Presence Of Dodecyl Sulfate Micelles Research Articles

Determination of norfloxacin by sensitized terbium fluorescence in the presence of silver nanoparticles and surfactant micelles

The influence of silver nanoparticles and surfactant micelles on the signal intensity of the sensitized fluorescence of the norfloxacin complex with the Tb3+ ion was studied. It was shown that the intensity of the intrinsic fluorescence of norfloxacin and its complex with Tb3+ ions slightly decreases in the presence of silver nanoparticles. It was found that the presence of dodecyl sulfate micelles leads to the modification of the silver nanoparticle surface, which is accompanied by a change in the ζ-potential of the nanoclusters. The addition of surfactant-modified silver nanoparticles to aqueous solutions of terbium chelate increases the intensity of sensitized fluorescence by 11 times. The increase in the efficiency of intramolecular energy transfer in the Tb3+ complex with norfloxacin in the presence of silver nanoparticles and dodecyl sulfate micelles made it possible to propose a method for the fluorimetric determination of the antibiotic in natural water in the concentration range of 2 × 10-7 −1 × 10-5 M. The calibration graph equation is y = 1.0 × 107x − 1.0, R2 = 0.991, detection limit 5 × 10–8 M (3σ).

Analysis of codeine, dihydrocodeine and their glucuronides in human urine by electrokinetic capillary immunoassays and capillary electrophoresis–ion trap mass spectrometry

Screening for and confirmation of illicit, abused and banned drugs in human urine is a timely topic in which capillary separation techniques play a key role. Capillary electrophoresis (CE) represents the newest technology employed in this field of analysis. Two rapid competitive binding, electrokinetic capillary-based immunoassays are shown to be capable of recognizing the presence, but not the identity, of urinary opioids, namely codeine (COD), codeine-6-glucuronide, dihydrocodeine (DHC), dihydrocodeine-6-glucuronide, morphine (MOR), morphine-3-glucuronide and ethylmorphine (EMOR). In these approaches, aliquots of urine and immunoreagents of a commercial, broadly cross-reacting fluorescence polarization immunoassay for opiates were combined and analyzed by capillary zone electrophoresis or micellar electrokinetic capillary chromatography with laser induced fluorescence detection. With the fluorescent tracer solution employed, the former method is shown to provide simple electropherograms which are characterized by an opioid concentration dependent magnitude of the free tracer peak. In presence of dodecyl sulfate micelles, however, two tracer peaks with equal opioid concentration sensitivity are monitored. These data suggest the presence of two fluorescent tracers which react competitively with the urinary opioids for the binding sites of the antibody. Assay sensitivities for COD and MOR are comparable (10 ng/ml), whereas those for DHC and EMOR are about four-fold lower. Furthermore, glucuronides are shown to react like the corresponding free opioids. Analysis of urines that were collected after administration of 7 mg COD and 25 mg DHC tested positively in both assay formats. The presence of the free and conjugated codeinoids in these urines and their identification was accomplished by capillary electrophoresis–ion trap mass spectrometry (CE–MS). This confirmatory assay is based upon solid-phase extraction using a mixed-mode polymer cartridge followed by CE hyphenated to the LCQ mass spectrometer with electrospray ionization in the positive ion mode. With this technology, MS 2 is employed for proper identification of COD ( m/z 300.4) and DHC ( m/z 302.4) whereas MS 3 provides unambiguous identification of the glucuronides of COD ( m/z 476.5) and DHC ( m/z 478.5) via their fragmentation to COD and DHC, respectively. MS n ( n≥2) is shown to be capable of properly identifying the urinary codeinoids on the 100–200 ng/ml concentration level.