新規ガス透過装置の試作とそれを用いるフローインジェクション分析法による天然水中の総炭酸及びアンモニア態窒素の吸光光度定量

今回新たに多孔質PTFE(polytetrafluoroethylene)チューブを分離膜とするガス透過装置を試作し,その性能について総炭酸定量用FIA装置を用いて検討した.新しいガス透過装置は組み立てが簡単で,前回製作のものに比べ,約10%の感度向上が達成され,更にピークのテイリングも減少した.本装置を組み込んだFIAにより環境水中の総炭酸,アンモニア態窒素の定量が可能である.いずれの場合もpH変化に伴うクレゾールレッドの呈色変化を測定に利用した.本法によれば多孔質ガス透過チューブ長8cmのとき,172mg dm(-3)(4×10(-3)mol dm(-3))以下の総炭酸を1時間当たり20試料,3.6mg dm(-3)(2.6×10(-4)mol dm(-3))以下のアンモニア態窒素を1時間当たり30試料の速さで測定できた.この際の検出限界(S/N=3に相当)は総炭酸の場合,0.96mg dm(-3)(2×10(-5)mol dm(-3)),アンモニア態窒素の場合は30μg dm(-3)(2×10(-6)mol dm(-3))であった.

A new gas-diffusion unit was constructed and applied to determine total carbonate or ammoniacal nitrogen in water by spectrophotometric FIA. The gas diffusion unit, which was constructed without any glue, could be assembled easily by fastening the screws to tee connectors with ferrules. The new gas-diffusion unit was improved to decrease the dead volume. The unit gave sharper peaks than the previous one, and peaks higher by 10% in the case of CO(2) determination. The gas-diffusion part consisted of an inner microporous polytetrafluoroethylene (PTFE) tube (GORE-TEX®, 1.0 mm i.d., 1.8 mm o.d., pore size 2.0 μm, porosity 50%) and an outer PTFE tube (2.0 mm i.d., 3.0 mm o.d.). Sample solution was injected into the carrier solution (CS), in which the analyte was converted to a gaseous substance which passed through the microporous PTFE membrane to be mixed with the reagent solution (RS) flowing in the space between the outer and the inner tubings. The resulting pH shift caused the color of the indicator in RS to change. The conditions for the determination of total carbonate are as folows; CS was 1.8X×10(-3) mol dm(-3) H(2)SO(4), RS contained Cresol Red (at pH 9.0) and the detection wavelength was 410 nm. The detection limit was 0.96 mg dm(-3) CO(2) (S/N=3), the response was linear up to 172 mg dm(-3), and the sampling rate was 20 h(-1). For ammoniacal nitrogen, CS was 10(-2) mol dm(-3) NaOH, RS contained Cresol Red (pH 7.0) and absorbance was measured at 550 nm. The detection limit was 30μg dm(-3)NH(4)(+)-N (S/N=3), the response was linear up to 3.5 mg dm(-3), and the sampling rate was 30 h(-1). Total carbonate and ammoniacal nitrogen in river and seawater samples were determined satisfactorily.