James D. Ingle

Determination of cobalt by pyrogallol chemiluminescence

The chemiluminescence reaction involving pyrogallol in alkaline hydrogen peroxide solution is described. With reaction conditions selected for the determination of Co(II), the detection limit for Co(II) was at least two orders of magnitude below the detection limit of all other species tested. The results suggest that Ca, Mg, Mn, and Fe are the most likely interferents for environmental and biological samples. The log-log calibration graph for Co(II) is linear from a detection limit of 0.5 ng/ml up to 10 microg/ml.

Two-column ion-exchange method for the determination of copper-complexing capacity and conditional stability constants of copper complexes for ligands in natural waters

Sample solutions titrated with Cu(2+) ions are passed sequentially through two ion-exchange columns in an automated flow system. The first column is packed with Chelex-100 resin and retains Cu(2+) ions that are free or derived from copper complexes that dissociate in the column. The second column is packed with AG MP-1 anion-exchange resin and retains negatively charged Cu(II) complexes. The retained copper species are then eluted from the columns and determined on-line with a flame atomic-absorption spectrophotometer. It is necessary to correct for a small fraction of free Cu(2+) ions that pass through the first column and are retained by the second column. The Cu(II)-complexing capacity of sample solutions is determined from plots of the concentration ratio of free Cu(2+) ions to Cu(II) complexes vs. the concentration of free Cu(2+) ions. Conditional stability constants of the copper complexes are also estimated from these plots. The complexing capacity of sample solutions is also determined rapidly by measuring the concentration of complexed Cu(II) after spiking the sample with an excess of Cu(2+) ions. The sample solutions tested were 4.0muM NTA, 4.0-mg/l. humic acid, and a river water.

Chemiluminescence during the oxidation of alcohols by permanganate: Application to the determination of ethanol in gin

Chemiluminescence is observed during the oxidation of ethanol with potassium permanganate under very acidic conditions. Factors affecting the chemiluminescence signal are discussed. Based on this chemiluminescence reaction, a method for the determination of alcohol in gin was developed. The method, which has a detection limit of 0.3% (v/v) and a relative standard deviation of about 1% at 40.0% (v/v), was used in the determination of ethanol in three different brands of gin with no sample preparation.

KINETIC FLUOROMETRIC FIA DETERMINATION OF TOTAL ASCORBIC ACID, BASED ON USE OF TWO SERIAL INJECTION VALVES

The kinetic determination of total ascorbic acid with a flow-injection analysis system is described. The sample is loaded into two serial sample injection valves and injected into a carrier system containing mercuric chloride and o-phenylenediamine. The formation of a fluorescent product is monitored. The single-point and double-point kinetic methods are compared by using both peak height and peak area as the analytical signal. A detection limit of 0.1 mu/ml for vitamin C was achieved with a sample throughput rate of 30 per hour.

Design and characterization of an intensified diode array data-acquisition system for spectrometric measurements

A computer-based data-acquisition system for an intensified diode array (IDA) detector is described. A unique combination of hardware and software provides many data-acquisition and calculation options useful for multiple-wavelength spectrometric measurements. The data-acquisition system is used to evaluate critically many characteristics of the IDA detector, including the dependence of the light and dark signals and noise on experimental variables, and the linearity, memory effects and resolution.

Construction of a microcumputer-based reaction-rate ratemeter.

The design and construction of a ratemeter based on a KIM-1 single-board microcomputer are discussed. The reaction monitor signal is digitized with a voltage-frequency converter and the resulting data points are stored in computer memory. Through software, the reaction-rate is calculated by the fixed-time computation method. A unique software-hardware combination is used for conversion from binary to binary-coded decimal format so that the results are printed in decimal notation. The characteristics of the ratemeter are compared with those of earlier ratemeters.

Application of an intensified diode array system to diagnosis of matrix effects and the rapid sequential determination of thiamine and riboflavin with fluorescence detection

The unique capabilities of a multiple wavelength spectrofluorometer based on an intensified diode array detector are used for diagnosis of matrix effects and for rapid sequential determination of two analytes. This system is used to investigate problems due to background fluorescence, blank reactions, and scattering for the determination of thiamine in cereal and urine samples by a fluorometric kinetic procedure. A novel determination of thiamine and riboflavin in vitamin pills is based on monitoring the native fluorescence of riboflavin over one wavelength region, and the rate of formation of fluorescent thiochrome from thiamine over another wavelength region, after a computer-controlled change in the pH of the reaction mixture.

Simple and inexpensive microcomputer-controllable stepping motor and drive circuit

The construction of a simple stepper motor and drive circuit made from commercial components is described. The use of the stepper motor for a monochromator wavelength drive is discussed. The rate and direction of scan can be controlled by either a hardwired timer circuit or by a microcomputer.

Monitoring of redox state in a dechlorinating culture with immobilized redox indicators

During the dechlorination of tetrachloroethene (PCE) to ethene (ETH) in a microcosm bottle containing an enriched chlororespiring culture, redox conditions were spectrophotometrically monitored with the redox indicators thionine (THI) and cresyl violet (CV) immobilized on transparent films. Measurements were taken with a unique flow redox monitoring system based on circulating solution from the bottle through a specially constructed flow cell and returning it to the bottle. An enclosure for a peristaltic pump was constructed to minimize contamination of the solution with atmospheric O(2). The redox monitoring instrumentation was shown to be an excellent tool to evaluate the ability of an enclosure for anoxic samples to prevent diffusion of very small amounts of oxygen from the atmosphere into the sample. With careful design of the apparatus, the O(2) permeation rate into a solution of THI in a microcosm bottle during redox monitoring was reduced to less than 40 nmol h(-1). When monitoring a dechlorinating culture, dechlorination was not observed until immobilized THI was completely reduced and vinyl chloride was not produced until partial reduction of CV.

Optimization of atomic fluorescence measurements with a microcomputer-based time-multiplex multiple-slit spectrometer

An automated multielement flame atomic fluorescence (AF) spectrometer is described. The instrument employs a multiple exit slit monochromator and a single detector. Each element is excited to fluoresce with a single-element hollow cathode lamp (HCL) and a time-multiplex mode is used for pulsing the HCLs and gated data acquisition. A microcomputer controls the pulsing of HCLs, sample introduction into the flame and data acquisition. Optimization of the HCL pulse width and peak current is shown to be critical. With an air/H(2) flame sheathed with Ar, the following single-element detection limits (in mug/ml) were obtained: Au, 0.2; Cd, 0.005; Co, 0.03; Cu, 0.003; Fe, 0.05; Mg, 0.0008; Mn, 0.007; Ni, 0.04; Pb, 1 and Zn, 0.02. Some multielement detection limits were a factor of 2-5 worse. At higher analyte concentrations, the signal to noise ratio decreased due to an increase in the relative analyte fluorescence flicker noise.