Analytica Chimica Acta (v.678, #1)
Editorial Board (iii).
Broad specificity indirect competitive immunoassay for determination of nitrofurans in animal feeds by Jun Li; Jing Liu; Hui-Cai Zhang; Hui Li; Jian-Ping Wang (1-6).
A generic hapten of nitrofurans was synthesized by derivatization of 5-nitrofurfural with diamine, and the hapten was coupled to carrier protein to prepare different immunogens and coating antigens by using diazotization method and glutaraldehyde method. The obtained novel polyclonal antibodies from immunized rabbits showed broad cross reactivity among seven nitrofurans. After assessment of four coating antigen/antibody combinations, an indirect competitive immunoassay was developed to simultaneously detect the seven nitrofurans in animal feeds. The limits of detection for these analytes were in the range of 5–16 μg kg−1 depending on the compound. Recoveries from nitrofurans fortified blank feeds at levels of 30 and 100 ng g −1 were in a range of 82.6–108.4% with coefficients of variation lower than 11.4%. The immunoassay was further validated by a HPLC method and the two methods showed good correlation (r = 0.9924). Therefore, the proposed immunoassay could be used as a practical method to monitor the illicit use of nitrofurans in animal feeds.
Keywords: 5-nitrofurfural; Nitrofurans; Broad specificity; Immunoassay; Feeds;
Use of nanomaterials for impedimetric DNA sensors: A review by A. Bonanni; M. del Valle (7-17).
This review presents the state of the art of DNA sensors (or genosensors) that utilize electrochemical impedance spectroscopy as the transduction technique. As issue of current interest, it is centered on the use of nanomaterials to develop or to improve performance of these specific biosensors. It will describe the different principles that may be employed in the measuring step and the different formats adopted for detection of a DNA sequence or confirmation or amplification of the finally obtained signal. The use of nanomaterials for the above listed aspects, viz. the use of carbon nanotubes or other nanoscopic elements in the construction of the electrodes, or the use of nanoparticles, mainly gold or quantum dots, for signal enhancement will be fully revised.
Keywords: Biosensor; Genosensor; Carbon nanotube; Gold nanoparticles; Quantum dots; Electrochemical impedance spectroscopy;
Comparison of inductively coupled plasma spectrometry techniques for the direct determination of rare earth elements in digests from geological samples by Francisco Ardini; Francesco Soggia; Francesco Rugi; Roberto Udisti; Marco Grotti (18-25).
Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS), ICP sector field mass spectrometry (ICP-SFMS) and ICP atomic emission spectrometry (ICP-AES) were compared with regard to the direct determination of rare earth elements (REEs) in geological samples. In order to reduce the polyatomic interferences occurring in ICP-QMS, the use of a cooled spray chamber was optimized, obtaining a significant decrease of the oxide ions formation (about 50%) and a consequent mitigation of the interfering effects. Precision and accuracy of the method were demonstrated by the analyses of sediment and soil certified reference materials. ICP-SFMS working in high-resolution mode also provided accurate results, with similar precision to ICP-QMS (RSD%: 3–8%) and comparable or better limits of detection. Quantification limits of the procedures were 18–52 ng g−1 and 10–780 ng g−1 for sector field- and quadrupole-ICP-MS, respectively. Accurate and precise determination of most REEs was also achieved by ICP-AES using both pneumatic and ultrasonic nebulization, after a careful selection of the emission lines and compensation for non-spectral interferences by internal standardization. The three techniques were finally applied to glaciomarine sediment samples collected in Antarctica, providing comparable analytical data on REE abundance and depth pattern.
Keywords: Inductively coupled plasma; Atomic emission spectrometry; Atomic mass spectrometry; Rare earth elements; Cooled spray chamber; Ultrasonic nebulization;
Quantitative analysis of triazine herbicides in environmental samples by using high performance liquid chromatography and diode array detection combined with second-order calibration based on an alternating penalty trilinear decomposition algorithm by Yuan-Na Li; Hai-Long Wu; Xiang-Dong Qing; Quan Li; Shu-Fang Li; Hai-Yan Fu; Yong-Jie Yu; Ru-Qin Yu (26-33).
A novel application of second-order calibration method based on an alternating penalty trilinear decomposition (APTLD) algorithm is presented to treat the data from high performance liquid chromatography-diode array detection (HPLC-DAD). The method makes it possible to accurately and reliably analyze atrazine (ATR), ametryn (AME) and prometryne (PRO) contents in soil, river sediment and wastewater samples. Satisfactory results are obtained although the elution and spectral profiles of the analytes are heavily overlapped with the background in environmental samples. The obtained average recoveries for ATR, AME and PRO are 99.7 ± 1.5, 98.4 ± 4.7 and 97.0 ± 4.4% in soil samples, 100.1 ± 3.2, 100.7 ± 3.4 and 96.4 ± 3.8% in river sediment samples, and 100.1 ± 3.5, 101.8 ± 4.2 and 101.4 ± 3.6% in wastewater samples, respectively. Furthermore, the accuracy and precision of the proposed method are evaluated with the elliptical joint confidence region (EJCR) test. It lights a new avenue to determine quantitatively herbicides in environmental samples with a simple pretreatment procedure and provides the scientific basis for an improved environment management through a better understanding of the wastewater–soil–river sediment system as a whole.
Keywords: Atrazine; Ametryn; Prometryne; Second-order calibration; High performance liquid chromatography-diode array detection; Alternating penalty trilinear decomposition algorithm;
Partial least squares and principal components analysis of wine vintage by high performance liquid chromatography with chemiluminescence detection by S.A. Bellomarino; R.M. Parker; X.A. Conlan; N.W. Barnett; M.J. Adams (34-38).
HPLC with acidic potassium permanganate chemiluminescence detection was employed to analyse 17 Cabernet Sauvignon wines across a range of vintages (1971–2003). Partial least squares regression analysis and principal components analysis was used in order to investigate the relationship between wine composition and vintage. Tartaric acid, vanillic acid, catechin, sinapic acid, ethyl gallate, myricetin, procyanadin B and resveratrol were found to be important components in terms of differences between the vintages.
Keywords: Wine; High performance liquid chromatography; Chemiluminescence; Chemometrics; Partial least squares regression; Principal components analysis;
Simultaneous determination of electroactive and non-electroactive food preservatives by novel capillary electrophoresis with amperometric detection by Weiyu Wang; Yiping Wang; Junbo Zhang; Qingcui Chu; Jiannong Ye (39-43).
A novel capillary electrophoresis and amperometric detection method was achieved by adding an electroactive additive (3,4-dihydroxybenzylamine, 3,4-DHBA) to the running buffer, so that both electroactive and non-electroactive food preservatives were simultaneously determined. Under the selected optimum conditions, four electroactive preservatives (methylparaben, ethylparaben, propylparaben and butylparaben) and two non-electroactive preservatives (potassium sorbate and sodium lactate) were well separated and sensitively detected with detection limits (S/N = 3) ranging from 1.06 × 10−8 to 2.73 × 10−6 g mL−1. This method has been successfully employed for the determination of both electroactive and non-electroactive preservatives in several food commodities.
Keywords: Capillary electrophoresis; Amperometric detection; Running buffer additive; Food preservative;
Preparation and evaluation of graphene-coated solid-phase microextraction fiber by Jinmei Chen; Jing Zou; Jingbin Zeng; Xinhong Song; Jiaojiao Ji; Yiru Wang; Jaeho Ha; Xi Chen (44-49).
In this paper, a novel graphene (G) based solid-phase microextraction (SPME) fiber was firstly prepared by immobilizing the synthesized G on stainless steel wire as coating. The new fiber possessed a homogeneous, porous and wrinkled surface and showed excellent thermal (over 330 °C), chemical and mechanical stability, and long lifespan (over 250 extractions). The SPME performance of the G-coated fiber was evaluated in detail through extraction of six pyrethroid pesticides. Although the thickness of G-coated fiber was only 6–8 μm, its extraction efficiencies were higher than those of two commercial fibers (PDMS, 100 μm; PDMS/DVB, 65 μm). This high extraction efficiency may be mainly attributed to huge delocalized π-electron system of G, which shows strong π-stacking interaction with pyrethroid pesticide. The G-coated fiber was applied in the gas chromatographic determination of six pyrethroids, and their limits of detection were found to be ranged from 3.69 to 69.4 ng L−1. The reproducibility for each single fiber was evaluated and the relative standard deviations (RSDs) were calculated to be in the range from 1.9% to 6.5%. The repeatability of fiber-to-fiber and batch-to-batch was 4.3–9.2% and 4.1–9.9%. The method developed was successfully applied to three pond water samples, and the recoveries were 83–110% at a spiking of 1 μg L−1.
Keywords: Graphene; Solid-phase microextraction; Pyrethroid pesticide; π-Stacking interaction;
Development of superparamagnetic high-magnetization C18-functionalized magnetic silica nanoparticles as sorbents for enrichment and determination of methylprednisolone in rat plasma by high performance liquid chromatography by Panfeng Yu; Qi Wang; Xifeng Zhang; Xuesong Zhang; Shun Shen; Yan Wang (50-55).
In this study, a novel extraction and enrichment technique based on superparamagnetic high-magnetization C18-functionalized magnetic silica nanoparticles (C18-MNPs) as sorbents was successfully developed for the determination of methylprednisolone (MP) in rat plasma by high performance liquid chromatography (HPLC). The synthesized silica-coated magnetite modified with chlorodimethyl-n-octadecylsilane was about 320 nm in diameter with strong magnetism and high surface area. It provided an efficient way for extraction and concentration of MP in the samples through hydrophobic interaction by the interior C18 groups. Moreover, MP adsorbed with C18-MNPs could be simply and rapidly isolated through placing a strong magnet on the bottom of container, and then easily eluted from C18-MNPs by n-hexane solution. Extraction conditions such as amounts of C18-MNPs added, adsorption time and desorption solvent, were investigated. Method validations including linear range, detection limit, precision, and recovery were also studied. The results showed that the proposed method based on C18-MNPs was a simple, accurate and high efficient approach for the analysis of MP in the complex plasma samples.
Keywords: C18-functionalized magnetic silica nanoparticles; Sorbents; Methylprednisolone; Rat plasma; High performance liquid chromatography;
Simultaneous determination of pyrethrins residues in teas by ultra-performance liquid chromatography/tandem mass spectrometry by Caihong Lu; Xingang Liu; Fengshou Dong; Jun Xu; Wencheng Song; Changpeng Zhang; Yuanbo Li; Yongquan Zheng (56-62).
A sensitive and effective method for the simultaneous quantitative determination of pyrethrin residues in teas was developed and validated using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). The six major constituents of the pyrethrins (pyrethrin I and II, jasmolin I and II, and cinerin I and II) were successfully separated and independently confirmed in a single run within approximately 5 min. The multi-residue analysis of pyrethrins in teas involved simply extraction with acetonitrile, clean-up using a multilayer solid phase extraction cartridge, and subsequent separation by a hydrophilic end-capped Aquasil C18 columns with detection by tandem mass spectrometry using an electrospray ionization source in positive mode (ESI+). Recovery studies were carried out at three spiked levels (0.05, 0.1, 0.5 mg kg−1). The overall average recoveries using this method in green teas and black teas at the three concentration levels ranged from 76.15% to 101.86% with relative standard deviations (RSDs) in the range of 2.71–12.93% (n = 5) for all analytes. The limits of detections (LODs) were below 0.009 mg kg−1, which were lower than the maximum residue limits (MRLs) of 0.5 mg kg−1 in tea samples established by the European Union legislations in 2008, while the limits of quantification (LOQ) did not exceed 0.03 mg kg−1. This study provides a theoretical basis for China to draw up MRLs for pyrethrins in teas.
Keywords: Tea; Pyrethrins; Ultra-performance liquid chromatography coupled with tandem mass spectrometry; Multi-residue; Solid-phase extraction;
Determination of pesticides in surface and ground waters by liquid chromatography–electrospray–tandem mass spectrometry by Nikolina Dujaković; Svetlana Grujić; Marina Radišić; Tatjana Vasiljević; Mila Laušević (63-72).
The sensitive multiresidual analytical method for simultaneous analysis of 14 most commonly used agricultural pesticides in Serbia was developed and optimized. The selected insecticides, fungicides and herbicides belong to seven chemical classes (organophosphates, neonicotinoids, carbamates, diacylhydrazines, benzimidazoles, triazines and phenylureas). The method was based on solid-phase extraction followed by liquid chromatography–tandem mass spectrometry. The following parameters that may affect the SPE procedure efficiency were optimized: the sorbent type in combination with different elution solvents, the sample pH and the sample volume. For each pesticide, MS n analysis was performed and distinctive ions and transitions were selected for identification and quantification, as well as for confirmation purposes. External matrix-matched calibration method was used to eliminate variable matrix effect and ensure precise quantification. Good recoveries (72–129%), and low limits of detection (0.4–5.5 ng L−1) and quantification (1.1–18.2 ng L−1) were achieved for all selected pesticides. The developed and optimized method was successfully applied in the analysis of several river waters, as well as ground waters in Serbia, influenced by agriculture. The most frequently detected pesticide was carbendazim. Dimethoate, carbofuran and propazine were also found in the investigated samples.
Keywords: Pesticides; Liquid chromatography–tandem mass spectrometry; Ion trap; Solid-phase extraction; Water analysis;
Suitability of selective pressurized liquid extraction combined with gas chromatography–ion-trap tandem mass spectrometry for the analysis of polybrominated diphenyl ethers by S. Losada; J. Parera; M. Abalos; E. Abad; F.J. Santos; M.T. Galceran (73-81).
A one-step extraction and clean-up method using pressurized liquid extraction (PLE) (selective PLE) combined with gas chromatography–ion-trap tandem mass spectrometry (GC–ITMS–MS) was evaluated for the analysis of polybrominated diphenyl ethers (from tri- to hepta-PBDEs) at low concentrations in fish and shellfish samples. To this end, the performance of an on-line PLE extraction/clean-up method and of a classical Soxhlet extraction and clean-up method using a multi-layer modified silica column were compared. The two sample treatment methods provided similar results, although an important reduction in the sample treatment time (40 min per sample) was achieved using the selective PLE method. In addition, the suitability of the PLE combined with GC–ITMS–MS method was evaluated by comparing the results obtained in the analysis of fish samples with those obtained by gas chromatography–high resolution mass spectrometry (GC–HRMS). Good agreement between both techniques was obtained with differences between the mean values of less than 16%. The selective PLE method coupled to GC–ITMS–MS produced accurate results for PBDE determination with low limits of detection (1.0–16.8 pg g−1 wet weight) and quantification (3.1–51 pg g−1 wet weight) as well as good precision (RSD < 16%). This method has been applied to the analysis of PBDEs in fish and shellfish samples collected at fish markets in Catalonia (NE Spain).
Keywords: Polybrominated diphenyl ethers; Flame retardants; Pressurized liquid extraction; Gas chromatography-high resolution mass spectrometry; Gas chromatography-tandem mass spectrometry; Ion-trap tandem mass spectrometry; Fish analysis;
A simple; efficient and environmentally friendly method for the extraction of pesticides from onion by matrix solid-phase dispersion with liquid chromatography–tandem mass spectrometric detection by Sherol Acosta Rodrigues; Sergiane Souza Caldas; Ednei Gilberto Primel (82-89).
An evaluation of the extraction of pesticides from onion by matrix solid-phase dispersion (MSPD) with the determination by liquid chromatography tandem mass spectrometry using electrospray as the ionization source (LC-ESI-MS/MS) was carried out. The performance of different sorbents, including reused C18 bonded silica, was evaluated. Different parameters affecting the extraction efficiency were evaluated, such as the type and amount of sorbent, the time of interaction after the fortification step, the time of sample dispersion and the elution solvent. The matrix effect regarding the recovery of the pesticides by MSPD was also investigated. The best results were obtained using 0.5 g of sample, 1.0 g reused C18, interaction time of 1 h, dispersion time of 5 min, and acetonitrile as the elution solvent. The method was validated by the fortification of the onion sample, free of pesticides, at different concentration levels (0.01, 0.1 and 1.0 mg kg−1). Average recoveries ranged from 78.3 to 120.4% and relative standard deviation below 20% was obtained. Detection and quantification limits ranged from 0.003 to 0.03 mg kg−1 and from 0.01 to 0.1 mg kg−1, respectively.
Keywords: Sorbent; Matrix solid-phase dispersion; Onion; Pesticide; Liquid chromatography–tandem mass spectrometry;
An improved method for analyzing chlormequat and mepiquat in source waters by solid-phase extraction and liquid chromatography–mass spectrometry by Zhiyong Yu; Fen Jin; Jianying Hu; Xi Zhang; Jingfang Sun; Min Yang (90-95).
A liquid chromatography–mass spectrometry (LC–MS) method for the identification and quantification of chlormequat (CQ) and mepiquat (MQ) in source waters with high sensitivity and specificity was established using WCX cartridges (150 mg/6 mL) for pre-concentration of the samples and using the CAPCELL PAK CR 1:4 (2.0 mm × 150 mm 5 μm, SCX:C18 = 1:4) column containing strong cationic exchange resins and C18 for separation. The method could solve the problem for pre-concentrating ionic compounds from water samples and avoid the MS instrument fouling problem accompanied with the use of ion-pair reagents. After the optimization of analytical conditions, quantification was achieved in the positive electrospray ionization mode using selected ion monitoring. The samples were analyzed with multi-channel mode with quantification performed at 30 V cone voltage to ascertain the sensitivity and qualitative analysis performed at 60 V cone voltage simultaneously. The method detection limits (MDLs) of CQ and MQ in source water were determined to be 14 and 22 ng L−1. Finally, the method was used to quantify CQ and MQ in several source waters, which gave a level ranging from below the quantitation limit to 28 ng L−1.
Keywords: Liquid chromatography–mass spectrometry; Plant growth regulator; Source water; Chlormequat; Mepiquat;
Qualitative and quantitative analysis of polycyclic polyprenylated acylphloroglucinols from Garcinia species using ultra performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry by Yan Zhou; Stephanie Lee; Franky Fung Kei Choi; Gang Xu; Xin Liu; Jing-Zheng Song; Song-Lin Li; Chun-Feng Qiao; Hong-Xi Xu (96-107).
Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a group of natural products isolated from different Garcinia species with a wide range of important biological activities. In this study, an ultra performance liquid chromatography (UPLC) coupled to photodiode-array detection and quadrupole time-of-flight mass spectrometry (Q-TOF) method was developed to characterize 16 PPAPs in 10 Garcinia species. In source dissociation techniques based on cone voltage fragmentation were used to fragment the deprotonated molecules and multiple mass spectrometry (MS/MS) using ramping collision energy were used to further break down the resulting product ions. The resulting characteristic fragment ions were generated by cleavage of C1–C5 bond and C7–C8 bond through concerted pericyclic reaction, which is especially valuable for differentiating three types of PPAPs isomers. As such, two new PPAPs isomers present in minor amount in the extracts of Garcinia oblongifolia were tentatively characterized by comparing their tandem mass spectra to the known ones. In addition, an UPLC–Q-TOF-MS method was validated for the quantitative determination of PPAPs. The method exhibited limits of detection from 2.7 to 21.4 ng mL−1 and intra-day and inter-day variations were less than 3.7% and the recovery was in the range of 89–107% with RSD less than 9.0%. This UPLC–Q-TOF-MS method has successfully been applied to quantify 16 PPAPs in 32 samples of 10 Garcinia species, which were found to be a rich source of PPAPs.
Keywords: Polycyclic polyprenylated acylphloroglucinols (PPAPs); Garcinia species; Ultra performance liquid chromatography; Quadrupole time-of-flight mass spectrometry;
Simultaneous determination of sex hormones in egg products by ZnCl2 depositing lipid, solid-phase extraction and ultra performance liquid chromatography/electrospray ionization tandem mass spectrometry by Quan-lin Wang; Ai-zhi Zhang; Xu Pan; Li-ren Chen (108-116).
A method was developed for simultaneous determination of residues of 17 sex hormones in egg products. Target compounds were extracted from samples with methanol in an ultrasonic bath, effectively separated from lipids in the extracts by ZnCl2 depositing filtration and purified using a C18 solid-phase extraction (SPE) and followed by NH2 SPE cartridge. The analytes were quantified by liquid chromatography using a BEH C18 column coupled to an electrospray ionization tandem mass spectrometer (LC–ESI-MS/MS) operating in negative mode for estrogens and in positive multiple reaction monitoring mode for androgens. The parameters of the mass spectrometer and the composition of mobile phase and additives were also optimized to enhance detection sensitivity. Average recoveries of the target compounds varied from 70.0% to 121.0% with relative standard deviations ranging from 2.3% to 11.2% at two fortification levels. The limits of detection (LOD) of the method were from 0.002 μg kg−1 to 0.23 μg kg−1 and the limits of quantification (LOQ) were in the range of 0.007–0.76 μg kg−1.
Keywords: Sex hormone; Egg products; ZnCl2 depositing lipid; Ultra performance liquid chromatography/electrospray ionization tandem mass spectrometry;
Determination of aromatic amines in aqueous extracts of polyurethane foam using hydrophilic interaction liquid chromatography and mass spectrometry by Jakob Riddar Johnson; Daniel Karlsson; Marianne Dalene; Gunnar Skarping (117-123).
A method is presented for the determination of aromatic amines in aqueous extracts of polyurethane (PUR) foam. The method is based on the extraction of PUR foam using aqueous acetic acid (0.1%, w/v) followed by determination of extracted aromatic amines using hydrophilic interaction liquid chromatography (HILIC) and tandem mass spectrometry (MS/MS) with positive electrospray ionisation. The injections of volumes up to 5 μL of aqueous solutions were made possible by on-column focusing with partially filled loop injections. The fragmentation patterns for 2,4- and 2,6-toluene diamine (TDA) and 4,4′-methylene dianiline (MDA) were clarified by performing a hydrogen–deuterium exchange study.TDA and MDA were determined using trideuterated 2,4- and 2,6-TDA and dideuterated 4,4′-MDA as internal standards. Linear calibration graphs were obtained over the range 0.025–0.5 μg mL−1 with correlation coefficients >0.996 and the instrumental detection limit for each compound was <50 fmol. The stability of the amines was influenced by the matrix, so their concentrations decreased over time.Agreement was observed between the results of analyses of PUR foam extracts by HILIC–MS/MS and results obtained by ethyl chloroformate derivatisation and reversed phase (RP) liquid chromatography–mass spectrometry (LC–MS/MS).TDA was observed to be unstable in extracts of foam but not in pure solutions.
Keywords: Polyurethane (PUR) foam; Hydrogen–deuterium exchange; Liquid chromatography–electrospray tandem mass spectrometry; Hydrophilic interaction liquid chromatography (HILIC); Toluene diamine (TDA); Methylene dianiline (MDA);
G-quadruplex–hemin DNAzyme-amplified colorimetric detection of Ag+ ion by Xue-Hui Zhou; De-Ming Kong; Han-Xi Shen (124-127).
A G-quadruplex–hemin DNAzyme-amplified Ag+-sensing method was developed based on the ability of Ag+ to stabilize C–C mismatches by forming C–Ag+–C base pairs. In this method, only one unlabelled oligonucleotide strand was used. In the absence of Ag+, the oligonucleotide strand formed an intramolecular duplex. The G-rich sequence in the oligonucleotide was partially caged in this duplex structure and cannot fold into the G-quadruplex structure. The addition of Ag+ promoted the formation of another intramolecular duplex in which C–C mismatches were stabilized by C–Ag+–C base pairs, leading to the release of the G-rich sequence which can fold into a G-quadruplex capable to bind hemin to form a catalytically active G-quadruplex–hemin DNAzyme. As a result, a UV–vis absorbance increasing was observed in the H2O2–ABTS (2,2′-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid) reaction system. This “turn-on” process allowed the detection of aqueous Ag+ at concentrations as low as 6.3 nM using a simple colorimetric technique, showing a high selectivity over a range of other metal ions.
Keywords: G-quadruplex; DNAzyme; Ag+ ion detection; Hemin;
Capillary electrophoresis–mass spectrometry of intact basic proteins using Polybrene–dextran sulfate–Polybrene-coated capillaries: System optimization and performance by Rob Haselberg; Gerhardus J. de Jong; Govert W. Somsen (128-134).
A capillary electrophoresis–mass spectrometry (CE–MS) method using sheath liquid electrospray ionization interfacing was studied and optimized for the analysis of intact basic proteins. To prevent protein adsorption, capillaries with a noncovalent positively charged coating were utilized. Capillaries were coated by subsequent rinsing with solutions of Polybrene, dextran sulfate and Polybrene. The coating proved to be fully compatible with MS detection, causing no background signals and ionization suppression. The composition of the sheath liquid and BGE was optimized using the model proteins α-chymotrypsinogen A, ribonuclease A, lysozyme and cytochrome c. A sheath liquid of isopropanol–water–acetic acid (75:25:0.1, v/v/v) at 2 μL min−1 resulted in optimal signal intensities for most proteins, but caused dissociation of the heme group of cytochrome c. Optimum protein responses were obtained with a BGE of 50 mM acetic acid (pH 3.0), which allowed a baseline separation of the test protein mixture. Several minor impurities present in the mixture could be detected and provisionally identified using accurate mass and a protein modification database. The selectivity of the CE–MS system was investigated by the analysis of acetylated lysozyme. Eight highly related species, identified as non-acetylated lysozyme and lysozyme acetylated in various degrees, could be distinguished. The CE–MS system showed good reproducibility yielding interday (three weeks period) RSDs for migration time and peak area within 2% and 10%, respectively. With the CE–MS system, determination coefficients (R 2) for protein concentration and peak area were higher than 0.996, whereas detection limits were between 11 and 19 nM.
Keywords: Basic proteins; Capillary coating; Capillary electrophoresis; Mass spectrometry;