Practical approaches to fast gas chromatography-mass spectrometry

Fast gas chromatography–mass spectrometry (GC–MS) has the potential to be a powerful tool in routine analytical laboratories by increasing sample throughput and improving laboratory efficiency. However, this potential has rarely been met in practice because other laboratory operations and sample preparation typically limit sample throughput, not the GC–MS analysis. The intent of this article is to critically review current approaches to fast analysis using GC–MS and to discuss practical considerations in addressing their advantages and disadvantages to meet particular application needs. The practical ways to speed the analytical process in GC and MS individually and in combination are presented, and the trade-offs and compromises in terms of sensitivity and/or selectivity are discussed. Also, the five main current approaches to fast GC–MS are described, which involve the use of: (1) short, microbore capillary GC columns; (2) fast temperature programming; (3) low-pressure GC–MS; (4) supersonic molecular beam for MS at high GC carrier gas flow; and (5) pressure-tunable GC–GC. Aspects of the different fast GC–MS approaches can be combined in some cases, and different mass analyzers may be used depending on the analytical needs. Thus, the capabilities and costs of quadrupole, ion trap, time-of-flight, and magnetic sector instruments are discussed with emphasis placed on speed. Furthermore, applications of fast GC–MS that appear in the literature are compiled and reviewed. At this time, the future usefulness of fast GC–MS depends to some extent upon improvement of existing approaches and commercialization of interesting new techniques, but moreover, a greater emphasis is needed to streamline overall laboratory operations and sample preparation procedures if fast GC–MS is to become implemented in routine applications.     

Evaluation of common organic solvents for gas chromatographic analysis and stability of multiclass pesticide residues

In this study, we evaluated the suitability of six common organic solvents for gas chromatographic (GC) analysis of pesticides. Three of these, acetone, acetonitrile (MeCN) and ethyl acetate (EtAc), represent extraction solvents commonly used in multiresidue methods for determination of pesticides in produce. The other three, isooctane, hexane and toluene, often serve as exchange solvents before a GC analysis. An ideal solvent for GC analysis of multiclass pesticide residues should be compatible with: the analytes, sample preparation, and GC analysis. This study addresses each aspect with emphasis placed on stability of selected pesticides in the given solvents. In this respect, the exchange solvents proved to be superior to the more polar extraction solvents. Degradation of N-trihalomethylthio fungicides (e.g., captan, folpet, dichlofluanid) in MeCN was observed only in certain lots of the tested MeCN, but even if it occurred, the stability of these analytes as well as that of dicofol and chlorothalonil was dramatically improved by the addition of 0.1% (v/v) acetic acid. Dicofol and chlorothalonil were also unstable in acetone, and pesticides with a thioether group (e.g., fenthion, disulfoton) degraded in the tested EtAc. Formation of isomers of certain pyrethroids (deltamethrin, lambda-cyhalothrin) was recorded in the chromatograms from MeCN and acetone solutions, but this effect more likely occurred during the GC injection than in solution. For several reasons, MeCN was found to be the most suitable solvent for extraction of a wide polarity range of pesticide residues from produce. After acidification, the stability of problematic pesticides in MeCN is acceptable, and MeCN can also serve as a medium for GC injection; therefore solvent exchange is generally not required before GC analysis. If sensitivity is an issue in splitless injection, then toluene was demonstrated to be the best exchange solvent due to its miscibility with MeCN and stronger responses of relatively more polar pesticides (e.g., acephate, methamidophos) as compared to hexane and isooctane.     

Mitochondrial and endoplasmic reticulum stress-induced apoptotic pathways are activated by 5-aminolevulinic acid-based photodynamic therapy in HL60 leukemia cells

We studied the mechanism of the cytotoxic effects of 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT; induction with 1 mM ALA for 4 h followed by a blue light dose of 18 J/cm(2)) on the human promyelocytic leukemia cell line HL60 using biochemical and electron microscopy methods. The disruption of mitochondrial membrane potential, deltapsi(m), was paralleled by a decrease in ATP level, unmasking of the mitochondrial antigen 7A6, release of cytochrome c into the cytoplasm, activation of caspases 9 and 3 and cleavage of poly(ADP-ribose) polymerase (PARP). This was followed by DNA fragmentation. These data suggest that ALA-PDT activates the mitochondrial apoptotic pathway. The level of endoplasmic reticulum Ca(2+)-binding chaperones ERp57 and ERp72 and of anti-apoptotic proteins Bcl-2 and Bcl-x(L) was decreased whereas that of Ca(2+)-binding protein calmodulin and the stress protein HSP60 was elevated following ALA-PDT. Inhibition of the initiator caspase 9, execution caspase 3 and Ca(2+)-dependent protease m-calpain, did not prevent DNA fragmentation. We conclude that, in our in vitro model, ALA-based photodynamic treatment initiates several signaling processes in HL60 cells that lead to rapidly progressing apoptosis, which is followed by slow necrosis. Two apoptotic processes proceed in parallel, one representing the mitochondrial pathway, the other involving disruption of calcium homeostasis and activation of the endoplasmic reticulum stress-mediated pathway.     

Naphthalene sulphonic acids--new test compounds for characterization of the columns for reversed-phase chromatography

Non-substituted naphthalene sulphonic acids are strong acids, which are completely ionised in aqueous and aqueous-organic solutions. Because of repulsive electrostatic interactions, they are more or less excluded from the pores of the column packing materials commonly used in reversed-phase chromatography. The ionic exclusion can be suppressed by increasing the ionic strength of the mobile phase. In aqueous sodium sulphate solutions, very good selectivity was observed for isomeric naphthalene di- and tri-sulphonic acids, allowing reversed-phase separations of these strongly ionic compounds without addition of ion-pairing reagents to the mobile phase. The retention of the isomeric acids increases proportionally to the dipole moment, which can be explained by its effect on increasing exposure of the naphthalene ring to hydrophobic interactions with the non-polar stationary phases. Chromatographic behaviour of isomeric naphthalene di- and trisulphonic acids was investigated on 25 different columns for reversed-phase chromatography. The elution order of the isomers is the same on all the columns, but very strong stationary phase effects were observed on the retention and on the band asymmetry, depending on polar interactions with residual silanol groups and other polar adsorption centres in the stationary phases. These effects are independent of the organic solvents, as the tests are performed in purely aqueous mobile phases and allow classification of the columns into several groups.     

Evaluation of analyte protectants to improve gas chromatographic analysis of pesticides

A common problem in gas chromatography (GC) applications is the analyte losses and/or peak tailing due to undesired interactions with active sites in the inlet and column. Analytes that give poor peak shapes or degrade have higher detection limits, are more difficult to identify and integrate, and are more prone to interferences than stable analytes that give narrow peaks. For susceptible analytes, significant peak quality improvements are obtained when matrix components are present because they fill active sites, thus reducing analyte interactions. This phenomenon is called "matrix-induced chromatographic response enhancement." Several approaches have been proposed to minimize peak distortion phenomena and compensate for matrix-induced effects, which is especially important for accurate quantitation, but each approach has serious limitations for routine multi-pesticide analysis. In this study, we demonstrate the feasibility of using "analyte protectants" to provide a more convenient and effective solution to the problem than other approaches developed thus far. The protecting agents are added to extracts and matrix-free standards alike to provide the chromatographic enhancement effect even for the most susceptible analytes in a very dirty GC system. In this study, we evaluated 93 different compounds to find the most suitable ones for improving chromatographic quality of the signal. Because hydrogen bonding has been shown to be an important factor in analyte interactions with active sites, we mainly focused on additives with strong hydrogen bonding capabilities. Dramatic peak enhancements were achieved using compounds containing multiple hydroxy groups, such as sugars and sugar derivatives, and gulonolactone appears to be the most effective protecting agent for the most pesticides that we tested. The benefits of using analyte protectants versus alternative procedures for overcoming matrix-induced effects in quantitation include: (a) simpler procedure; (b) easier integration of peaks; (c) lower detection limits; (d) better quantitation; (e) less maintenance of the GC inlet; and (e) lower cost. However, long-term influences on the performance of the chromatographic system have yet to be established.     

Eigenmobilities in background electrolytes for capillary zone electrophoresis: II. Eigenpeaks in univalent weak electrolytes

We analyze in detail a mathematical model of capillary zone electrophoresis (CZE) based on the conception of eigenmobilities, which are eigenvalues of the matrix tied to the linearized continuity equations. Our model considers CZE systems, where constituents are weak electrolytes and where pH of the background electrolyte may reach the full range from 0 to 14. Both hydrogen and hydroxide ions are taken into account in relations for conductivity and electroneutrality. An electrophoretic system with N constituents has N eigenmobilities. We reveal that two of the eigenmobilities have a special meaning as they exist due to the presence of hydrogen ions and hydroxide ions (in water solutions). These two eigenmobilities are responsible for the existence of two corresponding system zones (system peaks). We show that the stationary zone (injection zone, water zone, gap, peak, dip) is in many common background electrolytes composed of these two eigenzones which overlap, due to their very low electrophoretic mobility, into one zone. Other eigenmobilities give rise to system zones originating due to a possible existence of double (or multiple) coconstituents in the background electrolyte. The last group of eigenmobilities is connected with the movement of eigenzones accompanying analytes and enabling their indirect UV or conductivity detection. The model allows assessing experimentally available quantities such as effective mobility of the analyte, molar conductivity detection response, transfer ratio, and relative velocity slope and gives a picture about migration of analytes, their electromigration dispersion and signals obtained in detectors. It allows computer simulation of electropherograms and enables optimization of background electrolytes.     

”Eau de graphene” from a KC8 graphite intercalation compound prepared by a simple mixing of graphite and molten potassium

We synthesized KC₈ by simply mixing molten potassium and graphite at 180 °C under inert atmosphere. The KC₈ shows typical shiny bronze color, Raman characteristics and XRD pattern of an efficiently intercalated stage 1 GIC, and is of sufficient quality to produce fully exfoliated graphenide solutions in tetrahydrofuran (THF) and subsequently single layer graphene in water as ”eau de graphene” (EdG). The evolution of absorption and Raman spectroscopic signatures of the EdG as a function of processing conditions give key indications on the number of layers of the graphene flakes dispersed in EdG. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoelectron spectroscopy of gramicidin polyanions: competition between delayed and direct emission

We present the first photoelectron (PE) spectra of polypeptide polyanions. Combining PE spectroscopy and mass spectrometry provides a direct measurement of the stability of the polyanions with respect to electron detachment and of the repulsive energy between excess charges. The second electron affinity of gramicidin was found to amount to 2.35 +/- 0.15 eV, and the value of the repulsive Coulomb barrier was estimated to be 0.5 +/- 0.15 eV. The spectra are interpreted as resulting from a competition between delayed and direct emission.     

Geissospermiculatine,a New Alkaloid from Geissospermum reticulatum Bark

A new alkaloid, geissospermiculatine was characterized in Geissospermum reticulatum A. H. Gentry bark (Apocynaceae). Here, following a simplified isolation protocol, the structure of the alkaloid was elucidated through GC-MS, LC-MS/MS, 1D, and 2D NMR (COSY, ROESY, HSQC, HMBC, ¹H-¹⁵N HMBC). Cytotoxic properties were evaluated in vitro on malignant THP-1 cells, and the results demonstrated that the cytotoxicity of the alkaloid (30  μg/mL) was comparable with staurosporine (10  μM). Additionally, the toxicity was tested on zebrafish (Danio rerio) embryos in vivo by monitoring their development (0–72 h); toxicity was not evident at 30  μg/mL.