Determination of calcium by FIA with glyoxal bis(2-hydroxyanil)

Glyoxal bis(2-hydroxyanil) (GBHA) reacts with calcium to form a red complex in alkaline solution. On the basis of this color reaction, FIA is proposed for the simple and rapid determination of calcium in natural waters. Three streams, a reagent solution (0.05% GBHA), a buffer solution (0.20 M NaOH) and a carrier solution (water) were propelled at the same flow rate of 0.6 ml min-1 by using plunger micropumps. Sample solution (290 μl) was injected into the carrier solution and an eight meter long Teflon tubing (0.5 mm i.d.) was used as the reaction coil. The absorbance of Ca-GBHA complex was measured at 520 nm using a flow cell (8 μl, 1 cm long). The calibration curve was linear up to 1.2 ppm Ca, and the detection limit corresponding to S/N =2 was 5 ppb Ca. At the sampling rate of 20 samples per hour, the relative standard deviations were 1.2 and 0.22% (n =10) for the determination of 0.4 and 1 ppm Ca respectively. The results for the analysis of natural waters (rain, river, tap and well waters) agreed well with those obtained by AAS (JIS method).