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136	Zhang et al.

Figure 7 Typical electropherogram of the separation of metal ions using the CE-CL technique. (1) Co(II); (2) Cu(II); (3) Ni(II); (4) Fe(III); (5) Mn(II). (From Ref. 97, with permission.)

Mn(II), respectively, were reached. The CE-CL detector was used to separate five metal ions, Co(II), Cu(II), Ni(II), Fe(III), and Mn(II), within 8 min, with an average theoretical plate number of 4.6 105. A rapid separation and quantification of nitrite from nitrate ions in biological fluids using CE-CL was reported by Trushina et al. [97]. Nitrites and nitrates can be efficiently reduced to NO at 37°C using vanadium chloride (100%) or HgCl2 (80%). However, these CEderived conditions cannot be simply extrapolated to CL measurements. Vanadium(III) yields high backgrounds in the PMT, which diminishes the sensitivity of CL measurement to that outside of physiological ranges. The present method has been applied to measure nitrites and nitrates in biological fluids. Figure 7 shows a typical electropherogram from the separation of metal ions using the CE-CL technique.

4. CONCLUSIONS

The CL-based technique has been successfully applied to the determination of inorganic compounds, e.g., Cu(II), Co(II), Cr(III), and H2 O2, among many others, with lowest detection limits among the current techniques available.

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CL-based techniques require only simple instrumentation, which offers promising opportunities for analysts who are active in the trace analysis area but who do not have sophisticated instruments available in their laboratories.

It should be noted, however, that among the various analytical methods currently available for the determination of inorganic compounds, CL-based techniques are still not yet being considered as important techniques because only limited CL systems are available, so far.

Hence it is a great challenge for the analyst to develop new CL analytical systems and apply them to real samples and complicated matrices, though it would also be important to extend the applications of classical CL systems such as the luminol-based system as described in this chapter.

REFERENCES

1.JR Lu, XR Zhang. Fenxi Huaxue (Chinese J Anal Chem) 15:1120–1122, 1987.

2.WRG Baeyens, SG Schulman, AC Calokerinos, Y Zhao, AM Garcı´a-Campan˜a, K Nakashima, D De Keukeleire. J Pharm Biomed Anal 17:941–953, 1998.

3.LP Palilis, AC Calokerinos, WRG Baeyens, Y Zhao, K Imai. Biomed Chromatogr 11:85–86, 1997.

4.K Nakashima. Bunseki 7:518–524, 1996.

5.WRG Baeyens, B Lin Ling, UATh Brinkman, SG Schulman. J Biolum Chemilum 4:484–499, 1989.

6.AM Garcı´a-Campan˜a, WRG Baeyens, Y Zhao. Anal Chem 69:83A–88A, 1997.

7.WRG Baeyens, B Lin Ling, K Imai, AC Calokerinos, SG Schulman. J Microcol Sep 6:195–206, 1994.

8.R Escobar, Q Lin, A Guiraum, FF de la Rosa. Int J Environ Anal Chem 61:169–

175, 1995.

´

9. R Escobar, MS Garcia-Dominguez, A Guiraum, FF de la Rosa. Fresenius J Anal Chem 361:509–511, 1998.

10. H Nakamura, K Ikebukuro, S Mcniven, I Karube, H Yamamoto, K Hayashi, M Suzuki, I Kubo. Biosens Bioelectron 12:959–966, 1997.

11. U Quass, D Klockow. Int J Environ Anal Chem 60:361–375, 1995. 12. K Sato, S Tanaka. Microchem J 53:93–98, 1996.

13. XW Zheng, ZJ Zhang. Gaodeng Xuexiao Huaxue Xuebao (Chem J Chinese Univ) 20:209–213, 1999.

14. W Qin, ZJ Zhang, BX Li, YY Peng. Talanta 48:225–229, 1999. 15. CX Zhang, SC Zhang, ZJ Zhang. Analyst 123:1383–1386, 1998. 16. W Qin, ZJ Zhang, HJ Liu. Anal Chem 70:3579–3584, 1998.

17. SV Lotnik, LA Khamidullina, VP Kazakov. Kinet Catal 36:179–182, 1995.

18. XR Zhang, JR Lu, K Yang, ZJ Zhang. Fenxi Shiyanshi (Chinese J Anal Lab) 5:47– 50, 1986.

19. AK Babko, AV Terletskaya, LI Dubovenko. Zh Anal Kim 23:932–934, 1968. 20. S Steig, TA Nieman, Anal Chem 49:1322–1325, 1997.

138	Zhang et al.

21.H Sakai, T Fujiwara, T Kumamaru. Bull Chem Soc Jpn 67:2317–2319, 1996.

22.J Ouyang, JR Lu, LD Zhang. Fenxi Shiyanshi 9:25–27, 1990.

23.JR Lu, XR Zhang, WZ Fan, ZJ Zhang. Anal Chim Acta 262:225–229, 1992.

24.F Zhang, ZM Liu. Fenxi Huaxue 16:485–489, 1988.

25.F Zhang, ZM Liu. Fenxi Huaxue 16:1119–1121, 1988.

26.SH Jia, ZJ Zhang. Huaxue Xuebao (Acta Chim Sinica) 42:1257–1261, 1984.

27.LA Montano, JD Ingle. Anal Chem 51:919–926, 1979.

28.F Zhang, YH Mei, H Chen. Fenxi Huaxue 16:5–8, 1988.

29.MF Ling, MG Lu, NB Tao, H Cui, XH Lu, F Yin. Fenxi Huaxue 14:941–943, 1986.

30.ZJ Zhang, JR Lu. Huaxue Tongbao 5:25–29, 1984.

31.F Zhang, YL Chen. Fenxi Shiyanshi 5:1–3, 1986.

32.ZJ Zhang and WB Dong. Kexue Tongbao 29:447–480, 1984.

33.S Pantel, H Weisz. Anal Chim Acta 74:275–280, 1975.

34.GH Xie, ZA Yu. Fenxi Huaxue 21:1052–1054, 1993.

35.H Li, ZA Yu. Gaodeng Xuexiao Huaxue Xuebao 14:1076–1078, 1993.

36.IE Kalinichenko, OM Grishchenko. Ukr Khim Zh 36:610–613, 1970.

37.WR Seitz, DM Hercules. Anal Chem 44:2143–2149, 1972.

38.SM Zhong, H Chen, WM Zhang. Fenxi Ceshi Tongbao 8:44–47, 1989.

39.AT Pilipenko, AV Terletskaya, TA Bogoslovskaya, NM Lukovskaya. Zh Anal Khim 38:807–810, 1983.

40.NM Lukovskaya, TA Bogoslovskaya, Ukr Khim Zh 48:842–844, 1982.

41.IE Kalinichenko. Ukr Khim Zh 7:755–757, 1969.

42.F Zhang, QX Lin. Talanta 40:1557–1561, 1993.

43.WR Seitz. In: MJ Cormier, DM Hercules, J Lee, eds. Chemiluminescence and Bioluminescence. New York: Plenum, 1973, p 427.

44.GZ Fang, L Liu. Fenxi Huaxue 24:743–743, 1996.

45.H Li, ZA Yu. Fenxi Huaxue, 21:1052–1054, 1993.

46.NM Lukovskaya, LV Markova, NF Evtushenko. Zh Anal Khim 29:767–772, 1974.

47.T Hara. Bull Chem Soc Jpn 60:2031–2035, 1987.

48.NM Lukovskaya, AV Terletskaya. Zh Anal Khim 31:751–756, 1976.

49.JL Burguera. Talanta 27:309–314, 1980.

50.H Sakai, T Fujiwara, T Kumamaru. Anal Chim Acta 302:173–177, 1995.

51.T Fujiwara, K Kurahashi, T Kumamaru, H Sakai. Appl Organomet Chem 10:675– 681, 1996.

52.DF Marino, JD Ingle. Anal Chem 53:455–458, 1981.

53.DF Marino, JD Ingle. Anal Chim Acta 123:247–253, 1981.

54.Z Geng, JR Lu. Shaanxi Shida Xuebao 17:31–35, 1989.

55.WM Hardy, WR Seitz, DM Hercules. Talanta 24:297–302, 1977.

56.GE Collins, SL Ross-Pehrsson. Anal Chem 67:2224–2230, 1995.

57.JR Lu, XR Zhang, WD Han, ZJ Zhang. Fenxi Huaxue 20:575–577, 1992.

58.JZ Lu, W Qin, ZJ Zhang, ML Feng, YJ Wang. Anal Chim Acta 304:369–373, 1995.

59.JR Lu, XR Zhang, ML Feng, JQ Zhang, ZJ Zhang. Chem Res Chinese Univ 8:360– 364, 1992.

60.JR Lu, XR Zhang, ZJ Zhu, ZJ Zhang, MQ Li. Gaodeng Xuexiao Huaxue Xuebao 12:1595–1598, 1991.

61.JR Lu, XR Zhang, ML Feng, ZJ Zhang. Fenxi Huaxue 21:1000–1003, 1993.

Chemiluminescence in Inorganic Analysis

139

62.JR Lu, XR Zhang, ML Feng, ZJ Zhang. Fenxi Shiyanshi 13:3–7, 1994.

63.JR Lu, ZJ Zhu. Shaanxi Shida Xuebao 22:57–60, 1994.

64.JR Lu, ZJ Zhu. Shaanxi Shida Xuebao 22:39–42, 1994.

65.ZJ Zhu, JR Lu. Fenxi Huaxue 22:909–912, 1994.

66.ZJ Zhu, JR Lu. Shaanxi Shida Xuebao 23:59–62, 1995.

67.XR Zhang, JR Lu, JX Zhu, ZJ Zhang. Fenxi Huaxue 16:806–808, 1988.

68.XR Zhang, JR Lu, YP Xue, ZJ Zhang. Shaanxi Shida Xuebao 2:66–70, 1987.

69.ZJ Zhang, JR Lu, XR Zhang, YM Liang. Gaodeng Xuexiao Huaxue Xuebao 9:519– 521, 1988.

70.WB Ma, W Zhang, ZJ Zhang. Fenxi Huaxue 16:818–820, 1988.

71.ZJ Zhang, XR Zhang, JR Lu, CS Pan. Yejin Fenxi 7:110–112, 1987.

72.ZJ Zhang, WB Ma, P Wang. Huaxue Xuebao 46:543–547, 1988.

73.JR Lu, XR Zhang, JK Tie. Shaanxi Shida Xuebao 17:42–47, 1989.

74.XR Zhang, JR Lu, XH Lu. Shaanxi Shida Xuebao 17:113–116, 1989.

75.WH Li, ZL Wang, JZ Li, ZJ Zhang, XQ Zhang. Fenxi Huaxue 26:219–221, 1998.

76.Z Geng, JC Wu, BJ Hui, ZJ Zhang. Fenxi Huaxue 20:423–425, 1992.

77.JR Lu, XR Zhang, ZJ Zhang. Fenxi Huaxue 20:61–63, 1992.

78.Z Geng, JG Zhang. Fenxi Shiyanshi 9:6–8, 1990.

79.ZZ Gao, FC Cai, L Wang, ZJ Zhang. Shaanxi Shida Xuebao 17:108–112, 1989.

80.Z Geng, JW Da. Shaanxi Shida Xuebao 16:47–50, 1988.

81.Z Geng, JC Wu, BJ Huang. Fenxi Shiyanshi 13:15–17, 1994.

82.JR Lu, XR Zhang, J Zhang. Fenxi Huaxue 17:542–544, 1989.

83.XR Zhang, JR Lu, ZJ Zhang. Huaxue Xuebao 47:481–484, 1989.

84.J Ouyang. Time-resolved chemiluminescence determination of Ag(I). Proceedings of the 4th Asian Chemical Congress, Beijing 2:144, 1991.

85.HY Han, QY Luo, XM Yu. Rare Met 16:195–200, 1997.

86.XR Zhang, JR Lu, ML Feng, ZJ Zhang. Fenxi Huaxue 21:575–577, 1993.

87.ZJ Zhang, WP Yang, JR Lu. Gaodeng Xuexiao Huaxue Xuebao 15:1146–1148, 1994.

88.WP Yang, ZJ Zhang. Fenxi Huaxue 22:27–30, 1994.

89.WP Yang, ZJ Zhang. Fenxi Huaxue 22:71–74, 1994.

90.ZJ Zhang, WP Yang, XR Zhang, JR Lu. Fenxi Huaxue 22:23–26, 1994.

91.HG Beere, P Jones. Anal Chim Acta 293:237–243, 1994.

92.B Gammelgaard, YP Liao, O Jons. Anal Chim Acta 354:107–113, 1997.

93.H Sakai, T Fujiwara, T Kumamaru. Anal Chim Acta 331:239–244, 1996.

94.T Fujiwara, K Kurashashi, T Kumamaru, H Sakai. Appl Organomet Chem 10:675– 681, 1996.

95.TB Ryerson, AJ Dunham, RM Barkley, RE Sievers. Anal Chem 66:2841–2851, 1994.

96.B Huang, JJ Li, L Zhang, JK Cheng. Anal Chem 68:2366–2369, 1996.

97.EV Trushina, RP Oda, JP Landers, CT McMurray. Electrophoresis 18:1890–1898, 1997.

7

Mechanism and Applications of Peroxyoxalate Chemiluminescence

Malin Stigbrand, Tobias Jonsson, Einar Ponte´n, and Knut Irgum

Umea˚ University, Umea˚ , Sweden

Richard Bos

Deakin University, Geelong, Victoria, Australia

1.	INTRODUCTION		141
2.	REACTION MECHANISM		146
	2.1	Reactive Intermediates	147
	2.2	General-Base and Nucleophilic Catalysis	150
	2.3	Chemically Initiated Electron Exchange Luminescence
		(CIEEL)	154
3.	ANALYTICAL APPLICATIONS		154
	3.1	Determination of Hydrogen Peroxide	154
	3.2	Detection of Fluorescent Compounds	159
	3.3	Miscellaneous Applications	165
4.	CONCLUSIONS AND FUTURE TRENDS		166

1. INTRODUCTION

Peroxyoxalate chemiluminescence (POCL) was first reported in 1963 by Chandross [1], who observed emission of light from a mixture consisting of oxalyl

141

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chloride, hydrogen peroxide, and the fluorescent compound 9,10-diphenylanthra- cene dissolved in 1,4-dioxane. The light emitted was found to be spectrally identical to the fluorescence emission spectrum of 9,10-diphenylanthracene. POCL is thus an indirect or sensitized type of chemiluminescence, as the intermediates or reaction products from the primary reaction do not emit a significant quantity of light. Instead, the in situ–generated intermediate transfers its energy to an energyaccepting fluorophore (denoted F in the following scheme), which becomes electronically excited (denoted F*) and subsequently emits light.

The steps in the light-generating process can be described as follows:

Oxalic acid derivative H2 O2 → intermediates	(1)
Intermediates F → F*	(2)
F* → F hν	(3)

The intermediates generated in the POCL reaction are capable of exciting fluorophores that emit light from the near-ultraviolet to the near-infrared region; it is this defining characteristic that establishes the usefulness of this reaction to analytical chemistry.

Much of the early development of POCL was performed by researchers at American Cyanamid [2–4]. The primary focus of their research was the investigation of reagents and reaction formulations that could emit light efficiently. This led to the successful development of practical, spark-free light sources that serve as emergency lighting. A high quantum yield in combination with a long duration of the emission are regarded as optimal properties in these devices. The first study dealing with different oxalic acid derivatives was published in 1967 by Rauhut and co-workers [3]. They found that diaryloxalate esters with strongly electronwithdrawing substituents provided the highest quantum yields, whereas diaryloxalate esters with electron-donating or weak electron-withdrawing groups were found to result in either ineffective or poor production of chemiluminescence. The most efficient diaryloxalate ester reported was bis(2,4-dinitrophenyl) oxalate (DNPO), and although this reagent finds occasional use analytically [5–8], it has been surpassed in popularity by 2,4,6-trichlorophenyl oxalate (TCPO), which is not quite as efficient but has the virtue of being more conveniently handled.

An early investigation [9] of oxamide derivatives as alternate sources of excitation in POCL did not initially yield great success in the context of the research work performed by American Cyanamid. In common with the earlier work on diaryloxalate ester derivatives, there appeared to be a general relationship between the electron-withdrawing ability of the substituent(s) and POCL efficiency. In later works, they developed a new class of oxamide reagents, which resulted in a substantial improvement in CL performance of oxamide derivatives [10]. These oxamides featured the strongly electron-withdrawing trifluoromethylsulfonyl moiety attached to the oxamide nitrogen. One of the compounds described in the cited work, N,N′-bis(2,4,5-trichlorophenyl)-N,N′-bis(trifluoro-

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Figure 1 Structure of N,N′-bis(2,4,5-trichlorophenyl)-N,N′-bis(trifluoromethylsulfonyl) oxamide.

methylsulfonyl) oxamide (see Fig. 1) was reported (and still remains) to be the most efficient reagent presently known, with a claimed quantum yield of 34%.

The development of reagents for aqueous POCL received attention early. The impetus for this research was, again, to provide spark-free light sources for emergency use in both civilian and military applications. The first report published on aqueous POCL [11] attempted to adapt diaryloxalate ester reagents that had been found useful in nonpolar solvents, by adding functionalities that would assist in their water solubility. This approach gave rise to one reportedly useful compound, bis-{2,4-dichloro-6-[(2-dimethylaminoethyl)methylsulfamoyl]phe- nyl} oxalate dihydrochloride (see Fig. 2) that was claimed by the authors to be the first example of water-soluble POCL, producing a short-lived emission.

Further progress [12] in this field focused on developing the aforementioned trifluoromethylsulfonyl substituted oxamides [10]. Of the numerous molecules synthesized and tested, 4,4′-{oxalyl bis[(trifluoromethylsulfonyl)imino]- ethylene}bis(4-methylmorpholinium trifluoromethansulfonate) (METQ) and 2,2′ - oxalyl - bis[(trifluoromethanesulfonyl)imino]ethylene - bis(N - methylpyridi - nium) trifluoromethanesulfonate (PETQ) (see Fig. 3) were found to be the most

Figure 2 Structure of bis-{2,4-dichloro-6-[(2-dimethylaminoethyl)methylsulfamoyl]- phenyl oxalate dihydrochloride.

144	Stigbrand et al.

Figure 3 Structures of 4,4′-{oxalyl bis[(trifluoromethylsulfonyl)imino]-ethylene}bis (4-methylmorpholinium trifluoromethansulfonate) (METQ) and 2,2′-oxalyl-bis[(triflu- oromethanesulfonyl)imino]ethylene-bis(N-methylpyridinium) trifluoromethanesulfonate (PETQ).

efficient. Of these two molecules, only METQ [13–17] and a homolog 3,3′-oxa lyl-bis[(trifluoromethylsulfonyl)imino]trimethylene-bis(N-methylmorpholinium) trifluoromethanesulfonate (MPTQ) [18] have been employed analytically. Although the work was performed in a largely aqueous environment, the reagents were kept in acetonitrile prior to the reaction, to prevent preliminary hydrolysis. It has been reported that the half-life of METQ is of the order of 8 min under purely aqueous conditions [13].

Van Zoonen et al. [19,20] employed an alternative approach, in an attempt to overcome the limited aqueous solubility of diaryloxalate ester–type POCL reagents. In this work, granular TCPO was mixed with controlled pore glass and packed in a flow cell, forming a solid-state TCPO reactor. When this was used in conjunction with a flow system, some of the TCPO dissolved in the carrier solution. Numerous difficulties were encountered with this approach, namely, limited reactor lifetime (approximately 8 h) and low CL emission obtained as the carrier became more aqueous (a 90% reduction of CL intensity occurred when the aqueous content of the carrier stream comprised 50% water, as compared to pure acetonitrile). The samples also required dilution with acetonitrile to increase the solubility of TCPO in the sample plug.

The complex and sometimes competing issues of solubility, stability, and reactivity of reagents designed for purely aqueous POCL were addressed by Barnett et al. [21,22], who furthered the development of the trifluormethylsulfonylsubstituted oxamide class of reagents. They prepared disulfonic acid functionalised oxamides (see Fig. 4), which were found to possess a considerably improved degree of stability at both ambient and low temperature when compared to METQ, in addition to showing some promise as potential reagents in analytical applications.

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Figure 4 Structures of disulfonic acid functionalized oxamides.

As the POCL reaction began to find use in analytical chemistry, more researchers became interested in developing new reagents to address the specific requirements of this application [23–25]. In analytical flow systems, it is desirable for the light production to occur over a much shorter period of time, i.e., seconds instead of hours, and it is therefore usually inappropriate to employ reagents that have been developed with a long duration as the primary design criterion. Quantum yield is of course important, but equally critical for success in an analytical application is the intensity of the initial burst of light. In Table 1, some of the reagents used for analytical applications are listed.

The POCL reaction scheme can be used to detect several classes of analytes, depending on the limiting compound in the reaction, i.e.,

1.Hydrogen peroxide [26–33] and analytes converted to hydrogen peroxide via either an enzymatic [34–52] or a photochemical postcolumn reaction [53–55]

2.Fluorophores and analytes derivatized with a fluorophoric label [56– 105]

3.Analytes that efficiently quench or enhance the CL reaction [106,107].

In addition to these three groups, there are some other examples, e.g., amines [108–110], phenols [111–113], metal ions [114–117], oxalic acid [118,

Table 1 The Most Commonly Used Oxalic Reagents (R-COCO-R) in Analytical Applications

Side chain, R-	Abbreviation	Ref.
2,4,6-Trichlorophenyl	TCPO	76, 78
2,4-Dinitrophenyl	DNPO	45, 78, 99, 183
2,4,5-Trichloro-6-carbopentoxyphenyl	CPPO	47
2-(3,6,9-Trioxadecyloxycarbonyl)-4-nitrophenyl	TDPO	91, 92, 109, 110, 160
2-Nitrophenyl	2-NPO	43, 79
Pentachlorophenyl	PCPO	111
Imidazole	ODI	29, 50, 151