Capillary Electrophoresis Separation Research Articles

Development and validation of a novel 133-plex forensic STR panel (52 STRs and 81 Y-STRs) using single-end 400bp massive parallel sequencing.

Short tandem repeats (STRs) are the preferred genetic markers in forensic DNA analysis, routinely measured by capillary electrophoresis (CE) method based on the fragment length features. While, the massive parallel sequencing (MPS) technology could simultaneously target a large number of intriguing forensic STRs, bypassing the intrinsic limitations of amplicon size separation and accessible fluorophores in CE, which is efficient and promising for enabling the identification of forensic biological evidence. Here, we developed a novel MPS-based Forensic Analysis System Multiplecues SetB Kit of 133-plex forensic STR markers (52 STRs and 81 Y-STRs) and one Y-InDel (M175) based on multiplex PCR and single-end 400bp sequencing strategy. This panel was subjected to developmental validation studies according to the SWGDAM Validation Guidelines. Approximately 2185 MPS-based reactions using 6 human DNA standards and 8 male donors were conducted for substrate studies (filter paper, gauze, cotton swab, four different types of FTA cards, peripheral venous blood, saliva, and exfoliated cells), sensitivity studies (from 2ng down to 0.0625ng), mixture studies (two-person DNA mixtures), PCR inhibitor studies (seven commonly encountered PCR inhibitors), species specificity studies (11 non-human species), and repeatability studies. Results of concordance studies (413 Han males and 6 human DNA standards) generated by STRait Razor and in-house Python scripts indicated 99.98% concordance rate in STR calling relative to CE for STRs between 41,900 genotypes at 100 STR markers. Moreover, the limitations of present studies, the nomenclature rules and forensic MPS applications were also described. In conclusion, the validation studies based on ~ 2200 MPS-based and ~ 2500 CE-based DNA profiles demonstrated that the novel MPS-based panel meets forensic DNA quality assurance guidelines with robust, reliable, and reproducible performance on samples of various quantities and qualities, and the STR nomenclature rules should be further regulated to integrate the inconformity between MPS-based and CE-based methods.

Optimization of Capillary Electrophoresis Separation Conditions ofChlorpromazine, Promethazineand Their Main Metabolitesby RSM

Optimization of Capillary Electrophoresis Separation Conditions ofChlorpromazine, Promethazineand Their Main Metabolitesby RSM

Pseudophase microextraction for in-line sample concentration in micellar electrokinetic chromatography

Pseudophase microextraction (PPME) as a simple in-line sample concentration technique in micellar electrokinetic chromatography (MEKC) is presented. In contrast to popular electric-field driven stacking techniques in MEKC such as sweeping, PPME is pressure-driven. The technique afforded up to 403-2968x improvements in peak heights for fenoprop, dichlorprop, 1- and 2-naphthol compared to typical injection. Under the same MEKC conditions, the improvements in PPME were up to 23-59x better compared to sweeping. Briefly in PPME, the entire capillary was loaded (up to 20 capillary volumes) with the sample prepared in a dilute solution of cetyltrimethylammonium bromide ([CTAB] > critical surface aggregation concentration). The CTAB formed aggregates at the inner capillary walls and these aggregates acted as a stationary chromatographic pseudophase. After clean-up via flushing the capillary with purified water, the MEKC background solution (BGS) with sodium dodecyl sulfate was then introduced by pressure from the outlet end to elute the retained analytes. The analytes concentrate at front of the BGS and the front was moved to the inlet end of the capillary prior to MEKC. Optimization strategies and current limitations in PPME-MEKC are described. The linear ranges using a 4 capillary volume sample load obtained for fenoprop, dichlorprop, 1- and 2-naphthol were between 1 and 160 ng/mL (r2s ≥ 0.996), LOQs = 1–2.5 ng/mL and repeatability %RSDs (n = 6) were ≤5% (intra-day) and ≤7% (inter-day) (using low analyte concentrations 1-5x LOQ). PPME-MEKC with simple dilution of fortified real samples (no off-line sample concentration) was also able to detect low levels of dichlorprop (10 ng/mL, limit set in Australia) and 1- and 2−naphthol (7.5–15 ng/mL) in a drinking water and natural water sample, respectively (% recovery = 84–108%). The concept of PPME may find use in other modes of capillary electrophoresis and other nano-microscale separations.

Simple, rapid, and reproducible capillary gel electrophoresis separation and laser-induced fluorescence detection of DNA topoisomers with unmodified fused silica separation capillaries.

The topology of DNA is a critical quality attribute for plasmid-based pharmaceuticals, making quantification of trace levels of plasmid topoisomers an important analytical priority. An automated and cost-effective method based on capillary gel electrophoresis laser-induced fluorescence detection is described. The method outlined in this report is significant because it is easily implemented by any laboratory for which routine analyses of plasmid topology are critical for the development of new plasmid-based therapies as well as for quality control of gene therapies utilizing supercoiled DNA. Detection of topoisomers was achieved by incorporating ethidium bromide in the separation medium. The detector response was improved by 3 orders of magnitude by utilizing a 605-nm optical filter with a 15-nm bandwidth. Separations of linear, open circle, supercoiled, and multimer DNAplasmids ranging from 4.2 to 10.5kbp were accomplished in under 6min using an unmodified fused silica capillary (50-μm internal diameter). The background electrolyte was comprised of 0.5% gel, which was hydroxypropylmethyl cellulose, 1mM ethylenediaminetetraacetic acid, and 50mMN-(2-acetamido)-2-aminoethanesulfonic acid (pH of 6.25). The separations, which balanced the bulk electroosmotic flow, the electrophoretic mobility of the DNA, and gel sieving were dependent upon the pH of the electrolyte and the gel concentration. Reproducibility was dependent upon the procedure used to prepare the gel as well as other factors including the ethidium bromide concentration and capillary conditioning. A single unmodified capillary operated for more than 150 runs had an across-day migration time precision of 1% relative standard deviation and percent area precision of 10% relative standard deviation.

Current applications of capillary electrophoresis-mass spectrometry for the analysis of biologically important analytes in urine (2017 to mid-2021): A review.

Capillary electrophoresis coupled online with mass detection is a modern tool for analyzing wide ranges of compounds in complex samples, including urine. Capillary electrophoresis with mass spectrometry allows the separation and identification of various analytes spanning from small ions to high molecular weight protein complexes. Similarly to the much more common liquid chromatography‐mass spectrometry techniques, the capillary electrophoresis separation reduces the complexity of the mixture of analytes entering the mass spectrometer resulting in reduced ion suppression and a more straightforward interpretation of the mass spectrometry data. This review summarizes capillary electrophoresis with mass spectrometry studies published between the years 2017 and 2021, aiming at the determination of various compounds excreted in urine. The properties of the urine, including its diagnostical and analytical features and chemical composition, are also discussed including general protocols for the urine sample preparation. The mechanism of the electrophoretic separation and the instrumentation for capillary electrophoresis with mass spectrometry coupling is also included. This review shows the potential of the capillary electrophoresis with mass spectrometry technique for the analyses of different kinds of analytes in a complex biological matrix. The discussed applications are divided into two main groups (capillary electrophoresis with mass spectrometry for the determination of drugs and drugs of abuse in urine and capillary electrophoresis with mass spectrometry for the studies of urinary metabolome).

Integrated workflow for urinary prostate specific antigen N-glycosylation analysis using sdAb partitioning and downstream capillary electrophoresis separation

Prostate cancer represents the second highest malignancy rate in men in all cancer diagnoses worldwide. The development and progression of prostate cancer is not completely understood yet at molecular level, but it has been reported that changes in the N-glycosylation of prostate-specific antigen (PSA) occur during tumor genesis. In this paper we report on the development and implementation of a high-throughput capillary electrophoresis based glycan analysis workflow for urinary PSA analysis. The technology utilizes selective, high yield single domain antibody based PSA capture, followed by preconcentration and capillary electrophoresis coupled with laser-induced fluorescence detection, resulting in high resolution N-glycan profiles. Urinary PSA glycan profiles were compared to a commercially available PSA standard revealing differences in their α2,3- and α2,6-sialylated isomers, proving the excellent selectivity of the suggested workflow. This is important as sialylation classification plays an important role in the differentiation between indolent, significant and aggressive forms of prostate cancer.

Ultrasensitive determination of underivatized adamantane analogs in biological fluids by capillary electrophoresis with contactless conductivity detection

Separation techniques are promising for the detection of adamantane analogs with various functional groups. The derivatization of adamantane analogs with chromophores or fluorophores should be conducted using a separation technique combined with a common ultraviolet–visible or fluorescence detector. However, limited research has been conducted on underivatized adamantane analogs. Therefore, we present a highly rapid and sensitive method for detecting underivatized adamantane analogs by integrating ultrasound-assisted dispersive liquid–liquid microextraction (UADLLME), field-amplified sample stacking (FASS)-related capillary electrophoresis (CE), and capacitively coupled contactless conductivity detection (C4D). In the proposed system, UADLLME is used for sample clean up and analyte enrichment, whereas FASS-related CE provides on-line concentration of underivatized adamantane analogs during CE separation. A mixture of memantine (MT), amantadine (AT), and rimantadine (RT) was separated at baseline within 8 min through the application of optimized UADLLME (mixing extraction solvent, 50 μL of 1,1,2,2-tetrachloroethane (C2H2Cl4) and dispersive solvent, 200 μL of acetonitrile; mixing solution was injected into 1 mL of the sample solution at pH 12.5), FASS (buffer, 1.5 M acetic acid; additive, 0.05 mM β-cyclodextrin; pH 2.5), and C4D (amplitude, 2 Vpp; frequency, 500 kHz). The calibration curve exhibited acceptable linearity, with a coefficient of determination higher than 0.99. The limits of detection (signal-to-noise ratio of 3) were estimated to be 0.9, 1.0, and 1.2 nM for MT, AT, and RT, respectively. The relative standard deviations of peak areas varied from 8.9% to 9.3% (n = 5), whereas the sensitivity improvement of three underivatized adamantane analogs ranged from 1342 to 1766. The feasibility and accuracy of the present method for the determination of MT, AT, and RT in human serum and urine was satisfactorily confirmed by the excellent recovery and relative error. The proposed method exhibited high enrichment factors and offers excellent precision, high accuracy, and a short analysis time.

Covalent cationic copolymer coatings allowing tunable electroosmotic flow for optimization of capillary electrophoretic separations

Electroosmotic flow (EOF) plays a pivotal role in optimization of capillary electrophoresis (CE) separations of (bio)molecules and (bio)particles. EOF velocity is directly related to analysis time, peak resolution and separation efficiency. Here, we report a concept of charged polymer coatings of the inner fused silica capillary wall, which allows anodic EOF with mobility ranging from 0 to ∼(30–40) × 10−9 m2V−1s−1. The capillary wall is modified by covalently bound cationic copolymer poly(acrylamide-co-(3-acrylamidopropyl)trimethylammonium chloride) (PAMAPTAC) containing variable ratio of the charged monomer in the 0–60 mol. % interval. The EOF mobility showed minor variability with composition of background electrolyte (BGE) and pH in the 2–10 interval. The coatings were evaluated by CE-UV and nanospray CE-MS in the counter-EOF arrangement for a series of basic drug molecules in acetic acid based acidic BGE. Tunable EOF velocity was demonstrated as a useful tool for optimization of peak resolution, separation efficiency and migration time of analytes. Electrostatic repulsion of positively charged capillary surface was shown as beneficial for suppression of analyte adsorption, notably for hydrophobic cationic analytes.

Polyimide removal, cleaving, and fusion splicing of cylindrical and square fused silica capillaries for new separation and detection layouts in capillary electrophoresis and chromatography.

Fusion splicing is an already mature technology used to join the ends of optical fibers in the telecommunication industry. However, there is a lack of reliable and well-described protocols to join the ends of fused silica microtubes or capillaries using fusion splicing. In this work, a step-by-step procedure is proposed and demonstrated to find the optimal operation conditions to splice the ends of fused silica capillaries by fusion. The two most appropriate and known technologies were tested and optimized: the microfurnace technique (or hot filament technique) and the electric arc technique. It is shown that both produce good splices when the capillaries are well cleaved. For this reason, the removal of the external coating, which is important for good cleavage, was also revised. The cleaving techniques were also compared among themselves. As a result, fusion splices of cylindric-to-cylindric, cylindric-to-square, and square-to-square capillaries are demonstrated. They have potential applications in new detection schemes and separation layouts in capillary electrophoresis, electrophoresis-based hydrodynamic concentrators, chromatography, cell sorters, and microfluidics in general.

Charge-Based Separation of Acid-Functional Polymers by Non-aqueous Capillary Electrophoresis Employing Deprotonation and Heteroconjugation Approaches.

Water-borne polymers are in ever-increasing demand due to their favorable ecological profile compared to traditional solvent-borne polymer systems. Many water-borne polymer particles are stabilized in aqueous media by the incorporation of acid-functional monomers. Due to the large variety of comonomers applied, these water-borne polymers have various superimposed statistical distributions, which make it challenging to obtain in-depth information regarding incorporation of the acidic monomers. For selective analysis of the incorporated acidic monomers, a charge-based non-aqueous capillary electrophoresis (NACE) separation was developed. Two approaches were developed: (i) deprotonation of the acid functionality with an organically soluble strong base and (ii) heteroconjugation of anions of carboxylic acids with incorporated acid functionality. In both approaches, N-methylpyrrolidone, as a strong solvent for polymers with a favorable relative permittivity for the presence of dissociated ionic species, was used for the separation. It was shown that anions of carboxylic acids specifically associate with the incorporated acid groups in the polymers, resulting in negatively charged complexes that could be separated based on charge-to-size ratio by NACE. Although both approaches give comparable results with respect to acid distribution for acid-functional polymers, the effective mobility of the deprotonated polymers is roughly double that obtained from the heteroconjugation approach. Unlike the heteroconjugation approach, deprotonation conditions were detrimental to the fused-silica capillary, limiting practical use. Polymers with different chemical compositions, molecular weights, and acid contents were subjected to the CE approaches developed. Polymers with varying molecular weight but similar relative acid monomer content were shown to have similar migration times, which confirms that this approach separates polymers based on charge-to-size ratio.

Recent (2018-2020) development in capillary electrophoresis.

Development of new capillary electrophoresis (CE) methodology and instrumentation, as well as application of CE to solve new problems, remains an active research area because of the attractive features of CE compared to other separation techniques. In this review, we focus on the representative works about sample preconcentration, separation media or capillary coating development, detector construction, and multidimensional separation in CE, which are judiciously selected from the papers published in 2018–2020.

3D printed two-in-one on-capillary detector: Combining contactless conductometric and photometric detection for capillary electrophoresis

In this work, for the first time, a 3D printed two-in-one on-capillary detector, combining contactless conductometric detection (C4D) and photometric detection (PD), is fabricated for capillary electrophoresis (CE). The C4D Faraday shield (FS) is printed using electrically conductive composite polylactic acid (PLA) to minimize the stray capacitance. Non-conductive PLA is also used to print the insulator of FS to prevent the electrical conduction with two stainless steel electrodes. A novel collimator, consisting of two partially aligned pinholes, is printed by conductive material to collimate the light-emitting diode beam. The C4D detection has a signal-to-noise ratio of 1092 ± 2 for 200 μM potassium on a 25 μm id capillary. The PD detection shows excellent linearity with stray light down to 8% and an effective path length at 73% of a 75 μm id capillary. The analytical performance is demonstrated by CE separation and detection of cations. PD shows limits of detection (LODs) of 1.3, 0.9, and 1.7 μM for cobalt, copper and zinc, which are complexed with 4-(2-Pyridylazo) resorcinol, while C4D shows LODs of 1.2, 1.4, 21 and 2.6 μM for potassium, sodium, cobalt and zinc, respectively.

Immunoassay of Small Molecule Mediated by a Triply Functional DNA.

Benefiting from specific target recognition by antibodies, the immunoassay is one of the widely used assays for the detection of biologically and environmentally important small molecules in broad fields. It can be challenge to isolate small molecules from their antibody complex in an immobilization-free immunoassay with separation for the detection of small-molecule targets. Here we present an immunoassay mediated by a triply functional DNA probe. A DNA strand is dually labeled with a fluorophore and the target small molecule. This DNA probe integrates three functions, including specific binding to the antibody, signal reporting for sensitive fluorescence detection, and carrying negative charges to facilitate capillary electrophoresis (CE) separation. The binding of the probe to an antibody brings many negative charges in the complex and causes significant changes in mass-to-charge ratios, so the antibody-probe complex can be well separated from the unbound probe in CE analysis. A simple immunoassay is achieved by target competition with this DNA probe for antibody binding in CE coupled to ultrasensitive laser-induced fluorescence (LIF) detection. To show a proof of concept, we detected two model small-molecule targets, digoxin, a therapeutic drug, and ochratoxin A (OTA), an important mycotoxin for food safety. In addition, the use of two DNA probes with distinguished migration times in CE allowed the simultaneous detection of OTA and digoxin. This immunoassay provides new opportunities for wide applications.

Development of a Mobile Analytical Chemistry Workstation Using a Silicon Electrochromatography Microchip and Capacitively Coupled Contactless Conductivity Detector.

Capillary electrochromatography (CEC) is a separation technique that hybridizes liquid chromatography (LC) and capillary electrophoresis (CE). The selectivity offered by LC stationary phase results in rapid separations, high efficiency, high selectivity, minimal analyte and buffer consumption. Chip-based CE and CEC separation techniques are also gaining interest, as the microchip can provide precise on-chip control over the experiment. Capacitively coupled contactless conductivity detection (C4D) offers the contactless electrode configuration, and thus is not in contact with the solutions under investigation. This prevents contamination, so it can be easy to use as well as maintain. This study investigated a chip-based CE/CEC with C4D technique, including silicon-based microfluidic device fabrication processes with packaging, design and optimization. It also examined the compatibility of the silicon-based CEC microchip interfaced with C4D. In this paper, the authors demonstrated a nanofabrication technique for a novel microchip electrochromatography (MEC) device, whose capability is to be used as a mobile analytical equipment. This research investigated using samples of potassium ions, sodium ions and aspirin (acetylsalicylic acid).

Capillary Electrophoresis Separation of Artepillin C: Determination in Brazilian Green Propolis.

Propolis is important in complementary and alternative medicine having well-known therapeutic applications. Artepillin C, a main component of Brazilian (green) propolis, has attracted great attention for its anticancer action. Consequently, the synthesis of artepillin C has been reported but, due to the limited yield and elevated costs, this biomolecule is largely produced from Brazilian propolis. We report the capillary electrophoresis (CE) separation of artepillin C in Brazilian propolis also comparing the results with those of HPLC-UV-MS. Optimal separation was obtained with a simple buffer constituted of sodium tetraborate 30 mM pH 9.2 and detection at 210 nm. Artepillin C and the polyphenols of propolis were fully separated with a voltage gradient of 30 to 8 kV and a current of 300 μA for a total run of 50 min. The sensitivity of CE-UV was 22 times greater than HPLC-UV and 100 times more than HPLC-MS with also a stronger reduction in the run time and a greater robustness and reproducibility. The development of CE as an effective and reliable method for the analysis of artepillin C is desired as the standardized quality controls are essential before propolis or its biomolecules can be adopted routinely in nutraceuticals, food ingredients and therapeutic applications.

A review article on Ciprofloxacin determination with various analytical techniques.

Ciprofloxacin belongs to the fluoroquinolone family, which exhibits biological activity against both gram-positive and gram-negative bacteria. The previously mentioned drug is of utmost importance due to the high incidence of resistance caused by other antibiotics. Thus, numerous research studies has been conducted to determine Ciprofloxacin as well as its metabolites owing to their contribution in the drug’s biological activity. Liquid chromatography, gas chromatography, capillary electrophoresis and other separation techniques were used to develop, adapt and implement analytical techniques for the drug analysis. Other studies has made use of the hyphenation between liquid chromatography and mass spectrometry for Ciprofloxacin assay for quality control, biological fluids, animal tissues and numerous sample types. The recent advances in the ionization methods has led to the use of direct mass spectrometry techniques to analyze various sample types. This mini review aims to focus on the various analytical techniques and recent technologies implemented for Ciprofloxacin analysis.

Protein Sieving with Capillary Nanogel Electrophoresis.

Protein sieving, which is a fundamental tool in the biotechnology field, can be automated using capillary gel electrophoresis. The high-viscosity and biocompatible linear gels required for capillary sieving must be replaced for each run using high pressures. Thermally responsive gels are easier to renew in the capillary as they can be repetitively switched between low- and high-viscosity solutions. A thermally responsive sieving gel was recently demonstrated to separate DNA, which is a larger biomolecule than proteins. This material required no synthesis as it was self-assembled from common phospholipids. Nanogels composed of dimyristoyl-sn-glycero-2-phosphocholine and 1,2-dihexanoyl-sn-glycero-3-phosphocholine exhibit thermally reversible viscosity within a 10 °C temperature change, forming a sieving matrix above 24 °C. Additionally, these nanogels are nondenaturing and have been demonstrated to preserve the activity of enzymes. In this report, a phospholipid nanogel is used for the first time for capillary gel electrophoresis separations of proteins. The mobilities in buffer and nanogel demonstrated that 20-30% nanogel supports sieving of proteins ranging from 20 to 80 kDa. Capillary separations based on sieving rather than electrophoresis had similar precision in both area and migration time as well as similar separation efficiencies. However, the migration time increased with gel concentration. The nanogel was used for the analysis of proteins in human serum. Proteins in the sample were more effectively resolved and quantified with capillary sieving compared to free-solution capillary electrophoresis. This allowed for accurate quantification.

Machine Learning Based Analysis of Human Serum N-glycome Alterations to Follow up Lung Tumor Surgery

Simple SummaryGlobally, there were around 2.1 million lung cancer cases and 1.8 million deaths in 2018. Hungary—where this study was carried out—had the highest rate of lung cancer in the same year. We developed a new analytical method which can be readily used to follow up the tumor surgery by investigating the glycan (sugar) structures of proteins. As the results of such investigations are very complex, computer-assisted machine learning methods were utilized for data interpretation.The human serum N-glycome is a valuable source of biomarkers for malignant diseases, already utilized in multiple studies. In this paper, the N-glycosylation changes in human serum proteins were analyzed after surgical lung tumor resection. Seventeen lung cancer patients were involved in this study and the N-glycosylation pattern of their serum samples was analyzed before and after the surgery using capillary electrophoresis separation with laser-induced fluorescent detection. The relative peak areas of 21 N-glycans were evaluated from the acquired electropherograms using machine learning-based data analysis. Individual glycans as well as their subclasses were taken into account during the course of evaluation. For the data analysis, both discrete (e.g., smoker or not) and continuous (e.g., age of the patient) clinical parameters were compared against the alterations in these 21 N-linked carbohydrate structures. The classification tree analysis resulted in a panel of N-glycans, which could be used to follow up on the effects of lung tumor surgical resection.

Tetraalkylammonium-l-tartrate ionic liquids as sole chiral selectors in capillary electrophoresis

In the field of separation science, the use of tartaric acid-based ionic liquids (TTILs) for chiral separation has not yet been reported. In this work, six novel mono- and di-tetraalkylammonium l-tartrate ILs (TAA-l-TTs) with different alkane chain length were evaluated for their potential as sole chiral selectors in capillary electrophoresis (CE). In comparison with conventional l-tartaric acid (l-TT) chiral selector, these IL-type chiral selectors exhibit remarkably improved enantioseparation performance, which is even better than most previously reported TT ester-type chiral selectors. Major factors influencing CE separation were investigated, including the background electrolyte (BGE) composition, ILs concentration, type and proportion of organic modifier, buffer pH, etc. The results show that the l-TT-based IL-type chiral selectors prefer a weak acid buffer (150 mM boric acid at pH 4.5) with a high proportion of methanol (80%-90%). The best resolutions (Rs) were obtained when the IL concentration was set at 60 mM. We further carried out a series of comparative experiments and a molecular simulation study to explore the enantiorecognition mechanism of TTILs. The result indicates that the TAA-l-TTs cannot be considered as a simple combination of TAA salt and l-TT. The dissociation degree of TTILs may be an important factor influencing the enantiorecognition process.

Recent progress in capillary electrophoresis-based high-sensitivity proteomics

In recent years, proteomic techniques have undergone rapid progress in terms of sample pretreatment, separation, and mass spectrometry (MS) detection. The current MS-based proteomic techniques can be used to identify up to 10000 proteins both qualitatively and quantitatively within a few hours. However, the current mainstream proteomic approaches do not fulfill the need to analyze minute amounts of biological samples, especially rare cells and single mammalian cells. Capillary electrophoresis (CE)-based separation offers many advantages, such as narrow peaks, high separation efficiency, and low sample requirement, which make it an ideal separation approach for combination with high-resolution MS. We have reviewed the state-of-the-art development of integrated and online sample preparation methods and nanoscale liquid chromatography-mass spectrometry (nanoLC-MS) for high-sensitivity proteomics, and described the associated challenges. Integrated and online sample preparation methods can minimize sample loss and improve lysis and digestion efficiencies. The simple and integrated spintip-based proteomics technology (SISPROT) developed by our group has shown robust performance for the comprehensive profiling of various types of samples and the sensitive analysis of small numbers of cells, down to a few hundred. A few groups have applied integrated/online sample preparation methods, such as nanodroplet processing in one pot for trace samples (nanoPOTS) and integrated proteome analysis system for one cell (iPAD-1), to achieve the identification of hundreds of proteins from a single HeLa cell. We propose that one of the key technical challenges in this field is that the performance of current nanoLC separation techniques cannot match modern high-resolution MS techniques, with ultrahigh scan rates of over 40 Hz; therefore, the insufficient chromatographic performance results in reduced utilization of MS/MS scan capacity. Wide chromatographic peaks result in insufficient precursors to trigger MS/MS scans and redundant sampling, irrespective of whether dynamic exclusion has been enabled. In view of the above mentioned technical challenges, we have focused on discussing the unique technical advantages and potential opportunities of CE-MS, which mainly include the following. (1) High-performance capillary electrophoresis (HPCE) separation for minute amounts of tryptic peptide samples. Capillary electrochromatography can further improve the column capacity limit of HPCE. (2) CE-MS interfaces for high-sensitivity proteomics. Although sheath liquid interfaces have proven versatile and robust and are currently more commonly used, sheathless interfaces can significantly enhance the signal/noise ratio owing to decreased analyte dilution and background noise. Thus, sheathless interfaces are potentially more suitable for ultrasensitive proteomics. (3) Synergetic utilization of HPCE separation and MS detection at high scan rates. The most promising way to fully utilize the ultrahigh scan rates of modern high-resolution MS is to enhance the quality of peptide separation. Narrower peptide peaks in HPCE separation may greatly reduce redundant sampling and boost sensitivity. Overall, we anticipate that, after further improvement, CE-MS-based proteomics will be more widely applied to proteomic analysis of minute amounts of biological samples, such as single mammalian cells. Furthermore, more sensitive data acquisition modes, such as data-independent acquisition, may be used for global proteomic profiling, and parallel reaction monitoring may be used to target a limited number of important proteins. Matching between runs and machine learning algorithms may improve the accuracy of proteomic analysis of minute amounts of samples.