Fast direct determination of strontium in seawater using high-performance chelation ion chromatography

A new method for the fast direct chromatographic determination of strontium in seawater has been developed. Two coupled silica monolithic columns (total dimensions 200×4.6 mm I.D.) chemically modified with iminodiacetic acid (IDA) functional groups were used for baseline separation of all alkaline-earth metals in seawater in less than 4 min at flow rate of 4.0 mL min⁻¹, using an eluent containing 0.25 M sodium chloride and 2 mM glycolic acid, pH 5.11. Several colour-forming ligands, including o-cresolphthalein complexone (o-CPC), methylthymol blue (MTB), xylenol orange (XO), 4-(2-pyridylazo)resorcinol (PAR) and ZnEDTA-CPAR were evaluated as reagents for post-column reaction (PCR) based spectrophotometric detection. Sensitivity of the developed method for strontium was at the low mg L⁻¹ level in undiluted seawater samples, in the presence of excessive amounts of calcium and magnesium, using post-column reaction detection with o-CPC at 570 nm. The method allowed quantitative determination of strontium in seawater samples (LOD 3.23 ± 0.15 mg L⁻¹, s_r = 4.6%), with direct injection of just 4 μL of seawater onto the chromatographic column.