Determination of Fatty Acids in Three Nitraria Species by Precolumn Fluorescence Labeling for High-Performance Liquid Chromatography and Atmospheric Pressure Chemical Ionization–Mass Spectrometry

A novel fluorescence method using 2-(7-methyl-1H-pyrazolo-[3,4-b] quinoline-1-yl) ethyl-4-methyl benzenesulfonate as the labeling reagent was established for high-performance liquid chromatography determination of fatty acids. The conditions were optimized, including the identity of the organic solvent, identity, and amount of catalyst, amount of derivatization reagent, derivatization temperature, and derivatization time. The results indicated that quantitative yields of derivative were obtained with a five-fold molar excess of reagent at 90°C for 30 min using 25 mg of potassium carbonate as the catalyst. Atmospheric pressure chemical ionization mass spectrometry results indicated that collision-induced dissociation of protonated fatty acid derivatives produced fragments at m/z 228.2, m/z 210.2, and m/z 183.8. The method was validated in terms of linearity, limits of detection, limits of quantification, precision, and accuracy, and the results showed that the method exhibited excellent sensitivity, selectivity, and reproducibility. Limits of detection and limits of quantification were in the ranges of 0.52–2.34 ng mL^?1 and 1.23–6.63 ng mL^?1, respectively. This method was successfully applied to the determination of fatty acids in sarcocarps, seeds, and leaves of Nitraria tangutorum Bobr., Nitraria sibirica Pall., and Nitraria roborowskii Kom. The results indicated that the main components were oleic, linoleic, linolenic, and hexadecanoic acids. However, the composition of fatty acids in the tissues varied considerably.     

Thin-Film Microextraction Coupled with Mass Spectrometry and Liquid Chromatography–Mass Spectrometry

Thin-film microextraction (TFME) is a format of solid-phase microextraction (SPME) technique which offers improvement of sensitivity without sacrificing time through the increase of available surface area and extractive phase volume. This technique offers significant advantages which make it attractive for many analytical/bioanalytical applications. This review discusses the fundamental principle of TFME and its benefits versus the rod fiber geometry of SPME, and demonstrates the agreements of the experimental data for the available TFME systems with the theoretical concept. The current configurations, coating chemistries, coating preparation methods, and applications for TFME system are reported.     

Exact Mass Measurements for a-Allenic Alcohol by Atmospheric Pressure Chemical Ionization／Time-of-flight Mass Spectrometry

The atmospheric pressure chemical ionization/time,of-flight mass speetrmtry (APEI/TOF-MS) was applied to determine the mass of five a.aIIenic alcohols via their vrotonated molecu.lar ions nslna Imsifive ion mode. Polyethylene Idycol (PEG) was used as the hlternal reference. All results were obtained under the resolution of about 5000 FWHM (full width at the half maximum). Solvent effects were studied and the satired results were obtained in acetonitrile. Comvared with the theoreflcal values, nun absolute errors were less thRn 1.0 mmu. The efTeets Of nozzle pote.Jldal, push pulse potential, pug pulse potentlai, puO bias potential and ic(lulsltion rate on exact mass determina/lon were also discussed. APCI/TOF.MS is proven to be a very semi/ire analytical technique and an alternative ionizafion mode in analytical technique lablle compounds with relatively weak polarity, such as a-allenic alcohol.     

Exact Mass Measurements for α-Allenic Alcohol by Atmospheric Pressure Chemical Ionization/Time-of-flight Mass Spectrometry

Introduction　　α Allenicalcoholsareanimportantkindofusefulcompoundsinsyntheticchemistrybecauseoftheirunusualstructuresandhavebeenwidelyappliedtothesynthesisofthree orfive memberedoxygen containingcycliccom pounds.1 4 Thestructuresoffiveα allenicalcoholsareshowninFig .1.Theirmolecularstructuresbecomeunstablewhenion izedbyelectronimpact (EI) ,thusthedetectionoftheirmolecularionsM+ isalwaysnoteasy .SoitisdifficulttodeterminetheirexactmolecularmassbyEI (Fig .2 ) .Whentheyareionizedbychemica…     

Determination of Phenylethanoid Glycosides in Lagotis brevituba Maxim. by High-Performance Liquid Chromatography–Electrospray Ionization Tandem Mass Spectrometry

High performance liquid chromatography coupled with electrospray ionization quadrupole-time-of-flight tandem mass spectrometry was used to profile the phenylethanoid glycosides in Lagotis brevituba. A total of twenty-three phenylethanoid glycosides were characterized by comparing the retention time and fragmentation with standards, accurate mass measurements, and fragmentation at low and high collision energies. Most phenylethanoid glycosides were reported in L. brevituba for the first time. This established method may be employed for comprehensive quality control of L. brevituba.     

Liquid Chromatography‐Electrospray Ionization Mass Spectrometric Method for Determination of Gliclazide in Human Plasma

Abstract

A rapid, sensitive, and specific liquid chromatography‐electrospray ionization mass spectrometric (LC‐ESI‐MS) method has been developed for quantification of gliclazide in human plasma. The analyte and tolbutamide (internal standard, I.S.) were extracted from plasma samples with n‐hexane–dichloromethane (1:1, v/v) and analyzed on a C₁₈ column. The chromatographic separation was achieved within 4.0 min by using methanol–0.5% formic acid (80:20, v/v) as mobile phase and the flow rate was 1.0 mL/min. Ion signals m/z 324.0 and 271.0 for gliclazide and internal standard were measured in the positive mode, respectively. The method was linear within the range of 2.5–2000 ng/mL. The lower limit of quantification (LLOQ) was 2.5 ng/mL. The intra‐ and inter‐day precisions were lower than 2.8% in terms of relative standard deviation (RSD). The inter‐day relative error (RE) as determined from quality control samples (QCs) ranged from ?1.93% to 1.85%. This validated method was successfully applied for the evaluation of pharmacokinetic profiles of gliclazide modified‐release tablets in 20 healthy volunteers.     

Rapid Determination of Coumatetralyl in Human Serum by High‐Performance Liquid Chromatography Coupled with Electrospray Ionization Tandem Mass Spectrometry

Abstract

A rapid, sensitive, and selective high‐performance liquid chromatography‐tandem mass spectrometric method (HPLC‐MS‐MS) for the determination of coumatetralyl in human serum using warfarin as an internal standard has been developed and validated. Coumatetralyl and the internal standard were extracted from the human serum samples by liquid‐liquid extraction with ethyl acetate, followed by separation on a XDB C₁₈ reversed‐phase column (150 mm×2.1 mm i.d., 5 µm) using a mobile phase consisting of acetic acid‐ammonium acetate (5 mmol/L, pH=4.5)/methanol (20:80, v/v) at a constant flow rate of 0.40 mL/min. Coumatetralyl and the internal standard were ionized by negative ion pneumatically assisted electrospray and detected in the multiple‐reaction monitoring mode using precursor→product ion combinations at m/z 291→247 and 307→161, respectively. The calibration curve was linear (r²=0.9945) in the concentration range of 0.5～100.0 ng/mL, with a lower limit of quantification of 0.5 ng/mL in human serum. Intra‐ and inter‐day relative standard deviations were less than 6.3 and 11.0%, respectively. The mean extraction recovery was 87.9% for coumatetralyl and 90.1% for the internal standard. This method is found to be able to determine trace coumatetralyl in human serum and can be used for the diagnosis of poisoned human beings.     

Mass Spectrometry and Liquid Chromatography - Mass Spectrometry of β-Amino ß-Nitrostilbenes

Abstract

(Z)-α-amino ß-nitrostilbenes are obtained by the reaction of either ammonia or primary or secondary amines on (Z)-α, ß-dinitrostilbene (DNS). The fragmentometric study of these compounds by electron impact and chemical ionization was carried out. The conditions in which it may be possible to determine the purity of these compounds were obtained by HPLC on reversed phase.

However the resolution factor between DNS and benzyl- or phenyl-aminonitroenamine is not sufficient for UV detection; only liquid chromatography-mass spectra coupling with negative ionization enables the detection of the possible presence of DNS in these nitro enamino derivatives.     

Liquid Chromatography–Electrospray Ionization–Mass Spectrometric Method for the Determination of Hydrochlorothiazide in Human Plasma: Application to a Pharmacokinetic Study

Abstract

A rapid, convenient, and sensitive liquid chromatography–electrospray ionization–mass spectrometry method was developed and validated for the quantification of hydrochlorothiazide in human plasma. The samples were first spiked with the internal standard, and the analyte was then extracted with ethyl acetate. The chromatographic separation was achieved on a C₁₈ column by using water–acetonitrile (68:32, v/v) as mobile phase. The method was linear within the range of 2.5–200 ng/ml. The lower limit of quantification was 1.0 ng/ml. Finally, the validated method was successfully applied for the evaluation of the pharmacokinetic profiles of hydrochlorothiazide in healthy male Chinese volunteers.     

Ion-Pairing Liquid Chromatography Coupled with Mass Spectrometry for the Simultaneous Determination of Nucleosides and Nucleotides

Adenosine and its corresponding nucleotides adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate ( ADP ) and adenosine 5'-triphos-phate (ATP) are important biomolecules that provide energy and substrates for various cellular bio-chemical processes. There have been strong     

Ion-Pairing Liquid Chromatography Coupled with Mass Spectrometry for the Simultaneous Determination of Nucleosides and Nucleotides

Adenosineanditscorrespondingnucleotidesadenosine 5′monophosphate (AMP) ,adenosine 5′diphosphate (ADP)andadenosine 5′triphosphate(ATP)areimportantbiomoleculesthatprovideen ergyandsubstratesforvariouscellularbiochemicalprocesses[1] .Therehavebeenstrongde…     

Preliminary Characterization of the Composition and Phenolic Fragmentation of Olive Byproducts by Gas Chromatography–Mass Spectrometry and High-Performance Liquid Chromatography–Tandem Mass Spectrometry

Olive waste is a potential resource due to its rich variety of biologically active compounds. To investigate chemical components of olive waste, the selected samples were extracted using ultrasound assisted enzyme hydrolysis and petroleum ether, ethyl acetate and n-butyl alcohol were used to obtain a series of solvent extracts. Gas chromatography–mass spectrometry analysis showed hydrocarbons, esters, acids, alcohols, and ketones present in the extracts. Some fatty acids were considered to be predominant; it is noteworthy that phenolic compounds were detected in the ethyl acetate extract fraction. Furthermore, the primary phenolic compounds were also determined by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. The possible fragmentation patterns have been proposed in positive and negative ion modes; the main fragment ions were observed from the loss of methyl, hydroxyl, or carboxyl groups. The compounds showed different fragmentation ions types in both positive and negative ionization modes and gave structural information on the main phenolic compounds in olive waste. The results of this study may be used to identify valuable active compounds and guide commercial applications of olive waste.     

Qualitative Gas Chromatography–Mass Spectrometry Analyses Using Amines as Chemical Ionization Reagent Gases

Ammonia is a very useful chemical ionization (CI) reagent gas for the qualitative analyses of compounds by positive ion gas chromatography–mass spectrometry (GCMS). The gas is readily available, inexpensive, and leaves no carbon contamination in the MS source. Compounds of interest to our laboratory typically yield abundant protonated or ammoniated species, which are indicative of a compound’s molecular weight. Nevertheless, some labile compounds fragment extensively by substitution and elimination reactions and yield no molecular weight information. In these cases, a CI reagent gas mixture of methylamine in methane prepared dynamically was found to be very useful in obtaining molecular weight data. Likewise, deuterated ammonia and deuterated methylamine are useful CI reagent gases for determining the exchangeable protons in organic compounds. Deuterated methylamine CI reagent gas is conveniently prepared by dynamically mixing small amounts of methylamine with excess deuterated ammonia.

Rapid Preconcentration for Liquid Chromatography–Mass Spectrometry Assay of Trace Level Neuropeptides

Measurement of neuropeptides in the brain through in vivo microdialysis sampling provides direct correlation between neuropeptide concentration and brain function. Capillary liquid chromatography-multistage mass spectrometry (CLC-MSⁿ) has proven to be effective at measuring endogenous neuropeptides in microdialysis samples. In the method, microliter samples are concentrated onto nanoliter volume packed beds before ionization and mass spectrometry analysis. The long times required for extensive preconcentration present a barrier to routine use because of the many samples that must be analyzed and instability of neuropeptides. In this study, we evaluated the capacity of 75 μm inner diameter (i.d.) capillary column packed with 10 μm reversed phase particles for increasing the throughput in CLC-MSⁿ based neuropeptide measurement. Coupling a high injection flow rate for fast sample loading/desalting with a low elution flow rate to maintain detection sensitivity, this column has reduced analysis time from ～30 min to 3.8 min for 5 μL sample, with 3 pM limit of detection (LOD) for enkephalins and 10 pM LOD for dynorphin A_1-8 in 5 μL sample. The use of isotope-labeled internal standard lowered peptide signal variation to less than 5 %. This method was validated for in vivo detection of Leu and Met enkephalin with microdialysate collected from rat globus pallidus. The improvement in speed and stability makes CLC-MSⁿ measurement of neuropeptides in vivo more practical.

Supercritical Fluid Chromatography–Mass-Spectrometry of Nitrogen-Containing Compounds: Atmospheric Pressure Ionization

Journal of Analytical Chemistry - Supercritical fluid chromatography (SFC) in combination with mass spectrometry is a promising alternative to traditional chromatographic methods for the separation...     

Separation and Quantification of Key Starting Materials of Irbesartan Using Liquid Chromatography–Mass Spectrometry as a Separation and Identification Tool

Abstract

A liquid chromatography–mass spectrometry (LC-MS) method was developed and validated for determining the levels of 4-methyl-2-cyano biphenyl and 4-bromomethyl-2-cyano biphenyl, which are key starting materials of an antihypertensive drug substance, irbesartan. An active pharmaceutical ingredient of irbesartan was synthesized by using these two starting materials for its therapeutic use. We have explicated the LC-MS method to separate and quantify these two compounds in irbesartan at nanogram levels. The method was capable of separating irbesartan and its starting materials, which were monitored for their absence in the finished product of irbesartan. The separation was carried out at 40°C on a 150- × 4.6-mm cyano column by using the mobile phase containing 60 volumes of water adjusted to pH 3.2 with formic acid and 40 volumes of acetonitrile. The detection wavelength was 220 nm. The MS involved an electrospray ionization (ESI) probe and ion-trap analyzer and was validated with respect to its specificity, accuracy, and precision.     

Elucidation of O-Phosphoryl and N-Phosphoryl Amino Acids by Electrospray Ionization Tandem Mass Spectrometry

Mass spectroscopic characteristics of phosphoryl amino acids were studied in detail by positive and negative electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). Besides N-diisopropyloxyphosphoryl amino acids (N-DIPP-AA), O-phospho- and O-diisopropyloxyphosphoryl amino acids (O-DIPP-AA) were studied and compared to N-DIPP-AA. The fragmentation pathways of [M H]^ ,[M Na]^ and [M-H]^- ions of phosphoryl amino acids were summarized. In addition to several similar patterns, each of them showed its characteristic fragmention.     

The Study on the Noncovalent Complexes of Silver Ion with Xanthone Diglycosides by Electrospray Ionization with Tandem Mass Spectrometry

Xanthones are one species of C6-C1-C6 structure flavonoids, showing the various pharmacological activities, such as hepatocytes1 and antioxidative2 etc.. As one of the softest ionization technique, atmospheric pressure ionization mass spectrometry (API-MS…     

Determination of Phthalates in Milk by Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction and Gas Chromatography–Mass Spectrometry

Ultrasound-assisted dispersive liquid–liquid microextraction was coupled with gas chromatography—mass spectrometry for the determination of phthalate esters in milk. Dimethyl phthalate, diethyl phthalate, dibutyl phthalate, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, and dioctyl phthalate were analyzed in five brands of pasteurized Turkish milk. The efficiencies of the extraction procedure for the analytes were between 66 and 100%. The linear dynamic ranges of the calibration curves were from 0.025 to 1.000 µg/mL with correlation coefficients exceeding 0.99. The precision of the method is acceptable with relative standard deviation values below 5%. Dibutyl phthalate and bis(2-ethylhexyl) phthalate were commonly observed in milk.