Water-Soluble Humic Acid Quantification Using a Flow-Injection System with and without Sample Pretreatment

• Published in: Industrial & engineering chemistry research 2013-09, Vol.52 (36), p.12717-12722
• Main Authors: Palomeque, Miriam E, Ortiz, Patricia I
• Format: Article
• Language: English
• Subjects: Calibration; Dyes; Humic acids; Hydroxyapatite; Mathematical analysis; Pretreatment; Slopes
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie400980u

Two automated methods for the determination of humic acids (HAs) in natural water samples are presented. Flow injection systems were developed based on the formation of a complex between humic acids and toluidine blue dye. When the complex is formed, the dye absorbance signal decreases at selected operating conditions. Method A, without sample pretreatment, presents a linear calibration curve over HA concentration range 1.14–35.0 μg mL–1, with a limit of detection (LOD) of 0.4 μg mL–1 (3 Sy/x) and a sample throughput of 80 h–1. To determine lower HA concentration levels, a preceding separation/preconcentration step was included (method B). This method has a linear range of 1.5–20.0 μg mL–1 and a sample throughput of >8 h–1 and could detect humic substances at a concentration of 0.05 μg mL–1 after a 4-min retention time. The RSDs for methods A and B calculated using the slopes of seven independent calibration graphs obtained on different days and with different conditions (standard solution, reagent solution, etc.) were 4.5% and 4.2% respectively. Both methods were satisfactorily applied to natural water samples, with recovery percentages in the 95–107% range, and compare very well with other methods.