induced current changes, offering rapid results for continuous monitoring. Field-friendly variants include test strips impregnated with DPD or similar reagents, which change color upon contact for semi-quantitative assessment. Best practices involve sample preparation (e.g., filtering to remove solids), avoiding exposure to light to prevent reagent degradation, and performing replicate tests for precision. Detection limits range from 0.02 mg/L for sensitive instruments to 0.1 mg/L for simpler kits, with methods tailored to minimize interference from oxidants like bromine or manganese.

检测标准 (Detection Standards)

Chlorine detection is governed by rigorous standards to ensure consistency and compliance across industries. Key international standards include ISO 7393-1:1985 (Water quality – Determination of free chlorine and total chlorine – Part 1: Titrimetric method using DPD), which outlines titration protocols for precise measurements. In the United States, the Environmental Protection Agency (EPA) methods such as Method 330.5 (for DPD colorimetry) and Standard Methods 4500-Cl series (e.g., 4500-Cl G for DPD) are authoritative for drinking water compliance. Chinese standards, like GB/T 5750.11-2023 (Standard examination methods for drinking water – Disinfection by-products parameters), specify procedures for both free and total chlorine using DPD or iodometric techniques, with acceptable limits set by the Ministry of Ecology and Environment. For swimming pools, standards such as WHO's Guidelines for Safe Recreational Water Environments recommend free chlorine levels of 1–3 mg/L and total chlorine not exceeding free chlorine by more than 0.2 mg/L to prevent irritation. Adherence to these standards involves regular instrument calibration, proficiency testing, and documentation of results, with accreditation bodies like ISO/IEC 17025 ensuring laboratory competency. Updates, such as the push for lower detection limits to address emerging contaminants, highlight the evolving nature of these regulations in safeguarding public health.