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An automated colorimetric method for determining dissolved boron in water is described. The 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) and salicylaldehyde. The absorbance of the yellow complex formed is then measured colorimetrically at 410 nm. Interference effects from other dissolved species are minimized by the addition of diethylenetriaminepentaacetic acid (DTPA); however, iron, zinc, and bicarbonate interfere at concentrations above 400 pg/L, 2000 pg/L, and 200 mg/L, respectively. The 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 to exist primarily as the undissociated form of orthoboric acid (HSBO~) at the pH range of ordinary natural water and a t concentrations less than 1.0 mg/L ( I ) . It is probable that 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 to automated procedures is not feasible because either an evaporation to dryness or a strong acid medium is required prior to color development.The 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 et al. (9) successfully adapted azomethine H into an automated procedure for determination of boron in aqueous plant tissue extracts. Basson et 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.The purpose of this study was to adapt the azomethine H procedure for the routine determination of dissolved boron in natural water samples. The in situ preparation of azomethine H was found to be suitable for the boron concentration range 1 to 6 mg/L ( 4 ) , but it failed to provide the required sensitivity for determining boron concentrations normally present in natural waters (

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The kinetic parameters of [8- 14 C]adenosine transport by a general nucleoside uptake system were studied in germinated conidia of the ad 8 strain of Neurospora crassa . The apparent K m for adenosine uptake by this system was found to be 6.2 μM. The apparent K i values for other nucleosides competing with adenosine for uptake were measured by using Dixon plots. Nucleosides which were efficient competitive inhibitors of adenosine transport were found to inhibit severely the rate of growth of strain ad-8 on adenosine-supplemented medium. Xanthosine and thymidine did not inhibit [8- 14 C]adenosine uptake as severely as other nucleosides, nor did they cause significant inhibition of ad-8 growth rate on adenosine.