Optimization of capillary electrophoretic-electrospray ionization-mass spectrometric analysis of catecholamines

The capillary electrophoretic-mass spectrometric analysis (CE-MS) of catecholamines was optimized with coaxial sheath flow interface and electrospray ionization (ESI). The parameters studied included the sheath liquid composition and its flow rate, separation conditions in ammonium acetate buffer together with the ESI and cone voltages as mass spectrometric parameters. In addition, the effect of ESI voltage on injection as well as the siphoning effect were considered. The optimized conditions were a sheath liquid composition of methanol-water (80:20 v/v) with 0.5% acetic acid, with a flow rate of 6 microL/min. The capillary electrophoretic separation parameters were optimized with 50 mM ammonium acetate buffer, pH 4.0, to +25 kV separation voltage together with a pressure of 0.1 psi. The most intensive signals were obtained with an ESI voltage of +4.0 kV and a cone voltage of +20 V. The nonactive ESI voltage during injection as well as avoidance of the siphoning effect increased the sensitivity of the MS detection considerably. The use of ammonium hydroxide as the CE capillary conditioning solution instead of sodium hydroxide did not affect the CE-MS performance, but allowed the conditioning of the capillary between analyses to be performed in the MS without contaminating the ion source.     

Separation of antidepressants by capillary electrophoresis with in-line solid-phase extraction using a novel monolithic adsorbent

The separation of three selective serotonin reuptake inhibitors (SSRIs) by capillary electrophoresis (CE) with fully integrated solid-phase extraction (SPE) is described. Polymeric monolithic SPE modules were prepared in situ within a fused silica capillary from either butyl methacrylate-co-ethylene dimethacrylate or 3-sulfopropyl methacrylate-co-butyl methacrylate-co-ethylene dimethacrylate. Using a 1 cm SPE module placed at the inlet of the capillary, a mixture of sertraline, fluoxetine and fluvoxamine was extracted from aqueous solution by applying a simple pressure rinse. Under pressure-driven conditions, efficient elution was possible from both SPE materials investigated using 50 mM phosphate buffer, pH 3.5 in acetonitrile (20/80, v/v). Two different strategies were investigated for the efficient elution and subsequent CE separation. Injection of an aqueous sample plug directly into the non-aqueous elution/separation buffer was found to be unsuitable with poor elution profiles observed in the electrodriven mode. Alternatively, a sample plug equivalent to several capillary volumes could be injected by pressure followed by filling the capillary with the non-aqueous elution/separation buffer from the outlet end using a combination of pressure and electrodriven flow. Using a neutral monolith, efficient elution/separation was not possible due to an unstable electroosmotic flow (EOF), however, by adding the ionisable monomer, 3-sulfopropyl methacrylate to the SPE module to increase and stabilise the EOF, it was possible to achieve efficient elution from the SPE module, followed by baseline separation by CE using a 200 mM acetate buffer, pH 3.5 in acetonitrile (10/90, v/v). With enrichment factors of over 500 achieved for each of the analytes this demonstrates the potential of in-line SPE-CE for the sensitive analysis of these drugs.     

Capillary electrophoresis/mass spectrometry: a promising tool for the control of some physiologically hazardous compounds. I-derivatives of 3-quinuclidinol

A method based on the coupling of capillary electrophoresis with mass spectrometry (CE/MS) was developed for the monitoring of 3-quinuclidinol and its four N-alkyl derivatives (methyl, ethyl, propyl and isopropyl derivatives). A fragmentation study (collision-induced dissociation of ions in an ion trap) and optimization of the ion optics set-up for CE/MS experiments using direct infusion of a methanolic solution of the standards into the mass spectrometer were carried out in advance. Molecular ions of all quaternary compounds and the quasi-molecular ion [M + H]+ of free 3-quinuclidinol prevail in the mass spectra. In the MS/MS of propyl and isopropyl derivatives, the elimination of the alkyl chain dominates, leading to the ion at m/z 128. The fragmentation of the other compounds is more complex. Previous CE separation of the mixture of isobaric propyl and isopropyl derivatives is necessary for their unambiguous identification. A 10 mM ammonium acetate buffer (pH 4.0) is the optimum running electrolyte, allowing the CE separation of methyl, ethyl, propyl and isopropyl derivatives. A 0.5% (v/v) solution of acetic acid in methanol provides sufficient detection sensitivity when used as the sheath liquid. Limits of detection of 0.1 ppm for 3-quinuclidinol and 0.05 ppm for quaternary derivatives were achieved under the optimum conditions. The optimized method was applied to the determination of 3-quinuclidinol and related quaternary derivatives spiked into a sample of pond water. The experimental set-up for CE/MS/MS was investigated, which strongly increases the identification capability of the technique.     

Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80 : 20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL. Received: 4 May 1999 / Revised: 9 June 1999 / Accepted: 12 June 1999     

Advantages of using a modified orthogonal sampling configuration originally designed for LC-ESI-MS to couple CE and MS for the determination of antioxidant phenolic compounds found in virgin olive oil

A ThermoFinnigan sheath liquid flow capillary electrophoresis-mass spectrometry system designed for coupling via a co-axial interface was coupled through an adapted via an alternative, commercially available interface for orthogonal sampling. The affordable, reversible structural alterations made in the commercial LC-MS interface resulted in improved analytical performance.The results of a conventional capillary electrophoresis (CE) method using a commercial co-axial source to determine antioxidant phenolic acids present in virgin olive oil, were compared with those obtained by using a modified orthogonal sampling position. In both cases, separations were done using a 10 mM ammonium acetate/ammonium hydroxide buffer solution at pH 10.0 and a constant applied voltage of 25 kV. The operating variables for the mass spectrometry interface were re-optimized for the modified orthogonal orientation. This allowed the sheath liquid, sheath gas flow rates and capillary voltage to be lowered with respect to the co-axial coupling configuration. In addition, the orthogonal sampling position provided a higher selectivity by effect of ion sampling excluding larger droplets—with an increased momentum along the axis—which were drained through the sink at the bottom of the ion source. Also, the new configuration facilitated sample ionization, improved electrospray stability and led to stronger signals as a result.The new system was validated in terms of precision (repeatability), linearity, and limits of detection and quantification. A comparison of the validation data with the results previously obtained by using a commercial co-axial configuration revealed the adapted orthogonal sampling position to provide better repeatability in both migration times and relative peak areas (<1% and 7% respectively with n = 15 replicates), a good linear range (with levels in the microgram-per-litre region) and lower limits of detection—especially for the compounds detected with the lowest sensitivity when co-axial ESI was used, as HFA, GEN, FER and VAN finding LOD among 24-3.0 μg L⁻¹ respectively.     

Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80?:?20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL.     

Determination of cytokinins in coconut (Cocos nucifera L.) water using capillary zone electrophoresis-tandem mass spectrometry

The applicability of CZE in combination with MS and MS/MS methods for the simultaneous separation and determination of 12 cytokinins was investigated for the first time. Cytokinins were first completely separated by CZE within less than 20 min using a volatile buffer and then detected directly by MS or MS/MS. Satisfactory separation of the 12 cytokinin standards was achieved using a 25 mM ammonium formate/formic acid buffer (pH 3.4) and 3% ACN v/v with a separation voltage of 25 kV. On the basis of the resolution of the neighboring peaks, the various parameters for CZE-MS optimization, such as buffer pH value, concentration of buffer and organic modifier, applied voltage and sheath liquid, were evaluated systematically. MS/MS with multiple reaction monitoring detection was carried out to obtain sufficient selectivity and sensitivity. The combination of on-line sample stacking and CZE-MS/MS achieved a detection limit in the range of 0.05-0.18 microM for the 12 cytokinins at an S/N of 3. The optimized CZE-MS/MS method was simple, rapid, low cost, robust and highly selective. Furthermore, the developed method was successfully applied to screen for endogenous cytokinins in purified coconut water extract sample. Nine cytokinins were detected and quantified in coconut water after SPE.     

In-line coupling of two-phase single drop microextraction and large volume stacking using an electroosmotic flow pump in nonaqueous capillary electrophoresis

In order to improve the concentration sensitivity of capillary electrophoresis (CE), two sample preconcentration techniques, single drop microextraction (SDME) and large volume stacking using an electroosmotic flow pump (LVSEP), were coupled in-line in a commercial CE instrument. By simple programming of liquid handling sequences, a pentanol drop was prepared at the tip of a fused silica capillary over which a Teflon tube had been sleeved to serve as a hydrophobic support. After extraction of the analytes from an aqueous donor solution into the drop, the entire capillary column was filled with enriched pentanol extract. LVSEP, in which the sample matrix is automatically removed by the EOF, was then carried out using a methanolic run buffer. The overall enrichment factors for the analytes pentachlorophenol (PCP), 3-bromobenzoic acid (3-BBA), and 4-iodobenzoic acid (4-IBA), from a combination of 30 min SDME and LVSEP on a 27 cm capillary, were about 7000, even without agitation of the donor solution. The resulting limits of detection for PCP, 3-BBA, and 4-IBA were 0.7, 0.3 and 0.7 nM, respectively. Since no modification of the existing CE instrument is necessary and a bare capillary is used for LVSEP, this scheme can be adapted quite easily for many CE applications that require high concentration sensitivity.     

Sensitivity enhancement in capillary electrophoresis-mass spectrometry of anionic metabolites using a triethylamine-containing background electrolyte and sheath liquid

Analyte responses in CE‐ESI‐MS using negative ionization are frequently relatively low, thereby limiting sensitivity in metabolomics applications. In order to enhance the ionization efficiency of anionic metabolites, BGEs and sheath liquids (SLs) of various compositions were evaluated. Pressure‐induced infusion and CE‐MS experiments showed that addition of triethylamine (TEA) to the BGE and SL enhanced analyte intensities. A BGE consisting of 25 mM TEA (pH 11.7) and an SL of water–methanol (1:1, v/v) containing 5 mM TEA was selected, providing separation and detection of ten representative test metabolites with good reproducibility (migration time RSDs<1%) and linearity (R²>0.99). This BGE yielded lower limits of detection (0.7–9.1 μM) for most test compounds when compared with common CE‐MS methods using a BGE and SL containing ammonium acetate (NH₄Ac) (25 and 5 mM, respectively). CE‐MS of human urine revealed an average amount of 231 molecular features in negative ionization mode when TEA was used in the BGE and SL, whereas 115 and 102 molecular features were found with an NH₄Ac‐containing BGE and SL, employing a bare fused‐silica (BFS) and Polybrene‐dextran sulfate‐Polybrene (PB‐DS‐PB)‐coated capillary, respectively. With the CE‐MS method using TEA, about 170 molecular features were observed that were not detected with the NH₄Ac‐based CE‐MS methods. For more than 82% of the molecular features that were detected with the TEA as well as the NH₄Ac‐containg BGEs (i.e. common features), the peak intensities were higher using TEA with gain factors up to 7. Overall, the results demonstrate that BGEs and SLs containing TEA are quite favorable for the analysis of anionic metabolites in CE‐MS.     

Electroosmotic flow variations caused by the volatility of buffer components: diagnosis and therapy

In order to separate a polar amine pharmaceutical and its potential impurities, a micellar electrokinetic chromatography method was developed. The main compound and 11 other substances were completely separated using a 20 mM Tris buffer, pH 8.0, containing 50 mM sodium dodecylsulfate (SDS) and 24% (v/v) acetonitrile. However, a strong, continuous reduction in the EOF occurred and quantification was not possible. The EOF reproducibility could not be improved by suitable rinsing procedures. Surface effects or interactions did not cause the EOF changes, but the evaporation of acetonitrile was identified as the major source for EOF instability. However, a high concentration of acetonitrile was decisive for selectivity. Thus a reliable protection against the evaporation of this buffer constituent had to be found. Paraffin and various silicon oils were tested as covering film. In order to quickly test buffer systems if the evaporation of electrophoresis solutions is acceptable, an alternative experimental design without doing CE experiments had to be found. Electrical conductivity was chosen as parameter, because it can be determined simply and fast. The buffers under investigation were placed in a 50-ml beaker with a magnetic stirring rod, placed on a magnetic stirrer. The buffer solution was kept in motion at 120 rev./min. The beaker was covered around the measuring head with laboratory film and in addition to this with paraffin or silicon oil. An acetonitrile content up to 10% (v/v) was acceptable if a coverage was used. The various cover liquids had a similar effect. A content of 15% (v/v) already increased the evaporation effect significantly. Higher acetonitrile contents are not acceptable. A buffer similar to the originally transferred method, 20 mM Tris (pH 8.0), 50 mM SDS containing 10% (v/v) acetonitrile as well as 10% (v/v) isopropanol showed an acceptably low evaporation in the conductivity experiments. With this buffer, a stable EOF was also obtained. Conductivity measurements are generally applicable to quickly test buffers that contain organic solvents.     

Analyses of alkaloids in different products by NACE-MS

A simple method for the separation and characterization of five nicotine-related alkaloids by NACE employing UV and MS detections is described here for the first time. Several factors, including NACE parameters (compositions of running solution) and MS parameters (such as nature and flow rate of sheath liquid, pressure of nebulization gas, and flow rate of dry gas), were optimized in order to obtain both an adequate CE separation and high MS signals for the alkaloid compounds used in this study. A reliable CE separation of five alkaloids was achieved in 50 mM ammonium formate that was dissolved in an ACN/methanol mixture (50:50, v/v) of pH* 4.0 (apparent pH 4.0). The optimal electrospray MS measurement was carried out in the positive ionization mode using a coaxial sheath liquid composed of isopropyl alcohol and water in the ratio of 80:20 v/v at a flow rate of 180 microL/h. In addition, the proposed NACE method was also applied in the analyses of alkaloids in several products including chewing gums, beverages, and tobaccos. This NACE-MS method was found to provide a better detection ability and separation resolution for the analysis of nicotine alkaloids when compared to other aqueous CE-MS reports.     

CE‐MS method development for peptides analysis,especially hepcidin,an iron metabolism marker

A method for the resolution of a peptides mixture including hepcidin‐25, an iron metabolism marker, was developed by CE‐ESI‐MS. Several strategies were tested to optimize peptide separation, such as the addition of cyclodextrins or organic solvents in the BGE or the use of coated capillaries. Best results in terms of resolution, symmetry and efficiency were obtained with a BGE made of 500 mM ammonium acetate pH 4.5/ACN 70:30 v/v. Using the methodology of experimental design, BGE concentration, sheath liquid composition and MS‐coupling parameters were then optimized in order to obtain the best signal intensity for hepcidin. Finally, a 225 mM BGE and a sheath liquid composed of isopropanol/water 80:20 v/v containing 0.5% v/v formic acid were selected as it constitutes the best compromise for selectivity, peak shape and sensitivity.     

Ionic liquids as additives for separation of benzoic acid and chlorophenoxy acid herbicides by capillary electrophoresis

Ionic liquids (ILs) were tested as additives to phosphate-acetate buffer for the separation of chlorophenoxy and benzoic herbicide acids. The effects of buffer concentration, buffer pH, IL concentration, and concentration of organic solvent were investigated. It was found that in the presence of 40 mM phosphate-acetate containing 10% acetonitrile at pH 4.5, addition of 10 mM 1-butyl-3-methylimidazoium could reverse EOF. The shoulder-merged peaks of two herbicide acids, 2,4-dichlorobenzoic acid and 3,5-dichlorobenzoic acid, were successfully resolved by the addition of IL cation. Apart from these, results showed different IL cations had different influences on the migration behavior of some of the analytes, while IL anions did not lead to obvious difference on the separation.     

Hydrogels based on carboxymethyl cassava starch cross-linked with di- or polyfunctional carboxylic acids: Synthesis, water absorbent behavior and rheological characterizations

Carboxymethyl cassava starch (CMS) was synthesized and its hydrogels were prepared by cross-linking it with di- or polyfunctional carboxylic acids using glutaric (CASXGLU), suberic (CASXSUB), pimelic (CASXPIM) and butanetetracarboxylic acids (CASBTC) as the cross-linkers. The characterization of the CMS showed that its degree of substitution was 0.86, average molar mass (M_w) was 5.6 × 10⁶ g mol⁻¹ and the ¹³C NMR showed strong peak at δ = 180.42 ppm which was assigned to the CO carbon in the carboxymethyl group. The absorption under load (AUL) and free swelling capacity (FSC) studies showed that the hydrogels have fast swelling properties and that they reached equilibrium after 1 h. Furthermore, all the hydrogels were sensitive to the increasing salt concentrations and pH of the medium. Both AUL and FSC reduced in saline solution while their values increased in alkaline buffer solutions. The result indicate that the difunctional carboxylic acids produced hydrogels with stronger material functions compared with the polyfunctional carboxylic acid and the order of increases in both AUL and FSC was CASXBTC, CASXPIM, CASXSUB and CASXGLU.     

A new capillary electrophoresis buffer for determining organic and inorganic anions in electroplating bath with surfactant additives

Monitoring of trace impurities in electroplating bath is needed to meet EU requirements for WEEE and RoHS and for quality control of electrodeposits. Methods using IC and 100% aqueous CE buffer were found producing non-repeatable results attributed to interference of surfactants and major methanesulphonate anion. A new CE buffer containing 1.5 mM tetraethylenepentaamine, 3 mM 1,3,5-benzenetricarboxylic acid and 15 mM Tris in 20% (v/v) methanol at pH = 8.4 was shown to enhance the separation window, reduce interaction between buffer and bath constituents, and give satisfactory repeatability with baseline separation for 14 organic and inorganic anions within 14 min, good repeatability for migration time (0.32–0.57% RSD), satisfactory peak area and peak height (2.9–4.5 and 3–4.7% respectively), low detection limit (S/N = 2, 20–150 ppb), and wide working ranges (0.1–100 ppm). The CE buffer with 20% (v/v) methanol has demonstrated its capability for identifying anion impurities causing problem in aged tin bath and the use of only 10-fold dilution to produce reliable results for quality assessment in plating bath containing high surfactant additives.     

A highly sensitive isotope-coded derivatization method and its application for the mass spectrometric analysis of analytes containing the carboxyl group

A novel isotope labeling reagent d₀-/d₆-2, 4-dimethoxy-6-piperazin-1-yl pyrimidine (DMPP) has been developed for derivatization toward the carboxyl group based on carbodiimide chemistry for mass spectrometry (MS) analysis. The strengths of this derivatization strategy involve fast labeling (15 s), low chemical background and general access to most carboxylic analytes. This has been demonstrated using a series of compounds containing carboxylic acids, including peptides and proteins. To enhance the MS response of the derivatized analytes, the design of DMPP has been based on integration of the theoretical consideration of high gas-phase hydrogenation capacity and hydrophobicity. In addition, the high abundance product ions at m/z 225 and m/z 231 from d₀-/d₆-DMPP labeled carboxylic acids indicate high efficiency of the gas-phase cleavage induced by the labeling reagent. Quantitative determination of these ions can also be used in single reaction monitoring to achieve extremely high sensitivity toward the target analytes. This has subsequently been used to determine trace free fatty acids in human urine. Furthermore, the DMPP labeled peptides also provide additional sequence information in MALDI–MS/MS because of the formation of sequence-related isotope fragment ions. This DMPP-oriented labeling technique is expected to be a promising tool for the MS detection of many varieties of compounds containing carboxyl groups.     

Analysis of polar hydrophilic aromatic sulfonates in waste water treatment plants by CE/MS and LC/MS

The present work describes the development and optimization of a capillary (zone) electrophoresis/mass spectrometric (CE/MS) analysis method for polar hydrophilic aromatic sulfonates (ASs). The compounds were detected by negative ion electrospray ionization (NIESI) and selected ion monitoring (SIM). In comparison with CE/UV, for CE/MS a lower-concentration volatile ammonium acetate buffer (5 mM) without organic modifier and a higher separation voltage were better suited for separation. Sensitivity of CE/MS was slightly better than for CF/UV, with the limit of detection (LOD) ranging between 0.1 and 0.4 mg l(-1). For verification of the CE/MS results, ASs were also analysed by ion-pair liquid chromatography/diode array UV detection coupled in series with electrospray mass spectrometry (IPC/DAD/ESI-MS). Real water samples of different waste water treatment plants (WWTPs) in Catalonia (NE Spain) were extracted by solid-phase extraction (SPE) with LiChrolut EN and analysed with CE/MS and LC/MS. ASs were found in influent and effluent water samples of the WWTPs in the microg l(-1) concentration range. LC/MS offered a higher separation efficiency and sensitivity than CE/MS. Therefore with LC/MS more compounds could be identified in the WWTPs. The persistency of the ASs was distinct: some compounds were well degraded during the water treatment process, while others were quite persistent.     

Analysis of amino acids and biogenic amines in breast cancer cells by capillary electrophoresis using polymer solutions containing sodium dodecyl sulfate

We describe simultaneous analysis of naphthalene-2,3-dicarboxaldehyde (NDA)-amino acid and NDA-biogenic amine derivatives by CE in conjunction with light-emitting diode-induced fluorescence detection using poly(ethylene oxide) (PEO) solutions containing sodium dodecyl sulfate (SDS). After sample injection, via EOF 0.1% PEO prepared in 100 mM TB solution (pH 9.0) containing 30 mM SDS entered a capillary filled with 0.5 M TB solution (pH 10.2) containing 40 mM SDS. Under this condition, 14 NDA-amino acid and NDA-amine derivatives were separated within 16 min, with high efficiency ((1.0–3.2) × 10⁵ theoretical plates) and sensitivity (LODs at S/N = 3 ranging from 2.06 to 19.17 nM). In the presence of SDS and PEO, analytes adsorption on the capillary wall was suppressed, leading to high efficiency and reproducibility. The intraday analysis RSD values (n = 3) of the mobilities for the analytes are less than 0.52%. We have validated the practicality of this approach by quantitative determination of 9 amino acids in breast cancer cells (MCF-7) and 10 amino acids in normal epithelial cells (H184B5F5/M10). The concentrations of Tau and Gln in the MCF-7 cells were different than those in the H184B5F5/M10 cells, respectively. Our results show the potential of this approach for cancer study.     

Capillary electrophoresis-mass spectrometry for impurity profiling of basic pharmaceuticals using non-volatile background electrolytes

A generic approach has been developed for coupling capillary electrophoresis (CE) using non-volatile background electrolytes (BGEs) with mass spectrometry (MS) using a sheath liquid interface. CE-MS has been applied for basic and bi-functional compounds using a BGE consisting of 100 mM of TRIS adjusted to pH 2.5 using phosphoric acid. A liquid sheath effect is observed which may influence the CZE separation and hence may complicate the correlation between CE-UV and CE-MS methods. The influence of the liquid sheath effect on the migration behavior of basic pharmaceuticals has been studied by simulation experiments, in which the BGE outlet vial is replaced by sheath liquid in a CE-UV experiment. As a consequence of the liquid sheath effect, phosphate based BGEs can be used without significant loss of MS sensitivity compared to volatile BGEs. The use of buffer constituents such as TRIS can lead to lower detection limits as loss of MS sensitivity can be compensated by better CE performance. TRIS based BGEs permit relatively high injection amounts of about 100 pmol while maintaining high resolution. The ESI-MS parameters were optimized for a generic method with maximum sensitivity and stable operation, in which the composition of the sheath liquid and the position of the capillary were found to be important. Furthermore, the nebulizing pressure strongly influenced the separation efficiency. The system showed stable performance for several days and a reproducibility of about 15% RSD in peak area has been obtained. Nearly all test compounds used in this study could be analyzed with an MS detection limit of 0.05% measured in scan mode using extracted ion chromatograms. As a result, CE-MS was found to be a valuable analytical tool for pharmaceutical impurity profiling.     

Separation and identification of isomeric acidic degradation products of organophosphorus chemical warfare agents by capillary electrophoresis-ion trap mass spectrometry

Capillary electrophoresis (CE) coupled to ion trap mass spectrometry (MS) was evaluated for the separation and identification of chemical warfare agent degradation products (alkylphosphonic acids and alkyl alkylphosphonic acids). Different analytical parameters were optimized in negative ionization mode such as electrolyte composition (15 mM CH(3)COONH(4), pH 8.8), sheath liquid composition (MeOH/H(2)O/NH(3), 75:25:2, v/v/v), nebulization and ion trapping conditions. A standard mixture of five alkylphosphonic (di)acids and five alkyl alkylphosphonic (mono)acids containing isomeric compounds was used in order to evaluate CE selectivity and MS identification capability. The obtained electropherograms revealed that CE selectivity was very limited in the case of alkyl alkylphosphonic acid positional isomers, whereas isomeric isopropylphosphonic and propylphosphonic acids were baseline-separated. CE-MS-MS experiments provided an unambiguous identification of each isomeric co-migrating alkyl alkylphosphonic acids thanks to the presence of specific fragment ions. On the other hand, CE separation was mandatory for the identification of isomeric alkylphosphonic acids, which led to the same fragment ion and could not be differentiated by MS-MS. The developed method was applied to the analysis of soil extracts spiked with the analytes (before or after extraction treatment) and appeared to be very promising since resolution and sensitivity were similar to those observed in deionized water. Especially, analytes were detected and identified in soil extract spiked at 5 microg mL(-1) with each compound before extraction treatment.