Miniaturized chromate-free chloride assay in fish sauce based on linear height calibration of AgCl precipitate in inverted microtubes
Issued Date
2026-06-01
Resource Type
eISSN
27725774
Scopus ID
2-s2.0-105034690286
Journal Title
Green Analytical Chemistry
Volume
17
Rights Holder(s)
SCOPUS
Bibliographic Citation
Green Analytical Chemistry Vol.17 (2026)
Suggested Citation
Chantiwas R., Wilairat P., Putthasa P., Cheotchinda B., Teerasong S., Praditweangkum W. Miniaturized chromate-free chloride assay in fish sauce based on linear height calibration of AgCl precipitate in inverted microtubes. Green Analytical Chemistry Vol.17 (2026). doi:10.1016/j.greeac.2026.100343 Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/116085
Title
Miniaturized chromate-free chloride assay in fish sauce based on linear height calibration of AgCl precipitate in inverted microtubes
Corresponding Author(s)
Other Contributor(s)
Abstract
A miniaturized, chromate-free methodology for chloride determination in high-salt food matrices is presented in accordance with the principles of Green Analytical Chemistry. Classical argentometric precipitation is adapted to a microvolume, instrument-light assay by confining silver chloride formation within inverted microcentrifuge tubes and directly measuring the height of the compact precipitate layer using a simple ruler. Because the cylindrical tube region has a constant cross-sectional area, precipitate height is directly proportional to chloride concentration, enabling straightforward linear calibration without optical detection, signal transduction, or complex data processing. Controlled tube inversion and low-speed centrifugation ensure that precipitation occurs exclusively within this cylindrical zone, producing a sharp, reproducible solid–liquid interface. Under optimized conditions (150 µL sample volume and 180 µL of AgNO₃ in nitric acid; centrifugation at 600 rpm for 3 min followed by 5 min settling), the method provides a linear working range of 50–500 mM chloride (r² = 0.9988), a detection limit of 14 mM, and relative standard deviations of 3–4 % at 200–300 mM. Validation of 12 commercial Thai fish sauce samples showed no statistically significant differences compared to AOAC potentiometric titration at the 95% confidence level, with recoveries of 100–103 % and %RSD values of 1–4.2 %. The primary advantage of this method is its strictly linear height–concentration relationship, enabled by geometry-controlled confinement of the precipitate. Unlike other miniaturized or paper-based assays, it eliminates the need for image analysis or device fabrication. From a green chemistry perspective, the assay eliminates the use of potassium chromate indicators and disposable paper-based devices, operates at the microliter scale using reusable plastic microtubes, and requires only low-speed centrifugation. Analytical Greenness (AGREE), Analytical Eco-scale, Green Analytical Procedure Index (GAPI), and White Analytical Chemistry (WAC) evaluations (AGREE score: 0.76; Eco-scale: 83; WAC score: 88.9) classify the method as an excellent example of green analysis. The proposed approach offers a robust and sustainable screening tool for chloride determination in high-salt foods.