Plasma lipid analysis by hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A novel method for the analysis of endogenous lipids and related compounds was developed employing hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry. A hydrophilic interaction liquid chromatography with carbamoyl stationary phase achieved clear separation of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, ceramide, and mono‐hexsosyl ceramide groups with good peak area repeatability (RSD% < 10) and linearity (R² > 0.99). The established method was applied to human plasma assays and a total of 117 endogenous lipids were successfully detected and reproducibly identified. In addition, we investigated the simultaneous detection of small polar metabolites such as amino and organic acids co‐existing in the same biological samples processed in a single analytical run with lipids. Our results show that hydrophilic interaction liquid chromatography is a useful tool for human plasma lipidome analysis and offers more comprehensive metabolome coverage.     

A capillary electrophoresis system with dual capacitively coupled contactless conductivity detection and electrospray ionization tandem mass spectrometry

A commercial system that is comprised of a CE coupled to an ESI triple quadrupole mass spectrometer was equipped with two capacitively coupled contactless conductivity detectors (C⁴Ds). The first C⁴D was positioned inside the original cartridge, and the second C⁴D was positioned as close as possible to the ESI probe entrance by using a 3D‐printed support. The C⁴Ds electropherograms were matched to the ESI‐MS electropherogram by correcting their timescales by the factor L_T/L_D, where L_T and L_D are the total capillary length and the length until the C⁴D, respectively. A general approach for method development supporting the simultaneous conductivity and MS detection is discussed, while application examples are introduced. These examples include the use of C⁴D as a simple device that dismiss the use of an EOF marker, a low‐selectivity detector that continuously provide information about unexpected features of the sample, and even a detector that can be more sensitive than ESI‐MS. The C⁴D used in this setup proved to have a smaller contribution to the peak broadening than ESI‐MS, which allowed that a C⁴D, positioned at 12 cm from the inlet of an 80‐cm‐long capillary, could be used to foresee position and shape of the peaks being formed 6.8 times slower at the ESI‐MS electropherogram.     

Determination of perchlorate in river by ion-pair hollow-fiber liquid-phase microextraction coupled with electrospray ionization tandem mass spectrometry

This paper describes the analysis of perchlorate (ClO₄⁻) in surface water samples by a rapid and reliable ion-pair hollow-fiber liquid-phase microextraction (HF-LPME) method coupled with flow-injection electrospray ionization tandem mass spectrometry (ESI-MS-MS) technique. The effects of the type and concentration of ion-pairing reagents, extraction time, temperature and pH value on the quantitative extraction of perchlorate by ion-pair HF-LPME were investigated and optimized. Di-n-hexyl ammonium acetate (DHAA) was employed to form an extractable ion-pair complex with aqueous perchlorate. The characteristic ions [ClO₄-ClO₄-DHA]⁻ at m/z 384.6 and 386.7 were observed in the ESI negative-ionization mode. The predominant product ions [ClO₄]⁻ at m/z 99 and 101 were used for quantitation and to maximize the detection selectivity and sensitivity. The limit of detection (LOD) was 0.5 μg/L. The reliability and precision of the standard addition method of ion-pair HF-LPME for the determination of trace levels of perchlorate in surface water were demonstrated.     

Approaches to sample pretreatment in the determination of perchlorate in real world samples

Perchlorate can be determined by the tandem technique of ion chromatography (IC) coupled to electrospray ionization mass spectrometry (ESI-MS). However, detection by ESI-MS can be compromised by the coelution of matrix components that can suppress the analyte signal. In addition, the presence of surface-active and other types of matrix components can cause fouling of the electrospray inlet, reducing overall signal and requiring frequent maintenance. The influences of matrix components can be minimized by using analytical columns with different selectivities, in-line diversion of separated matrix components, and off-line selective removal of matrix components via ion exchange or adsorption. This paper will discuss these sample preparation approaches for samples containing anionic species including surfactants and inorganic ions that elute in the vicinity of perchlorate.     

Improved design for high resolution electrospray ionization ion mobility spectrometry

An improved design for high resolution electrospray ionization ion mobility spectrometry (ESI-IMS) was developed by making some salient modifications to the IMS cell and its performance was investigated. To enhance desolvation of electrospray droplets at high sample flow rates in this new design, volume of the desolvation region was decreased by reducing its diameter and the entrance position of the desolvation gas was shifted to the end of the desolvation region (near the ion gate). In addition, the ESI source (both needle and counter electrode) was positioned outside of the heating oven of the IMS. This modification made it possible to use the instrument at higher temperatures, and preventing needle clogging in the electrospray process. The ion mobility spectra of different chemical compounds were obtained. The resolving power and resolution of the instrument were increased by about 15-30% relative to previous design. In this work, the baseline separation of the two adjacent ion peaks of morphine and those of codeine was achieved for the first time with resolutions of 1.5 and 1.3, respectively. These four ion peaks were well separated from each other using carbon dioxide (CO₂) rather than nitrogen as the drift gas. Finally, the analytical parameters obtained for ethion, metalaxyl, and tributylamine indicated the high performance of the instrument for quantitative analysis.     

Separation and identification of ceramides in the human stratum corneum by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry and electrospray multiple-stage mass spectrometry profiling

Summary A sensitive, selective, and rapid method is described for analysis of ceramides in the human stratum coracum by direct coupling of HPLC with an electrospray ion-trap mass spectrometry. Nonaqueous reversed-phase chromatography stabilizes the electrospray ionization, resulting in sensitivity that enables direct measurement of skin lipid extracts with no special sample preparation. Assignment of individual signals to the corresponding ceramide species is based on interpretation of the fragment spectra from MS-MS experiments. This enables much finer differentiation between ceramdies than that achievable by thin-layer chromatography. Summary A sensitive, selective, and rapid method is described for analysis of ceramides in the human stratum corneum by direct coupling of HPLC with an electrospray ion-trap mass spectrometry. Nonaqueous reversed-phase chromatography stabilizes the electrospray ionization, resulting in sensitivity that enables direct measurement of skin lipid extracts with no special sample preparation. Assignment of individual signals to the corresponding ceramide species is based on interpretation of the fragment spectra from MS-MS experiments. This enables much finer differentiation between ceramides than that achievable by thin-layer chromatography.     

Coupling of capillary electrophoresis with electrospray ionization multiplexing ion mobility spectrometry

In this work, ion mobility spectrometry (IMS) function as a detector and another dimension of separation was coupled with CE to achieve two‐dimensional separation. To improve the performance of hyphenated CE‐IMS instrument, electrospray ionization correlation ion mobility spectrometry is evaluated and compared with traditional signal averaging data acquisition method using tetraalkylammonium bromide compounds. The effect of various parameters on the separation including sample introduction, sheath fluid of CE and drift gas, data acquisition method of IMS were investigated. The experimental result shows that the optimal conditions are as follows: hydrodynamic sample injection method, the electrophoresis voltage is 10 kilo volts, 5 mmol/L ammonium acetate buffer solution containing 80% acetonitrile as both the background electrolyte and the electrospray ionization sheath fluid, the ESI liquid flow rate is 4.5 μL/min, the drift voltage is 10.5 kilo volts, the drift gas temperature is 383 K and the drift gas flow rate is 300 mL/min. Under the above conditions, the mixture standards of seven tetraalkylammoniums can be completely separated within 10 min both by CE and IMS. The linear range was 5–250 μg/mL, with LOD of 0.152, 0.204, 0.277, 0.382, 0.466, 0.623 and 0.892 μg/mL, respectively. Compared with traditional capillary electrophoresis detection methods, the developed CE‐ESI‐IMS method not only provide two sets of qualitative parameters including electrophoresis migration time and ion drift time, ion mobility spectrometer can also provide an additional dimension of separation and could apply to the detection ultra‐violet transparent compounds or none fluorescent compounds.     

Simultaneous analysis of ten phytohormones in Sargassum horneri by high‐performance liquid chromatography with electrospray ionization tandem mass spectrometry

Phytohormones have attracted wide attention due to their important biological functions. However, their detection is still a challenge because of their complex composition, low abundance and diverse sources. In this study, a novel method of high‐performance liquid chromatography with electrospray ionization tandem mass spectrometry was developed and validated for the simultaneous determination of ten phytohormones including indole‐3‐acetic acid, isopentenyladenine, isopentenyl adenosine, trans‐zeatin riboside, zeatin, strigolactones, abscisic acid, salicylic acid, gibberellin A3, and jasmonic acid in Sargassum horneri (S. horneri). The phytohormones were extracted from freeze‐dried S. horneri with methanol/water/methanoic acid (15:4:1, v/v/v) analyzed on a Hypersil Gold C₁₈ column and detected by electrospray ionization tandem triple quadrupole mass spectrometry in the multiple reaction monitoring mode. The experimental conditions for the extraction and analysis of phytohormones were optimized and validated in terms of reproducibility, linearity, sensitivity, recovery, accuracy, and stability. Distributions of the phytohormones in the stems, blades, and gas bladder of the S. horneri in drift, fixed, and semi‐fixed growing states were investigated for the first time. The observed contents of the phytohormones in S. horneri range from not detected to 5066.67 ng/g (fresh weight). Most phytohormones are distributed mainly in the stems of S. horneri in drift and semi‐fixed states.     

High resolution electrospray ionization ion mobility spectrometry

Current commercially available ion mobility spectrometers are intended for the analysis of chemicals in the gas phase. Sample introduction methods, such as direct air sampling, a GC injector or a thermal desorber, are commonly an integral part of these instruments. This paper describes an electrospray ionization ion mobility spectrometer system that allows direct introduction samples in solution phase. This allows direct analysis of non-volatile organic and biological samples, and avoids decomposition of thermally liable samples, providing reliable chemical identification. In addition, the new ion mobility spectrometer allows mobility analysis with high resolving power. Commonly used commercial IMS systems provide resolving powers between 10 and 30; this new ion mobility spectrometer has resolving power greater than 60 for routine analysis. A high resolution instrument is necessary for many applications where a complex mixture needs to be separated and quantified. This paper demonstrates the advantages of using a high resolution ion mobility spectrometer and an electrospray ionization source for the analysis of non-volatile pharmaceuticals as well as dissolved explosive in solution phase.     

Simultaneous determination of trace oxyhalides and haloacetic acids using suppressed ion chromatography-electrospray mass spectrometry

A new analytical procedure for the simultaneous determination of trace oxyhalides and haloacetic acids (HAs) in drinking water and aqueous soil extracts is described. The method uses micro-bore ion chromatography (IC) coupled with suppressed conductivity (SC) and electrospray ionization mass spectrometric detection (ESI-MS). The IC-SC-ESI-MS system included a secondary flow of 100% MeOH, which was added to the column eluate (post-suppressor) and resulted in a significant increase in sensitivity for all analytes. All ESI-MS parameters were optimized for HA analysis and sensitivity quantitatively compared to suppressed conductivity. Full analytical performance characteristics for the developed method are presented for monochloro-, monobromo-, dichloro-, dibromo-, trichloro-, bromochloro, chlorodifluoro-, trifluoro-, dichlorobromo- and dibromochloroacetic acid, as well as the oxyhalides iodate, bromate, chlorate and perchlorate. In the case of the HAs, an optimised 25-fold SPE preconcentration method meant all analytes could be readily detected well below the USEPA 60 μg/L regulatory limit using conductivity and/or ESI-MS. The IC-ESI-MS method was applied to the determination of oxyhalides and HAs in both soil extracts and drinking water samples. Soil samples were extracted using ultra pure water with subsequent determination of perchlorate at 1.68 μg/g of soil. A drinking water sample containing HAs was preconcentrated using LiChrolut EN solid phase extraction cartridges with subsequent sulphate and chloride removal. Total HAs were determined at 13 μg/L.     

Quantitative analysis of memantine in human plasma by gas chromatography/negative ion chemical ionization/mass spectrometry

A sensitive and specific method for the determination of memantine in human plasma is presented. Memantine was extracted from plasma and derivatized to the pentafluorobenzoyl derivative in a one-step procedure avoiding any sample concentration steps. Amantadine was used as an internal standard. The compounds were measured by gas chromatography/negative ion chemical ionization mass spectrometry without any further processing. Using this detection mode, the fragment ions at m/z 353 and 325 were obtained at high relative abundance. Calibration graphs were linear over the range 0.117-30 ng ml(-1). At the limit of quantification (LOQ), the inter-assay precision was 2.00% and the intra-assay variability was 3.22%. The accuracy at the LOQ showed deviations of -1.42% (intra-assay) and -2.47% (inter-assay). The method is rugged, rapid and robust and was applied to the batch determination of memantine during pharmacokinetic profiling of the drug.     

Separation of benzodiazepines by electrospray ionization ion mobility spectrometry-mass spectrometry

Benzodiazepines are a commonly abused class of drugs; requiring analytical techniques that can separate and detect the drugs in a rapid time period. In this paper, the two-dimensional separation of five benzodiazepines was shown by electrospray ionization (ESI) ion mobility spectrometry (IMS)-mass spectrometry (MS). In this study, both the two dimensions of separation (m/z and mobility) and the high resolution of our IMS instrument enabled confident identification of each of the five benzodiazepines studied. This was a significant improvement over previous IMS studies that could not separate many of the analytes due to low instrumental resolution. The benzodiazepines that contain a hydroxyl group in their molecular structure (lorazepam and oxazepam) were found to form both the protonated molecular ion and dehydration product as predominant ions. Experiments to isolate the parametric reasons for the dehydration ion formation showed that it was not the result of corona discharge processes or the potential applied to the needle. However, the potential difference between the needle and first drift ring did influence both the relative intensity ratios of the two ions and the ion sensitivity.     

Determination of trace level of perchlorate in Antarctic snow and ice by ion chromatography coupled with tandem mass spectrometry using an automated sample on-line preconcentration method

A new ion chromatography coupled with tandem mass spectrometry（IC-ESI-MS/MS） method,with automated sampling and on-line preconcentration,has been developed for the determination of perchlorate in Antarctic snow and ice at low part-per-trillion（ng/L） levels.To the best of our knowledge, this is the first time that an analytical method is used for the determination of perchlorate in Antarctic snow and ice.The IC-ESI-MS/MS instrumentation consisted of an ICS2000 ion chromatography（IC） system coupled to an API3200 electrospray tandem mass spectrometer（ESI-MS/MS）.On-line preconcentration was realized through a six-port injector valve,a TAC-ULP1 concentrator column and an AS auto-sampler.Multiple reaction monitoring（MRM） mode was used to quantify the perchlorate anion.The transition of ³⁵Cl¹⁶O₄^-（m/z 98.9） into ³⁵Cl¹⁶O₃^-（m/z 82.9） was monitored for quantifying the main analyte,and the transition of ³⁷Cl¹⁶O₄^-（m/z 100.9） into ³⁷Cl¹⁶O₃^-（m/z 84.9） was monitored for examining a proper isotopic abundance ratio of ³⁵Cl to ³⁷Cl,which was used as a confirmation tool.The limit of detection（LOD） and limit of quantitation（LOQ） for the method was 0.2 ng/ L and 0.5 ng/L,respectively.And this new method exhibited acceptable accuracy and precision for samples at ng/L levels.All the tested snow and ice samples were found to contain measurable amount of perchlorate,ranging from 10 ng/L to 340 ng/L.     

Quantitative determination of domperidone in human plasma by ultraperformance liquid chromatography with electrospray ionization tandem mass spectrometry

A simple and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for determining domperidone in human plasma. The analyte and internal standard (IS; mosapride) were isolated from plasma samples by protein precipitation with methanol (containing 0.1% formic acid). The chromatographic separation was performed on an Xterra MS C(18) Column (2.1 x 150 mm, 5.0 microm) with a gradient programme mobile phase consisting of 0.1% formic acid and acetonitrile at a flow rate of 0.30 mL/min. The total run time was 4.0 min. The analyses were carried out by multiple reaction monitoring using the parent-to-daughter combinations m/z 426 --> 175 and m/z 422 --> 198 (IS). The areas of peaks from the analyte and IS were used for quantification of domperidone. The method was validated according to the FDA guidelines on bioanalytical method validation. Validation results indicated that the lower limit of quantification was 0.2 ng/mL, and the assay exhibited a linear range of 0.2-60.0 ng/mL and gave a correlation coefficient (r(2)) of 0.999 or better. Quality control samples (0.4, 0.8, 15 and 50 ng/mL) in six replicates from three different analytical runs demonstrated an intra-assay precision (RSD) 4.43-6.26%, an inter-assay precision 5.25-7.45% and an overall accuracy (relative error) of <6.92%. The method can be applied to pharmacokinetic and bioequivalence studies of domperidone.     

Gas chromatography electrospray ionization mass spectrometry analysis of trimethylsilyl derivatives

A method based on the analysis of trimethylsilyl (TMS) derivatives by capillary gas chromatography electrospray ionization mass spectrometry (GC–ESI/MS) was proposed. To improve separation, analytes were derivatized to their TMS derivative. During ESI analysis, TMS derivatives may hydrolyze back to their polar native form and are thus suitable for ESI analysis. Several types of analytes were studied to investigate the potential of the approach. Not all TMS derivatives hydrolyzed back to their native form as anticipated. Incomplete hydrolysis was observed for TMS‐organic acids and TMS‐nonchlorinated phenols. For TMS‐chlorophenols, the observation of only the [M ? H]^? ion suggested that these phenols were hydrolyzed back to their native form. For TMS‐beta agonists, the hydrolysis rate was low; therefore, the hydrolysis product was not detected. Both TMS‐chlorophenols and TMS‐beta agonists provide a sensitivity in the range of low parts per billion (0.25–5 ng/ml and 0.5–10 ng/ml respectively). Copyright © 2016 John Wiley & Sons, Ltd.     

Matrix diversion methods for improved analysis of perchlorate by suppressed ion chromatography and conductivity detection

Two inline matrix diversion methods were developed for the sensitive analysis of perchlorate in a matrix comprising up to 1000 mg l⁻¹ of chloride, sulfate and bicarbonate ions using suppressed ion chromatography and conductivity detection. The first method used a cryptand C1 concentrator column, which exhibited a high selectivity for perchlorate ion over the other matrix anions. After retaining the sample anions in a concentrator column derivatized with a crytpand phase, a rinse step was implemented with a weak base to divert the matrix ions to waste while selectively retaining perchlorate in the concentrator column for subsequent analysis. The analysis was done using a 2 mm IonPac^® AS16 or 2 mm IonPac^® AS20 separator column. The second method was a two-dimensional matrix diversion method with a focus on improving the detection sensitivity. The first dimension was used to achieve some resolution of the matrix ions from perchlorate. The perchlorate ion was then diverted into a concentrator column for subsequent analysis in the second dimension. By pursuing analysis using a 4 mm IonPac^® AS16 or IonPac^® AS20 column in the first dimension and subsequently pursuing analysis using a 2 mm IonPac^® AS16 or IonPac^® AS20 column format, excellent sensitivities were achieved when the first and second dimensions were operated at the same linear flow velocity (cm min⁻¹). While sensitive detection of perchlorate in the low μg l⁻¹ regime was achieved by the above methods in the presence of matrix ions, superior recovery for perchlorate was demonstrated under a variety of matrix concentrations by the second method.     

啤酒中单糖的衍生化HPLC-ESI-MS测定方法研究

单糖类样品在溶液中非常稳定,难于离子化,不适合于进行ESI-MS检测。采用1-苯基-3-甲基-5-吡唑啉酮(PMP)将糖类物质衍生化,HPLC-ESI-MS在线联用,选择性离子扫描方式对几种啤酒样品中的5种单糖进行了分离检测。检出限可达到80pg。     

Nano-flow multidimensional liquid chromatography with electrospray ionization time-of-flight mass spectrometry for proteome analysis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the top five cancers with the highest incident of a disease worldwide. To understand the mechanisms of hepatocarcinogenesis, proteomics analysis provides a powerful tool to identify proteins that associate with HCC. We developed a two-step procedure for mapping of HCC proteomics. In the first step, in order to simplify the complexity of proteomics of HCC, the subfractionation of complex protein mixtures in HCC into “subproteomes” is presented based on the solubility of protein. While in the second step an automate comprehensive two-dimensional (2D) separation system, coupling strong cation-exchange (SCX) in the first dimension with capillary reversed-phase chromatography (cRPLC) in the second dimension is developed further to separate and analyze proteins associated with HCC. By using this system, complex sample can be injected, desalted, separated and analyzed in complete automatization. The procedure for proteomics analysis was found to be applied for proteins with great molecular mass (>100 000), small molecular mass (<20 000), highly basic (pI > 9.5) and hydrophobicity, which are not well resolved in 2D-gel electrophoresis. In total 229 proteins were identified by using the described proteomics platform. Among them, several proteins related to the process of carcinogenesis were investigated further.     

Fesoterodine stress degradation behavior by liquid chromatography coupled to ultraviolet detection and electrospray ionization mass spectrometry

In the present study, a rapid validated stability-indicating LC method was established and comprehensive stress testing of fesoterodine was carried out according to ICH guidelines. Fesoterodine was subjected to stress conditions of acid and basic hydrolysis, oxidation, photolysis and thermal decomposition. The degradation products formed under stress conditions were investigated by LC-UV and LC-ESI-MS. Successful separation of the drug from its degradation products was achieved on a monolithic C₁₈ column (100 mm × 4.6 mm i.d.) maintained at 45 °C using acetonitrile-methanol-0.03 mol L⁻¹ ammonium acetate (pH 3.8) (30:15:55, v/v/v) as the mobile phase. The flow rate was 2.4 mL min⁻¹ and the detection wavelength was 208 nm. Validation parameters such as specificity, linearity, precision, accuracy, and robustness were evaluated. Chromatographic separation was obtained within 2.5 min and it was suitable for high-throughput analysis. Fragmentation patterns of degradation products formed under different stress conditions were studied and characterized through LC-ESI-MS fragmentation. Based on the results, a drug degradation pathway was proposed, and the validated LC method was successfully applied to the quantitative analysis of fesoterodine in tablet dosage forms, helping to improve quality control and to assure therapeutic efficacy.