Liane Maldaner

O estado da arte da cromatografia líquida de ultra eficiência

Ultra Performance Liquid Chromatography (UPLC) retains the same principles as High Performance Liquid Chromatography (HPLC), but uses 1-2.1 mm i.d. columns with sub-2 µm particles. It is considered the newest advance in analytical separation science. The use of these small particles with mobile phases at high linear velocities increases resolution and detectability and decreases analysis time. Thus, the analyses are faster, the solvent volume is smaller, the efficiency is higher and the detectability is 2-3 times higher when compared with HPLC analysis.

Some new selective stationary phases for RP-HPLC

At the present time, more complex analyses of apolar compounds with similar chemical structures or of polar compounds, especially basic ones, having diverse properties require more selective stationary phases having better stabilities. This paper describes several new stationary phases with directed selectivities that were prepared by immobilizing two different phenyl group-containing siloxanes and a trifluoropropyl-containing siloxane onto chromatographic silica and, in the case of the fluorinated siloxane, onto zirconized silica, using thermal treatment or microware radiation. The chromatographic properties and stabilities of these new phases were determined and several applications were evaluated. The phenyl-containing phases showed excellent characteristics related to the separation of several different types of aromatic compounds while the fluorinated phases, which present a more polar character, revealed selectivity for the separation of positional isomers as well as for a mixture of basic pharmaceuticals. Stability tests indicate that immobilization of the polysiloxanes increases column lifetimes by making the stationary phases less susceptible to dissolution, while the phases immobilized with microwave radiation were somewhat more stable than those immobilized by thermal treatments.

Determination of some organic contaminants in water samples by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

Independent methods for determination of organic contaminants such as pharmaceuticals and pesticides in drinking water samples, using SPE as the extraction technique and LC-MS/MS in the MRM mode with electrospray ionization, were developed and validated. Different SPE sorbents were evaluated, including lab-made fluorinated and phenyl and commercial Oasis HLB and C18, with the commercial phases being more suitable for the target compounds. Recoveries in the range of 70-120% were obtained for all target compounds, with the exception for paracetamol (acetaminophen), and precision values (inter-day and intra-day), expressed in terms of relative standard deviations (RSD), lower than 20% were obtained for all target compounds. Quantification limits were in the range of 0.006-0.208 μg L(-1) and the methods developed were successfully applied for the analysis of drinking water samples, detecting some pharmaceuticals and pesticides, but at concentration levels lower than the MRL.

HPLC Determination of Pesticides in Soybeans using Matrix Solid Phase Dispersion

Abstract A method to determine six pesticides applied in soy cultivation (imazethapyr, imazaquin, metsulfuron‐methyl, carboxin, chlorimuron‐ethyl, and tebuconazole) using matrix solid phase dispersion (MSPD) as the extraction technique followed by a clean‐up step, using a C8 co‐column, and subsequent chromatographic analysis by high performance liquid chromatography diode array detection (HPLC‐DAD) was developed. The validated method showed good recuperation for all pesticides (60–120%), except for metsulfuron‐methyl and tebuconazole at their lowest concentration levels, and the quantification limits of the method (0.04–0.08 µg g−1) were below the maximum residue limits imposed by the principal regulatory agencies. This article not subject to U.S. copyright law.

A new thermally immobilized fluorinated stationary phase for RP-HPLC

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl-3,3,3-trifluoropropylsiloxane) onto 5 microm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical-chemical characterization using solid-state (29)Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.

Fases estacionárias modernas para cromatografia líquida de alta eficiência em fase reversa

This review first discusses the limitations of many of the supports and stationary phases used in reversed phase high performance liquid chromatography and then describes those, developed more recently, that present better stabilities and more versatile selectivities. Emphases will be given to stationary phases that use higher purity silicas, hybrid silicas, monolithic silicas, metallic oxides and mixed oxides as supports and those that have embedded polar groups or contain phenyl or fluoro groups as the stationary phase as well as the phases used for mixed mode or hydrophilic interaction separations. These modern stationary phases facilitate the analysis of complex mixtures.

Evaluation of an alternative fluorinated sorbent for dispersive solid-phase extraction clean-up of the quick, easy, cheap, effective, rugged, and safe method for pesticide residues analysis

In this study, the efficiency of a new fluorinated sorbent for dispersive solid-phase extraction (d-SPE) clean-up in extracts provided by the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) acetate method from tomato and sweet pepper samples was evaluated by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Clean-up using d-SPE technique has been widely used associated with the QuEChERS method. The most commonly sorbents used in d-SPE are primary secondary amine (PSA), octadecylsilane (C18) and graphitized carbon black (GCB), which are indicated to remove sugars, fatty acids, pigments, among others. The performance of an alternative fluorinated sorbent was compared with PSA and C18 sorbents for representative pesticides and better results were obtained when the fluorinated sorbent was used. Validation presented acceptable results for trueness and precision, with method limit of detection between 0.9 and 1.8μgkg-1 and limit of quantification from 2.6 to 5.4μgkg-1. Most of the compounds presented low matrix effect. Results showed that the fluorinated sorbent contribute to the clean-up of the tomato extract and is an effective alternative, with lower costs and greater efficiency. Commercial tomato samples were analyzed using the proposed method and residues of dimethoate, tetraconazole and thiamethoxam were detected.