Chemical Analysis through CL-Detection Assisted by Periodate Oxidation

The progress of the research work of the author and his colleagues on the field of CL-emission generated by pyrogallol oxidation and further application for the direct determination of periodate and indirect or direct determination of other compounds through flow-injection manifold/CL-detection set up is described. The instrumentation used for these studies was a simple flow-injection manifold that provides good reproducibility, coupled to a red sensitive photomultiplier that gives sensitive CL-detection. In addition, recent reports on studies and analytical methods based on CL-emission generated by periodate oxidation by other authors are included

Membrane sampler for interference-free flow injection NO determination in biological fluids with chemiluminescence detection

Abstract The development of a chemiluminescence (CL) method based on the perm-selective properties of a Nafion-cellulose acetate (CA) composite membrane for the monitoring of nitric oxide (NO) in biological fluids is described. Horseradish peroxidase (HRP) was used as NO trapping solution, forming the stable compound HRP-NO. The HRP was denatured and the trapped NO was released and detected by using the luminol-H 2 O 2 system. Using a mixed (size-exclusion and polar-based) transport control, the interference effects of various compounds were minimized. The method was used for NO monitoring in simulated samples, by using a blood specimen as sample matrix. The 3σ detection limit is 0.9 × 10 −6 mol and linear semi-log calibration plot in the range 1.8 × 10 −6 to 2.7 × 10 −3 mol NO was constructed. The applied methodology was further used to prolong the NO lifetime in order to increase the sensitivity of its determination. This was based on the increase of the response in the presence of certain reductive species, which act as NO preservatives in biological fluid samples

Determination of phosphate using a highly sensitive paired emitter-detector diode photometric flow detector

The use of a novel inexpensive photometric device, Paired Emitter Detector Diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit. The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert Law were obtained for phosphate in the range of 0.02-2 µM. The dynamic range, sensitivity and limits of detection are reported

Colorimetric and visual read-out determination of cyanuric acid exploiting the interaction between melamine and silver nanoparticles

We present two colorimetric procedures for the determination of cyanuric acid, using silver nanoparticle-based (AgNPs) probes. The first is making use of melamine-modified AgNPs which bind to cyanuric acid through hydrogen bonding to form a large conjugate network that enhances the aggregation of AgNPs to produce an absorbance peak at 640 nm and a green coloration. In the second assay, melamine is directly added to the sample in order to form a stable complex with cyanuric acid. AgNPs are then added, resulting in the formation of an absorbance peaking at 525 nm and a color change from green (blank sample) to purple or orange-red as a function of cyanuric acid concentration. Matrix effects, that originate from the interaction of alkaline earth metals with the charged surface of the AgNPs, are mitigated through a matrix-matched calibration. In this manner, spectral transitions can be selectively attributed to the concentration of cyanuric acid, which can be even visually quantified at low mg L-1 levels with minimum sample pre-treatment and without sophisticated instrumentation. [Figure not available: see fulltext.] © 2014 Springer-Verlag Wien

Concentration of organic compounds in natural waters with solid-phase dispersion based on advesicle modified silica prior to liquid chromatography

Abstract The ability of vesicle-coated silica to aid the extraction of organic compounds from water prior to liquid chromatographic analysis is presented for the first time. The method is based on the formation of silica supported cationic multi-lamellar vesicles of gemini surfactants inherently ensuring the presence of hydrophilic and hydrophobic sites for the partitioning of analytes bearing different properties. Method development is illustrated by studying the adsolubilization of UV absorbing chemicals from swimming pool water. Due to the requirement for external energy input (intense shearing) a method based on solid-phase dispersion (SPD) was applied producing better results than off-line solid-phase extraction (SPE). Meticulous investigation of the experimental parameters was conducted in order to elucidate the mechanisms behind the proposed extraction pattern. Analyte recoveries were quantitative under the optimum experimental conditions offering recoveries higher than 96% with RSD values below 5%

Gold-Modified Micellar Composites as Colorimetric Probes for the Determination of Low Molecular Weight Thiols in Biological Fluids Using Consumer Electronic Devices

This work describes a new, low-cost and simple-to-use method for the determination of free biothiols in biological fluids. The developed method utilizes the interaction of biothiols with gold ions, previously anchored on micellar assemblies through electrostatic interactions with the hydrophilic headgroup of cationic surfactant micelles. Specifically, the reaction of AuCl4− with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) produces an intense orange coloration, due to the ligand substitution reaction of the Br− for Cl− anions, followed by the coordination of the AuBr4− anions on the micelle surface through electrostatic interactions. When biothiols are added to the solution, they complex with the gold ions and disrupt the AuBr4−–CTAB complex, quenching the initial coloration and inducing a decrease in the light absorbance of the solution. Biothiols are assessed by monitoring their color quenching in an RGB color model, using a flatbed scanner operating in transmittance mode as an inexpensive microtiter plate photometer. The method was applied to determine the biothiol content in urine and blood plasma samples, with satisfactory recoveries (i.e., >67.3–123% using external calibration and 103.8–115% using standard addition calibration) and good reproducibility (RSD < 8.4%, n = 3)

Generic Assay of Sulfur-Containing Compounds Based on Kinetics Inhibition of Gold Nanoparticle Photochemical Growth

This work describes a new, equipment-free, generic method for the determination of sulfur-containing compounds that is based on their ability to slow down the photoreduction kinetics of gold ions to gold nanoparticles. The method involves tracking the time required for a red coloration to appear in the tested sample, indicative of the formation of gold nanoparticles, and compare the measured time relative to a control sample in the absence of the target analyte. The method is applicable with minimal and simple steps requiring only two solutions (i.e., a buffer and a gold solution), a source of light (UV or visible), and a timer. The method responds to a large variety of sulfur-containing compounds including thiols, thioesters, disulfides, thiophosphates, metal–sulfur bonds, and inorganic sulfur and was therefore applied to the determination of a variety of compounds such as dithiocarbamate and organophosphorous pesticides, biothiols, pharmaceutically active compounds, and sulfides in different samples such as natural waters and wastewater, biological fluids, and prescription drugs. The analytical figures of merit of the method include satisfactory sensitivity (quantitation limits at the low μM levels), good recoveries (from 93 to 109%), and satisfactory reproducibility (from 4.8 to 9.8%). The method is easily adoptable to both laboratory settings and nonlaboratory conditions for quantitative and semiquantitative analysis, respectively, is user-friendly even for the minimally trained user, and can be performed with limited resources at low cost