Electrospray ionization ion-trap multistage mass spectrometric study of sodium cationized aldobiuronic and pseudoaldobiuronic acid derivatives

Fragmentation mechanisms of electrospray ionization (ESI) mass spectrometry of aldobiuronic and pseudoaldobiuronic acid derivatives were elucidated by multistage mass spectrometric (MS(n), n = 2-5) measurements of selected ions. Characteristic under the conditions of ESI-MS analysis is the production of alkali metal (Na and K) cationized adducts. The probability the of locations of Na cations in per-O-methylated compounds was proved by quantum chemical calculations, using the Jaguar program. The most probably position of alkali metal attachment is the carboxy group of the methoxycarbonyl C-5 group of the uronic acid unit. Characteristic cleavages vary according the kind of O-derivatization. In most cases they take place on the acidic part of the dimer and at the interglycosidic oxygen atom. As a result, the criteria for the differentiation of aldobiouronic and pseudoaldobiouronic acids derivatives were elucidated.     

Characterization of peptides by liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a post-column complexant

Two model peptides, des-Arg1-bradykinin (DAB) and bradykinin (B), were cationized by Ag+ after their separation by reversed-phase liquid chromatography (RPLC) prior to mass spectrometry (MS). Silver nitrate solution was used as a post-column reagent. The RPLC and MS experimental conditions were optimized using flow injection in order to obtain sufficiently abundant silver adducts to permit MS/MS experiments. The use of water-methanol with 0.1% formic acid as mobile phase allowed a good chromatographic separation of the two peptides with a polymeric stationary phase and sufficiently abundant silver-containing adducts, [M + Ag + H]2+ and [M + 2Ag]2+. The gas-phase dissociation of [DAB + Ag + H]2+ and [DAB + 2Ag]2+ led to interpretable mass spectra during the on-line cationization experiment. Most of the ions obtained by dissociating [DAB + Ag + H]2+ and [DAB + 2Ag]2+ species are silver-containing ions but the ions produced depend on the parent. The ions coming from the dissociation of the doubly charged silver adducts [DAB + Ag + H]2+ or [DAB + 2Ag]2+ are of interest compared with those coming from the singly charged silver species or doubly charged protonated species. The fragmentation of the doubly charged silver adducts provides ions over the entire mass range. Although the presence of several prolines in des-Arg1-bradykinin prevents the formation of some expected ions, the observation of triplets [an-H + Ag]+, [bn-H + Ag]+ and [bn + OH + Ag]+ produced by the dissociation of on-line Ag(+)-cationized peptides could contribute to greater success of automatic sequencing of peptides.     

Determination of clindamycin in animal plasma by high-performance liquid chromatography combined with electrospray ionization mass spectrometry

A method for the quantification of clindamycin in animal plasma using high-performance liquid chromatography combined with electrospray ionization mass spectrometry (LC/ESI-MS/MS) is presented. Lincomycin is used as the internal standard. The sample preparation includes a simple deproteinization step with trichloroacetic acid. Chromatographic separation is achieved on an RP-18 Hypersil column using gradient elution with 0.01 M ammonium acetate and acetonitrile as mobile phase. Good linearity was observed in the range 0-10 microg ml(-1). The limit of quantification of the method is 50 ng ml(-1) and the limit of detection is 1.3 ng ml(-1). The method was shown out to be of use for pharmacokinetic studies of clindamycin formulations in dogs.     

飞秒强激光场下亚硝酰氯分子的电离和解离

Ionization and dissociation of nitrosyl chloride ClNO were studied using femtosecond laser mass spectra tech-nique.Strong fragmental ions NO~ and Cl~ were observed with the laser intensity varied from 3.2×10~(14) to 2.5×10~(15) W/cm~2.These fragmental ions were attributed to the direct dissociation of the parent ions.Electronic structurecalculations were also carried out with Hartree-Fock,density functional and correlated levels of theory to under-stand the possible fragmentation pathways.The very low N-Cl bond energy in the parent ion of nitrosyl chloride isa clear reason for the absence of ClNO~ and ClN~ ion peaks from the femtosecond laser mass spectrum.     

Highly sensitive determination of haloperidol in human serum by capillary gas chromatography using a surface ionization detector

A method has been developed for highly sensitive determination of haloperidol in human serum involving a simple extraction procedure followed by gas chromatographic separation. Target components were separated from the extracting solvents with a Van den Berg type solventless sample injector before introduction Into a DB-1 capillary separation column. A surface ionization detector (SID), which has highly selective sensitivity for Substituted amines, was employed for quantitation using bromperidol as an internal standard. Chloroform proved to be the best extracting solvent, yielding a quantitative detection limit of 5 ng/ml (S/N = 2). Comparison of the response to target compounds obtained by the SID, FTD (flame thermionic detector), and FID (flame ionization detector) showed the SID to be superior.     

2,5—双（4—羟基苯亚甲基）环戊酮中双电荷离子存在的串联质谱证据

应用串联质谱的碰撞诱导解离和联动扫描技术，研究了２，５－双（４－羟基苯亚甲基）环戊酮的质谱解离特征，提供了双电荷离子存在的实验证据。进一步对双电荷离子（ｍ／ｚ１４６）的碰撞诱导解离碎裂进行了讨论。     

Quantitative analysis of perchlorate in extracts of whole fish homogenates by ion chromatography: comparison of suppressed conductivity detection and electrospray ionization mass spectrometry

The perchlorate anion (ClO ₄ ^– ) is an anthropogenic contaminant of increasing concern in water supplies, and has been shown to disrupt thyroid activity. Most perchlorate analyses are currently carried out by ion chromatography (IC) with suppressed conductivity detection (SCD). While this procedure has been demonstrated to provide acceptable performance for analysis of water samples, the determination of perchlorate in high-conductivity aqueous extracts of plant or animal material is not readily accomplished by IC-SCD unless lengthy cleanup protocols are applied. With the addition of electrospray ionization mass spectrometry (ESI-MS) to IC, it was hypothesized that the interference imposed by various ionic species could be significantly reduced without the need for purification; however, the analysis of perchlorate in relatively unpurified extracts of biologically derived homogenates by IC-ESI-MS has not previously been described in the literature. The research presented here represents a comparison of the capabilities of IC-SCD and IC-ESI-MS to detect perchlorate in reagent water and in crude extracts of perchlorate-exposed fish (threespine stickleback, Gasterosteus aculeatus). ESI-MS was found to compare favorably to SCD for the detection of perchlorate in deionized water, and to exceed SCD performance in perchlorate analysis of fish-derived extracts.     

Thermodynamic characteristics of thermal dissociation of platinum tetrachloride

The pressure of thermal dissociation of platinum tetrachloride by the first step PtCl₄(s) = PtCl₃(s) + 0.5 Cl₂(g) was measured by the static method with a quartz membrane-gauge zero-pressure manometer. An approximating equation for the dissociation pressure vs. temperature was found. The enthalpy (52160±880 J mol⁻¹) and entropy (72.1±1.6 J mol⁻¹ K⁻¹) of dissociation were calculated. The heat of formation found for platinum tetrachloride (−246.3±1.3 kJ mol⁻¹) at 298.15 K agrees well with the value obtained by the calorimetric method (−245.6±1.9 kJ mol⁻¹).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2028–2031, October, 2004.     

Assignment of the first photoelectron band of the CH<Subscript>3</Subscript>CHCl radical using ab initio quantum mechanical calculations

HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl chloride at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded with adiabatic and vertical ionization energies of (7.84±0.02) and (8.18±0.02) eV respectively. An average vibrational separation of (680±30) cm^–1was observed in this band. Comparison between the experimental vertical and adiabatic ionization energies and ionization energies computed for CH₃CHCl (X²A) and CH₂CH₂Cl (X²A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH₃CHCl (X²A). The observed vibrational structure was assigned to excitation of the C–Cl stretching mode in CH₃CHCl⁺(X¹A).Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

化妆品中氯霉素的气相色谱-质谱快速分析

研究了用气相色谱-质谱分析化妆品中氯霉素(CAP)的方法.以乙酸乙酯作为提取溶剂,BSTFA TMCS(99 1)作为衍生化试剂,在70℃衍生化60min,用GC-MS(NCI)进行测定.方法的检出限为10 μg/kg,线性范围在0.5～500 ng/mL之间,在10、100、500 μg/kg 3个添加水平,方法回收率为94.4%～95.7%,相对标准偏差为0.23%～1.3%.方法操作快速简单,3 h可以完成整个样品分析.方法已用于化妆品中氯霉素的测定.