Shuiping Yang

Detection of Melamine in Milk Products by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Without any sample pretreatment, trace amounts of melamine in various milk products were rapidly detected noting the characteristic fragments (i.e., m/z 110, 85, and 60) in the MS/MS spectrum of protonated melamine molecules (m/z 127) recorded by using surface desorption atmospheric pressure chemical ionization mass spectrometry. Signal responses of the most abundant ionic fragment (m/z 85) of protonated melamine were well correlated with the amounts of melaime in milk products, showing a dynamic range about 5 orders of magnitude. The limit of detection (LOD) was found to be 3.4 x 10(-15) g/mm(2) (S/N = 3) for the detection of pure melamine deposited on the paper surface, which was much lower than that for detection of melamine in powdered milk (1.6 x 10(-11) g/mm(2), S/N = 3) or liquid milk (1.3 x 10(-12) g/mm(2), S/N = 3). The significant difference in LOD was ascribed to the relatively strong molecular interactions between melamine and the matrix such as proteins in the milk products. As demonstrated using desorption electrospray ionization (DESI) for melamine detection, weakening the molecular interaction between analytes and proteins is proposed as a general strategy to improve the sensitivity of ambient mass spectrometry for direct detection of analytes bound in protein matrixes. The relative standard deviation (RSD) and the recovery of this method were found to be 5.2 approximately 11.9% and 87 approximately 113%, respectively, for the detection of melamine in milk products. A single sample analysis was completed within a few seconds, providing a particularly convenient way to rapidly screen melamine presence in milk products.

Sensitive Detection of Native Proteins Using Extractive Electrospray Ionization Mass Spectrometry

Real-world protein sam-ples such as cell materials contain intrinsically complexmixtures including liquids, salts, and almost every type ofspecies involved in biological processes. Prior to proteinanalysis, specific sample pretreatments (separation, precon-centration, digestion, etc.) are usually required for mostanalytical techniques.

Development of extractive electrospray ionization ion trap mass spectrometry for in vivo breath analysis

In metabolomics studies and clinical diagnosis, interest is increasing in the rapid analysis of exhaled breath. In vivo breath analysis offers a unique, unobtrusive, non-invasive method of investigating human metabolism. To analyze breath in vivo, we constructed a novel platform of extractive electrospray ionization (EESI) ion trap mass spectrometry (ITMS) using a home-made EESI source coupled to a linear trap quadrupole mass spectrometer. A reference compound (authentic n-octyl amine) was used to evaluate effects of systematically varying selected characteristics of the EESI source on signal intensity. Under the optimized working conditions, metabolic changes of human bodies were in vivo followed by performing rapid breath analysis using the multi-stage EESI-ITMS tandem mass spectrometry platform. For nicotine, a limit of determination was found to be 0.05 fg mL(-1) (S/N = 3, RSD = 5.0 %, n = 10) for nicotine in aerosol standard samples; the dynamic response range was from 0.0155 pg mL(-1) to 155 pg mL(-1). The concentration of nicotine in the exhaled breath of a regular smoker was in vivo determined to be 5.8 pg mL(-1), without any sample pre-treatment. Our results show that EESI-ITMS is a powerful analytical platform to provide high sensitivity, high specificity and high throughput for semi-quantitative analysis of complex samples in life science, particularly for in vivo metabolomics studies.

Selective detection of diethylene glycol in toothpaste products using neutral desorption reactive extractive electrospray ionization tandem mass spectrometry.

A rapid, sensitive method based on neutral desorption (ND) reactive extractive electrospray ionization mass spectrometry (EESI-MS) has been established for the selective quantitative detection of diethylene glycol (DEG) in toothpaste products without any sample pretreatment. The sensitivity and specificity of DEG detection were enhanced by implementing selective ion/molecule reactions in the EESI process, featuring the EESI mass spectra with the characteristic signals of DEG. The method provided a low limit of detection (LOD) (approximately 0.00002%, weight percent of DEG in toothpaste), reasonable recovery (97.6-102.4%), and acceptable relative standard deviations (RSD < 8%, n = 8) for direct measuring of DEG in the spiked toothpaste samples. Trace amounts of DEG in commercial toothpaste products have been quantitatively detected without any sample manipulation. The results demonstrate that nonvolatile compounds such as DEG can be sensitively liberated using the neutral gas beam for quantitative detection from the extremely viscous toothpaste containing solid nanoparticles, showing that ND-EESI-MS is a useful tool for the rapid characterization of highly complex and/or viscous samples at molecular levels.

Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry

Without any sample pretreatment, effervescent beverage fluids were manually sprayed into the primary ion plume created by using a nanoelectrospray ionization source for direct ionization, and the analyte ions of interest were guided into an ion trap mass spectrometer for tandem mass analysis. Functional ingredients (e.g., vitamins, taurine, and caffeine, etc.) and spiked impurity (e.g., cocaine) in various beverages, such as Red Bull energy drink, Coco-cola, and Pepsi samples were rapidly identified within 1.5 s. The limit of detection was found to be 7 ∼ 15 fg (S/N = 3) for cocaine in different samples using the characteristic fragment (m/z 150) observed in the MS3 experiments. Typical relative standard deviation and recovery of this method were 6.9% ∼ 8.6% and 104% ∼ 108% for direct analysis of three actual samples, showing that nanoextractive electrospray ionization tandem mass spectrometry is a useful technique for fast screening cocaine presence in beverages.

Geometry-independent neutral desorption device for the sensitive EESI-MS detection of explosives on various surfaces

A novel geometry-independent neutral desorption (GIND) device was successfully developed, which made neutral desorption (ND) sampling easier and more robust on virtually all types of surfaces. The GIND device features a small air-tight enclosure with fixed space between the ND gas emitter, the sample surface, and the sample collector. Besides easy fabrication and convenient use, this configuration facilitates efficient neutral sample transfer and results in high sensitivity by preventing material loss during the ND process. The effects of various operating parameters of the GIND device such as desorption gas composition, surface wetness, gas flow rate, distance between the surface and the gas emitter, internal diameter of the sample outlet, and GIND device material were experimentally investigated. By using the GIND device, trace amounts of typical explosives such as TNT, RDX, HMX, TATP, etc., were successfully sampled from many different kinds of surfaces, including human skin, glove, glass, envelope, plastic, leather, glass, and clothes. GIND-sampled explosives were detected by multiple-stage extractive electrospray ionization mass spectrometry (EESI-MS). Ion/molecule reactions of explosives such as RDX and TATP were implemented in the EESI source for the rapid detection with enhanced sensitivity and specificity. The typical time for a single sample analysis was a few seconds. Successful transportation of the neutral analytes over a distance longer than 10 m was demonstrated, without either significant signal loss or serious delay of signal response. The limit of detection for these explosives in the study was in the range of ca. 59-842 fg (S/N = 3, n = 8) on various surfaces. Acceptable relative standard deviation (RSD) values (ca. 4.6-10.2%, n = 8) were obtained for all the surfaces tested, showing the successful sampling of trace non-volatile explosive compounds (sub-picogram) by the GIND device for the EESI mass spectrometric analysis.

Rapid analysis of aerosol drugs using nano extractive electrospray ionization tandem mass spectrometry.

Aerosol drugs dominate a significant share of pharmaceutical preparations on the market. A novel sensitive method utilizing nano extractive electrospray ionization mass spectrometry (nanoEESI-MS) has been developed for the rapid analysis of aerosol drug samples with quantitative information. Without any sample pretreatment, aerosol drugs were manually sprayed into the primary ion plume created by a nano electrospray emitter for direct ionization under ambient conditions. The analyte ions of interest were guided into an ion trap mass spectrometer for tandem mass analysis. The active ingredients of various aerosol drugs, such as econazole nitrate, beclomethasone dipropionate, binary mixture of methyl salicylate and diphenhydramine, terbutaline, and salbutamol, were rapidly detected using nanoEESI-MS. A single sample analysis could be completed within 1.2 s. Tandem mass spectrometry was used to confirm the identification of important compounds in each aerosol drug sample. Reasonable relative standard deviation (RSD = 6.39%, n = 13) and acceptable sensitivity (10 ppt, 100 muL) were found for the salbutamol aerosol sample, which suggests that nanoEESI-MS has the quantitative capacity for analyzing complex pharmaceutical samples. This method was further extended to study the thermal decomposition process of salbutamol, showing that the degradation kinetics of salbutamol can be conveniently tracked. Our data demonstrate that nanoEESI tandem mass spectrometry is a fast and sensitive technique for the analysis of aerosol drug preparations, showing promising applications in pharmacology studies and in situ analysis of aerosol drugs on the market.

Rapid Determination of Dimethoate in Nanoliter of Juice Using Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract A rapid analytical method based on nanoliter-level sampling technique and surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS) has been developed for the determination of trace dimethoate in juices without any sample preparation. The nanoliter-level juices were sampled by a home-made sampler equipped with a stainless steel sampling probe. The minimum sampling volume was suggested to be 0.11 nL. Based on the experimental results, the linear correlation between dimethoate signal and concentration was significant in the range of 0.001−10.0 mg kg −1 with the correlation coefficient ( R ) of 0.988. The recoveries were in the range of 80.5%–120.6%, and the detection limit of dimethoate was determined to be 1.2×10 −11 mg kg −1 .

Direct Detection of Amino Acids Using Extractive Electrospray Ionization Tandem Mass Spectrometry

Abstract A novel method was developed for the direct detection of amino acids in biological fluids by extractive electrospray ionization (EESI) tandem mass spectrometry (MS) with minimal sample pretreatment. Based on our previous research, a novel EESI ion source was constructed to improve analytical performance and operation safety. The EESI-MS conditions were optimized using representative amino acid standards. The methanol-water reagent solvent (1:1, v/v) was electrosprayed at 5 μL min−1 at a high voltage (+4 kV, positive ion detection mode). The temperature of the heated capillary was optimized to be 150 °C. Collision induced dissociation (CID) experiments were performed by applying 17%−25% of the collision energy to the precursor ions isolated with a window width of 1.5 mass/charge (m/z) units. The limit of detection (LOD) for these amino acids was in the range of 0.14−26.2 μg L−1, and the linear dynamic range was larger than two orders of magnitude. The average time for a single amino acid analysis using a typical human urine sample was less than 0.5 min. The recovery rates for different concentrations of amino acids ranged from 82.6% to 105.6%, and the relative standard deviations (RSD) ranged from 2.2% to 11.4%. The results showed that EESI-MS is a powerful tool for the rapid, sensitive, and quantitative detection of amino acids in complex biological samples.