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A new microextraction method named salt and pH–induced homogeneous liquid-liquid microextraction has been developed in a home–made extraction device for the extraction and preconcentration of some pyrethroid insecticides from different fruit juice samples prior to gas chromatography–mass spectrometry. In the present work, an extraction device made from two parallel glass tubes with different lengths and diameters was used in the microextraction procedure. In this method, a homogeneous solution of a sample solution and an extraction solvent (pivalic acid) was broken by performing an acid–base reaction and the extraction solvent was produced in whole of the solution. The produced droplets of the extraction solvent went up through the solution and solidified using an ice-bath. They were collected without centrifugation step. Under the optimum conditions, limits of detection and quantification were obtained in the ranges of 0.006–0.038, and 0.023–0.134 ng mL –1 , respectively. The enrichment factors and extraction recoveries of the selected analytes ranged from 365–460 to 73–92%, respectively. The relative standard deviations were lower than 9% for intra– (n = 6) and inter–day (n = 4) precisions at a concentration of 1 ng mL –1 of each analyte. Finally, some fruit juice samples were effectively analyzed by the proposed method. [ABSTRACT FROM AUTHOR]

Recent studies have revealed a significant influx of anthropogenic aerosol from South Asia to the Himalayas and Tibetan Plateau (TP) during pre-monsoon period. In order to characterize the chemical composition, sources, and transport processes of aerosol in this area, we carried out a field study during June 2015 by deploying a suite of online instruments including an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) and a multi-angle absorption photometer (MAAP) at Nam Co station (90°57' E, 30°46' N; 4730ma.s.l.) at the central of the TP. The measurements were made at a period when the transition from premonsoon to monsoon occurred. The average ambient mass concentration of submicron particulate matter (PM1/ over the whole campaign was ~2.0 μgm-3, with organics accounting for 68 %, followed by sulfate (15 %), black carbon (8 %), ammonium (7 %), and nitrate (2 %). Relatively higher aerosol mass concentration episodes were observed during the pre-monsoon period, whereas persistently low aerosol concentrations were observed during the monsoon period. However, the chemical composition of aerosol during the higher aerosol concentration episodes in the pre-monsoon season was on a case-by-case basis, depending on the prevailing meteorological conditions and air mass transport routes. Most of the chemical species exhibited significant diurnal variations with higher values occurring during afternoon and lower values during early morning, whereas nitrate peaked during early morning in association with higher relative humidity and lower air temperature. Organic aerosol (OA), with an oxygen-to-carbon ratio (O / C) of 0.94, was more oxidized during the pre-monsoon period than during monsoon (average O/C ratio of 0.72), and an average O/C was 0.88 over the entire campaign period, suggesting overall highly oxygenated aerosol in the central TP. Positive matrix factorization of the high-resolution mass spectra of OA identified two oxygenated organic aerosol (OOA) factors: a less oxidized OOA (LO-OOA) and a more oxidized OOA (MO-OOA). The MO-OOA dominated during the pre-monsoon period, whereas LO-OOA dominated during monsoon. The sensitivity of air mass transport during pre-monsoon with synoptic process was also evaluated with a 3-D chemical transport model. [ABSTRACT FROM AUTHOR]

Tobacco (Nicotiana tabacum L.) expressing a modified Escherichia coli gdhA gene encoding NADPH-dependent glutamate dehydrogenase (GDH) was resistant to the herbicide glufosinate. Differential plant sensitivity to glufosinate may result from changes in foliar absorption, translocation, plant metabolism, or metabolism around the blocked pathway(s). The objectives here were to determine if foliar absorption, translocation, or metabolism of glufosinate or metabolism around the blocked pathway(s) contribute to the resistance to glufosinate in gdhA-transformed tobacco and to characterize changes in the metabolic profile in response to glufosinate as a result of transformation with gdhA. Foliar uptake and translocation of glufosinate was largely independent of the gdhA transgene or its expression. Thus, gdhA does not confer resistance to the transformed plants by altering the uptake or movement of glufosinate within tobacco plants. Using direct-injection electrospray ionization and quadrupole time-of-flight mass spectrometry, the metabolic profiles of the two tobacco genotypes were different in response to glufosinate treatment, as determined by principal component analysis. The metabolic perturbation induced by glufosinate was lower in gdhA line 9 than gusA line 1, as evidenced by the reduced number of altered peaks recorded in leaves. Thus, gdhA-transformed tobacco plants with low and high expression of GDH activity showed more stability of metabolism following the application of glufosinate than control plants. The predicted identity of ions suggested metabolic perturbations were lessened by gdhA in nitrogen assimilation, photorespiration, amino acid metabolism, nucleic acid metabolism, and cell signaling. Thus, use of the modified E. coli gdhA gene in transgenic plants can provide an additional mechanism for resistance to glufosinate. [ABSTRACT FROM AUTHOR]

Nylon bags are used for packaging fire debris in several countries, particularly in Europe. The possibility of cross‐contamination during transport from the fire scene to the laboratory, in normal casework conditions in the U.K., was studied for two brands of nylon bags, using simulated heavy‐loaded fire debris. Three experiments were carried out with each brand, using as sample a piece of cotton fabric soaked with gasoline. One experiment was carried out using automotive paint thinner (oxygenated solvent). Each sample was sealed in a nylon bag and stored in contact with eight empty bags. The empty bags were analysed at regular intervals for a period of time up to 8 weeks, using SPME and GC/MS. Cross‐contamination was found for components of gasoline (toluene and C2‐alkylbenzenes) in the two brands of nylon bags used, after 4 days and 2 weeks. Cross‐contamination using automotive topcoat thinner was detected after 2 days. [ABSTRACT FROM AUTHOR]

The authors comment on the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry profiling (MALDI-TOF MS profiling) approach used for the accurate identification of microorganism species in the field of proteomics. Topics include the advances and applications of the approach, the use of MALDI-TOF MS profiling in plant proteomics, and the challenge of identifying the proteins detected in the MALDI-TOF MS profiles.

Because of the high complexity of petroleomic-type samples, there is a need for efficient ways of visualizing and interpreting the resulting data in mass spectrometry-based petroleomics. Over the years, several graphing approaches have become widespread, yet they mostly deal with a particular subset of compounds detected within a given sample. Here, we present an alternative and complementary sample visualization method, the hexagonal class representation, based on relative abundance vs compound classes plot. The representation can be used to "fingerprint" a petroleomic-type sample, provide a simple means of sample comparison, as well as allow for a fast overview and detection of any compound of interest based on its elemental composition and chemical properties [ABSTRACT FROM AUTHOR]