Chloride analysis of botanical samples by ICP-OES

Abstract

A unique method for chloride analysis of botanical samples by axially viewed ICP-OES with a modified optical system is described. Calibration on the most sensitive wavelength (134.7 nm) between 1 and 200 mg Cl L⁻¹ yielded a curvilinear relationship (R² = 1.000) across three orders of magnitude. The instrumental limits of detection in solution of 0.041 mg L⁻¹ and background equivalent concentration of 5.29 mg L⁻¹ are similar to those of other methods using pneumatic nebulisers. Matrix matching of calibration standards with respect to nitric acid concentration (4% v/v) and carbon levels (0.15% sucrose m/v) of extracted sample solutions produced consistent responses from plant material. High carbon concentrations (up to 8% sucrose m/v) caused matrix interferences that decreased blank values by 4.5 mg L⁻¹ and suppressed Cl signals by 20%. No interferences from countercations were observed. A simple extraction process for dried plant samples (0.1 g in 40 mL of 4% HNO₃) was developed and tested with plant standard reference materials. Recovery of Cl from the majority of materials was close to 100% of established values while relative standard deviations were below 4% except when chloride concentration was close to the method detection limit. The extraction method was robust to modifications for samples with low mass or high Cl concentrations.