Search results for "Micellar liquid chromatography"
showing 10 items of 108 documents
RAPID LIQUID CHROMATOGRAPHIC DETERMINATION OF TETRACYCLINES IN ANIMAL FEEDS USING A SURFACTANT SOLUTION AS MOBILE PHASE
2002
ABSTRACT A chromatographic procedure was developed for the determination of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC), doxycycline (DC) and minocycline (MINO) in animal feeds. Clear analyte-rich extracts were obtained using a 1 : 1 acetonitrile/water mixture buffered at pH 3. The extracts were injected into a conventional unprotected C18 chromatographic column and eluted with a mobile phase of 0.05 M sodium dodecyl sulfate/5% 1-butanol/0.01 M oxalic acid at pH 3. Good resolution was achieved for the five compounds, whereas OTC and TC coeluted with an optimized aqueous-organic mobile phase of methanol/acetonitrile/0.01 M oxalic acid at pH 3. Mean recoveries from spike…
Determination of clenbuterol in urine by azo-dye precolumn derivatization and micellar liquid chromatography
1997
Clenbuterol has been determined in urine by solidphase extraction on a C18 cartridge, diazotization of the eluate with nitrite, coupling of the diazonium ion with 1-(naphthyl)ethylenediamine, and separation of the azo dye formed by HPLC with a C18 column and a micellar mobile phase containing 0.1 M sodium dodecyl sulphate, 12%n-butanol and 0.05 M citrate buffer, pH 3. Recoveries higher than 90% were obtained by mixing the samples with a 20% 0.2 M NaOH before extraction. Limits of detection of 51 and 6.7 ng L−1 were obtained with spectrophotometric and thermal lens spectrometric detection, respectively; respective repeatabilities were 3.1% (5 μg mL−1) and 5.6% (0.16 μg mL−1).
Determination of catecholamines in urine by micellar liquid chromatography with coulometric detection
1994
The determination of catecholamines by HPLC with a sodium dodecyl-sulphate (SDS), micellar mobile phase on a C18 column and with coulometric detection was studied. The eluate was conditioned at +0.25 and +0.00 V, and the current at −0.16V was recorded. A previously developed model which describes the chromatographic behaviour of solutes in HPLC with hybrid, micellar mobile phases was used to optimize the SDS and ethanol concentrations. A mobile phase of 0.15M SDS in a phosphate buffer of pH 3.4 and without ethanol is recommended. The limits of detection were 0.4–0.7 ng ml−1. The procedure was applied to the determination of unconjugated L-dopa, norepinephrine and dopamine in urine. Direct i…
Determination of synthetic antioxidants in dairy products and dietetic supplements by micellar liquid chromatography with direct sample injection
2000
A simple and rapid HPLC method for the determination of synthetic antioxidants (propyl gallate, tert-butylhydroquinone, 2,4,5-trihydroxybutyrophenone, nordihydroguaiaretic acid, octyl gallate, 3-tert-butyl-4-hydroxyanisole and dodecyl gallate) in powdered and liquid milk, cream of milk and dietetic supplements is described. The samples are diluted or solved in a micellar solution, filtered and directly injected. The retention behavior of the antioxidants on a C18 column, with micellar mobile phases containing SDS (0.05–0.15 M), n-propanol (1–9%, v/v) and 10 mM phosphate at pH 3, has been studied by using mathematical models. Retention is predicted with errors below 3%. To optimize the mobil…
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…
Direct injection of edible oils as microemulsions in a micellar mobile phase applied to the liquid chromatographic determination of synthetic antioxi…
1999
Abstract A simple and quick procedure for analysis of hydrophobic samples by direct injection in a liquid chromatograph, without previous extraction, has been developed. The sample is solved in a water/sodium dodecyl sulphate/n-pentanol microemulsion without destroying the microemulsion structure, and injected. A micellar mobile phase containing 0.1 M SDS, 2.5% n-propanol and 10 mM phosphate of pH 3 is used. The procedure is applied to the determination of synthetic antioxidants (propyl gallate, tert-butylhydroquinone, 2,4,5-trihydroxybutyrophenone, nordihydroguaiaretic acid, octyl gallate, 3-tert-butyl-4-hydroxyanisole and dodecyl gallate) in sunflower, corn and olive oils. Linear calibrat…
Simultaneous detection of hazardous skin whitening agents in Indian cosmetic products using a green chromatographic technique
2021
The present work mainly highlights the simultaneous detection of four skin whitening agents i.e. hydroquinone (HQ), resorcinol (RS), catechol (CC) and 3,3′-dichlorobenzidine (DCB) in facial creams and body lotion. Among these, the first three are positional isomers of dihydroxybenzene so simultaneous separation is difficult with the conventional reverse-phase high-performance liquid chromatographic technique (RP-HPLC). The selected skin whitening agents were detected in facial cream and body lotion using micellar liquid chromatography coupled to a photodiode array detector (MLC-PDA). In the present study, optimization of the method was accomplished using response surface methodology (RSM) w…
Determination of catecholamines as aminochromes by micellar liquid chromatography with thermal lens spectrophotometric detection
1994
The determination of catecholamines (CAs) using micellar liquid chromatography with thermal lens spectrophotometric detection has been studied. CAs are oxidized with hexacyanoferrate(III) to aminochromes which are separated with a mobile phase of 0.05 M sodium dodecyl sulphate, 7% propanol and 0.03 M citrate buffer, pH 4.8, on a partially endcapped C18 column. The aminochrome-micelles and aminochrome-stationary phase association constants are evaluated. Using the 488 nm line of an Ar+ laser with 250 mW pump power the limits of detection are about 4 ng mL−1. The technique is applied to the determination of unconjugated CAs in urine using isoproterenol as internal standard.
DETERMINATION OF PENTOBARBITAL IN BIOLOGICAL SAMPLES BY MICELLAR LIQUID CHROMATOGRAPHY
1999
A liquid chromatographic procedure for the determination of pentobarbital in urine and plasma samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C18 analytical column, a guard column of similar characteristics, and a 0.02 M CTAB-15% 1-propanol at pH 7.5 mobile phase. The UV detector was set at 250 nm. Pentobarbital was isolated from urine and plasma samples by using a single solid phase extraction procedure with LMS cartridges. Mephobarbital was used as internal standard. Limits of detection were 0.53 μg/mL and 0.60 μg/mL in urine and plasma samples respectively. In both cases the coefficients of variation were lower than 6.5%, and the recoveries ranged betwe…
Determination of sulphonamides in human urine by azo dye precolumn derivatization and micellar liquid chromatography
1995
Abstract A high-performance liquid chromatographic method for the determination of sulphonamides in urine is reported. The drugs (sulphadiazine, sulphaguanidine, sulphamethizole, sulphamethoxazole, and sulphathiazole) were diazotized with nitrite and coupled with N-(1-naphthyl)ethylenediamine dihydrochloride in a sodium dodecyl sulphate (SDS) micellar medium. Separation of the sulphonamide azo dyes was performed on a C18 column with a 0.05 M SDS-2.4% pentanol mobile phase, which permitted the direct injection of the urine samples. The limits of detection were in the 0.1–0.3 μg/ml range.