Use of a sheath flow cuvette for chemiluminescence detection of isoluminol thiocarbamyl-amino acids separated by capillary electrophoresis

Migration behavior of isoluminol isothiocyanate-labeled α-amino acids in capillary electrophoresis with an absorption/chemiluminescence dual detection system

In our previous study, we developed capillary electrophoresis with an ultraviolet absorption/chemiluminescence dual detection system. Here, to demonstrate one of the possible applications of the capable system as well as confirm the advantage, migration behavior of isoluminol isothiocyanate-labeled alpha-amino acids was examined in the capillary electrophoresis with a dual detection system. The labeled samples were first analyzed by absorption detection with an on-capillary, followed by chemiluminescence detection with an end-capillary. The system easily, rapidly, and simultaneously produced useful information concerning chemiluminescence quenching and amino group-labeling due to the presence of both absorption and chemiluminescence detections.

Determination of phenothiazines in pharmaceutical formulations and human urine using capillary electrophoresis with chemiluminescence detection

A CE instrument coupled with chemiluminescence (CL) detection was designed for the determination of promethazine hydrochloride (PTH) and promazine hydrochloride (PMH) in real samples. An important enhancement of the CL emission of luminol with potassium ferricyanide was observed in the presence of these phenothiazines; so this system was selected for their detection after CE separation. Parameters affecting the electrophoretic separation were optimized in a univariate way, while those affecting CL detection were optimized by means of a multivariate approach based on the use of experimental designs. Chemometrics was also employed for the study of the robustness of the factors influencing the postcolumn CL detection. The method allows the separation of the phenothiazines in less than 4 min, achieving LODs of 80 ng/mL for PMH and 334 ng/mL for PTH, using sample injection by gravity. Electrokinetic injection was used to obtain lower LODs for the determination of the compounds in biological samples. The applicability of the CE-CL method was illustrated in the determination of PTH in pharmaceutical formulations and in the analysis of PMH in human urine, using a previous SPE procedure, achieving an LOD of 1 ng/mL and recoveries higher than 85%.

Indirect chemiluminescence detection for capillary zone electrophoresis of monoamines and catechol using luminol-K3[Fe(CN)6] system

Indirect chemiluminescence (ICL) detection for capillary electrophoresis (CE) of monoamines and catechol using luminol-K3 [Fe(CN)6] system was described. A strong and stable background chemiluminescence (CL) signal can be generated by luminol-K3 [Fe(CN)6] reaction. Based on the principle of that some phenolic compounds may be oxidized in the presence of K3 [Fe(CN)6], quenching effect of catecholamines for luminol-K3[Fe(CN)6] CL reaction results in a quantifiable decrease in the background signal. The conditions for CE separation and the CL detection for four standard catecholamines were systematically investigated using a homemade CE-ICL system. Under the optimum conditions, the detection limits of dopamine (DA), epinephrine (EP), norepinephrine (NE) and catechol (CA) were determined to be 0.18 mciroM 0.39 microM 0.48 microM and 0.09 microM, respectively. It also has been successfully applied to analyze seven pharmaceutical samples and seven human urine samples.

A sensitive and rapid immunoassay for quantification of CA125 in human sera by capillary electrophoresis with enhanced chemiluminescence detection

In this paper we have presented a sensitive and rapid immunoassay (IA) method by capillary electrophoresis with an enhanced chemiluminescence detection system (CE-CL) based on the catalytic effects of horseradish peroxidase (HRP) on the luminol-hydrogen peroxide reaction. The conditions for the CL reaction and electrophoresis were systematically investigated using HRP as a model sample. The linear range from 2.5 x 10(-11) to 1.0 x 10(-9) mol/L (R = 0.999), and the detection limit of 1.0 x 10(-12) mol/L (signal-to-noise ratio = 3) for HRP were achieved using para-iodophenol as CL enhancer. The relative standard deviations of the migration time and peak area for 5.0 x 10(-10) mol/L HRP (n = 7) were 0.26 and 4.8%, respectively, using a CE system with a home-built CL detector. Under the optimal condition, the HRP-labeled CA125 antibody (Ab) and the Ab-antigen complex were well separated within 4 min by CE using a high-pH buffer (pH 10.20). The assay was successfully used for quantification of CA125 in human sera from health controls and patients associated with ovarian cancer, and the recoveries of the standard addition experiments were 93-109%. Our primary results demonstrated that IA based on CE-CL detection is a powerful tool for clinical diagnosis combined with these commercial IA kits.

A facile and sensitive chemiluminescence detection of amino acids in biological samples after capillary electrophoretic separation

It was found that native amino acids enhanced the chemiluminescence (CL) reaction between luminol and BrO(-) in an alkaline aqueous solution. This has led to the development of a facile and highly sensitive CL detection scheme for the determination of amino acids in biological samples after capillary electrophoretic (CE) separation. The CE-CL conditions were optimized. An electrophoretic buffer of 2.5 x 10(-2) M sodium borate (pH 9.4) containing 1 x 10(-4) M luminol was used. The oxidizer solution of 8 x 10(-4) M NaBrO in 0.1 M sodium carbonate buffer solution (pH 12.5) was introduced post-column. Under the optimal conditions, the detection limits were 1.0 x 10(-7) M for glutamic acid (Glu) and 1.3 x 10(-7) M (S/N = 3) for aspartic acid (Asp). The relative standard deviations (RSDs) of peak area and migration time were in the ranges of 3.8-4.3% and 1.4-1.6%, respectively. The present method was applied to the determination of excitatory amino acids (i.e., Asp and Glu) in rat brain tissue and monkey plasma. The levels of these major excitatory amino acids in monkey plasma were quantified for the first time and found to be 1.17 +/- 0.17 x 10(-5) M (mean +/- SD, n = 6) for Glu and 1.64 +/- 0.19 x 10(-6) M for Asp, which were comparable with the levels in human plasma.

Characteristics of a Liquid/Liquid Optical Waveguide Using Sheath Flow and Its Application to Detect Molecules at a Liquid/Liquid Interface

The formation conditions and characteristics of a liquid/liquid optical waveguide (LLW) were studied using a two-phase sheath flow, where the inner organic phase flow acted as the core and the outer aqueous flow acted as the clad. In immiscible solvent systems, i.e., toluene/water and diethyl ether/water systems, the LLWs were formed in the range of higher than ca. 600 of the Reynolds number (Re), where the linear velocity of the organic solvent was much higher than that of the aqueous solution. On the other hand, in a miscible solvent system, i.e., a tetrahydrofuran/water system, a stable LLW was formed in the range of a much lower Re than in immiscible systems. Moreover, the molecules at the toluene/water interface of the LLW were observed with both fluorescence and absorbance measurement systems. In particular, the change in the fluorescence spectrum of 1-anilino-8-naphthalenesulfonate (ANS) at the interface within 1 ms was observed by this method, indicating the usefulness of the LLW for a fast kinetic study of a liquid/liquid interface.

Derivatization of biomolecules for chemiluminescent detection in capillary electrophoresis

An overview is presented on the power and drawbacks of the relatively unfamiliar chemiluminescence-based detection technique applied in analysis by capillary electrophoresis, for determining chemically derivatized biomolecules. Examples of the most common systems are given for many series of biologically active compounds as well as for some pharmaceuticals. The most common chemiluminescent systems include the application of peroxyoxalate ester chemiluminescence, acridinium esters, luminol and derivatives, detection based on the tris(2,2'-bipyridine)ruthenium(III) system, the huge potentials offered by direct oxidations-though often with still unelucidated reaction mechanisms-and the powerful area of bioluminescence techniques, revealing as well the fast developing area of microchip-based analysis employing this specific luminescence principle.

Liquid/liquid optical waveguides using sheath flow as a new tool for liquid/liquid interfacial measurements

A liquid/liquid optical waveguide was constructed using a sheath flow. Since the refractive index of an organic solvent is generally higher than that of water (nD = 1.33), light introduced into the inner organic flow should proceed with total multi-reflection within the inner flow, so that the inner part of the sheath flow acts as the core of an optical waveguide. This sheath flow liquid/liquid optical waveguide was stable and showed no substantial background scattering. Moreover, it is applicable to both miscible and immiscible liquid/ liquid interfaces. Thus, it may become a new tool for studying liquid/liquid interfaces as well as for sensitive optical measurements.

Determination of carbohydrates as their 3-aminophthalhydrazide derivatives by capillary zone electrophoresis with on-line chemiluminescence detection

A method based on pre-capillary derivatization with luminol (3-aminophthalhydrazide) for carbohydrate analysis using capillary electrophoresis with on-line chemiluminescence (CL) detection was developed. The derivatives of seven monosaccharides were separated and detected by using 200 mM borate buffer containing 100 mM hydrogen peroxide at pH 10.0 as separation electrolyte and 25 mM hexacyanoferrate in 3 M sodium hydroxide solution as post-capillary chemiluminescence reagent with separation efficiencies ranging from 160,000 to 231,000 plates per metre. The minimum amount of carbohydrate derivatized was 2 pmol (corresponding to the concentration of 2 microM). The method also provided a linear response for glucose in the concentration range of 0.1-250 microM with a mass detection limit of 420 amol or a concentration detection limit of 0.1 microM. Preliminary work using the CE-CL format to determine glucose in a rat brain microdialysis sample is presented as a typical case.

Chemiluminescence detection in HPLC and CE for pharmaceutical and biomedical analysis

The present paper reviews the developments and applications of chemiluminescence detection with HPLC and CE in pharmaceutical and biomedical analysis. The chemiluminescence systems, chemiluminogenic reagents and derivatization reagents, improvements in instrumental design as well as their contributions to the practical applications, are all presented. The advantages and limitations of current detection methodology and future prospects for improvement are briefly discussed.

Ultrasensitive chemiluminescence detection in capillary electrophoresis

Capillary electrophoresis techniques offer high plate numbers and are highly suited for the efficient separations of a wide variety of chemical components in diverse matrices. Because of the small capillary and detection cell dimensions, together with the minute volumes of samples to be injected, sensitive detection schemes based on different physicochemical principles are being developed. One logical approach to increased sensitivity in capillary electrophoresis detection has been the development of chemiluminescence-based detectors. The development of on-line ultrasensitive chemiluminescence detection (referred to the concentration detection limit of nM order of magnitude or mass detection limit of amol order of magnitude) in capillary electrophoresis system is reviewed. The applications and limitations of the current detection methodology are briefly considered and future prospects for the development are discussed.

Luminol-type chemiluminescence derivatization reagents for liquid chromatography and capillary electrophoresis

The present paper provides the principles for chemiluminescence of luminol-type compounds and their wide and powerful application to the detection system in liquid chromatography and capillary electrophoresis as derivatization reagents. The reagents can be classified into two types, chemiluminescence labeling and chemiluminogenic reagents. The former reagents are highly chemiluminescent themselves and used for tagging their intense chemiluminophores to analytes, whereas the latter are weakly chemiluminescent but generate intense chemiluminescence by reaction with analytes. The liquid chromatographic methods utilizing chemiluminescence derivatizing reactions with luminol-type reagents allow the analytes to be detected at pmol-sub-fmol levels. Furthermore, the chemiluminogenic reactions show high selectivity owing to their selective reaction against the analytes permitting facile and reproducible detection.

Highly sensitive chemiluminescence detection of copper(II) in capillary electrophoresis with field-amplified sample injection

Field-amplified sample injection of copper(II) was investigated using capillary electrophoresis with chemiluminescence detection. The sensitivity of copper(II) has been improved markedly by the field-amplified sample injection technique and the detection limit reaches 2 x 10(-11) M. By injection of a short plug of water before sample introduction, the sensitivity can be further improved 5-fold and the detection limit reaches 4 x 10(-12) M. The relative standard deviations (n = 6) of the migration time and the peak height are 0.61% and 4.7% at 1.0 x 10(-9) M Cu(II), respectively. Parameters affecting the field-amplified sample injection, such as separation voltage and concentration of electrophoretic buffer, have been investigated.

Microchip capillary electrophoresis using on-line chemiluminescence detection

Chemiluminescence detection was used in capillary electrophoresis integrated on a microchip. Quartz microchips have two main channels and four reservoirs. Dansyl-lysine and -glycine were separated and detected with bis[(2-(3,6,9-trioxadecanyloxycarbony)-4-nitrophenyl]oxalate as peroxyoxalate chemiluminescent reagent. These dansyl amino acids came into contact with the chemiluminescence reagent to produce visible light at the interface between the separation channel and chemiluminescence reagent-containing reservoir. The detection limit (S/N = 3) for dansyl-lysine was 1 x 10(-5) M, which corresponded to the very small mass detection limit of ca. 0.4 fmol. However, the concentration sensitivity in the present system was approximately two orders of magnitude lower than that in the conventional capillary electrophoresis-chemiluminescence detection system. The relative standard deviations of migration time and peak height for dansyl-lysine were 4.2 and 4.5%, respectively. A channel conditioning before every run and an appropriate control of voltages were needed for the reproducible results. The present system had advantages in rapid separation time (within 40 s), small (several 10 pI) and accurate sample injection method using a cross-shaped injector, and simplification and miniaturization of the detection device.

Capillary electrophoresis separation and permanganate chemiluminescence on-line detection of some alkaloids with beta-cyclodextrin as an additive

Capillary electrophoresis has been used in combination with on-line permanganate chemiluminescence detection for the simultaneous determination of morphine, 6-monoacetylmorphine and heroin. It was found that beta-cyclodextrins could improve the separation efficiency and enhance the chemiluminescence signal. Improved sensitivity over capillary electrophoresis with UV detection was obtained. The procedure has detection limits of 23, 66 and 115 fmol for morphine, 6-monoacetylmorphine and heroin, respectively.

Capillary electrophoresis of monoamines and catechol with indirect chemiluminescence detection

A capillary electrophoresis (CE)/indirect chemiluminescence (CL) detection method is described for monoamines, viz., serotonin (5-HT), dopamine (DA), epinephrine (EP), and norepinephrine (NE) and for catechol (CA). Optimal separation and detection were obtained with an electrophoretic buffer of 10 mM sodium borate (pH 9.5) containing 5 mM luminol and 25 mM H2O2, and a catalyst solution of 30 microM CuSO4 in 30 mM borate buffer (pH 10.0). Complete separation of 5-HT, DA, EP, NE and CA was achieved in less than 5 min. The Cu(II)-catalyzed luminol CL reaction was employed to provide the high and constant background. Since monoamines and catechol can form stable complexes with Cu(II), inverted analyte peaks due to decreased catalytic activity of Cu(II) can be detected. The degree of CL suppression is proportional to the analyte concentrations. Linearity (r> or =20.99) over two orders of magnitude was generally obtained. The concentration limits of detection (CLODs) for the monoamines and catechol studied were between 0.5 and 3.1 uM. The relative standard deviation (RSD) values on peak size and migration time were in the ranges 3.2-4.4% and 0.4-0.5%, respectively. The applicability of the method for the analysis of pharmaceutical and biological samples was examined.

Chemiluminescence detection of heme proteins separated by capillary isoelectric focusing

Chemiluminescence detection was combined with capillary isoelectric focusing to perform protein analysis with high sensitivity. Luminol-H2O2 chemiluminescence was utilized, and heme proteins such as cytochrome c, myoglobin and peroxidase were analyzed. The proteins were focused by use of Pharmalyte 3-10 as ampholytes. Hydroxypropylmethyl-cellulose was added to the sample solution in order to easily reduce protein interactions with the capillary wall as well as the electroendoosmotic flow. The focused proteins were transported by salt mobilization to chemiluminescence detection cell equipped with an optical fiber. The present method showed significantly high sensitivity and wide dynamic range; the detection limit for cytochrome c was 6 x 10(-9) M and the linear dynamic range was greater than two-orders of magnitude (up to 2 x 10(-6) M).

Fluorescence detection of proteins and amino acids in capillary electrophoresis using a post-column sheath flow reactor

A simple laser-induced fluorescence detection method for proteins and amino acids in capillary electrophoresis is reported. A sheath flow cell is utilized as a post-column reactor for fluorescence derivatization of proteins and amino acids by addition of o-phthaldialdehyde-2-mercaptoethanol to the sheath fluid. With the use of a 50 microns I.D. capillary, the limits of detection for carbonic anhydrase are 0.73 nM or 1.8 amol which represents a five- and two-fold improvement, respectively, over the best results previously reported for post-column detection. In addition, separation efficiencies up to 8.07 x 10(5) are achieved and the detector response is linear over three-orders of magnitude. These results demonstrate that mixing is adequate and the reaction kinetics are rapid enough to provide sensitive detection with this approach. Also, because this post-column derivatization scheme requires no instrumental changes to a typical sheath flow cell detector, the system can be used for detection of pre-column labeled analytes and for native fluorescence detection.

Chemiluminescence detection in integrated post-separation reactors for microchip-based capillary electrophoresis and affinity electrophoresis

Chemiluminescence (CL) detection based on the horseradish peroxidase (HRP) catalyzed reaction of luminol with peroxide was investigated as a post-separation detection scheme for microchip-based capillary electrophoresis. An integrated injector, separator and post-separation reactor was fabricated on planar glass wafers. The fluorescein conjugate of HRP (HRP-F1) was used as a sample for optimization of the CL detector response. In devices etched 10 microm deep, with an aluminum mirror integrated onto the backside of the detection zone to enhance collection efficiency, the detection limit, estimated at 3 standard deviations (SD) above background noise, for 1 nL injected sample plugs was 35 nM in HRP-F1. In devices etched 40 microm deep, 8 nL plugs gave a detection limit of 7 nM. Separation and CL detection of the products of an immunological reaction of a F(ab')2 fragment of the HRP conjugate of goat anti-mouse immunoglobulin G (IgG) with mouse IgG was performed on-chip. A linear calibration curve was obtained for the decrease in peak height of the HRP conjugate (53 microg/mL) with increasing mouse IgG (0-60 microg/mL). When microperoxidase was used as an internal standard, the R2 value of a linear least-squares fit was 0.9867, and the relative errors in the slope and intercept were +/- 5.8 and +/- 1.3 %, respectively.

Chemiluminescence-based detection: principles and analytical applications in flowing streams and in immunoassays

The present paper provides the principles of chemiluminescence (CL) and its powerful applications in analytical chemistry, mainly in the area of flow injection analysis, column liquid chromatographic and capillary electrophoretic separating systems, and its potential in immunoassays. CL is light produced by a chemical reaction. The most common advantages of chemiluminescent reactions are the relatively simple instrumentation required, the very low detection limits and wide dynamic ranges, which have contributed to the interest of CL detection in flow injection analysis, high performance liquid chromatography, including miniaturized systems, and, most recently, the exploding area of capillary electrophoresis. The latter powerful microanalytical separation technique offers high numbers of theoretical plates and relatively short analysis times requiring only small sample volumes, the migrating system comprising aqueous buffer solutions. In non-isotopic immunoassays, covering a great variety of applications in human and veterinary medicine, forensic medicine, agriculture and food industry, the radioisotope is replaced by a fluorescence or chemiluminescent label. The use of CL as a detection principle permits quantitative determination of various compounds at low concentrations. Disadvantages of the CL-based technique may include lack of sufficient selectivity and sensitivity to various physicochemical factors.

Post-column derivatization for fluorescence and chemiluminescence detection in capillary electrophoresis

Instrumental developments and applications of post-column derivatization for fluorescence and chemiluminescence detection in capillary electrophoresis (CE) are reviewed. Various systems to merge the reagent solution with the separation medium have been developed, including coaxial capillary reactors, gap reactors and free solution or end-column systems. For all reactor types the geometry of the system, as well as the method to propel the reaction mixture (by pressure or by voltage) appeared to be critical to preserve the separation efficiency. Plate numbers of over 100,000 could be realised with different reactors. The strict requirements on the rate of post-column derivatization reactions to be applied in CE limit the number of different reagents that have been used. For fluorescence detection, with laser or lamps as the excitation source, so far mainly o-phthalaldehyde and its naphthalene analogue have been used as reagent. Derivatization systems that are based on complexation reactions also showed good promise for application in CE. Detection limits could be obtained that were comparable to those obtained after pre-column derivatization. Various reagents for chemiluminescence detection (e.g. the luminol and peroxyoxalate systems) have been studied. The often complicated chemistry involved made application of these reagents in CE even more difficult. Results obtained so far, in terms of sensitivity, have not been up to expectation, with detection limits usually in the order of micromol l(-1).

Derivatization in capillary electrophoresis

In recent years capillary electrophoresis (CE) has been developed into a versatile separation technique, next to gas and liquid chromatography (LC), well suited for the determination of a wide variety of e.g., pharmaceutical, biomedical and environmental samples. The main advantages of CE over chromatographic separation techniques are its simplicity and efficiency. It is well recognized, however, that the sensitivity and selectivity of the detection are relatively weak points of CE. One way to overcome these limitations is the conversion (derivatization) of the analytes into product(s) with more favourable detection characteristics. Although, in principle, almost any detection mode can be combined with a derivatization procedure, in practice, fluorescence monitoring is favoured in most cases. This paper aims to give a short overview on the various reagents that can be used for pre-, post- and on-column derivatization in CE. First, a short introduction is given on CE as an analytical technique, followed by a discussion of the pros and cons of the various modes of derivatization, a comparison of derivatizations in CE with derivatizations in LC, the principles of fluorescence and prerequisites for a good fluorophore and the potential of using diode lasers in combination with a labelling procedure. With respect to the derivatization reagents the emphasis is on the labelling of amino, aldehyde, keto, carboxyl, hydroxyl and sulfhydryl groups.

Pre-, on- and post-column derivatization in capillary electrophoresis

This survey gives a short overview of the various reagents and procedures that can be used for pre-, post- and on-column derivatization in capillary electrophoresis. First there is an introduction about capillary electrophoresis as an analytical technique; this is followed by a discussion of the pros and cons of the various modes of derivatization and a comparison with liquid chromatography. In the following paragraphs the reagents for a number of functional groups are discussed. The emphasis is on derivatization of the amino group. Most of the information on the reagents and derivatization procedures is listed in tables together with information on the detection mode, analytes, sensitivity and samples. In addition to the amino group, information is given on labeling of aldehyde, keto, carboxyl, hydroxyl and sulfhydryl groups.

Developments in amino acid analysis using capillary electrophoresis

The current status in the analysis of amino acids using capillary electrophoresis is addressed. This area of biological analysis has received increased attention with more than 200 articles being published in the last five years. This review discusses pre-, post-, and on-column derivatization techniques used to tag amino acids providing a detectable moiety. Several separation methodologies which provided resolution for large sets of amino acids are presented. An overview of advances in the enantiomeric resolution methodologies for amino acids is given. Both direct and indirect enantiomeric separation schemes are summarized. Recent advances in detection strategies for both derivatized and underivatized amino acids are presented. Applications utilizing amino acid analysis by capillary electrophoresis are described. This review covers articles published between 1991 and 1996.

Chemiluminescence detection in capillary electrophoresis

Capillary electrophoresis (CE) and related techniques yield highly efficient separations while requiring only minute amounts of sample. Thus, these techniques are amenable to analyses of complex samples in diverse matrices and in situations where sample is extremely limited. The constraints of on-column detection generally result in poor detection limits and have reduced the overall application of CE. One logical approach to increased sensitivity in CE detection has been the development of chemiluminescence (CL)-based detectors. The current state of post-column detector development, CL applications, and limitations of the technique are reported herein.