Search results for "COLUMN"
showing 10 items of 1301 documents
Advantages of monolithic over particulate columns for multiresidue analysis of organic pollutants by in-tube solid-phase microextraction coupled to c…
2011
Abstract The performance of a monolithic C 18 column (150 mm × 0.2 mm i.d.) for multiresidue organic pollutants analysis by in-tube solid-phase microextraction (IT-SPME)-capillary liquid chromatography has been studied, and the results have been compared with those obtained using a particulate C 18 column (150 mm × 0.5 mm i.d., 5 μm). Chromatographic separation has been carried out under isocratic elution conditions, and for detection and identification of the analytes a UV-diode array detector has been employed. Several compounds of different chemical structure and hydrophobicity have been used as model compounds: simazine, atrazine and terbutylazine (triazines), chlorfenvinphos and chlorp…
A rapid procedure for the determination of caffeine, theophylline and theobromine in urine by micellar liquid chromatography and direct sample inject…
1995
Abstract A liquid chromatographic procedure for the determination of caffeine, theophylline and theobromine in urine samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C18 analytical column and a guard column of similar characteristics. The UV detector was set at 273 nm. A study to adequately select the composition of the micellar mobile phase for the separation of these compounds in urine samples is performed. Maximum resolution was achieved with a 0.075 M sodium dodecylsulphate-1.5% propanol eluent. Limits of detection at 273 nm ranged between 0.4 μg/ml for theobromine and theophylline and 1.2 μg/ml for caffeine. The procedure allows the determination of th…
In-tube solid-phase microextraction and liquid chromatography using a monolithic column for the selective determination of residual ethylenediamine i…
2009
The selective determination of the diamine ethylenediamine (EDA) in the presence of a higher amount of residual dimethylamine in cationic polymers has been developed. The strategy uses both a solution derivatization with a selective agent of primary amines such as o-phthaldialdehyde-N-acetyl-L-cysteine (OPA-NAC) and an in-tube solid-phase microextraction (IT-SPME) coupled to liquid chromatography (LC). A 70 cm long, 0.32 mm internal diameter, and 3 microm thick commercially available capillary column coated with 95% polydimethylsiloxane and 5% polydiphenylsiloxane was employed to replace the injection loop of a Rheodyne injection valve. A volume of 1 mL of derivatized sample was passed thro…
Determination of caffeine in tea samples by Fourier transform infrared spectrometry
2002
A sustainable and environmentally friendly procedure has been developed for the FTIR determination of caffeine in tea leaf samples. The method is based on the extraction with ammonia and CHCl3 and direct determination of caffeine on the chloroform extracts using peak height absorbance measurements at 1658.5 cm(-1) and external calibration. The method provides a sensitivity of 0.2142 absorbance units mg(-1) mL and a limit of detection of 1 mg L(-1), corresponding to 0.002% m/m caffeine in tea leaves. As compared with a reference procedure, based on UV absorbance measurement at 276 nm after low pressure column chromatography, the developed procedure reduces the consume of CHCl3 by a factor of…
Automated determination of reboxetine by high-performance liquid chromatography with column-switching and ultraviolet detection.
2000
A fully automated method including column-switching and isocratic high-performance liquid chromatography (HPLC) was developed for quantitative analysis of the new antidepressant reboxetine, a noradrenaline reuptake inhibitor. After serum injection into the HPLC system and on-line sample clean-up on a silica C8 (10x4.0 mm I.D.) clean-up column with an eluent consisting of 2.5% acetonitrile in deionized water, the chromatographic separation was performed on an analytical column (Lichrospher CN; 250x4.6 mm I.D.) with an eluent of acetonitrile-aqueous potassium phosphate buffer (0.008 M, pH 6.4) (50:50). The UV detector was set at 273 or 226 nm. The limit of quantification was about 15 ng/ml at…
Automated determination of amisulpride by liquid chromatography with column switching and spectrophotometric detection.
2003
A fully automated chromatographic method including on-line blood serum or plasma clean-up, isocratic high-performance liquid chromatography (HPLC) and spectrophotometric detection was developed for quantitative analysis of the new antipsychotic drug amisulpride. After injection of serum or plasma onto the HPLC system and clean-up on a pre-column (10x4.0 mm I.D.) filled with Silica CN 20 micrometer (pore size 10 nm) by an eluent consisting of 8% acetonitrile in deionized water, the chromatographic separation was performed on Lichrospher CN (5 micrometer; 250x4.6 mm I.D.) by an eluent consisting of 50% acetonitrile and 50% aqueous potassium phosphate buffer (0.008 M, pH 6.4). The UV detector …
Use of gold nanoparticle-coated sorbent materials for the selective preconcentration of sulfonylurea herbicides in water samples and determination by…
2012
Abstract Two new gold nanoparticle (NP) coated materials (silica supported on gold NP with and without ionic liquid) were synthesized for solid phase extraction of sulfonylurea herbicides (SUHs), such as bensulfuron-methyl (BSM), metsulfuron-methyl (MSM), pyrazosulfuron-methyl (PSM), thifensulfuron-methyl (TFM) and triasulfuron (TS), from water samples, followed by capillary liquid chromatography coupled to diode array detection (CLC–DAD). Several factors influencing the preconcentration efficiency of SUHs and its subsequent determination, such as pH of the sample, eluent and reusability of sorbents, have been investigated. Under the optimum conditions, the developed method allowed the dete…
Determination of glyphosate and aminomethylphosphonic acid in natural water using the capillary electrophoresis combined with enrichment step
2005
A previously elaborated capillary electrophoresis (CE) method used for the determination of glyphosate and aminomethylphosphonic acid (AMPA) was slightly modified in order to improve the sensitivity. However, detection limits attained (5 μg mL−1 for glyphosate and 4 μg mL−1 for AMPA) were still not satisfactory for analytical purposes, thus the addition of a preconcentration step before the CE analysis was proposed. AMBERLITE®IRA-900, a strong anion-exchange resin, was used to preconcentrate both analytes in environmental aqueous samples. The experimental conditions optimised in a previous work were readapted, by decreasing the eluent concentration due to CE limitations. Satisfactory result…
A Branch-Price-and-Cut Algorithm for the Min-Max k -Vehicle Windy Rural Postman Problem
2013
[EN] The min-max k -vehicles windy rural postman problem consists of minimizing the maximal distance traveled by a vehicle to find a set of balanced routes that jointly service all the required edges in a windy graph. This is a very difficult problem, for which a branch-and-cut algorithm has already been proposed, providing good results when the number of vehicles is small. In this article, we present a branch-price-and-cut method capable of obtaining optimal solutions for this problem when the number of vehicles is larger for the same set of required edges. Extensive computational results on instances from the literature are presented.