Rapid determination of C6-aldehydes in tomato plant emission by gas chromatography-mass spectrometry and solid-phase microextraction with on-fiber derivatization

A simple, rapid, sensitive, and solvent-free method was developed for determination of plant-signalling compounds, the three C6-aldehydes hexanal, (Z)-3-hexenal, and (E)-2-hexenal, in tomato plant emission by gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME) with on-fiber derivatization. In this method, O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) in aqueous solution was first headspace adsorbed onto a 65 microm poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber at 25 degrees C for 5 min, and then the fiber with adsorbed PFBHA was used for headspace extraction of tomato plant emission at 25 degrees C for 6 min. Finally, the resulting oximes adsorbed on the fiber were desorbed and analyzed by GC-MS. Extraction conditions and method validation were studied. The proposed method had low detection limit values for the three aldehydes from 0.1 to 0.5 ng/L and good precision (RSD less than 10%). In this work, the method was applied to investigation of tomato plant defense response to Helicoverpa armigera.     

An isocratic HPLC method for the quantitation of eicosanoids in human platelets

We describe here a modified protocol for the simultaneous quantification of specific eicosanoids formed during stimulation of human platelets in vitro with adenosine diphosphate. The eicosanoids thromboxane B(2) (TXB(2)), arachidonic acid (AA), 12-R-hydroxyeicosatetraenoic acid (12-R-HETE), 12-S-hydroxyheptadecatrienoic acid (12-S-HHTrE) and the internal standard prostaglandin B(1) (PGB(1)) were extracted from human platelets by liquid-liquid extraction using ethyl acetate. This was followed by derivatization and fluorescent detection prior to analysis by reversed phase liquid chromatography. The high-performance liquid chromatographic method consisted of ODS reversed-phase column (3 microm) and a mobile phase of acetonitrile-water (85:15). TXB(2) and AA plasma calibration curves were linear between 6.25 and 125 ng mL(-1) (r(2) > 0.997), whereas for 12-R-HETE and 12-S-HHTrE the curves were linear between 5.0 and 40 ng mL(-1) (r(2) > 0.998). All calibration curve standards had <15% CV (coefficient of variation) and between-run precision, and the percentage relative deviation for replicate (n = 6) quality controls was less than 5.5%. The method was adapted to allow the screening of drugs that may affect either one or both of the lipoxygenase and cyclo-oxygenase pathways.     

Evaluation of experimental strategies for the development of chiral chromatographic methods based on diastereomer formation

The past two decades has seen explosive growth in the field of chirality as illustrated by the rapid progress in the various facets of this intriguing field. Firstly, it is the basic understanding of the importance of chirality and, secondly, the awareness of the therapeutic pitfalls due to failure to recognize chirality that have paved the way for a rejuvenated interest in the field. Needless to say that the impetus for chiral separation advancement and enhancement has been found to be the highest in the past decade and still continues to be an area of high focus. In this regard, both direct and indirect separation approaches have been instrumental in placing into literature stereoselective pharmacokinetic and pharmacodynamic data of plethora of drug racemates. Also, today, the cloud of uncertainty associated with the development of a chiral molecule is a thing of the past because the field is so evolved and numerous options are available for stereoselective analysis. However, the decision to advance either a single enantiomer or a racemate for development has to be made by a rational approach with adequate justification. Although indirect method of chiral separation has been well established with numerous examples of well-documented cases of stereoselective pharmacokinetic data, there is a growing need for a review that provides a strategic overview of considerations and key issues for developing chromatographic methods based on diastereomer formation. This review provides a general framework for the exploratory planning and a definitive game plan for the establishment of chiral methods based on diastereomer formation. Also, it provides an exhaustive list of applications of numerous chiral derivatization reagents that have been used in the generation of stereoselective pharmacokinetic data.     

Subminute and sensitive determination of the neurotransmitter serotonin in urine by capillary electrophoresis with laser-induced fluorescence detection

In this work, a sub-minute and sensitive capillary electrophoresis with laser-induced fluorescence (CE-LIF) method was developed for the analysis and quantitation of the neurotransmitter 5-hydroxytryptamine (5-HT) or serotonin in urine. The method involves precolumn derivatization with fluorescein isothiocyanate isomer I (FITC) using an excitation light from an argon ion laser of 488 nm and a 520 nm band pass emission filter. Different variables that affect derivatization (pH, FITC concentration, reaction time and temperature) and separation (buffer concentration, pH, applied voltage and injection time) were studied. The linear dynamic range obtained was between 0 and 188 nM with a detection limit of 16 nm with a RSD between 2 and 9%. The applicability of the proposed method was demonstrated by analysis of 5-HT in human urine, establishing a concentration of 57 nM in control urine. The method was validated by standard-addition methodology.     

伯胺化合物的化学衍生萤光法研究

用邻苯二甲醛和邻萘二甲醛对伯胺化合物包括有机胺和氨基酸进行化学衍生萤光测定,方法灵敏度高、操作简便,用于某些试样分析,结果良好。还研究了有关反应的动力学参数。     

Determination of thiamine and thiamine phosphates as thiochrome derivatives by reversed-phase chromatography on polystyrene packing materials

Summary The chromatography of thiochrome and related phosphate esters was studied on two different polystyrene packing materials.The adsorbents were compared with respect to capacity factors, plate heights and resolution factors measured with different mixtures of phosphate buffer (pH 8.5) and methanol.In contrast with derivatized silica, these phases were found to be stable using an alkaline mobile phase and sample. Fast separations were possible with good peak symmetry at all organic modifier concentrations.     

Screening of amino acids in dried blood spots by stable isotope derivatization-liquid chromatography-electrospray ionization mass spectrometry

Direct infusion mass spectrometry (DIMS) is a powerful technique in clinical diagnosis for screening neonatal amino acid metabolic disorders from dried blood spots (DBS). However, DIMS sometimes generated false-positive results for analysis of amino acids. In this work, we utilized a stable isotope derivatization method, combining with liquid chromatography tandem mass spectrometry (SID-LC-MS), to improve the specificity for screening amino acids in DBS specimens. A pair of isotope reagents, p-(dimethylamino)phenyl isothiocyanate (DMAP-NCS) and 4-isothiocyanato-N,N-bis(methyl-[²H₂])aniline ([²H₄]DMAP-NCS), was synthesized and used to label amino acids in DBS specimens. The [²H₄]DMAP-NCS labelled amino acid standards were used as internal standards to compensate the matrix effect. This method was validated by measuring linearity, recovery and accuracy. The results showed that the developed SID-LC-MS method can be used for sensitive and selective determination of 12 diagnostically important amino acids in DBS specimens.