Check out this answer from Consensus:
Chloride testing is a vital analytical procedure across various fields. From simple test strips for environmental water to sophisticated methods for concrete and biological fluids, advancements in chloride testing techniques continue to improve accuracy and reliability. Regular participation in quality assessment programs and the development of innovative testing devices further enhance the precision of chloride measurements, ensuring better monitoring and control in diverse applications.
A chloride test is a method used to determine the concentration of chloride ions (Cl⁻) in various samples, including environmental water, concrete, biological fluids, and more. Chloride testing is crucial in multiple fields such as environmental monitoring, construction, healthcare, and food safety. This article explores different methods and applications of chloride tests, highlighting their significance and the advancements in testing techniques.
Methods of Chloride Testing
Test Strips for Environmental Water
One of the simplest methods for chloride testing in environmental water involves the use of disposable test strips. These strips contain a sensing zone with reagents that produce a selective response to chloride ions. When introduced into a water sample with a pH 2.0 buffer, the strip changes color from red to orange, and the absorbance at 534 nm is measured to determine the chloride concentration. This method is inexpensive, selective, and sensitive, with a detection limit of 0.15 mM1.
Chloride Testing in Concrete
Chloride testing in concrete is essential for assessing the durability and longevity of concrete structures. Two common methods are ASTM C1152 (acid-soluble) and ASTM C1218 (water-soluble) tests. These tests measure the chloride concentration in concrete mixtures, which is crucial for quality control in construction. However, the reliability of these tests can vary, with ASTM C1218 generally providing more accurate results in systems with admixed chlorides2.
Argentometric Determination
The argentometric method, specifically Mohr’s precipitation titration, has been adapted into a portable, low-cost paper-based microfluidic device. This device allows for rapid and quantitative analysis of chloride in small sample volumes (as little as 5 µL). The method involves a distance-based detection technique, making it fully instrument-free and suitable for various matrices, including body fluids and water samples5.
Chloride Diffusion in Concrete
Measuring chloride diffusion coefficients in concrete is another critical aspect of chloride testing. This involves submitting concrete specimens to controlled conditions and studying the kinetics of chloride transport from the surface inwards. The diffusion coefficients are then determined using mathematical models that account for chloride binding by concrete6 9.
Sweat Chloride Test
The sweat chloride test is the gold standard for diagnosing cystic fibrosis (CF). It measures the chloride concentration in sweat, with specific thresholds indicating the likelihood of CF. The test’s accuracy can be influenced by biological variability, and repeated tests may show significant differences in chloride levels, especially in the intermediate range8.
Improving Accuracy in Chloride Testing
To enhance the accuracy of chloride measurements, participation in regular external quality assessment (EQA) programs is recommended. For instance, a method based on sector field inductively coupled plasma isotope dilution mass spectrometry (SF-ICP-IDMS) has been developed to assign target values in EQA programs. This method has shown to reduce variability and improve the reliability of chloride test results over time4.