CE Separation Research Articles

Derivatisation for separation and detection in capillary electrophoresis (2012–2015)

Derivatisation is a well-established and mature form of sample preparation for CE. The modification of the analyte can cause superior analysis characteristics such as better sensitivity and selectivity, however, derivatisation of the analyte introduces an additional step into the analytical workflow. This review covers articles from January 2012 to January 2015 on derivatisation in CE. The main sections are on the derivatisation modes (i.e. pre-capillary, in-line, in-capillary and post-capillary), separation and detection modes (i.e. LIF and others). LIF is discussed in more detail since this detection mode was most prevalent. A table of the common labelling agents and wavelengths for excitation and emission and the common derivatisation reactions are included. In addition, a comprehensive table which summarises all research articles is provided. This review is suitable for analytical chemists as a guide for 'how to get started' with derivatisation for separation and detection in CE.

Capillary electrophoretic study of green fluorescent hollow carbon nanoparticles.

CE coupled with laser-induced fluorescence and UV absorption detections has been applied to study the complexity of as-synthesized green fluorescent hollow carbon nanoparticles (HC-NP) samples. The effects of pH, type, and concentration of the run buffer and SDS on the separation of HC-NP are studied in detail. It is observed that phosphate run buffer is more effective in separating the HC-NP and the optimal run buffer is found to be 30 mM phosphate and 10 mM SDS at pH 9.0. The CE separation of this HC-NP is based on the difference in size and electrophoretic mobility of HC-NP. Some selected HC-NP fractions are collected and further characterized by UV-visible absorption and photoluminescence (PL) spectroscopy, MS, and transmission electron microscopy. The fractionated HC-NP show profound differences in absorption, emission characteristics, and PL quantum yield that would have been otherwise misled by studying the complex mixture alone. It is anticipated that our CE methodology will open a new initiative on extensive studies of individual HC-NP species in the biomedical, catalysis, electronic, and optical device, energy storage, material, and sensing field.

Field‐amplified sample injection in capillary electrophoresis with amperometric detection for the ultratrace analysis of diastereomeric ephedrine alkaloids

A coupling method of field-amplified sample injection (FASI) CE with amperometric detection is developed for ultratrace analysis of ephedrine alkaloids stereoisomers. FASI was introduced by injecting electrokinetically the sample solution for 10 s into the capillary filled with highly conductive background electrolyte (BGE). The diastereomeric selectivity and the detection sensitivity were improved by using borate buffer of high ionic strength as BGE. Parameters affecting FASI and CE separation were investigated to achieve the optimal conditions. Four analytes were separated within 15 min using 200 mmol/L borate buffer (pH 9.5) and separation voltage of +18 kV, with detection potential at +1.0 V (vs. Ag/AgCl) and carbon disc electrode as working electrode. Excellent linearity was observed between peak current and concentration of analytes in the range of 0.1-100 ng/mL. The LODs (S/N = 3) for (-)-ephedrine, (+)-pseudoephedrine, (-)-N-methylephedrine and (+)-N-methylpseudoephedrine were 39.3, 54.9, 30.8, and 44.1 pg/mL, respectively. The proposed method was successfully applied to the determination of alkaloids in Ephedra sinica, with results agreed well with HPLC method. Mean recoveries of 102.1-109.7% and RSDs less than 6% were found. And the merits of high sensitivity and selectivity, as well as a simple and stable operation, have been demonstrated.

Weak hybridization and isolated localized magnetic moments in the compounds CeT2Cd20 (T = Ni, Pd)

We report the physical properties of single crystals of the compounds CeT2Cd20 (T = Ni, Pd) that were grown in a molten Cd flux. Large separations of ∼6.7–6.8 Å between Ce ions favor the localized magnetic moments that are observed in measurements of the magnetization. The strength of the Ruderman–Kittel–Kasuya–Yosida magnetic exchange interaction between the localized moments is severely limited by the large Ce–Ce separations and by weak hybridization between localized Ce 4 f and itinerant electron states. Measurements of electrical resistivity performed down to 0.138 K were unable to observe evidence for the emergence of magnetic order; however, magnetically-ordered ground states with very low transition temperatures are still expected in these compounds despite the isolated nature of the localized magnetic moments. Such a fragile magnetic order could be highly susceptible to tuning via applied pressure, but evidence for the emergence of magnetic order has not been observed so far in our measurements up to 2.5 GPa.

Microchip electrophoretic separation and fluorescence detection of chelerythrine and sanguinarine in medicinal plants

A new method has been developed for separation of chelerythrine and sanguinarine in medicinal plants used in traditional Chinese medicine (TCM). The separation is achieved by microchip electrophoresis (CE) using laser-induced fluorescence detection. The CE separation is achieved by using a hydro-organic medium as the electrolyte buffer. The experimental results are consistent with the prediction by theory in terms of resolution and migration speed because of the low Joule heat generated in microchip CE. In addition, formamide was found to have a potential for separation of molecules with similar chemical structures. Based on these findings, a run buffer containing 50% formamide was used to separate chelerythrine (CHE) and sanguinarine (SAN). The influencing factors, such as solvent of run buffer, pH of buffer, separation distance, and separation voltage, were optimized. Baseline separation of chelerythrine and sanguinarine was achieved within 120s under an electrical voltage of 1.8kV. Good linearity was observed in the concentration range of 0.15–550μgmL−1 (r=0.9993) for CHE and in the range of 0.3–600μgmL−1 (r=0.9998) for SAN. A low limit of detection (LOD) was achieved because of the high sensitivity achieved by laser-induced fluorescence detection (i.e. 5.0ngmL−1 and 2.0ngmL−1 for CHE and SAN, respectively). The contents of CHE are found to be 641.8±7.5 and 134.0±2.3mg/kg in extracts of Macleaya cordata and Chelidonium majus, respectively, with good recovery of above 99%. The corresponding values for SAN found in these Chinese herbal extracts are 681.8±7.9mg/kg and 890.5±8.9mg/kg, respectively.

Rapid determination of branched chain amino acids in human blood plasma by pressure-assisted capillary electrophoresis with contactless conductivity detection.

A CE method with contactless conductivity detection has been developed for the clinical determination of the branched chain amino acids (BCAAs) valine, isoleucine and leucine in human blood plasma. The CE separation was performed in an optimised BGE with composition of 3.2 M acetic acid in 20% v/v methanol, pH 2.0. The achieved separation time was 125 s when using a capillary with an effective length of 14.7 cm, electric field intensity of 0.96 kV/cm and simultaneous application of a hydrodynamic pressure of 50 mbar. The separation efficiency in blood plasma equalled 461 000 theoretical plates/m for valine and isoleucine, and 455 000 theoretical plates/m for leucine; the detection limits are equal to 0.4 μM for all three amino acids. The RSD values for repeatability of the migration time equalled 0.1% for measurements during a single day and 0.3% for measurements on different days; the RSD values for repeatability of the peak areas equalled 2.3-2.6% for measurements during a single day and 2.7-4.6% for measurements on different days. It followed from the performed tests that the plasmatic levels of BCAAs attain a maximum 60 min after intravenous application of an infusion of BCAAs.

Dereplication of known nucleobase and nucleoside compounds in natural product extracts by capillary electrophoresis-high resolution mass spectrometry.

Nucleobase and nucleoside compounds exist widely in various organisms. An often occurring problem in the discovery of new bioactive compounds from natural products is reisolation of known nucleobase and nucleoside compounds. To resolve this problem, a capillary electrophoresis-high resolution mass spectrometry (CE-HR-MS) method providing both rapid separation and accurate mass full-scan MS data was developed for the first time to screen and dereplicate known nucleobase and nucleoside compounds in crude extracts of natural products. Instrumental parameters were optimized to obtain optimum conditions for CE separation and electrospray ionization-time-of-flight mass spectrometry (ESI-TOF/MS) detection. The proposed method was verified to be precise, reproducible, and sensitive. Using this method, known nucleobase and nucleoside compounds in different marine medicinal organisms including Syngnathus acus Linnaeus; Hippocampus japonicus Kaup and Anthopleura lanthogrammica Berkly were successfully observed and identified. This work demonstrates that CE-HR-MS combined with an accurate mass database may be used as a powerful tool for dereplicating known nucleobase and nucleoside compounds in different types of natural products. Rapid dereplication of known nucleobase and nucleoside compounds allows researchers to focus on other leads with greater potential to yield new substances.

Sensitive CE–MS analysis of potentially genotoxic alkylation compounds using derivatization and electrokinetic injection

A CE–MS method has been developed to detect trace levels of potentially genotoxic alkyl halides. After derivatization of the target components with 4-dimethylaminopyridine (DMAP) or butyl 1-(pyridinyl-4yl) piperidine 4-carboxylate (BPPC), the natively positively charged derivatives are pre-concentrated by applying electrokinetic injection and separated by a highly efficient CZE method using a background electrolyte (BGE) consisting of 100mM of TRIS adjusted to pH 2.5 with phosphoric acid. Using a sheath liquid interface, subsequent MS detection allows highly specific and sensitive analysis of alkyl halides.Conditions for electrokinetic injection were optimized to allow selective and effective injection. Injection of samples with low water content at 10kV for 150s using a high concentration of buffer in the BGE resulted in optimum sample stacking during injection and a highly efficient CE separation. At the sample pH applied, neutral and negatively charged components are shown to be selectively discarded, resulting in injection of positively charged ions only. The sample matrix influences the efficiency of the injection, but when using an internal standard, reproducibilities better than 10% RSD are obtained. Relative recoveries of the derivatives spiked to different types of model API between 85 and 115% demonstrate that the method can be applied for quantitative analysis. Detection limits of lower than 1mgkg−1 for the tested alkyl halides obtained in CE–MS at least equal the sensitivity obtained in LC–MS. The CE–MS method is a valuable alternative for the LC–MS method used for analysis of alkylation compounds.

Capillary electrophoresis-mass spectrometry determination of morphine and its isobaric glucuronide metabolites.

The determination of morphine and its isobaric metabolites morphine-3-beta-d-glucuronide (M3G) and morphine-6-beta-d-glucuronide (M6G) is useful for therapeutic drug monitoring and forensic identification of drug use. In particular, capillary electrophoresis with mass spectrometry (CE-MS) represents an attractive tool for opioid analysis. Whereas volatile background electrolytes in CE often improve electrospray ionization for coupled MS detection, such electrolytes may reduce CE separation efficiency and resolution. To better understand the effects of background electrolyte (BGE) composition on separation efficiency and detection sensitivity, this work compares and contrasts method development for both volatile (ammonium formate and acetate) and nonvolatile (ammonium phosphate and borate) buffers. Peak efficiencies and migration times for morphine and morphine metabolites were optimal with a 25mM ammonium borate buffer (pH=9.5) although greater sensitivities were achieved in the ammonium formate buffer. Optimized CE methods allowed for the resolution of the isobaric morphine metabolites prior to high mass accuracy, electrospray ionization quadrupole time-of-flight (ESI-QTOF) MS detection applicable to the analysis of urine samples in under seven minutes. Urine sample preparation required only a 10-fold dilution with BGE prior to analysis. Limits of detection (LOD) in normal human urine were found to be 1.0μg/mL for morphine and 2.5μg/mL for each of M3G and M6G by CE-ESI-QTOF-MS. These LODs were comparable to those for CE-UV analysis of opioid standards in buffer, whereas CE-ESI-QTOF-MS analysis of opioid standards in buffer yielded LODs an order of magnitude lower. Patient urine samples (N=12) were analyzed by this new CE-ESI-QTOF-MS method and no significant difference in total morphine content relative to prior liquid chromatography-mass spectrometry (LC-MS) results was found as per a paired-t test at the 99% confidence level. Whereas the LC-MS method applied to these samples determined only total morphine content, this new CE-ESI-QTOF-MS method allowed for species differentiation in addition to total morphine determination. By this method, it was found that M3G and M6G metabolites were present in a 5:1 concentration ratio, on average, in patient samples. Therefore, the CE-ESI-QTOF-MS method not only allows for total morphine concentration determination comparable to established LC-MS methods, but also allows for differentiation between morphine and its trace glucuronides, yielding additional biochemical information about drug metabolism.

Azo resorcin[4]calixpyrrole grafted Amberlite XAD-2 polymer: an efficient solid phase extractant for separation and preconcentration of La(III) and Ce(III) from natural geological samples

The impregnation of new azocalixpyrroles obtained from resorcinol derivative into a polymeric chelating resin, Amberlite XAD-2. A simple and effective method is presented for the separation and preconcentration of U(VI)] and Thorium Th(IV) by solid phase extraction on synthesized modified polymeric chelating resin. The synthesized chelating polymeric sorbent showed superior binding affinity towards U(VI) and Th(IV) under selective pH conditions. The optimum pH range was established and the flow rates for U(VI) and Th(IV) were studied respectively. U(VI) and Th(IV) are quantitatively eluted with suitable eluants like HCl and HNO3 and determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Other parameters such as total sorption capacity, exchange kinetics, preconcentration factor, distribution coefficient, breakthrough capacity and resin stability. The uptake and stripping of these metal ions on the resin were fast, indicating a better accessibility of the metal ions towards the chelating sites. Chromatographic separation of Th(IV) and U(VI) was accomplished by adjustment of pH in the range of 3.0–9.0 pH, respectively. Separation of Th(IV) and U(VI) from other metal cations, in synthetic solution was achieved. The synthesized resins were recycled at least 14–16 times without much affecting column sorption capacity.

Extraction and separation of Ce(iii) and Pr(iii) in the system containing two complexing agents with di-(2-ethylhexyl) phosphoric acid

In order to develop a novel separation technology superior to the current extraction systems, the extraction behaviors of Ce(III) and Pr(III) from chloride medium with P204 in the presence of two complexing agents lactic acid (LA) and citric acid (H3cit) have been reported. The distribution ratios increase with the increase of the equilibrium pH and the ratio of [H3cit] : [LA] under certain conditions. The separation factors of Ce(III) and Pr(III) increase with the ratio of [H3cit] : [LA] at fixed pH, and the maximum value is as high as 5.78 in this complexing system. The maximum saturated extraction capacity is 27.08 g L−1 which is close to that in the current saponified P507 extraction system. The equilibrium constants and thermodynamic functions, ΔG, ΔH and ΔS have been calculated. Lactic acid and citric acid can be effectively recycled and enriched, providing possibilities for dissolving minerals in the circular process. By comparison with the experimental results, this complexing extraction method could be regarded as an effective strategy for separating REs.

Low pH capillary electrophoresis application to improve capillary electrophoresis-systematic evolution of ligands by exponential enrichment

In this work, a novel low pH CE-SELEX (LpH-CE-SELEX) as a CE-SELEX variant is proposed. Transferring (Trf), bovine serum albumin (BSA) and cytochrome c (Cyt c) as model protein are incubated with a FAM labeled ssDNA library, respectively. Incubation mixture is separated in low pH CE (pH 2.6), where positively charged protein, protein–ssDNA complex and negatively charged ssDNA library migrate oppositely without EOF driven. Analysis of protein–ssDNA complex under positive voltage and unbound ssDNA library under negative voltage by CE–UV are applied for interactive evaluation. By increasing injection time, larger amount protein–ssDNA complex can be collected conveniently at the cathode end whereas ssDNA migrates to anode. Finally, stability of protein–ssDNA complex in low pH CE separation is discussed.

Microemulsions: As drug delivery system

Microemulsions are excellent candidates as potential drug delivery systems because of their improved drug solubilization, long shelf life, and ease of preparation and administration. The formulation of microemulsion for pharmaceutical use requires a thorough understanding of the properties, uses, and limitations of microemulsion. Three distinct microemulsions – oil external, water external and middle phase can be used for drug delivery, depending upon the type of drug delivery upon the type of drug and the site of action. In this article, Since the term ‘microemulsion’ was first coined almost fifty years ago to describe clear, isotropic, thermodynamically stable systems composed of oil, water, surfactant and cosurfactant, numerous and varied reports of the applications of microemulsions have appeared in the literature. Reports of the use of microemulsions in separation science began to appear in the literature in the early 1990’s when they were first used as mobile phases for HPLC and as carrier electrolytes for CE separations, particularly for pharmaceutical applications.

Fast and versatile fabrication of PMMA microchip electrophoretic devices by laser engraving.

This paper describes the effects of different modes and engraving parameters on the dimensions of microfluidic structures produced in PMMA using laser engraving. The engraving modes included raster and vector, while the explored engraving parameters included power, speed, frequency, resolution, line-width, and number of passes. Under the optimum conditions, the technique was applied to produce channels suitable for CE separations. Taking advantage of the possibility to cut-through the substrates, the laser was also used to define solution reservoirs (buffer, sample, and waste) and a PDMS-based decoupler. The final device was used to perform the analysis of a model mixture of phenolic compounds within 200 s with baseline resolution.

Separation of Ce and La from Synthetic Chloride Leach Solution of Monazite Sand by Precipitation and Solvent Extraction

Precipitation and solvent extraction experiments have been performed to recover light rare earths from simulated monazite sand chloride leach solutions. Precipitation conditions were obtained to recover Ce by adding NaClO as an oxidant. Among some cationic extractants (PC 88A, D2EHPA, Cyanex 272, LIX 63), PC 88A showed the best performance to separate La from the resulting chloride solution. Furthermore, the mixture of PC 88A with other solvating (TBP, TOPO) and amine extractants (Alamine 336, Aliquat 336) was tested to increase the separation factor of La from Pr and Nd. The use of mixed extractants greatly enhanced the separation of La from the two other metals. McCabe–Thiele diagrams for the extraction of Pr and Nd with the PC 88A/Alamine 336 mixture were constructed.

Velocity gap mode of capillary electrophoresis developed for high‐resolution chiral separations

A new CE method based on velocity gap (VG) theory has been developed for high-resolution chiral separations. In VG, two consecutive electric fields are adopted to drive analytes passing through two capillaries, which are linked together through a joint. The joint is immersed inside another buffer vial which has conductivity communication with the buffer inside the capillary. By adjusting the field strengths onto the two capillaries, it is possible to observe different velocities of an analyte when it passes through those two capillaries and there would be a net velocity change (NVC) for the same analyte. Different analytes may have different NVC which may be specifically meaningful for enantioseparations because enantiomers are usually hard to resolve. By taking advantage of this NVC, it is possible to enhance the resolution of a chiral separation if a proper voltage program is applied. The feasibility of using NVC to enhance chiral separation was demonstrated in the separations of three pairs of enantiomers: terbutaline, chlorpheniramine, and promethazine. All separations started with partial separation in a conventional CE and were significantly improved under the same experimental conditions. The results indicated that VG has the potential to be used to improve the resolving power of CE in chiral separations.

Comparison of hydrodynamically closed isotachophoresis–capillary zone electrophoresis with hydrodynamically open capillary zone electrophoresis hyphenated with tandem mass spectrometry in drug analysis: Pheniramine, its metabolite and phenylephrine in human urine

The advanced two dimensional isotachophoresis (ITP)–capillary zone electrophoresis (CZE) hyphenated with tandem mass spectrometry (MS/MS, here triple quadrupole, QqQ) was developed in this work to demonstrate analytical potentialities of this approach in the analysis of drugs in multicomponent ionic matrices. Pheniramine (PHM), phenylephrine (PHE), paracetamol (PCM) and their potential metabolic products were taken for the analysis by the ITP–CZE–ESI–QqQ technique working in hydrodynamically closed CE separation system and then a comparison with the conventional (hydrodynamically open) CZE–ESI–QqQ technique was made. The ITP–CZE–ESI–QqQ method was favorable in terms of obtainable selectivity (due to highly effective heart-cut analysis), concentration limits of detection (LOD at pgmL−1 levels due to enhanced sample load capacity and ITP preconcentration), sample handling (on-line sample pretreatment, i.e. clean-up, preconcentration, preseparation), and, by that, possibilities for future automation and miniaturization. On the other hand, this experimental arrangement, in contrast to the CZE–ESI–QqQ arrangement supported by an electroosmotic flow, is principally limited to the analysis of uniformly (i.e. positively or negatively) charged analytes in one run without any possibilities to analyze neutral compounds (here, PCM and neutral or acidic metabolites of the drugs had to be excluded from the analysis). Hence, these general characteristics should be considered when choosing a proper analytical CE–MS approach for a given biomedical application. Here, the analytical potential of the ITP–CZE–ESI–QqQ method was demonstrated showing the real time profiles of excreted targeted drugs and metabolite (PHM, PHE, M-PHM) in human urine after the administration of one dose of Theraflu® to the volunteers.

Ion pair hollow fiber liquid–liquid–liquid microextraction combined with capillary electrophoresis-ultraviolet detection for the determination of thyroid hormones in human serum

In this study, a novel, inexpensive, sensitive and selective analytical method that combines ion pair hollow fiber liquid–liquid–liquid microextraction (IP-HF-LLLME) with capillary electrophoresis-ultraviolet detection (CE-UV) was developed for the simultaneous determination of six thyroid hormones (including diiodothyronine (T2), 3,3,5-triiodo-l-thyronine (T3), 3,5,3,5-tetraiodolthyronine (T4), 3,3,5-triiodothyronine (rT3), monoiodotyrosine (MIT) and diiodotyrosine (DIT)) in human serum samples. By the addition of a low concentration of sodium dodecyl sulfate (SDS) into the donor phase as an ion pair reagent, octanol as the organic extraction solvent and 30mmol/L Na2CO3 as acceptor phase, six analytes with different polarity and water solubility were successfully extracted simultaneously using HF-LLLME. To the best of our knowledge, this is the first time that a liquid phase microextraction technique was proposed for the extraction of thyroid hormones in real samples. The CE separations were investigated in detail. When 20kV of voltage was applied, the six compounds were separated within 13min in 25mmol/L phosphate buffer (pH 2.15) containing 10% (v/v) acetonitrile and 0.5% (m/v) polyethylene glycol (PEG). Under the optimized conditions, enrichment factors (EFs) ranging from 183- to 366-fold were obtained and the limits of detection (at a signal-to-noise ratio of 3) were at sub μg/L level. The established IP-HF-LLLME-CE-UV method was successfully applied to simultaneous determination of thyroid hormones and relative compounds in human serum samples with good recoveries for the spiked samples.

Simple Capillary Electrophoresis–Mass Spectrometry Method for Complex Glycan Analysis Using a Flow-Through Microvial Interface

A flow-through microvial is used to interface capillary electrophoresis and mass spectrometry (CE-MS) to develop a method for simultaneous profiling both neutral and sialylated glycans without derivatization or labeling. The CE separation was performed at near-zero electroosmotic flow in a capillary with neutral, hydrophilic coating, using 50 mM ammonium acetate in 20% methanol (pH 3.1) as the background electrolyte. The method was optimized with reversed CE polarity and negative ion ESI-MS. Enzymatically released N-glycans from human immunoglobulin G (IgG) were used as the test sample. The approach was also used to study the more complex N-glycans from recombinant human erythropoietin (rHuEPO) expressed in Chinese hamster ovary (CHO) cells. Glycoscreening of rHuEPO was performed using a triple quadrupole MS and an ultrahigh resolution TOF-MS. The high sensitivity and high mass accuracy of the TOF-MS revealed the presence of more than 70 glycans. Three mono- and di-sialylated tetra-antennary N-glycans and one mono-sialylated tri-antennary N-glycan of rHuEPO are reported for the first time. Further glycan heterogeneity was identified of the highly sialylated N-glycans of rHuEPO by extensive acetylation, Neu5Ac/Neu5Gc variation and the presence of N-acetyl-lactosamine repeats. For comparative purposes, porous graphitic carbon-based LC-MS/MS was also used to glycoprofile rHuEPO. This work demonstrates the potential of CE-MS to provide a comprehensive glycosylation profile with detailed features of the secondary glycan modifications. The CE-MS based method eliminates the need to label the N-glycans, as well as the requirement to desialylate before analysis, and could complement other established techniques for glycan characterization of therapeutic glycoproteins.

Pneumatic microvalve-based hydrodynamic sample injection for high-throughput, quantitative zone electrophoresis in capillaries.

A hybrid microchip/capillary electrophoresis (CE) system was developed to allow unbiased and lossless sample loading and high-throughput repeated injections. This new hybrid CE system consists of a poly(dimethylsiloxane) (PDMS) microchip sample injector featuring a pneumatic microvalve that separates a sample introduction channel from a short sample loading channel, and a fused-silica capillary separation column that connects seamlessly to the sample loading channel. The sample introduction channel is pressurized such that when the pneumatic microvalve opens briefly, a variable-volume sample plug is introduced into the loading channel. A high voltage for CE separation is continuously applied across the loading channel and the fused-silica capillary separation column. Analytes are rapidly separated in the fused-silica capillary, and following separation, high-sensitivity MS detection is accomplished via a sheathless CE/ESI-MS interface. The performance evaluation of the complete CE/ESI-MS platform demonstrated that reproducible sample injection with well controlled sample plug volumes could be achieved by using the PDMS microchip injector. The absence of band broadening from microchip to capillary indicated a minimum dead volume at the junction. The capabilities of the new CE/ESI-MS platform in performing high-throughput and quantitative sample analyses were demonstrated by the repeated sample injection without interrupting an ongoing separation and a linear dependence of the total analyte ion abundance on the sample plug volume using a mixture of peptide standards. The separation efficiency of the new platform was also evaluated systematically at different sample injection times, flow rates, and CE separation voltages.