Characterization of polar organosulfates in secondary organic aerosol from the green leaf volatile 3-Z-hexenal.

Evidence is provided that the green leaf volatile 3-Z-hexenal serves as a precursor for biogenic secondary organic aerosol through the formation of polar organosulfates (OSs) with molecular weight (MW) 226. The MW 226 C6-OSs were chemically elucidated, along with structurally similar MW 212 C5-OSs, whose biogenic precursor is likely related to 3-Z-hexenal but still remains unknown. The MW 226 and 212 OSs have a substantial abundance in ambient fine aerosol from K-puszta, Hungary, which is comparable to that of the isoprene-related MW 216 OSs, known to be formed through sulfation of C5-epoxydiols, second-generation gas-phase photooxidation products of isoprene. Using detailed interpretation of negative-ion electrospray ionization mass spectral data, the MW 226 compounds are assigned to isomeric sulfate esters of 3,4-dihydroxyhex-5-enoic acid with the sulfate group located at the C-3 or C-4 position. Two MW 212 compounds present in ambient fine aerosol are attributed to isomeric sulfate esters of 2,3-dihydroxypent-4-enoic acid, of which two are sulfated at C-3 and one is sulfated at C-2. The formation of the MW 226 OSs is tentatively explained through photooxidation of 3-Z-hexenal in the gas phase, resulting in an alkoxy radical, followed by a rearrangement and subsequent sulfation of the epoxy group in the particle phase.

[Hexane-2,5-dione bis-(thio-semi-carba-zon-ato)]nickel(II).

In the title compound, [Ni(C8H14N6S2)], the Ni(II) ion is coordinated by N2S2 donor atoms of the tetradentate thio-semicarbazone ligand, and has a slightly distorted square-planar geometry. In the crystal, inversion-related mol-ecules are linked via pairs of N-H⋯N and N-H⋯S hydrogen bonds, forming R 2 (2)(8) ring motifs. Mol-ecules are further linked by slightly weaker N-H⋯N, N-H⋯S and C-H⋯S hydrogen bonds, forming two-dimensional networks which lie parallel to the bc plane.

Coupling stir bar sorptive extraction-dispersive liquid-liquid microextraction for preconcentration of triazole pesticides from aqueous samples followed by GC-FID and GC-MS determinations.

Stir bar sorptive extraction (SBSE) combined with dispersive liquid-liquid microextraction (DLLME) has been developed as a new approach for the extraction of six triazole pesticides (penconazole, hexaconazole, diniconazole, tebuconazole, triticonazole and difenconazole) in aqueous samples prior to GC-flame ionization detection (GC-FID). A series of parameters that affect the performance of both steps were thoroughly investigated. Under optimized conditions, aqueous sample was stirred using a stir bar coated with octadecylsilane (ODS) and then target compounds on the sorbent (stir bar) were desorbed with methanol. The extract was mixed with 25 microL of 1,1,2,2-tetrachloroethane and the mixture was rapidly injected into sodium chloride solution 30% w/v. After centrifugation, an aliquot of the settled organic phase was analyzed by GC-FID. The methodology showed broad linear ranges for the six triazole pesticides studied, with correlation coefficients higher than 0.993, lower LODs and LOQs between 0.53-24.0 and 1.08-80.0 ng/mL, respectively, and suitable precision (RSD < 5.2%). Moreover, the developed methodology was applied for the determination of target analytes in several samples, including tap, river and well waters, wastewater (before and after purification), and grape and apple juices. Also, the presented SBSE-DLLME procedure followed by GC-MS determination was performed on purified wastewater. Penconazole, hexaconazole and diniconazole were detected in the purified wastewater that confirmed the obtained results by GC-FID determination. In short, by coupling SBSE with DLLME, advantages of two methods are combined to enhance the selectivity and sensitivity of the method. This method showed higher enrichment factors (282-1792) when compared with conventional methods of sample preparation to screen pesticides in aqueous samples.

Dispersive liquid-liquid microextraction using extraction solvent lighter than water.

For the first time a dispersive liquid-liquid microextraction method on the basis of an extraction solvent lighter than water was presented in this study. Three organophosphorus pesticides (OPPs) were selected as model compounds and the proposed method was carried out for their preconcentration from water samples. In this extraction method, a mixture of cyclohexane (extraction solvent) and acetone (disperser) is rapidly injected into the aqueous sample in a special vessel (see experimental section) by syringe. Thereby, a cloudy solution is formed. In this step, the OPPs are extracted into the fine droplets of cyclohexane dispersed into aqueous phase. After centrifuging the fine droplets of cyclohexane are collected on the upper of the extraction vessel. The upper phase (0.40 microL) is injected into the gas chromatograph (GC) for separation. Analytes were detected by a flame ionization detector (FID) (for high concentrations) or MS (for low concentrations). Some important parameters, such as the kind of extraction and dispersive solvents and volume of them, extraction time, temperature, and salt amount were investigated. Under the optimum conditions, the enrichment factors (EFs) ranged from 100 to 150 and extraction recoveries varied between 68 and 105%, both of which are relatively high over those of published methods. The linear ranges were wide (10-100 000 microg/L for GC-FID and 0.01-1 microg/L for GC-MS) and LODs were low (3-4 microg/L for GC-FID and 0.003 microg/L for GC-MS). The RSDs for 100.0 microg/L of each OPP in water were in the range of 5.3-7.8% (n = 5).