Sample preparation and direct electrospray ionization on a tip column for rapid mass spectrometry analysis of complex samples

A handheld pipette tip column electrospray ionization source (PTC-ESI source) was developed for rapid mass spectrometry analysis at ambient pressure. The PTC-ESI source was made up of three main component parts including a micro DC high voltage (HV) power supply, a micropipette and a disposable micropipette tip filled with a plug of adsorbent. A DC high voltage was applied to the sharp point of the micropipette tip column to induce electrospray ionization. The PTC-ESI source was successfully used for direct analysis of basic organic compounds, organic acids and peptides in a simple matrix. In the case of complex samples, micro-extraction based on the adsorbent phase filled in the pipette tip was used to remove impurities and concentrate target analytes prior to ionization. The eluting solution was not pipetted out, but directly dispersed in the form of electrospray from the pipette tip for ionization. The effectiveness of the PTC-ESI source has been further demonstrated by fast analysis of therapeutic compounds and endogenous bioactive chemicals in complex biological samples.     

Rapid determination of carbendazim in complex matrices by electrospray ionization mass spectrometry with syringe filter needle

The determination of pesticide residues is an indispensable task in controlling food safety and environment protection. Carbendazim is one of the extensive uses of pesticides in the agricultural industry. In this study, a simple method utilizing syringe filter has been applied as electrospray ionization emitter for mass spectrometric identification and quantification of carbendazim in complex matrices including soil, natural water, and fruit juice samples, which contain many insoluble materials. With online syringe filter of the complex samples, most of insoluble materials such as soil were excluded in spray ionization process due to the filter effect, and analytes were subsequently sprayed out from syringe needle for mass spectrometric detection. The pore sizes of filters and diameters of syringe needles also were investigated. The analytical performances, including the linear range (1–200 ng·mL⁻¹), limit of detection (0.2–0.6 ng·mL⁻¹, S/N > 3), limit of quantitation (3.5–8.6 ng·mL⁻¹, S/N > 10), reproducibility (6.4%–12.5%, n = 6), and recoveries (72.1%–91.0%, n = 6) were well acceptable for direct analysis of raw samples. Matrix effect for detection of carbendazim in soil samples also was experimentally investigated. This study demonstrated that syringe filter needle coupled with electrospray ionization mass spectrometry is a simple, efficient, and sensitive method for detection of pesticide residues in water, soil, and fruit juice for risk assessment.     

Utilizing the inherent electrolysis in a chip-based nanoelectrospray emitter system to facilitate selective ionization and mass spectrometric analysis of metallo alkylporphyrins

A commercially available chip-based infusion nanoelectrospray ionization system was used to ionize metallo alkylporphyrins for mass spectrometric detection and structure elucidation by mass spectrometry. Different ionic forms of model compounds (nickel (II), vanadyl (II), copper (II), and cobalt (II) octaethylporphyrin) were created by using two different types of conductive pipette tips supplied with the device. These pipette tips provide the conductive contact to solution at which the electrolysis process inherent to electrospray takes places in the device. The original unmodified, bare carbon-impregnated plastic pipette tips were exploited to intentionally electrochemically oxidize (ionize) the porphyrins to form molecular radical cations for detection. Use of modified pipette tips, with a surface coating devised to inhibit analyte mass transport to the surface or slow the kinetics of the analyte electrochemical reactions, was shown to limit the ionic species observed in the mass spectra of these porphyrins largely, but not exclusively, to the protonated molecule. Under the conditions of these experiments, the effective upper potential limit for oxidation with the uncoated pipette tip was 1.1 V or less, and the coated pipette tips effectively prevented the oxidation of analytes with redox potentials greater than about 0.25 V. Product ion spectra of either molecular ionic species could be used to determine the alkyl chain length on the porphyrin macrocycle. The utility of this electrochemical ionization approach for the analysis of naturally occurring samples was demonstrated using nickel geoporphyrin fractions isolated from Gilsonite bitumen. Acquiring neutral loss spectra as a means to improve the specificity of detection in these complex natural samples was also illustrated.     

Direct Detection of Pharmaceuticals and Personal Care Products from Aqueous Samples with Thermally-Assisted Desorption Electrospray Ionization Mass Spectrometry

An ambient mass spectrometric method based on desorption electrospray ionization (DESI) has been developed to allow rapid, direct analysis of contaminated water samples, and the technique was evaluated through analysis of a wide array of pharmaceutical and personal care product (PPCP) contaminants. Incorporating direct infusion of aqueous sample and thermal assistance into the source design has allowed low ppt detection limits for the target analytes in drinking water matrices. With this methodology, mass spectral information can be collected in less than 1 min, consuming ~100 μL of total sample. Quantitative ability was also demonstrated without the use of an internal standard, yielding decent linearity and reproducibility. Initial results suggest that this source configuration is resistant to carryover effects and robust towards multi-component samples. The rapid, continuous analysis afforded by this method offers advantages in terms of sample analysis time and throughput over traditional hyphenated mass spectrometric techniques.     

高效液相色谱-串联质谱法分析姜黄中微量的姜黄素类化合物

建立了同时检测中药姜黄中3种微量的姜黄素类化合物的高效液相色谱-电喷雾串联质谱分析方法。姜黄根茎经乙醇超声提取后,无需其他处理可直接进样分析。以Microsorb C18色谱柱(250 mm×4.6 mm,5 μm)分离,乙腈和0.1%甲酸水梯度洗脱,在多反应监测模式(MRM)下对目标成分进行定性分析。利用质谱碎裂规律,分别对每个目标成分同时监测8个母离子/特征子离子对的反应过程,首次从姜黄中发现了3个微量的姜黄素类化合物成分。一次性完成了目标成分的同时定性,方法的检出限为0.2 μg/L。结果表明,该方法具有简便、快速、准确、灵敏度高的优点,适用于中药复杂体系中姜黄素类化合物的分析检测。     

Electrostatic field–induced tip‐electrospray ionization mass spectrometry for direct analysis of raw food materials

Rapid characterization of metabolites and risk compounds such as chemical residues and natural toxins in raw food materials such as vegetables, meats, and edible living plants and animals plays an important part in ensuing food quality and safety. To rapidly characterize the analytes in raw food materials, it is essential to develop in situ method for directly analyzing raw food materials. In this work, raw food materials including biological tissues and living samples were placed between an electrode and mass spectrometric (MS) inlet under a strong electrostatic field; analytes were rapidly induced to generate electrospray ionization (ESI) from the sample tip by adding a drop of solvent onto the sample. Therefore, the electrostatic field–induced tip‐ESI‐MS allows raw samples to avoid contacting high voltage, and thus this method has the advantage for in vivo analysis of food living plants and animals. Metabolite profiling, residues of pesticides and veterinary drugs, and natural toxins from raw food materials have been successfully detected. The analytical performances, including the linear ranges, sensitivity, and reproducibility, were investigated for direct sample analysis. The ionization mechanism of electrostatic field–induced tip‐ESI was also discussed in this work.     

Direct analysis of herbal powders by pipette-tip electrospray ionization mass spectrometry

Conventional electrospray ionization mass spectrometry (ESI-MS) is widely used for analysis of solution samples. The development of solid-substrate ESI-MS allows direct ionization analysis of bulky solid samples. In this study, we developed pipette-tip ESI-MS, a technique that combines pipette tips with syringe and syringe pump, for direct analysis of herbal powders, another common form of samples. We demonstrated that various herbal powder samples, including herbal medicines and food samples, could be readily online extracted and analyzed using this technique. Various powder samples, such as Rhizoma coptidis, lotus plumule, great burdock achene, black pepper, Panax ginseng, roasted coffee beans, Fructus Schisandrae Chinensis and Fructus Schisandrae Sphenantherae, were analyzed using pipette-tip ESI-MS and quality mass spectra with stable and durable signals could be obtained. Both positive and negative ion modes were attempted and various compounds including amino acids, oligosaccharides, glycosides, alkaloids, organic acids, ginosensides, flavonoids and lignans could be detected. Principal component analysis (PCA) based on the acquired mass spectra allowed rapid differentiation of closely related herbal species.     

Direct Determination of Creatinine in Urine and Analysis of Pure Aniline by Extractive Electrospray Ionization Mass Spectrometry

The direct mass spectrometric determination of highly concentrated analytes in human urine was demonstrated using extractive electrospray ionization without sample dilution or complex preparation. By increasing the distance between the extractive electrospray source and ion inlet of the mass spectrometer from 5 millimeters to 15 centimeters, the fraction of free analyte ions and charged microdroplets introduced into the mass spectrometer was substantially reduced. Consequently, detector saturation, instrument contamination, and space charge effects were greatly diminished for the analysis of highly concentrated samples. Under the optimized experimental conditions, pure aniline and creatinine (>1 millimolar) in human urine were directly characterized by extractive electrospray ionization without any pretreatment. The urinary creatinine concentrations from two adults were 424 ± 30 and 635 ± 32 micrograms per milliliter and were in good agreement with those obtained by a spectrophotometric method based on the Jaffe reaction. The results show that extractive electrospray ionization is suitable for the direct determination of highly concentrated analytes or even pure compounds, allowing rapid characterization of samples in the chemical industry and clinical studies.     

Coupling corona discharge for ambient extractive ionization mass spectrometry

Unlike the extractive electrospray ionization (EESI) technique described elsewhere, a corona discharge instead of electrospray ionization has been utilized to charge a neutral solvent spray under ambient conditions for the generation of highly charged microdroplets, which impact a neutral sample plume for the extractive ionization of the analytes in raw samples without any sample pretreatment. Using the positive ion mode, molecular radical cations were easily generated for the detection of non-polar compounds (e.g., benzene, cyclohexane, etc.), while protonated molecular ions of polar compounds (e.g., acetonitrile, acetic ether) were readily produced for the detection. By dispensing the matrix in a relatively large space, this method tolerates highly complex matrices. For a given sample such as lily fragrances, more compounds were detected by the method established here than the EESI technique. An acceptable relative standard deviation (RSD 8.9%, n = 11) was obtained for the direct measurement of explosives (10 ppb) in waste water samples. The experimental data demonstrate that this method could simultaneously detect both polar and non-polar analytes with high sensitivity, showing promising applications for the rapid detection of a wide variety of compounds present in complex matrices.     

Determination of faropenem in human plasma and urine by liquid chromatography-tandem mass spectrometry

A simple, rapid and sensitive liquid chromatography/electrospray tandem mass spectrometry (LC-MS/MS) quantitative detection method, using cefalexin as internal standard, was developed for the analysis of faropenem in human plasma and urine. After precipitation of the plasma proteins with acetonitrile, the analytes were separated on a C18 reversed-phase column with 0.1% formic acid-methanol (45:55, v/v) and detected by electrospray ionization mass spectrometry in positive multiple reaction monitoring mode. Calibration curves with good linearities (r=0.9991 for plasma sample and r=0.9993 for urine sample) were obtained in the range 5-4000 ng/mL for faropenem. The limit of detection was 5 ng/mL. Recoveries were around 90% for the extraction from human plasma, and good precision and accuracy were achieved. This method is feasible for the evaluation of pharmacokinetic profiles of faropenem in humans, and to our knowledge, it is the first time the pharmacokinetic of faropenem has been elucidated in vivo using LC-MS/MS.     

基于敞开式直接电离质谱技术的尿液中毒品检测北大核心CSCD

尿液作为一种易于获取的体内毒品检材,在吸毒人员快速筛查中被广泛应用。针对传统快速筛查技术存在假阳性率高、定量能力不足以及实验室质谱技术在快速检测中存在前处理复杂、检测耗时长、使用环境苛刻等问题,该文提出了一种基于敞开式直接电离质谱技术的生物样本快速检测方法。该研究采用探针式电喷雾离子源与便携式质谱仪联用快速检测平台,优化了喷雾电压和质谱入口毛细管温度,开发了高效快速的前处理技术。基于该平台和前处理技术,5种常规毒品(甲基苯丙胺、氯胺酮、可卡因、O^(6)-单乙酰吗啡和3,4-亚甲双氧甲基苯丙胺)的尿液加标溶液的检出限为0.5~30 ng/mL,且其中4种毒品定量检测的线性相关系数大于0.99。除此之外,5种常规毒品在3个不同水平下的加标回收率为56.1%~103.7%,多次检测结果的相对标准偏差为9.0%~27.8%,说明联用检测平台与前处理方法结合可以达到良好的准确度。为了进一步检验该联用仪器的实战能力,测试了某社区戒毒康复中心40份阳性和110份阴性实际尿液样本,总体检测的准确率接近99%,且通过一次进样在20 s内可同时检测多种毒品。该研究成果有利于推动快速检测技术的发展,促进敞开式直接电离质谱仪技术的推广应用,提升一线执法服务水平。     

Sheath liquid interface for the coupling of normal-phase liquid chromatography with electrospray mass spectrometry and its application to the analysis of neoflavonoids

A novel interface that allows normal-phase liquid chromatography to be coupled with electrospray ionization (ESI) is reported. A make-up solution of 60 mM ammonium acetate in methanol, infused at a 5 microl min(-1) flow-rate at the tip of the electrospray probe, provides a sheath liquid which is poorly miscible with the chromatographic effluent, but promotes efficient ionization of the targeted analytes. Protonated molecules generated in the ESI source were subjected to tandem mass spectrometric experiments in a triple-quadrupole mass spectrometer. The main fragmentation reactions were characterized for each analyte and specific mass spectral transitions were used to acquire chromatographic data in the multiple reaction monitoring detection mode. Results obtained during optimization of the sheath liquid composition and flow-rate suggest that the electrospray process was mainly under the control of the make-up solution, and that it forms an external charged layer around a neutral chromatographic mobile phase core. This sheath liquid interface was implemented for the analysis of some neoflavonoid compounds and its performance was evaluated. Limits of detection were established for calophillolide, inophyllum B, inophyllum P and inophyllum C at 100, 25, 15 and 100 ng ml(-1), respectively.     

Investigation of natural dyes occurring in historical Coptic textiles by high-performance liquid chromatography with UV-Vis and mass spectrometric detection

Liquid chromatography (LC) combined with ultraviolet-visible (UV-Vis) and mass spectrometric (MS) detection was utilized to study the chemical components present in extracts of natural dyes originating from fiber samples obtained from Coptic textiles from Early Christian Art Collection of National Museum in Warsaw. Chromatographic retention, ionization, UV-Vis and mass spectra of twenty selected dye compounds of flavanoid-, anthraquinone- and indigo-types were studied. Most of the investigated compounds could be ionized by positive and negative ion electrospray ionization. Difficulties with the ionization by electrospray were experienced for indigotin and brominated indigotins, but these were ionized by atmospheric pressure chemical ionization. Mass spectrometric detection, utilizing different scanning modes of a triple quadrupole mass spectrometer, combined with the UV-Vis detection was demonstrated to be a powerful approach to detection and identification of dyes in the extracts of archeological textiles. Using this approach the following compounds were identified in the extracts of Coptic textiles: luteolin, apigenin, rhamnetin, kaempferol, alizarin, purpurin, xanthopurpurin, monochloroalizarin, indirubin, and so the type of dye that was utilized to dye the textiles could be identified. Detection capabilities for several dye-type analytes were compared for the UV-Vis and mass spectrometric detection. The signal-to-noise ratios obtained for luteolin, apigenin, and rhamnetin were higher for the MS detection for most of the examined sample extracts. Purpurin, alizarin, and indirubin showed similar signal-to-noise ratios for UV-Vis and mass spectrometric detection.     

Validation of an HPLC-MS-MS method for the determination of urinary S-benzylmercapturic acid and S-phenylmercapturic acid

A high-performance liquid chromatography-tandem mass spectrometric (HPLC-MS-MS) method is presented and evaluated for the determination of S-benzylmercapturic acid (S-BMA) and S-phenylmercapturic acid (S-PMA) in human urine. Both of these compounds are important for occupational health owing to their use as biomarkers of exposure to toluene and benzene, respectively. Toluene is used extensively as a solvent, and the health hazards of benzene have been well established. The optimized urine sample preparation scheme consists of solid-phase extraction (SPE) followed by an acetone wash. The chromatographic analysis consists of a reversed-phase gradient system, which uses electrospray ionization in negative-ion mode with a triple-quadrupole mass spectrometric detector. Accuracy and precision of this method are demonstrated by a series of recovery studies of spiked human urine and synthetic urine substitute. Spike levels at 1, 2, 6, 8, and 30 ng/mL for both analytes demonstrate average recoveries (accuracy) ranging from 99 to 110%. Precision as measured by the relative standard deviation (%RSD) of multiple samples (n=9) at each concentration level was 5.3% or less for both analytes in urine. The limit of detection (LOD) is approximately 0.2 ng/mL for S-BMA and S-PMA. This data, other figures of merit and other factors, such as ion suppression of the electrospray ionization source, are discussed.     

Rapid detection of drugs in biofluids using atmospheric pressure chemi/chemical ionization mass spectrometry

We have demonstrated that, with simple pH adjustment, volatile drugs such as methamphetamine, amphetamine, 3,4‐methylenedioxymethamphetamine (MDMA), ketamine, and valproic acid could be analyzed rapidly from raw biofluid samples (e.g. urine and serum) without dilution, or extraction, using atmospheric pressure ionization. The ion source was a variant type of atmospheric pressure chemical ionization (APCI) that used a dielectric barrier discharge (DBD) to generate the metastable helium gas and reagent ions. The sample solution was loaded in a disposable glass pipette, and the volatile compounds were purged by nitrogen gas to be reacted with the metastable helium gas. The electrodes of the DBD were arranged in such a way that the generated glow discharge was confined within the discharge tube and was not exposed to the analytes. A needle held at 100–500 V was placed between the ion‐sampling orifice and the discharge tube to guide the analyte ions into the mass spectrometer. After pH adjustment of the biofluid sample, the amphiphilic drugs were in the form of a water‐insoluble oil, which could be concentrated on the liquid surface. By gentle heating of the sample to increase the evaporation rate, rapid and sensitive detection of these drugs in raw urine and serum samples could be achieved in less than 2 min for each sample. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrating tip spray ionization mass spectrometry for direct sample analysis

In this work, a vibrating tip spray ionization source was developed for direct mass spectrometric analysis of raw samples under voltage‐free condition. A solid tip was mounted on a vibrator, and the solid tip was placed on the front of MS inlet. Liquid, viscous, and bulk solid samples could be directly loaded on the tip‐end surface, and then a drop of solvent at microliter level was subsequently loaded on the tip for dissolution and extraction of analytes, and a vibrator was then started to atomize and ionize the analytes under ambient condition. We demonstrated vibrating tip spray mass spectrometry in various applications, including food safety, pharmaceutical analysis, and forensic science. Furthermore, in situ analysis of biological tissues and in vivo analysis of living plants were conveniently performed, due to voltage‐free. Different vibration frequencies and solvent compositions were investigated. The analytical performances, including sensitivity, reproducibility, and linear range, were investigated. The ionization process and mechanism were also discussed in this work.     

超高效液相-串联质谱法同时测定蜂蜜中15种喹诺酮类药物残留

建立了蜂蜜样品中15种喹诺酮类兽药残留的超高效液相色谱-串联质谱检测方法。蜂蜜样品用磷酸盐缓冲溶液溶解提取后,用Oasis HLB固相萃取柱净化,超高效液相-电喷雾串联四级杆质谱检测,外标法定量。测定时用Acquity UPLC BEHC18色谱柱(50 mm×2.1 mm,1.7μm)分离,体积分数0.1%甲酸溶液-乙腈系统梯度洗脱,质谱测定采用多重反应监测(MRM)模式。15种喹诺酮类兽药的检出限均低于或等于1.0 ng/mL,回收率均在78.6%～112.9%范围内,相对标准偏差均在10%范围内。该方法各项指标均能满足国内外各项法规的要求,可用于蜂蜜样品中喹诺酮类药物残留的定量和定性检测。     

Simultaneous determination of 17 ginsenosides in rat urine by ultra performance liquid chromatography-mass spectrometry with solid-phase extraction

A rapid analytical method for quantifying 17 ginsenosides in rat urine by ultra performance liquid chromatography (UPLC) coupled to electrospray ionization mass spectrometry (ESI-MS) is described. All analytes were extracted by solid-phase extraction optimized to obtain good recovery and quantified using digoxin as an internal standard. ESI-MS was optimized for different cone voltages at positive ionization mode to allow simultaneous analysis of all analytes in a relatively short time. Qualitative methodological considerations, including the linear range, precision, limit of quantification, limit of detection, recovery and sensitivity are also provided.     

Neutral desorption sampling coupled to extractive electrospray ionization mass spectrometry for rapid differentiation of biosamples by metabolomic fingerprinting

It is of increasing interest and practical importance to develop convenient methods based on mass spectrometry for high-throughput analyses of biological samples. This is usually difficult because of the complex matrix and ion suppression effects. Generation of ions at ambient conditions is a promising solution to these problems because the sample is easily accessible and the ion suppression effect is reduced significantly. A new method for rapid on-line detection of metabolic markers in complex biological samples is described here. It combines atmospheric pressure desorption sampling by a gentle stream of air or nitrogen with extractive electrospray ionization (EESI) and mass spectrometric analysis. The resulting mass spectral fingerprints are shown to be able to detect spoilage of meat even in the frozen (-20 degrees C) state and the contamination of spinach by E. coli, and to identify metabolites and contaminants on human skin within seconds, in an on-line and high-throughput fashion. Typical molecular markers are identified using MS/MS data and by comparison with reference compounds. Differences between closely related samples are easily visualized by using principal component analysis (PCA) of the mass spectra data. The detection limit achieved is 10 fg/cm2 (S/N = 3) for histamine on the surface of frozen meat. The technique reported here shows potential for more advanced applications in multiple disciplines, including food regulation, homeland security, in vivo metabolomics, and clinical diagnosis.     

High‐throughput polymer tip‐electrospray ionization mass spectrometry for enhanced detection of neopterin and biopterin in clinical urine samples

Urinary biopterin (Bio) and neopterin (Neo) are important markers for clinical diagnosis of hyperphenylalaninemia. Herein, we developed a high‐throughput analysis method based on electrospray ionization mass spectrometry (ESI‐MS) with polymer tips for the rapid quantitative detection of Bio and Neo in clinical urine samples. Different polymer tips were investigated. It is found that the best detection sensitivity was achieved with hydrophobic polymer tip, ie, polyethylene tips. The high‐throughput polymer tip‐ESI‐MS method allowed a rapid analysis speed at ~40 seconds per sample. The limits of quantification (LOQ) (S/N ≥ 10) for the detection of Bio and Neo were improved to be 5.0 ng/mL. Acceptable relative standard deviation (RSD) values for Neo and Bio were measured to be 12.2% and 13.4% for direct measurement of Bio and Neo in raw urine samples, respectively. Furthermore, Bio and Neo were directly quantified from 18 clinical urine samples by presented method. The ratios of urinary Bio‐to‐Neo were analyzed for diagnosis of hyperphenylalaninemia. The results demonstrated that the present polymer tip‐ESI‐MS method is a promising strategy for the rapid analysis of clinical samples.