Multiblock modelling on the study of the kinetic degradation of rosuvastatin calcium in the presence of retention time shifts and rank deficiency.

In pharmaceutical development, forced degradation studies are mandatory before the commercialization of any drug product. They aim at identifying the possible degradation routes and the potential products that may be formed during drug product shelf life. The most widely used techniques for monitoring this in the pharmaceutical industry are hyphenated techniques such as Liquid Chromatography coupled to ultraviolet diode array detector (LC-DAD).

Sequential design of experiments approach for the multiproduct analysis of cholesterol-lowering drugs by ultra-high-performance supercritical fluid chromatography.

A multiproduct approach toward method development is presented for a fast and reliable analysis of the eight most important cholesterol-lowering drugs via ultra-high-performance supercritical fluid chromatography. A two-step approach based on design of experiments was applied: (1) selection of the stationary phase, organic modifier, and diluent in the mobile phase through a multilevel categorical design and (2) optimization of the elution strength by varying the pressure, temperature, and gradient using a central composite design. Finally, the flow rate was adjusted.

Synthesis and evaluation of a pentafluorobenzamide stationary phase for HPLC separations in the reversed phase and hydrophilic interaction modes.

A pentafluorobenzamide stationary phase was synthesized by an easy method with no intermediate purification steps. Physicochemical characterization (elemental analysis, fourier transform infrared spectroscopy, Si and C nuclear magnetic resonance spectroscopy) confirmed the presence of pentafluorobenzamide functionalization on the surface of the silica particles. The pentafluorobenzamide stationary phase proved to be quite versatile as it can be used in two different modes in liquid chromatography: reversed phase and hydrophilic interaction liquid chromatography.

Study of the chromatographic parameters of ultra-high-performance supercritical fluid chromatography and method development using a design of experiments approach for the quantification of pesticides in lettuce.

We examine the potential of ultra-high-performance supercritical fluid chromatography for multiresidue quantification of ten pesticides commonly applied to lettuce and compares it to ultra-high-performance liquid chromatography. Initially, a thorough study of the stationary and mobile phase composition and injection solvent was carried out. In a second step, a chemometric approach based on design of experiments was used to simultaneously study the influence of temperature, pressure, and percentage of ethanol on the retention, resolution and symmetry of the peaks.

Pesticide determination in sweet peppers using QuEChERS and LC-MS/MS.

In this work, a rapid, effective, and safe method, generating only a small amount of waste, based on the citrate version of QuEChERS was optimized and validated for multiresidue determination of pesticides of different classes in sweet green peppers, determined by liquid chromatography coupled with tandem mass spectrometry. The matrix components influenced the measurement of the pesticides by the developed analysis technique, so that, analytical curves were prepared using pesticide-free matrix extracts for quantification of the analytes. The method provides satisfactory accuracy verified by recoveries of 70-120%, and good precision (coefficients of variation ≤20%).

Development and validation of an analytical method for multiresidue determination of pesticides in lettuce using QuEChERS-UHPLC-MS/MS.

A new analytical method for multiresidue determination of 16 multiclass pesticides in lettuce was developed using ultra-high performance liquid chromatography with tandem mass spectrometry with a triple quadrupole mass analyzer and positive mode electrospray ionization, using a previously optimized quick, easy, cheap, effective, rugged, and safe method for sample preparation. Validation studies, according to document SANTE/11945/2015, demonstrated that the developed method is selective, accurate, and precise, providing recoveries of 70-120%, relative standard deviations ≤20% and quantification limits from 3 μg/kg. The method was compared with one based on high-performance liquid chromatography with tandem mass spectrometry, in terms of chromatographic performance, detectability and matrix effect for five varieties of lettuce.

Revisiting quick, easy, cheap, effective, rugged, and safe parameters for sample preparation in pesticide residue analysis of lettuce by liquid chromatography-tandem mass spectrometry.

A new analytical method using a quick, easy, cheap, effective, rugged, and safe (QuEChERS) procedure for multi-residue determination of 16 multiclass pesticides in five different types of lettuce was developed using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The QuEChERS procedure was optimized in terms of extractor solvent, partitioning salts and clean-up salts, through recovery, gravimetric analysis and matrix-effect studies. Microwave extraction and the use of disposable pipette extraction in the clean-up step were also tested, providing interesting alternatives to the traditional QuEChERS method, depending on the pesticides properties.

Multiresidue determination of pesticides in industrial and fresh orange juice by hollow fiber microporous membrane liquid-liquid extraction and detection by liquid chromatography-electrospray-tandem mass spectrometry.

A procedure involving hollow fiber microporous membrane liquid-liquid extraction (HF-MMLLE) and detection by liquid chromatography with tandem mass spectrometry was developed and applied. The extraction is based on liquid-liquid microextraction with a polypropylene porous membrane as a solid support for the solvent. On the membrane walls the solvent forms a renewable liquid membrane which improves the trueness of the method and promotes the sample clean-up.

A simple hollow fiber renewal liquid membrane extraction method for analysis of sulfonamides in honey samples with determination by liquid chromatography-tandem mass spectrometry.

A sensitive and precise analysis using hollow fiber renewal liquid membrane (HFRLM) extraction followed by high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) is described for determination of five sulfonamides in honey samples. In this procedure, the organic solvent introduced directly into the sample matrix extracts the sulfonamides and carries them over the polypropylene porous membrane. An organic solvent is immobilized inside the polypropylene porous membrane, leading to a homogeneous phase.

Statistical designs and response surface techniques for the optimization of chromatographic systems.

This paper describes fundamentals and applications of multivariate statistical techniques for the optimization of chromatographic systems. The surface response methodologies: central composite design, Doehlert matrix and Box-Behnken design are discussed and applications of these techniques for optimization of sample preparation steps (extractions) and determination of experimental conditions for chromatographic separations are presented. The use of mixture design for optimization of mobile phases is also related.

Chromatographic and column stability at pH 7 of a C18 dimethylurea polar stationary phase.

Chromatographic evaluations of a C18 dimethylurea phase in 150 mm x 3.9 mm HPLC columns were performed using the Tanaka and Engelhardt test mixtures. The applicability of the new C18 dimethylurea phase was also evaluated with a mixture of some herbicides and their metabolites.

Preparation of a new C18 stationary phase containing embedded urea groups for use in high-performance liquid chromatography.

A new C18 urea stationary phase was prepared by a single-step modification process through the reaction of ProntoSil spherical silica (3 microm, Bischoff) with the trifunctional alkoxysilane (CH3CH2O)3-Si-(CH2)3-NH-C(O)-NH-(CH2)17-CH3, prepared in our laboratory. The phase was characterized by elemental analysis and solid-state 29Si and 13C nuclear mangnetic resonance spectrometry. Chromatographic evaluations of the new phase in 150 x 3.

Evaluation of the applicability and the stability of a C18 stationary phase containing embedded urea groups.

Chromatographic evaluations of a new C18 urea phase in 150x3.9 mm HPLC columns, involving the separation of different test mixtures, indicate good performance for both polar and basic compounds when compared with a commercial C18 reversed phase and also show promising results for the separation of some herbicides. An aging study was performed by passing a potassium phosphate mobile phase buffered at pH 7 through 50x3.

New generation of sterically protected C18 stationary phases containing embedded urea groups for use in high-performance liquid chromatography.

New monofunctional C18 urea stationary phases with sterically protecting dimethyl and diisopropyl groups were prepared by a single step modification process. ProntoSil spherical silica (3 microm) was chemically modified with the monofunctional ethoxysilanes, [(3-octadecylurea)propyl]dimethyl and [(3-octadecylurea)propyl]diisopropyl ethoxysilanes. The phases were characterized by elemental analysis, infrared and solid-state 29Si and 13C NMR spectroscopies.