Microchip separations of transition metal ions via LED absorbance detection of their PAR complexes.

Micellar electrokinetic chromatography was utilized in the electrophoretic separation of seven transition metal ions, colorimetrically complexed by 4-(2-pyridylazo)resorcinol (PAR) on a glass capillary electrophoresis microchip. Detection of the PAR metal chelates was demonstrated using a green light emitting diode (540 nm) and a miniature photomultiplier tube. Parameters investigated included the effect of buffer type, pH and surfactant concentration (sodium dodecyl sulfate, SDS) on the separation efficiency. The optimally determined background electrolyte contained 10 mM ammonium phosphate buffer (pH 7.5), 1 mM PAR to prevent kinetic lability problems and 75 mM SDS for enhanced resolution. The separation of seven transition metal ions, Co2+, V3+, Ni2+, Cu2+, Fe2+, Mn2+ and Cd2+, was achievable in under 65 s, with the resolution of each metal ion in excess of 1.60. Detection limits obtained ranged from 400 ppb for Ni2+ to 1.2 ppm for Mn2+.

Separation of uranium(VI) and transition metal ions with 4-(2-thiazolylazo)resorcinol by capillary electrophoresis.

A capillary electrophoresis method utilizing 4-(2-thiazolylazo)resorcinol (TAR) was developed to separate uranium, cobalt, cadmium, nickel, titanium and copper metal ions. TAR was chosen as the visible absorbing chelating ligand because of its ability to form stable complexes with a wide variety of metals. Several parameters that included pH, electrophoretic run buffer concentration, buffer type and the influence of chelating ligand in the electrophoretic run buffer were examined to determine the best separating conditions. Optimum separation of the six metal chelates was achieved in a 15 mM Na2B4O7-NaH2PO4, pH 8.3 buffer containing 0.1 mM TAR. Method validation included injection and method precision studies as well as detection limit and linear dynamic range determination. High-ppb to low-ppm (w/w ratio) detection limits were achieved with linear dynamic ranges between 0.1 and 75 ppm.

Selective metals determination with a photoreversible spirobenzopyran.

The photoreversible metal-ion complexation behavior of nitroquinolinospiropyranindoline (NQSP) was studied in combination with the selective identification of six different transition-metal ions, Zn(2+), Co(2+), Hg(2+), Cu(2+), Cd(2+), and Ni(2+), in single- and binary-component mixtures via partial least squares discriminant (PLSD) analysis. The plasticizer, dicapryl phthalate, was chosen as the support medium for this study on the basis of (1) its enhancement of the photoreversibility and hypsochromic shifts seen in metal complexation and (2) its potential application to supported liquid membranes for eventual sensor applications. Complexation of divalent transition-metal ions by NQSP in dicapryl phthalate produced variable hypsochromic shifts in the absorption spectra (30-60 nm), requiring chemometric techniques in order to overcome the spectral overlaps. PLSD analysis was used to build classification analysis models to differentiate between the six divalent transition-metal ions. The feasibility of performing mixture analysis was studied using the concept of net analyte signal prior to experimental verification. Single- and binary-component mixtures of metals were identified with 100 and 97.4% accuracy, respectively, which included no false positives in either the training or prediction sets.

Calixarene monolayers as quartz crystal microbalance sensing elements in aqueous solution.

We have examined p-tert-butylcalix[4]arenetetrathiolate (BCAT) monolayers for their potential use as molecular recognition elements for in situ aqueous chemical sensors. Spectroscopic and wetting studies of BCAT monolayers on Au{111} reveal that the calixarene molecules exist in monolayers, preferentially oriented with their phenyl rings parallel to the surface normal axis. Using quartz crystal microbalance (QCM) sensors with gold-coated electrodes, the chemical specificity of monolayers and thin films to a variety of aromatic and aliphatic analytes in aqueous solution was examined. The response of BCAT sensors was compared to the responses of p-tert-butylcalix[4]arene (BCA)- and decanethiolate (DT)-coated QCM electrodes. BCAT is very selective for alkylbenzenes, much more so than either its spray-coated thin-film analogue, BCA, or the highly ordered DT monolayer. From these measurements, the factors behind molecular differentiation in each film are explored. Drawing upon these findings, the roles of cavitation and film order in molecular recognition for calixarene films are discussed.

Chemiluminescence detection of hydrazine vapor.

An efficient, real-time chemiluminescence detector for hydrazine vapor, N(2)H(4)(g), is described, capable of monitoring sub part-per-billion levels of hydrazine in air. The catalytic oxidation of hydrazine by colloidal platinum forms an intermediate, oxidizing agent (e.g. OH or OOH) which subsequently oxidizes luminol, generating a chemiluminescence signal that is proportional to the hydrazine concentration. Major components of the instrument include a photomultiplier tube (PMT), a short length of glass tubing coiled directly in front of the PMT cathode surface, a vacuum pump for sampling the air, and a peristaltic pump for circulating the liquid reagent. The liquid reagent, a basic solution (pH 13) of luminol and colloidal platinum, is continuously recycled. The detection sequence is initiated by pumping the hydrazine vapor through a short length of teflon tubing that is concurrently transporting the liquid reagent. The liquid is separated from the gas stream in an impinger and quickly pumped to the PMT. We have evaluated the effect of solution pH, luminol and platinum concentrations, and air and liquid flow rates on the analytical characteristics of this system. A linear, dynamic detection range for hydrazine has been obtained from 1 to 2000 ppb in air, with an instrument response that is fully reversible and achieves plateau response in less than 2 min.

P300 from a single auditory stimulus.

The P3(00) event-related brain potential (ERP) was elicited with auditory stimuli to compare 2 different discrimination tasks. The oddball paradigm presented both target and standard tones; the single-stimulus paradigm presented a target but no standard tone stimulus. Experiment 1 manipulated target stimulus probability (0.20, 0.50, 0.80) and produced highly similar P3 amplitude and latency results across probability levels for each paradigm. Experiment 2 factorially varied inter-stimulus interval (2 sec, 6 sec) and target stimulus probability (0.20, 0.80). P3 amplitude and latency were highly similar for both the oddball and single-stimulus procedures across all conditions.

Preparation of cardioplegic solutions.

The manufacturing methods and quality control procedures for two cardioplegic solutions are described. Procedures for preparing individual bottles or batches of two cardioplegic solutions (one with and one without albumin) and a carbonate-bicarbonate buffer solution are described. Final buffered cardioplegic solutions with albumin are stable for seven days. Cardioplegic solutions without albumin and buffer are stable for 30 days. The chemical and physiological factors affecting the content and preparation of cardioplegic solutions used during intracardiac surgery are reviewed. Because consistency is attained more readily, and because control procedures, including quarantining, are applied more readily to batch production of cardioplegic solutions, it is advised that this method be used.