On-line hydrogenation of biodiesel-Toward a reference method for the determination of glycerides and total glycerol.

A reliable method with ensured traceability of the measurement results for free and bound glycerol (as monoacylglycerides, diacylglycerides and triacylglyerides) in biodiesel was developed, giving results beyond the state of the art of the current standard methodologies. The proposed method is based on an on-line hydrogenation using gas chromatography coupled to flame ionization detection and hydrogen as carrier gas. After sample introduction the hydrogenation takes place on a fused silica pre-column coated with a palladium catalyst.

In-capillary microextraction using monolithic polymers: application to preconcentration of carbamate pesticides prior to their separation by MEKC.

In the present work we report a novel procedure for in-capillary microextraction using a monolithic polymeric sorbent. In the proposed methodology, sample treatment takes place in the CE instrument but in a different capillary from that used for the electrophoretic separation. Polymers based on butyl methacrylate and divinylbenzene formed in situ inside a capillary column were assayed.

In-capillary preconcentration of pirimicarb and carbendazim with a monolithic polymeric sorbent prior to separation by CZE.

CZE was assayed for the separation of carbamate pesticides susceptible to protonation (Pirimicarb, Carbendazim). Different electrophoretic media with high organic contents were explored, adequate separation and resolution being achieved when a BGE based on ACN with acetic acid in the presence of SDS as an ionic additive was used. With a view to increasing the sensitivity of the method, an in-capillary SPE step prior to the electrophoretic separation was developed.

Use of a polar-embedded stationary phase for the separation of tocopherols by CEC.

A polar-embedded stationary phase (ULTIMA C18) has been investigated for the separation of alpha-, beta-, gamma- and delta-tocopherols by CEC in comparison with commercially available C(18) and C(30) n-alkyl RPs. The behavior of this stationary phase was tested for different mobile phases based on methanol, ACN, or mixtures thereof and different separation parameters such as retention factors and resolution were evaluated. The main feature of this stationary phase is the improved selectivity for the separation of beta- and gamma-tocopherols (positional isomers) when compared with the pure n-alkyl C(18) material, which was unable to resolve these compounds.

Behaviour of carbamate pesticides in gas chromatography and their determination with solid-phase extraction and solid-phase microextraction as preconcentration steps.

This work reports a study of the chromatographic behaviour of seven carbamate pesticides (aldicarb, carbetamide, propoxur, carbofuran, carbaryl, methiocarb, and pirimicarb) by gas chromatography-mass spectrometry (GC-MS). Variables such as injector temperature, solvent, injection mode, and the degree of ageing of the chromatographic column were studied. One of the aims of this work was to achieve a controlled decomposition of carbamates by a solid-phase microextraction (SPME) preconcentration step with a polyacrylate fibre in order to obtain reproducible chromatographic signals of the degradation products.