Analysis of trace levels of pesticides in rainwater by SPME and GC-tandem mass spectrometry after derivatisation with PFFBr

Solid-phase microextraction (SPME) was used for the analysis of some pesticides (bromoxynil, chlorotoluron, diuron, isoproturon, 2,4-MCPA, MCPP and 2,4-D) in rainwater after derivatisation with PFBBr and gas chromatography-ion trap mass spectrometry. The derivatisation procedure was optimized by testing different methods: direct derivatisation in the aqueous phase followed by SPME extraction, on-fibre derivatisation and derivatisation in the injector. The best result was obtained by headspace coating the PDMS/DVB fibre with PFBBr for 10 min followed by direct SPME extraction for 60 min at 68 °C (pH 2 and 75% NaCl). Good detection limits were obtained for all the compounds: these ranged between 10 and 1,000 ng L⁻¹ with a relatively high uncertainty due to the combination of derivatisation and SPME extraction steps. The optimized procedure was applied to the analysis of pesticides in rainwater and results obtained shows that this method is a fast and simple technique to assess the spatial and temporal variations of concentrations of pesticides in rainwater.     

非水滴定测定烟叶中烟碱含量实验的微型化

研制了一种微型滴定装置,利用该装置(WD-COⅡ型微型滴定装置)对烟叶中烟碱含量进行非水滴定,通过数理统计方法将微型滴定管与常规滴定管的平行测定结果进行了比较,得到相同样品的一对非常接近的测定结果。证明新型微量滴定管具有较好的操作性能和精密度。     

Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water = 80:19.3:0.7 at [K⁺] = 0.02 M enabled to measure the potential change in a wide range of pOH (=−log [OH⁻]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.     

Enzymatic kinetic resolution of 1,1-dioxo-2,3-dihydro-1H-1λ-thiophen-3-ol via temporary derivatisation

Following the thio-conjugate addition of (±)-9, its enantiomers were extremely efficiently discriminated using Novozym 435^®. The thio-differentiating unit may then be removed either under reductive conditions, using Raney nickel, or following an oxidation-elimination sequence. In this manner enantioenriched derivatives of 1,1-dioxo-2,3-dihydro-1H-1λ⁶-thiophen-3-ol 9 may be accessed.     

Capillary zone electrophoresis of basic drugs in non-aqueous acetonitrile with buffers based on a conventional pH scale

Summary The pK _a ^* values of 10 nitrogen-containing basic drugs in non-aqueous acetonitrile were determined from the pH^* dependence of their electrophoretic mobilities. The pH^* scale in the organic solvent was established using background electrolytes with known conventional pK _a ^* values, making further calibration with reference pH electrodes unnecessary. In acetonitrile the pK _a ^* values of analytes (or their conjugated cation acids, BH⁺, respectively) were 5.2±8.9 pK units>those in water. The observed change in pK _a ^* values of cationic analytes was, however, much less than the known respective change for neutral acids type HA. From the pK _a ^* values and the actual mobilities, it is possible to predict pH^* conditions to enable separation of analytes, and this was demonstrated for two pairs of common drugs.     

Determination of oxytetracycline and some impurities in plasma by non-aqueous capillary electrophoresis using solid-phase extraction

Summary The potential of a non-aqueous, capillary electrophoresis (NACE) system for separating oxytetracycline from three of its impurities—tetracycline, 4-epioxytetracycline and 4-epitetracycline—using UV detection has been studied. The running buffer was: 25 mM sodium acetate, 1 mM EDTA, methanesulfonic acid, pH 4, dissolved in MeOH-ACN (50∶50,v/v). The method was also used to determine these compounds in pig plasma. A solid-phase extraction (SPE) procedure as a clean-up step has also developed. For this we tested Sep Pak C₁₈, LiChrolut EN and OASIS cartridges. OASIS cartridges were best. Recoveries were 90–100% for all compounds except EOTC which had a recovery of 74%.     

Sample-stacking techniques in non-aqueous capillary electrophoresis

In sample-stacking techniques, the detection limit cannot be improved by simply increasing the length of the sample solution, because the individual electrophoretic parameters must be optimized. In an attempt to increase the amount of sample injected, as well as to focus them onto a small zone, two novel methods are proposed. One of these employs an "ultra-high conductivity zone", which was inserted between the sample zone and background solution to build an unequal conductivity gradient. The other employs a "low temperature bath". A portion of the capillary (near the junction between the sample solution and the background solution) was immersed in a low temperature bath, which served as a "pseudo-high-conductivity zone" due to the fact that conductivity would increases when the temperature is decreased. As a result, a large volume of sample injection can be achieved. Using 3,4-methylenedioxymethamphetamine as a model compound, the detection limit was determined to be 1.6 x 10(-6) M (S/N = 3) by means of normal non-aqueous capillary electrophoresis (NACE). This could be improved to 3.0 x 10(-8) M, 4.8 x 10(-9) M and 5.0 x 10(-9) M, respectively, when the normal stacking, ultra-high conductivity zone NACE-stacking and the low-temperature zone NACE-stacking methods were applied.     

非水介质毛细管电泳电导检测舒血宁片中槲皮素含量

以甲醇：水＝70：30的体系为分离介质，柠檬酸－三（羟甲基）氨基甲烷（Citric acid-Tris)为支持电解质，使用电导检测，对槲皮素及其制剂舒血宁片进行了毛细管电泳分离检测，对电泳介质的种类、浓度、表观pH值以及操作电压和进样时间对分离的影响进行了研讨，并对分离检测机理进行了探讨。建立的测定槲皮素的方法的线性范围为：8．0－160．0mg/L；峰面积的RSD（n=6)为1．7％，检出限为1．0mg/L；样品加标回收率为92．8％－98．2％。     

反相非水乳液法制备聚酰亚胺微球

在N,N-二甲基甲酰胺(DMF)/Pluronic-F127、十二烷基苯磺酸钠(SDBS)/液体石蜡(LP)反相非水乳液体系中,以均苯四甲酸二酐(PMDA)和4,4′-二氨基二苯醚(ODA)为单体合成聚酰胺酸(PAA),采用吡啶/乙酸酐脱水剂,对PAA化学酰亚胺化,并进一步热酰亚胺化,制得PI耐热微球.产物通过红外、热重、扫描电镜表征.结果表明,较高的固含量和良好的乳液分散性有利于PI微球的形成;反相非水乳液体系稳定的配比条件是,VDMF∶VLP为1∶4,MF127∶MSDBS为3:2,乳化剂用量为9 wt%;在此配比条件下,当固含量为20%,热酰亚胺化温度不高于330℃时,可制得分散良好、球形规整、高热稳定性的PI微球,其粒径约为10μm.     

Non-aqueous ion exchange chromatography,an alternative to buffered silica gel

A method is described for the HPLC separation of moderately acidic, dehydrated, and multi-oxygenated diterpenoids, compounds which hitherto could not be handled by HPLC. It is based on chemically bonded silica strong cation exchangers in the protonated form, using organic solvents of the full polarity range as eluents. Thus a stable and easy-to-regenerate substitute for buffered silica gel is obtained.