Azomethine H Colorimetric Method for Determining Dissolved Boron in Water Roberto R. Spencer* and David E. Erdmann U.S. Geological Survey, Box 25046, Denver Federal Center, MS 407, Denver, Colo. 80225 An automated colorimetric method for determining dissolved boron in water is described. T h e boron is complexed with azomethine H, which is readily available as the condensation product of H acid (8-amino-l-naphthol-3,6-disulfonic acid) a n d salicylaldehyde. T h e absorbance of the yellow complex formed is then measured colorimetrically a t 410 nm. Interference effects from other dissolved species are minimized by the addition of diethylenetriaminepentaacetic acid (DTPA); however, iron, zinc, and bicarbonate interfere a t concentrations above 400 pg/L, 2000 pg/L, and 200 mg/L, respectively. T h e bicarbonate interference can be eliminated by careful acidification of the sample with concentrated HCl to a p H between 5 and 6. Thirty samples per hour can be routinely analyzed over the range of from 10 to 400 pg/L boron. Since its chemical behavior in water is not well known, boron is assumed t o exist primarily as the undissociated form of orthoboric acid ( H S B O ~a)t the pH range of ordinary natural water and a t concentrations less than 1.0 mg/L ( I ) . It is probable t h a t complex solute species occur in natural waters draining evaporated boron deposits and in sewage and industrial wastes. Several complexing agents are commonly used for the spectrophotometric determination of boron in water including curcumin, carmine, and dianthrimide. However, their adaptation t o automated procedures is not feasible because either a n evaporation to dryness or a strong acid medium is required prior t o color development. T h e condensation product of H acid (8-amino-1-naphthol-3,6-disulfonic acid) and salicylaldehyde, azomethine H , was used by Shanina e t al. (2) for the manual determination of boron in complex borenes and boranes. Basson e t al. (9) successfully adapted azomethine H into an automated procedure for determination of boron in aqueous plant tissue extracts. Basson e t al. ( 4 )later incorporated an in situ preparation of azomethine H into the manifold to circumvent the time required for outside preparation of the complexing reagent. T h e purpose of this study was to adapt the azomethine H procedure for the routine determination of dissolved boron in natural water samples. T h e in situ preparation of azomethine H was found to be suitable for the boron concentration range 1to 6 mg/L ( 4 ) ,but it failed to provide the required sensitivity for determining boron concentrations normally present in natural waters (
