On-site analysis for nitrogen oxides using a newly developed portable flow injection analyzer

A new portable flow injection system was developed for on-site chemical analysis, which allows the rapid analysis of aqueous samples at sampling sites. The system comprises a newly designed double-plunger micro pump, a six-way sample injector, a reaction coil in a thermostated compartment and a detector. All of these units are connected with 0.5 mmi.d. PTFE tubing. A visible detector is assembled using a maximum wavelength of 525 nm of a light-emitting diode (LED) and 540 nm of an interference filter. The system is of the one-box type, whose dimensions are 160(W) x 160(H) x 320(D) mm, and is easy to carry to the analysis site; the weight is 8 kg. A thermostated compartment is incorporated into the proposed system in order to be used outdoors, where temperatures are changeable. The system can workwith DC 12Vas well as AC 100V; therefore, a car battery or a portable battery can be used as the power source. The analytical data can be memorized in IC cards or a note-book personal computer connected with a RS232C cable. Furthermore, software on the market can be easily used. By using the proposed system, the on-site determination of nitrogen oxides, such as nitrate and nitrite, could be carried out. Calibration graphs for nitrate and nitrite ions were linear over ranges of 0 to 1.0ppm and 0 to 100ppb ofN-NOs and N-NO2 with good precision; the sampling rate was 40~50 samples per hour. The detection limit for N-NO3 and N-NO2 was 0.5 ppb. By using the proposed system, the on-site determination of nitrate and nitrite in river water samples was carried out. The relative standard deviations of ten injections were 0.65% for nitrate and 0.15% for nitrite. Furthermore, nitrate and nitrite in biological samples as a metabolic products of nitric oxide, which have attracted a lot of attension as a messenger of diverse physiological processes, were also determined on-site with high sensitivity. By using a car battery as a power source, the proposed system worked continuously. In addition, it worked for about 5 hours continuously with a portable battery.試料採取現場での迅速な分析，すなわちオンサイト分析のための新しいポータブルフローインジェクション分析計の開発を行った・このFIA装置では，160×160誉320（mm）の箱の中にダブルプランジ ャーマイクロポンプ，試料注入語検出器及び反応恒温槽を組み入れ，重量8kgと小型・軽量化を達成し，持ち運び容易な分析計とした．特に，525nmの発光ダイオード（LED）を光源とする新規検出 器を開発することにより，小型，省電力化が可能となった．温度変化の大きな屋外での測定に耐えられるように，反応恒温槽も装備した．本FIA装置は交流100Vでのほか，直流12Vでも稼働し，カーバ ッテリーや市販のポータブルバッテリーを電源とするオンサイト分析に対応できるよう設計した．カーバッテリーを電源とした場合は長時間の連続運転が可能である．測定データはメモリーカードや RS232Cによりノート型パーソナルコンピュータへの通信も可能で，更に市販の表計算ソフトを利用してデータ処理が可能である．本装置を窒素酸化物のオンサイト分析に応用した．硝酸，亜硝酸イオン標準液による検量線は，0～1・Oppm，0～100ppbの範囲で直線性，再現性共に良好で，1時間当たり40～50試料の分析が可能であった・検出限界（5／Ⅳ＝3）は硝酸，亜硝酸態窒素として0．5ppbと通常のFIAシステムを用いる場合と全く変わらない優れた性能を有することが分かった．河川水中の硝酸，亜硝酸イオンのオンサイト分析では10回の繰り返し測定における相対標準偏差は0．65％及び0．15％と良好な結果が得られた．また，血清中の一酸化窒素（NO）の酸化代謝物としての硝酸，亜硝酸イオン濃度のオンサイト分析を行い，良好な結果を得た．本研究で検討したポータブルバッテリーでは1回の充電で5時間の連続運転が可能であった