Highly sensitive determination of hydrazine ion by ion-exclusion chromatography with ion-exchange enhancement of conductivity detection

https://doi.org/10.1016/j.chroma.2004.03.075Get rights and content

Abstract

An ion-exclusion chromatography method with ion-exchange enhancement of conductivity was developed for the selective separation and sensitive determination of hydrazine ion from alkali/alkaline earth metal cations and ammonium ion. Hydrazine ion was separated by ion-exclusion/penetration effect from other cations on a weakly basic anion-exchange column in the OH form (TSKgel DEAE-5PW). Moreover, two different ion-exchange resin columns were inserted between the separating column and conductimetric detector in order to improve the sensitivity of hydrazine ion. The first enhancement column packed with a strongly basic anion-exchange resin in the SO42− form (TSKgel SAX) for hydrazine ion can convert from N2H5OH to (N2H5)2SO4. Moreover, the second enhancement column packed with a strongly acidic cation-change resin in the H+ form (TSKgel SCX) can convert to H2SO4. As a result, the sensitivity of hydrazine ion using two conductivity enhancement columns could be 26.8-times greater than using the separating column alone. This method was effectiveness also for the enhancement of ammonium ion (6.1-times) and sodium ion (1.2-times). The calibration graph of hydrazine ion detected as H2SO4 was linear over the concentration range of 0.001–100 ppm (r2=0.9988). The detection limit of hydrazine ion in this system was 0.64 ppb. Therefore, hydrazine ion in real boiler water sample could be accurately determined, avoiding the interference of other cations.

Introduction

Hydrazine ion is a strong reducing agent in order to remove solved oxygen scavenger in boiler waters and hot-water systems [1]. Hydrazine ion as well as its derivatives has been also employed application in industry, agriculture, explosives and other field. However, hydrazine has been reported to be a toxic material which has to be treated with precaution [2]. Therefore, the monitoring system of hydrazine with high sensitive detection has been developed to determine trace levels of hydrazine in environmental samples such as the boiler, river and industrial waters [3]. Many methods for the determination of hydrazine have been proposed including colorimetric [4], spectrophotometric [5], [6], potentiometric [7], chemiluminescence [8], and titrimetric [9]. These could achieve the highly sensitive detection for hydrazine and its derivatives in the environments. However, some of these methods are sensitive to the interference of coexisted substances and/or require many procedures for pretreatment of samples.

Ion-exclusion chromatography has developed into a very useful technique for separating small weak acids or weak bases [10]. It is possible to determine a target sample without the interference of other samples. Ion-exclusion chromatographic separation of weak bases has been a packed column with a basic cation-exchange resin in the OH form as a separating column, in order to convert from salts to bases, [11], [12], [13], [14], [15]. Especially, the method is effectiveness for separating of very weak bases, such as ammonium ion (pKb=4.75) or hydrazine ion (pKb=5.77), due to its large penetration effect to the resin-phase based on the effect of Donnan equilibrium membrane. Commonly, the detection of analytes separated has been curried out by the conductivity detector. However, the conductivity responses are low due to its low limiting equivalent ionic conductance [16].

Previously, Tanaka et al. reported the high sensitive determination of ammonium ion in biological nitrification–denitrification process water by ion-exclusion chromatography with ion-exchange enhancement of conductivity detection [17]. Ammonium ion was selectivity separated by ion-exclusion effect from other cations on a strongly basic anion-exchange resin in the OH form with water eluent. The sensitivity was dramatically improved by two ion-exchange enhancement columns sited between the separating column and detector. However, measurement at ppb level of sample was difficult due to the high detection limit (530 ppb).

The purpose in this study is to achieve a sensitive detection of ppb level of hydrazine ion by the ion-exclusion chromatography with the conductivity enhancement columns, including the separation from ammonium ion and alkali metal/alkaline earth metal cations.

The separating column used in this study was a polymethacrylate-based weakly basic anion-exchange resin column (Tosoh TSKgel DEAE-5PW). A weakly anion-exchanger (tertiary amine functional groups) in the column is partially protonation and dissociation by OH in water eluent, and thus weak bases are easily penetrated into the resin-phase in the column rather than that in a strongly basic anion-exchange column [15]. The resolution of weak bases can be expected to be consequently improved.

The enhancement columns of conductivity detection used two sorts of ion-exchange columns. The first enhancement column was a strongly basic anion-exchange resin TSKgel SAX column formed by an anion that has a high limiting equivalent ionic conductance (e.g., Cl). The effect converts from a weak electrolyte (e.g., NH4OH) to a strong electrolyte (e.g., NH4Cl) by an anion-exchange reaction [17]. The second enhancement column was a strongly acidic cation-exchange resin TSKgel SCX column formed by H+ that has the highest limiting equivalent ionic conductance of cations. This can greatly emphasize the conductivity response, because analytes convert to strong acids (e.g., HCl) by a cation-exchange reaction passing through the column.

In this paper, we report the feature of this system in terms: (1) the ion-exclusion chromatography of hydrazine from other cations on a weakly basic anion-exchange resin column with water eluent, (2) the effect of two ion-exchange enhancement columns of conductivity detection, (3) the linearity of analytes in the optimum condition, and (4) the application to the boiler water samples.

Section snippets

Apparatus

The ion chromatograph (Tokyo, Japan) consisted of Tosoh LC-8020-Model II chromatographic data processor, DP-8020 dual pump operated at flow rate of 1 ml/min, SD-8022 on-line degasser, CO-8020 column oven operated at 40 °C and CM 8020 conductimetric detector. The injection volume was 100 μl.

Reagents

All reagents were of analytical reagent-grade, purchased from Wako (Osaka, Japan) and were dissolved in distilled and deionized water for the preparation of standard solutions and eluents. The stock solutions of

Ion-exclusion chromatographic separation of hydrazine ion

A 0.1 ml sample containing 1 ppm NaCl, 1 ppm NH4Cl, and 1 ppm N2H5Cl was injected to test the separation ability of the system used. In the elution with water, the weakly basic anion-exchange column in the OH form converts NaCl, NH4Cl and N2H5Cl to NaOH, NH4OH and N2H5OH, respectively. Good resolution of the sample bases was obtained depending on the degree of ion-exclusion/penetration effect for each other to the resin-phase of the separating column as shown in Fig. 2A [16]. However, the

Conclusions

This proposed method was the selective separation of ammonium and hydrazine ions from alkali/alkaline earth metal cations by the ion-exclusion chromatography on a weakly basic anion-exchange resin and the sensitive conductimetric determination by the enhancement columns. The good linearity of calibration curves over the concentration range of 0.001–100 ppm of the bases detected as H2SO4 was obtained by using the system. The results indicated that the present method was possible to accurately

Acknowledgements

We wish to thank S. Sato of Tosoh Co. Ltd., for providing many kinds of ion-exchange resins and several boiler water samples used in this research.

References (17)

  • G. Choudhary et al.

    Chemosphere

    (1998)
  • J.M. Pingarrón et al.

    Anal. Chim. Acta

    (2001)
  • A. Afkhami et al.

    Anal. Chim. Acta

    (2000)
  • P. Ortega-Barrales et al.

    Anal. Chim. Acta

    (1997)
  • A. Safavi et al.

    Anal. Chim. Acta

    (1998)
  • K. Tanaka et al.

    J. Chromatogr.

    (1979)
  • K. Tanaka et al.

    J. Chromatogr.

    (1979)
  • P.R. Haddad et al.

    J. Chromatogr. A

    (1994)
There are more references available in the full text version of this article.

Cited by (99)

  • Ion-exclusion chromatography

    2023, Ion-Exchange Chromatography and Related Techniques
View all citing articles on Scopus
View full text