Search results for "preparation"

1-Hexyl-3-methyl imidazolium tetrafluoroborate: an efficient column enhancer for the separation of basic drugs by reversed-phase liquid chromatograph…

2012

Abstract Ionic liquids are dual modifiers composed by a large anion and a large cation, which interact with both the hydrophobic alkyl-bonded phase and the anionic residual silanols in C18 columns. The deactivation of the silanol groups has important implications on the chromatographic analysis of basic drugs, being the improvement of peak profiles and shorter retention times the most noticeable features. However, other characteristics as selectivity or resolution are not usually considered, or are only examined for selected chromatographic conditions. In this work, the effect of the addition of the ionic liquid 1-hexyl-3-methyl imidazolium tetrafluoroborate to acetonitrile–water mixtures i…

Retention mechanisms for basic drugs in the submicellar and micellar reversed-phase liquid chromatographic modes.

2008

The reversed-phase liquid chromatographic (RPLC) behavior (retention, elution strength, selectivity, efficiency, and peak asymmetry) for a group of basic drugs (beta-blockers), with mobile phases containing the anionic surfactant sodium dodecyl sulfate (SDS) and acetonitrile, revealed different separation environments, depending on the concentrations of both modifiers: hydro-organic, submicellar at low surfactant concentration and high concentration of organic solvent, micellar, and submicellar at high concentration of both surfactant and organic solvent. In the surfactant-mediated modes, the anionic surfactant layer adsorbed on the stationary phase interacts strongly with the positively ch…

Evaluation by HPLC-UV of Polar Pesticides in Rice Fields

1999

Gas chromatography and mass spectroscopy techniques for the detection of chemical contaminants and residues in foods

2017

Gas chromatography-mass spectrometry (GC-MS) is a cornerstone for qualitative and quantitative analysis of food contaminants and residues. It is fast and sensitive, provides a high peak capacity, and allows determination of thermally stable and volatile compounds. Recent research has resulted in better chromatographic columns and methods for sample preparation that enable a significant expansion of the application range of GC-MS, profiling strategies for sample characterization being identified as important future drivers. Newer detection/separation solutions, such as fast chromatography, comprehensive two-dimensional GC (GC × GC), triple quadrupole MS, time-of-flight MS or orbitrap, atmosp…

Determination of phenoxy acid herbicides in drinking waters by HPLC and solid phase extraction

1998

Abstract An HPLC procedure for determining phenoxy acid herbicides in waters is described. A LichroSpher RP select B octadecyl-silane analytical column and spectrophotometric detection at 230 nm were used. Adequate retention was achieved with a mobile phase containing MeOH/phosphate buffer 10−2 M pH 2.5/PnOH (50/42/8, v/v). The herbicides were isolated from water samples by using a single solid phase extraction procedure with C18 solid-phase columns. An enrichment factor of 500 is achieved. The coefficients of variation of the method were generally lower than 2.7% at 0.4 μg L−1 herbicide concentration levels. Recoveries ranged between 93 and 118%. The results obtained indicate that the prop…

Direct determination of Mancozeb by photoacoustic spectrometry

2006

Abstract A solvent free, fast and environmentally friendly photoacoustic-infrared-based methodology (PAS-FTIR) was developed for the determination of Mancozeb in agrochemicals. This methodology was based on the direct measurement of the transmittance spectra of solid samples and a multivariate calibration model to determine the active ingredient concentration. The proposed partial least squares (PLS) model was made using nine standards prepared by mixing different amounts of kaolin and Mancozeb, with concentrations between 5.43 and 88.10% (w/w). A hierarchical cluster analysis was made in order to classify the samples in terms of similarity in the PAS-FTIR spectra. From their spectra differ…

Near-critical carbon dioxide extraction and liquid chromatography determination of UV filters in solid cosmetic samples: A green analytical procedure

2005

Near-critical carbon dioxide extraction of four UV filters used as sunscreens in lipsticks and makeup formulations is reported. Extraction parameters were optimized. Efficient recoveries were obtained after 15 min of dynamic extraction with a 80:20 CO2/ethanol mixture at 300 atm and 54 degrees C, using a 1.8 mL/min flow rate. Extracts were collected in ethanol, and appropriately diluted with ethanol and 1% acetic acid to obtain a 70:30 v/v ethanol/1% acetic acid solution. The four UV filters were determined by LC with gradient elution using ethanol/1% acetic acid as mobile phase. The accuracy of the analytical procedure was estimated by comparing the results with those obtained by methods b…

Extraction of clenbuterol from calf urine using a molecularly imprinted polymer followed by quantitation by high-performance liquid chromatography wi…

2002

A method for the extraction of clenbuterol from calf urine samples using a molecularly imprinted polymer (MIP) has been developed. The aim was that the final extracts from the MIP should allow quantitation of clenbuterol down to 0.5 ng/mL urine using HPLC with UV detection. The MIP was produced using brombuterol as a template and the selectivity of the MIP, for clenbuterol, was tested against a non-imprinted polymer (produced without template) and was found to be high. After loading of 5 mL diluted centrifuged urine, selective binding was established in acetonitrile-acetic acid (98:2). For further elution of interferences, 0.5 M ammonium acetate buffer pH 5 and 70% acetonitrile in water was…

Microwave-assisted extraction of polybrominated diphenyl ethers and polychlorinated naphthalenes concentrated on semipermeable membrane devices

2006

Abstract Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for the extraction of polybrominated diphenyl ethers (PBDEs) and polychlorinated naphthalenes (PCNs) sampled by semipermeable membrane devices (SPMDs), using gas chromatography coupled to tandem mass spectrometry (GC–MS–MS). For MAE optimization a two level full factorial design 2 3 , plus a centre point, which involves 11 randomized runs was used. The results showed that the temperature had a significant influence on the extraction of the nine PBDEs and four PCNs tested. Also, the solvent volume had a positive influence on the extraction of PBDEs and PCNs, but only in latter compounds, it achieves…

Determination of tetracyclines in multi-specie animal tissues by pressurized liquid extraction and liquid chromatography–tandem mass spectrometry

2009

Abstract A specific, sensitive and robust pressurized liquid extraction (PLE) and liquid chromatography tandem mass spectrometry (LC–MS/MS) method for determining tetracycline, chlortetracycline, oxytetracycline and doxycycline in bovine, swine, poultry and lamb muscle tissues is presented. PLE was performed using an ASE ® 200 from Dionex and water as extractant, followed by solid-phase extraction (SPE) using an Oasis HLB cartridge. The method was validated for beef, chicken, pork and lamb meat in compliance with the requirements set by Commission Decision, 2002/657/EC [Commission Decision 2002/657/EC (2002). Implementing Council Directive 96/23/EC concerning the performance of analytical m…