Electrochemical behavior and sensitive determination of L-tyrosine with a gold nanoparticles modified glassy carbon electrode.
(25/914)
The electrocatalytic oxidation of L-tyrosine was investigated on a gold nanoparticles self-assembled glassy carbon electrode (gold nanoparticles/cysteamine/glassy carbon) using cyclic voltammetry and differential pulse voltammetry. Cyclic voltammetry was carried out to study the electrochemical oxidation mechanism of L-tyrosine, which showed an irreversible oxidation process at a potential of 0.681 V at a modified electrode and 0.807 V at a bare glassy carbon electrode. The anodic peak current linearly increased with the square root of the scan rate, suggesting that the oxidation of L-tyrosine at this kind of modified electrode is a diffusion-controlled process. A good linear relationship between the oxidation peak current and the L-tyrosine concentration in the range of 1.0 x 10(-7) to 3.0 x 10(-4) mol L(-1) was obtained in a phosphate buffer solution at pH 7.0. Good sensitivity, selectivity and stability of the modified electrode make it very suitable for L-tyrosine determination in a commercial amino acid oral solution. (+info)
Quantitative analysis of epinephrine in human plasma samples using kinetic fluorometric method combined with second-order calibration.
(26/914)
A kinetic fluorometric method was proposed for the quantitative determination of epinephrine (EP) in human plasma samples with the aid of second-order calibration methods based on alternating trilinear decomposition (ATLD) and alternating fitting residue (AFR) algorithms. It was based on that EP could be gradually converted to a highly fluorescent intermediate product by an oxidation reaction, and further to a non-fluorescent degradation product (o-quinone). These methodologies fully exploit the second-order advantage of the employed three-way kinetic fluorescence data, allowing the concentrations of EP to be quantified even in the presence of uncalibrated interferences. The average recoveries obtained from ATLD and AFR with a factor number of 2 (N = 2) were 100.7 +/- 3.3 and 100.4 +/- 2.2%, respectively. In addition, elliptical joint confidence region (EJCR) tests as well as figures of merit (FOM) were employed to evaluate the accuracy of the two algorithms. (+info)
Simple and sensitive spectrofluorometric method for the determination of protein using an europium-thenoyltrifluoroacetone probe.
(27/914)
The fluorescence intensity of the europium (Eu3+)-thenoyltrifluoroacetone (TTA) complex can be remarkably enhanced by human serum albumin (HSA) in a Britton-Robinson buffer solution. Based on this fact, a simple, rapid, and sensitive method has been developed for the determination of proteins at the nanogram level by fluorescence spectroscopy. Under the optimum conditions, the enhanced fluorescence intensity is proportional to the concentration of HSA. The linear ranges for HSA are 0-5.1 and 5.1-44.4 microg ml(-1) and the limit of detection is 20.7 ng ml(-1). Moreover, there is very little interference from common inorganic ions and other coexisting compounds. The binding site number and the binding constant of Eu(3+)-TTA used as a fluorescence probe to HSA were calculated by using the Rosenthal graphic method. This method has been applied to the determination of total protein in human serum samples. The results are good agreement with data obtained by clinical physicians. (+info)
A semi-synthetic ion channel platform for detection of phosphatase and protease activity.
(28/914)
Direct detection of benzene, toluene, and ethylbenzene at trace levels in ambient air by atmospheric pressure chemical ionization using a handheld mass spectrometer.
(30/914)
Development and validation of an HPLC method for the simultaneous analysis of 23 selected drugs belonging to different therapeutic groups in human urine samples.
(31/914)
We have developed and validated a new and reliable gradient reversed-phase high-performance liquid chromatography (RP-HPLC) method with a diode array detector (DAD) for the simultaneous separation and determination of 23 frequently prescribed selected drugs belonging to different therapeutic groups in human urine samples. For the drugs listed below, this method of analysis for human urine was also successfully applied to determine urine concentrations of these drugs in samples from treated patients: enalapril (ENA), paracetamol (PAR), sotalol (SOT), dipyrone (DIP), vancomycin (VAN), captopril (CAP), fluconazole (FLU), cefazolin (CEF), metoprolol (MET), aspirin (ASP), ticlopidine (TIC), prednisolone (PRE), propranolol (PRO), digoxin (DIG), sildenafil (SIL), furosemide (FUR), dexamethasone (DEX), carvedilol (CAR), ketoprofen (KET), nifedipine (NIF), terbinafine (TER), acenocoumarol (ACE) and spironolactone (SPI). Separation of the analytes was achieved by RP-HPLC-DAD with a mobile phase composed of acetonitrile, methanol and 0.05% trifluoroacetic acid in water using a gradient elution program. Good linear relationships over the investigated concentration ranges were observed with values of r2 higher than 0.998 for all of the drugs. The intra-day and inter-day precisions of this method were evaluated with RSD values less than 4.26 and 5.42%, respectively. The relative recoveries of the 23 investigated compounds ranged from 93.60 to 106.00% with RSD values less than 4.46%. An expanded uncertainty budget was constructed for all investigated drugs in human urine samples. (+info)
Polymer microchip CE of proteins either off- or on-chip labeled with chameleon dye for simplified analysis.
(32/914)