A novel ion chromatographic method based on cation-exchange and acid-base interactions for the simultaneous determination of total alkalinity and monovalent cations in samples of mu l volume

An ion chromatographic (IC) method based on the use of titrant (strong acid ) as the stationary phase was developed for simultaneous determination of t otal alkalinity (TA) and monovalent cations. The titrant used in this study was obtained by initially loading lithium dodecylsulfate (Li-DS) onto a re versed-phase material and then conditioning the column with a slightly acid ified aqueous LiCl solution (a mixture of 50.0 mM LiCl and 0.1 mM H2SO4). W hen a small amount of a basic sample was injected onto a column prepared in this way, the basic species (Bn-) reacted predominantly with H+ on the sta tionary phase and the reaction with the eluent phase was negligible due to the very low concentration of eluent H+ (in the eluent, a molar ratio of [L i+]/[H+] = 250 : 1 applied). The stationary phase H+ consumed in the acid-b ase reaction was then re-supplied by H+ from the eluent. By monitoring the conductance of the eluent using conductivity, an induced peak resulting fro m the basic species was observed. Calibration graphs of peak areas vs. mola r concentration of the basic species for OH-, HCO3- and H2PO4- were found t o be identical. CO32-, HPO42-, and B4O72- also gave identical calibration c urves but their slope values were twice those for HCO3-. The detection limi t for HCO3- was less than 3.2 muM and the calibration curve was linear up t o 12.3 mM (injection volume, 100 muL). Seawater was directly analyzed and i ts total alkalinity was found to be 2.87 mM (RSD 0.53%, n = 5), which was i n good agreement with the result of 2.88 mM (RSD 3.2%, n = 5) obtained usin g auto-potentiometric titration. Na+ and K+ were determined simultaneously and the concentrations were 481.6 and 10.6 mM, respectively.