C.O. Huber

Amperometric detection of amines and amino acids in flow injection systems with a nickel oxide electrode

The use and characteristics of a nickel oxide electrode as a detector for amines in a flow injection system are described. The anodic electrode reaction mechanism involves a higher oxidation state of nickel maintained by the applied potential (+0.49 V vs. SCE). The electroanalytical parameters are investigated and the currents for a series of amines and amino acids are compared. Two electrode configurations are compared. The flow injection technique is shown to be suitable for buffered 25-μl samples of pH as low as 3. The linear range for glycine is 10-6–10-3 M with detection limits of a few nanograms.

Use of post-consumer waste plastics in cement-based composites

Abstract This paper describes an innovative use of post-consumer waste HDPE plastic in concrete as a soft filler. A reference concrete was proportioned to have the 28-day compressive strength of 5000 psi (35MPa). A high-density plastic was shredded into small particles for use in the concrete. These particles were subjected to three chemical treatments (water, bleach, bleach + NaOH) to improve their bonding with the cementitious matrix. The plastic particles were added to the concrete in the range of 0–5% of total mixture by weight. Compressive strengths were measured for each test mixture. The results showed that chemical treatment has a significant effect on performance of the plastic filler in concrete. Of the three treatments used on the plastic, the best performance was observed with the alkaline bleach treatment (bleach + NaOH) with respect to compressive strength of concrete.

Flow-injection amperometric determination of chlorine at a gold electrode

Abstract The applied potential is +0.2 V vs. SCE, flow rate is 1 ml min −1 and sample volume is 30 μ1. The background electrolyte is 0.05 M phosphate, pH 7.4. Electrode pretreatment is +1.3 V vs. SCE for 40 s, followed by a pre-injection delay of 20 s. Peak current over a receding baseline is used. Linear range extends down to 0.4 μM for chloramine and 0.2 μM for hypochlorite. Sensitivities are 70 and 95 nA μM − respectively. Time per determination is less than 1.5 min. Monochlorinated glycine is active whereas chlorinated cyanuratesshow no response. Chlorine and monochloramine in river water were determined.

Determination of ethanol by air-stream separation with flow injection and electrochemical detection at a nickel oxide electrode

Abstract Ethanol is separated by an air stream from a 1-ml sample with collection in 1 ml of 0.2 mol l -1 sodium hydroxide. Measurement is by voltammetry at a tubular, catalytic nickel oxide electrode with 30-μl sample injected into a continuous flow stream. Relative standard deviation for repetitive measurements is 1.8% for synthetic samples. Serum samples extracted for 100 s and then measured yielded linear results for concentrations of 2 × 10 -4 –5 × 10 -2 mol l -1 ethanol (0.001–0.23%), with relative standard deviation of 2.0%. The time per determination was about 2 min.

A coulometer for determination of residual sulfite following the dechlorination of water

Abstract The kinetics of dechlorination dictate that the measurement must be completed in neutral solutions. A portable, analog circuitry-based instrument with direct readout using constant current coulometry with amperometric end point detection was developed and evaluated. An optocoupler and separate power supplies were used for circuit isolation of the detector from the generator. A range of concentrations of 0.015–25 mg SO2−3/1 were determined with a relative standard deviation of 1–2%. Applications involved both iodine and bromine as intermediates. The instrument has also been applied to determinations of arsenic, mercaptans, thiosulfate, copper, cyanide and ammonia for a similar concentration range.

Flow injection sample processing with nickel oxide electrode amperometric detection of amino acids separated by ion-exchange chromatography

Abstract A new automatic post-column sampler has been designed and used for interfacing the column outlet to a flow injection system. Segments of the effluent from the column are injected into the flow injection apparatus at regular intervals. Separation and detection of several amino acids are described. A nickel oxide electrode detector yields characteristic, useful signals for concentrations as low as 10 -6 M. Samples containing 20–35 μg of total amino acids in 1 ml were chromatographed.

The determination of sulfate by atomic absorption inhibition titration

Sulfate can be rapidly and conveniently determined by titration with magnesium solution while the atomic absorption signal is monitored, i.e. atomic absorption inhibition titration (a.a.i.t.). Concentrations as low as 1 μg SO2-4 ml−1 can be determined. Alkali metals and commonly occurring monovalent anions do not interefere at 0.1 M levels.

Constant-current enhanced potentiometric stripping analysis

Abstract Constant-current enhanced potentiometric stripping analysis (CCEPSA) is similar to potentiometric stripping analysis (PSA) except that during the stripping step in CCEPSA a cathodic current is imposed on the electrode system. The freshly oxidized metal ions in the vicinity of the electrode surface are partially redeposited so that the stripping time is extended. The stripping time and potential-time equations for CCEPSA were derived and verified using the stripping of cadmium(II). Under the most favorable conditions, the sensitivity of cadmium(II) determination was enhanced by a factor of 15.

Atomic absorption inhibition titration of orthophosphate and polyphosphates

Abstract The atomic absorption inhibition titration of phosphates was studied for two types of burner. Dependence on gas Flow-rates was observed. The method with a pre-mix burner was employed to determine phosphate in surface and waste waters. The results are compared with those by the standard method. The proposed method was found to be rapid, simple and accurate.

Determination of polar organic compounds by potentiometry at an anodically pretreated nickel oxide electrode

Abstract The open-circuit potential drop of an oxidatively pretreated nickel electrode in 0.1 M NaOH was used to develop a technique for the determination of alcohols, amino acids, carbohydrates, etc., in aqueous solution. The electrode pretreatment consisted of the formation of nickel hydrated oxides on the electrode surface with an oxidation state > 2. Both electrochemical and chemical pre-oxidation of the electrode surface were examined. The analytical signal was the enhancement of the potential drop corresponding to analyte concentration. The analytical signal was linearly related to the logarithm of the analyte concentration. The limits of determination ranged from 1 mM for low-molecular-weight to 0.02 mM for alkyl polyether alcohols. The flow-injection technique allows convenient pretreatment and direct observation of the analytical signal. Interferences from chloride and calcium can be readily eliminated by excluding them during electrode pretreatment. Potentiometric measurements were correlated with amperometric anodic responses at the nickel oxide electrode, allowing an unusual direct comparison of the two methods.