Determination of micelle mass by electrospray ionization mass spectrometry

By electrospray ionization (ESI) mass spectrometry, micelle solutions of sodium cholate were investigated in detail in the presence and absence of ethanol. The average aggregation number could be evaluated from the spectra acquired under conditions where soft collisions adequate to measure the micelle solution were induced, and the value agreed well with that obtained previously by other methods. From the dependence on ethanol content, it was also found that the average aggregation number in aqueous solution without organic solvent could be reliably estimated. The ESI method proved to be a useful tool for determining the micelle mass in the original aqueous phase.     

Determination of tetrodotoxin in puffer-fish by liquid chromatography-electrospray ionization mass spectrometry

A simple and reliable method using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for the determination of tetrodotoxin in the puffer-fish has been developed. The LC separation was performed on a Shodex RSpak NN-414 column (15 cm x 4.6 mm id) using 20 mM ammonium acetate-methanol (75 + 25) as the mobile phase at a flow rate of 0.5 ml min(-1). The positive ionization produced the typical [M + H]+ molecular ion of tetrodotoxin (m/z 320). The calibration graph for tetrodotoxin was rectilinear from 0.01 to 1 microg ml(-1) with selected ion monitoring (SIM). Tetrodotoxin was extracted with 0.1% acetic acid by heating in a boiling water-bath and the extracts were cleaned up on a Bond Elut C18 (500 mg) cartridge. The recoveries of the tetrodotoxin from the puffer-fish fortified at 1 microg g(-1) were 77.7-80.7% and the detection limit was 0.1 microg g(-1) (equivalent to ca. 0.5 mouse units per gram).     

Determination of hydrogen in stainless steels by spark-source mass spectrometry

A spark-source mass spectrometric (SSMS) method capable of determining traces of hydrogen in micro-volumes of metals was developed by using a pointed metal probe technique. The hydrogen background was decreased to μg g^?1 levels by the combination of a method in which the sample in the ion source is baked under vacuum at 323–343 K for more than 25 ks and a liquid nitrogen or liquid helium cryogenic pump method. This method was applied to the analysis of austenitic stainless steels at μg g^?1 hydrogen levels, and the relative standard deviation was within 20% for samples with hydrogen concentrations ranging from 2 to 4 μg g^?1. The relative sensitivity coefficent was 2.3 (Fe=1).     

Determination of pyrrolizidine alkaloids in comfrey by liquid chromatography-electrospray ionization mass spectrometry

Symphytum officinale L. (comfrey) is a medicinal plant commonly used in decoctions and aliments. Besides therapeutic bioactive compounds present in the herb, it is found to contain hepatotoxic pyrrolizidine alkaloids (PAs), such as lycopsamine and others. In the present study, PAs such as lycopsamine, echimidine and lasiocarpine were determined using electrospray liquid chromatography-mass spectrometry (LC-MS) with the method precision (relative standard deviation, RSD) <10%. Detection of lycopsamine, symviridine and their N-oxides could be confirmed with a newly developed method based on HPLC ion-trap and orbitrap MS with electrospray ionization interface. With LC-MS, quantitative analysis of lycopsamine in the botanical extract was carried out. The effect of extraction solvent was optimized by sonication and methanol: H₂O (50:50) was selected. Then a rapid method based on pressurized hot water extraction (PHWE) was employed for the extraction of lycopsamine from comfrey followed by the comparison with heating under reflux with the RSD ranging from 2.49% to 19.32%. Our results showed a higher extraction efficiency for heating under reflux compared with PHWE. It was proposed that the lower extraction efficiency for PHWE was attributable to dissolved nitrogen from air which caused the reduction in the solubility of lycopsamine in the compressed hot solvent. In this study, quantitative analysis of PAs in comfrey was demonstrated. In addition, it was found that the use of subcritical water for extractions depended on the physical properties of the dissolved solutes and their tendency to degrade under the chosen extraction conditions.     

Determination of trace cobalt in fruit samples by resonance ionization mass spectrometry

1-color 2-photon resonance ionization mass spectrometry (RIMS) with a new electro-thermal atomizer equipped with six filaments has been applied for quantitative analysis of trace cobalt in fruit samples. The efficient transition lines for sensitive detection were investigated in the wavelength range of 283-302 nm and a transition at 298.71 nm was chosen as an excited state for the determination of Co. A proper calibration curve for cobalt up to 1 ppb has been constructed with satisfactory results. The minimum detectible amount of cobalt in this RIMS system was identified as less than 5 pg. The content of Co in three different fruits, pear, apple and Korean mandarin orange, have been determined by adopting standard addition to the fruit sample juice. The content of the Co in 5 μl of apple, pear and Korean mandarin juice was identified as 150, 45 and 100 pg, respectively.     

Determination of lithium isotopic composition by thermal ionization mass spectrometry in seawater

The isotopic composition of lithium in seawater has been determined by thermal ionization mass spectrometry (TIMS) based on the use of lithium hydroxide as the ion source. Isotopic measurements in a reference material supplied by IAEA (L-SVEC Li₂CO₃) were made to check the reproducibility of the method and ⁶Li indicates mobilization of light isotope of lithium form the sediment.     

Determination of abamectin in citrus fruits by liquid chromatography-electrospray ionization mass spectrometry

Liquid chromatography coupled to electrospray mass spectrometry (LC-ES-MS) with positive ion detection was used to determine abamectin in oranges. MS conditions were optimized to achieve maximum sensitivity. The main ion for abamectin was [M+Na]+ at a fragmentor voltage of 180 V. Abundant structural information can be obtained at different fragmentor voltages. The detection limit for the standard solution was 12 pg injected, and good linearity and reproducibility were observed. Abamectin residues were extracted using matrix solid-phase dispersion. Orange samples were homogenized with C18 bonded silica placed onto a glass column and eluted with dichloromethane. Recoveries of the abamectin from oranges fortified with approximately 0.01-10 mg/kg ranged from 94 to 99% with an overall average recovery of 96%. The quantification limit is 0.0025 mg/kg, which means detection limit for this analyte could be set at a few hundred picograms per gram of fruit. The presence in the electrosprayed solution of numerous citrus constituents did not interfere significantly with the ionization process of abamectin. The assay procedure provides a simple, rapid, and sensitive method for monitoring residues in oranges. The method was applied to field treatment orange samples.     

Study of small benzene clusters by pulse molecular beam mass spectrometry

A simple method for separating contributions of different-sized clusters formed in a pulse supersonic boum to a mass-spectral signal has been suggested. The method is based on the analysis of time pulse profiles measured for different ions of the beam and makes it possible to calculate mass spectra of small clusters. The electron impact mass spectrum of the benzene dimer has been obtained and analyzed in We framework of the concept of intracluster ion-molecular chemistry.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1726–1732, July, 1996.     

Exact molecular mass determination of various forms of native and de-N-glycosylated human plasma-derived antithrombin by means of electrospray ionization ion trap mass spectrometry

Human plasma-derived antithrombin was characterized in both the native and de-N-glycosylated forms (without separation of isoforms) by means of electrospray ionization ion trap mass spectrometry (ESI-ITMS). In order to determine the limits of the instrument set-up, the molecular mass precision and accuracy of the ESI-ITMS analysis was evaluated with the standard protein enolase and some instrumental data acquisition parameters were optimized. Mass precision was determined as a function of the number of averaged mass spectra (= scans) and data acquisition time. For this study, 20 and 50 scans were averaged and the data acquisition time was chosen to be between 0.5 and 5 min. It turned out that data acquisition times longer than approximately 2 min show no significant differences of the standard deviation of the determined molecular mass. Furthermore, the ion trap scan rate was varied at constant acquisition time of 2 min and the number of averaged scans was set to 20. At the scan rate of 13,000 u s(-1) a mass precision of +/-1.8 Da and a mass accuracy of +0.026% were determined. On reducing the scan rate to 5500 u s(-1), better agreement with the theoretical molecular mass was obtained, showing a mass accuracy of +0.012% but with a decrease in the mass precision to +/-3.0 Da. Using the optimized scan rate of 13,000 u s(-1) and a data acquisition time of 2 min, the exact molecular mass was determined of the three forms of antithrombin, namely the alpha-form, the beta-form and the natural mixture (present in human plasma) containing both forms. The protonated molecular masses were found to be 57,854 and 55,664 Da for the affinity chromatography-isolated alpha-and beta-form, respectively. The mass difference of 2190 Da is attributed to the known difference in carbohydrate content at one specific site. The protonated molecular mass of the dominating species of the natural mixture in human plasma was shown to be 57,850 Da, corresponding to the alpha-form, the major component in native plasma. In this mixture the beta-form was also detected, exhibiting a protonated molecular mass of 55,655 Da, but showing a much lower abundance, as expected. To obtain a complete release of the N-glycan residues by means of PNGase F, a denaturation, reduction and alkylation step of the glycoproteins was performed before the enzymatic reaction. After enzymatic removal of all N-glycans, the protonated molecular masses obtained were 49,399, 49,380 and 49,391 Da for the alpha-form, the beta-form and the unseparated natural mixture, respectively. These values are in good agreement (+0.026% for the alpha-form, -0.012% for the beta-form and +0.010% for the unseparated mixture) with the calculated molecular mass based on the SwissProt data. The determined molecular masses after reduction/alkylation and de-N-glycosylation of the alpha-and beta-forms are almost equal, indicating that no major differences exist between the three preparations on the amino acid level.     

Rapid analysis of aromatic contaminants in water samples by means of laser ionization mass spectrometry

Three different approaches to laser ionization mass spectrometric analysis of aromatic compounds in water samples are described and their performances are compared. Whereas the first two methods are based on direct laser desorption and subsequent laser ionization of either frozen or adsorbed samples in a time-of-flight mass analyzer, the third performs laser ionization in a quadrupole ion-trap into which the sample is transferred from a GC injector via a short piece of capillary tubing. For the laser-desorption method a detection limit in the 100 µg L^–1 range was determined for fluorene in frozen samples. The easier to handle analysis of adsorbed samples yielded sensitivities which were lower by about two orders of magnitude. As both direct techniques do not reach the sensitivity required for ultra trace analysis in water a preconcentration step in form of solid-phase microextraction was added before measurement using the laser ionization quadrupole ion-trap mass spectrometer. Sensitivity in the desired ng L^–1 range was easily achieved.     

Determination of pharmaceutical compounds in aqueous dimethyl sulfoxide by electrospray ionization mass spectrometry

Standard solutions of reserpine, dextromethorphan, imipramine and amitriptyline in dimethyl sulfoxide (DMSO), DMSO containing 0.1% formic acid, and DMSO/H(2)O (1:1, v/v) containing 0.1% formic acid were analyzed by positive electrospray ionization mass spectrometry (ESI-MS). A triple-quadrupole mass spectrometer equipped with a TurboIonspray (TIS) interface was used for the ESI-MS analyses. The samples dissolved in the respective DMSO solution were infused directly into the mass spectrometer at 10 microL/min using an infusion pump. The positive Q1 full-scan (m/z 50-650) mass spectrum of DMSO (MW = 78) showed three main peaks at m/z 79, 101 and 179, corresponding to the protonated molecule [DMSO+H](+), and the sodiated adducts [DMSO+Na](+) and [2DMSO+Na](+), respectively. The ESI of the compounds in DMSO and DMSO containing 0.1% formic acid was promoted by using the TIS gas (GS2) combined with the nebulizer gas (GS1), and TIS source temperature set to 250 degrees C. In contrast, samples dissolved in DMSO/H(2)O (1:1, v/v) containing 0.1% formic were sprayed at a lower temperature (100 degrees C) using only the nebulizer gas. The TIS voltage (V) was optimized in order to establish the lowest voltage necessary to achieve optimum ESI of each pharmaceutical compound with the voltage maintained below the onset potential required to produce a corona discharge at the TIS probe (sprayer). Detection limits of 10 ng/mL were achieved for reserpine, dextromethorphan, imipramine and amitriptyline in each solvent composition.     

Determination of cyclamate in foods by high performance liquid chromatography-electrospray ionization mass spectrometry

A high sensitive method for determination of cyclamate in foods by ion-pair high-performance liquid chromatography-electrospray ionization mass spectrometry was developed and validated. The separation was achieved on a C₈ column with 5 mM tris(hydroxymethyl)aminomethane aqueous solution (pH 4.5, adjusted by acetic acid) as mobile phase with an isocratic mode. The quantification of target compound was completed using a selected ion recording (SIR) at m/z 178 obtained from ESI-mode. Tiopronin was used as internal standard for the quantification of cyclamate. The correlation coefficient of the calibration curve were better than 0.996, in the range of 50-5000 ng/mL. The limit of detection is 5 ng/mL, the limit of quantification is 20 ng/mL. The inter- and intra-day accuracy, precision were investigated in detail. The method can be used to monitor effectively the content of the artificial sweetener in foods. The method has obvious merits such as high sensitivity, specificity and simply versus other methods reported.     

Determination of trace elements by resonant ionization mass spectrometry (RIMS)

Summary A resonant ionization mass spectrometer has been developed as an analytical tool for the detection of trace elements, especially of plutonium and other radionuclides. The sample, deposited on a rhenium filament, is evaporated by electrical heating and the atoms of the element under investigation are selectively ionized by laser light delivered from three dye lasers pumped by a copper vapour laser. The resulting photoions are detected in a time-of-flight spectrometer with a channelplate detector. For plutonium a mass resolution of M/M=1500 was obtained and an overall detection efficiency of 4×10^–6 was determined for stepwise excitation and ionization via autoionizing states. With a laser light bandwidth of 3–5 GHz neighbouring isotopes could be suppressed by a factor of 20 due to isotope shifts in the excitation transitions. The isotope composition of synthetic samples was measured and good agreement was found with mass spectroscopic results. The influence of the hyperfine structure on the isotope ratios is discussed.

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Bestimmung von Spurenelementen durch resonante Ionisations-Massenspektrometrie (RIMS)

     

Determination of oxatomide in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry

A rapid, sensitive and specific high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method has been developed and validated for the determination of oxatomide in human plasma. Flunarizine hydrochloride was employed as the internal standard (IS). The analytes were chromatographically separated on a Shimadzu Shim-pack VP-ODS C18 column (250 x 2.0 mm i.d.) with a mobile phase consisting of methanol and aqueous ammonium acetate solution (10 mm, pH 4.0; 85:15, v/v). Detection was performed on a single quadrupole mass spectrometer using an electrospray ionization interface with the selected-ion monitoring (SIM) mode. The method showed excellent linearity (r = 0.9995) over the concentration range of 0.5-500 ng/mL with good accuracy and precision. The intra- and inter-batch precisions were within 10% relative standard deviation. The recoveries were more than 90%. The validated method was successfully applied to a preliminary pharmacokinetic study of oxatomide in Chinese healthy male volunteers.     

气相色谱-负化学离子源质谱法检测胡萝卜中残留的环氟菌胺

建立了胡萝卜中环氟菌胺残留量的气相色谱-负化学离子源质谱(GC-NCI/MS)检测方法。用乙酸乙酯对胡萝卜中的环氟菌胺进行提取,并经固相萃取(SPE)净化后,由GC-NCI/MS在选择离子监测模式(SIM)下测定。该方法的准确度和精密度较高,在0.005,0.01,0.02,0.04 mg/kg 4个加标水平下,环氟菌胺的平均回收率均处于74.9%～96.4%之间,相对标准偏差(RSD)小于9.7%。在10～1000ng/mL范围内线性关系良好,检出限为0.001 mg/kg,定量限为0.005 mg/kg。该方法选择性好,抗干扰能力强,可作为胡萝卜中环氟菌胺残留检测的确证方法。     

Reaction of F atoms with dichloromethane by modulated molecular beam mass spectrometry

The reaction of atomic fluorine with dichloromethane has been studied by the diffusion cloud in a flow technique. Fluorine atoms were generated through F₂ dissociation in a high-frequency discharge. The reaction products were detected mass spectrometrically, applying the technique of focusing the paramagnetic component of the molecular beam in an inhomogeneous magnetic field to detect radical species. Cl atoms and CHCl₂ and CF₃ free radicals have been identified among the reaction products. The initial step was shown to be hydrogen atom abstraction. The room temperature rate constant of this reaction was found to be k₀ = (1.51 ± 0.28) X 10^?11 cm³/s. The rate constant of the secondary reaction of fluorine atoms with dichloromethyl radicals, which is suggested to produce mainly HCl, was evaluated as 3 X 10^?10 cm³/s.     

Recent trends in atomic spectrometry with microwave-induced plasmas

The state-of-the-art and trends of development in atomic spectrometry with microwave-induced plasmas (MIPs) since the 1998s are presented and discussed. This includes developments in devices for producing microwave plasma discharges, with reference also to miniaturized systems as well as to progress in sample introduction for microwave-induced plasmas, such as pneumatic and ultrasonic nebulization using membrane desolvation, to the further development of gaseous analyte species generation systems and to both spark and laser ablation (LA). The features of microwave-induced plasma mass spectrometry (MIP-MS) as an alternative to inductively coupled plasma (ICP)-MS are discussed. Recent work on the use of microwave-induced plasma atomic spectrometry for trace element determinations and monitoring, their use as tandem sources and for particle sizing are discussed. Recent applications of the coupling of gas chromatography and MIP atomic spectrometry for the determination of organometallic compounds of heavy metals such as Pb, Hg, Se and Sn are reviewed and the possibilities of trapping for sensitivity enhancement, as required for many applications especially in environmental work, are showed at the hand of citations from the recent literature.     

Determination of chlorantraniliprole residues in crops by liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry/mass spectrometry

An analytical method is presented for the determination of chlorantraniliprole residues in crops. Chlorantraniliprole residues were extracted from crop matrixes with acetonitrile after a water soak. The extracts were passed through a strong anion-exchange (SAX) SPE cartridge stacked on top of a reversed-phase (RP) polymer cartridge. After both cartridges were rinsed and vacuum-dried, the SAX cartridge was removed, and chlorantraniliprole was eluted from the RP polymer cartridge with acetonitrile. The acetonitrile eluate was evaporated to dryness, reconstituted, and analyzed using an LC/MS/MS instrument equipped with an atmospheric pressure chemical ionization source. The method was successfully validated at 0.010, 0.10, and 10 mg/kg for the following crop matrixes: potatoes, sugar beets (tops), lettuce, broccoli, soybeans, soybean forage, tomatoes, cucumbers, oranges, apples, pears, peaches, almonds (nutmeat), rice grain, wheat grain, wheat hay, corn stover, alfalfa forage, cottonseed, grapes, and corn grain. The average recoveries from all crop samples fortified at the method LOQ ranged from 91 to 108%, with an overall average recovery of 97%. The average recoveries from all crop samples fortified at 10 times the method LOQ ranged from 89 to 115%, with an overall average recovery of 101%. For all of the fortified control samples analyzed in this study, the overall average recovery was 99%.