Simultaneous determination of low concentrations of ammonium and potassium ions by capillary type isotachophoresis

Low concentrations of ammonium and potassium ions (<2.0 mg/l.) were determined simultaneously by capillary type isotachophoresis based on the interaction between potassium and 18-crown-6 in the aqueous leading electrolyte. The PU value of potassium ion increased with increasing concentration of 18-crown-6 up to 3mM, whereas that of the ammonium ion remained almost constant. Thus complete separation of ammonium and potassium ions could be obtained by using 1-3mM 18-crown-6. The error in the analysis of mixtures containing ammonium and potassium ions (250-mul sample injection) was less than +/- 20% with a leading electrolyte containing 3mM 18-crown-6. The analysis time was 18 min.     

Enzymatic determination of l-lysine by flow-injection techniques

An enzymatic assay that is highly selective for l-lysine, based on flow-injection techniques combined with spectrophotometric detection, is presented. l-Lysine-α-oxidase (E.C. 1.4.3.14) from Trichoderma viride and horseradish peroxidase were used in a coupled enzyme assay. Peroxide produced in the first reaction was converted by peroxidase with phenol and 4-aminoantipyrine to a quinoneimine dye detectable at 500 nm. An analytical enzyme reactor filled with coimmobilized enzymes was incorporated in the flow-injection system. The assay has a measuring frequency of 30 samples h^?1 and a response time of less than 2 min. To adapt the assay to high concentrations of l-Lysine and to minimize interferences, the injected sample volume was reduced to 2 μ-l, resulting in a linearity range of 1–16 mM l-lysine with a sensitivity of 6–7 mV 1 mmol^?1, a limit of detection (3σ) of 1 mM and a reproducibility of 0.5% (repetitive injection of a 10 mM l-lysine sample). The enzyme cartridge is stable for several months and thousands of measurements.     

Amperometric assay of glucose and lactic acid by flow injection analysis

A computer-controlled flow-injection system is described for the assay of D-glucose and L-lactic acid in undiluted plasma. Glucose or lactate is quantified by coupling an immobilized glucose oxidase or lactate oxidase membrane with an amperometric sensor; the hydrogen peroxide generated is directly related to the concentration of glucose or lactate. The linear range is 0–40 mM and 0–10 mM for glucose and lactic acid, respectively. The sample frequency is 60 h^?1 with a standard deviation of less than 1.5%. Correlation with the results for blood plasma obtained by routine clinical analyzers was good for both glucose and lactic acid.     

Determination of ammonium ion in a flow-injection system with a gas-diffusion membrane : Selection of Optimal Conditions for the pH Indicator

The spectrophotometric determination of ammonium ion in water by flow-injection analysis with a membrane-separator and a pH indicator for detection is studied in detail. The relations derived facilitate the selection of appropriate solution compositions or the prediction of sensitivity. It is shown that 1.5×10^?5 M bromocresol purple (pH 6.8) as acceptor solution gives the maximal sensitivity in the flow system with a laboratory-made separation unit. Application of ultrasonic radiation in the separation step and the use of different flow rates for the donor and acceptor streams may result in increased permeation of ammonia and a correspondingly high sensitivity. By modifying the acceptor solution so that the sensitivity is decreased, more concentrated samples such as urine can be analyzed by direct injection without prior dilution. In this procedure, the sample rate was 60 h^?1 for ammonium concentration of more than 10^?5 M and 30–40 h^?1 for concentrations in the range 3×10^?7?10^?5 M. The detection limit was about 3×10^?7 M.     

Tripodal Squaramide Derivative as a Neutral Chloride Ionophore for Whole Blood and Sweat Chloride Measurement

A tripodal squaramide derivative was synthesized and characterized as a new neural ionophore for chloride ion. Squaramide based compounds are known to be better hydrogen bonding receptors than urea derivatives because they donate four hydrogen bonds to anions, while the tripodal structure provides a 3D geometry optimum for spherical anion complexation. The ionophore demonstrated high selectivity over salicylate and heparin that are major interferences for chloride measurement in biological samples with direct potentiometric method. The new ionophore based solid‐contact electrodes were fabricated and showed the measuring range of 10^?5 to 1 M chloride ion in the presence of 1 mM of salicylate and heparin with near Nernstian slope of 55 mV/decade. The sensor was successfully applied for the chloride measurement in undiluted heparinized whole blood and artificial sweat samples with our clinical analyzer.     

Measurement of pH by flow injection over a wide dynamic range with PVC/neutral carrier electrodes

Two pH-sensitive neutral carrier/PVC electrodes are used simultaneously for the measurement of pH by flow injection. One of these is based on the neutral carrier tridodecylamine and the other on octadecyl isonicotinate, and together they allow the pH range 1–13 to be covered. These electrodes have been used in a very low dispersion miniature potentiometric flow cell designed specifically for use in flow injection in conjunction with a multi-channel data acquisition system. The effects of the solution ionic strength and buffer capacity on the pH measurement are discussed. A flow-injection manifold is proposed which can be used for high-accuracy pH measurements without ionic strength adjustment of the sample and for simultaneous pH and ion concentration measurements with ionic strength adjustment. This has been tested on some synthetic samples for the simultaneous determination of potassium and calcium and the measurement of pH.     

Bipolar pulse conductometric detection of enzyme reactions in flow-injection systems Urea in serum and urine

Conductometric monitoring of enzymatic reactions in a flow-injection system is described. Two conductance cells are used and the responses are manipulated automatically to provide a differential signal. The hydrolysis of urea, catalyzed by urease, is used as an example to illustrate the technique. Blood serum and urine control standards are used to assess the precision and accuracy. The conductometric method is shown to be equal to, or better than existing methods for urea with regard to detection limits (0.1 mM in urine, 0.01 mM in serum), working range, precision (3% RSD), accuracy, and sample preparation. The method has a sample throughput of 20 h^?1.     

A flow-injection system based on immobilized penicillinase and a linear pH-buffer for potentiometric determination of penicillin

Penicillin is determined in a flow-injection manifold by hydrolysis of the β-lactam ring by means of an on-line reactor containing immobilized penicillinase with detection of the produced acid by a glass electrode. The penicillin concentration is calculated as the difference in response between a sample passing through the enzyme reactor and a sample flowing directly to the glass electrode. The pH signal is made linearly dependent on the acid concentration by using a buffer mixture of constant buffer capacity and the reactor is designed so that hydrolysis of the penicillin is essentially complete in the reactor. The linear range is 0.1–15 mM penicillin and the sensitivity is 0.056 pH mM^?1. The sample throughput is 60 h^?1 and the relative standard deviation < 1%. The proposed method is primarily intended for the analysis of purified potassium salts of penicillins in pharmaceutical preparations.     

A Solid Ammonium Ion Selective Electrode

Abstract

A new ammonium ion selective electrode has been developed and found to be capable of measuring ammonium ion in the presence of other cations. The electrode's selectivity over other cations is reported as well as its response time to step changes in ammonium ion activity. In addition, blood serum samples have been analyzed for urea content by treatment with urease with no special sample pre-treatment required.     

Enzymatic analysis by means of the air-gap electrode determination of urea in blood

The newly developed air-gap electrode has been used for enzymatic assay of urea in serum and whole blood; analyses can be done accurately, reliably, simply and quickly. The determination is highly selective because the electrode senses only the ammonium ion, which is selectively released from urea by urease in a preliminary rapid incubation step. The reproducibility of the determination (standard deviation less than 2.4%) is sufficient for clinical purposes; the linear range of the method is 10^-2–lO^-4M urea. Since the electrode actually never touches the sample solution, the problems caused by the presence of proteins, blood cells etc. do not arise.     

Determination of urea by ion chromatography with an immobilized urease reactor

An immobilized urease reactor can be used with ion chromatography for the simultaneous determination of urea, and sodium, potassium and ammonium ions. The conversion of urea to ammonium ion was found to be 76.5%. The calibration graph for urea was linear over the range 1 × 10^?5?1 × 10^?3 M (RSD 3%). The method was applied to human urine and a chemical fertilizer.     

Different approaches to the determination of ammonium ions at low levels by flow injection analysis

Several flow-injection methods are examined critically for their suitability for determing submicromolar levels of ammonium ion on a routine basis. Nesslerization and the Berthelot reaction are not sufficiently sensitive. The gas-diffusion separation is more satisfactory. On the basis of a simple diffusion model, the effects of operating parameters on the ammonium concentration in the acceptor line of the gas-diffusion unit are discussed and experimentally verified. With the optimized gas-diffusion conditions, spectrophotometric detection with an acid-base indicator or the application of a liquid-membrane ammonium-sensitive electrode offers detection limits around 10 ^?8 mol 1^-1. Carbon dioxide interference in the acid-base indicator method causes problems with baseline stability and long-term drift. A severe limitation on futher enhancement of sensitivity by in-valve preconcentration is the contamination levelof ammonium present in water and reagents. Effective preconcentation (20-fold in 1 min) is obtained by using an ion-exchange microcolumn placed in the injection loop of the valve.     

Ion exchange in flow injection analysis: Determination of Ammonium Ions at the μg 1-1 level in Natural Waters with Pulsed Nessler Reagent

Ion exchange is incorporated in flow injection analysis by using a resin column in the sample loop of an electronically operated proportional injector. Effects of sample aspiration rate, sampling time, eluting agent concentration, pumping rate of the sample carrier stream, resin column size and sample acidity, were investigated to develop a preconcentration procedure for ammonium ion determination in natural waters at the μg 1^-1 level with pulsed Nessler reagent. The possibility of sample buffering before the adsorption step was studied. The proposed method is characterized by a precision of about 2%, a sampling rate of about 40 samples per hour. and a reagent consumption of 40 μl per sample, and is almost free of interferences. Recoveries from 95 to 105% were achieved in analysing rain-water samples with ammonium contents of less than 200 μg 1^-1. Alternative flow diagrams and the injector command unit are discussed.     

Influence of the main parameters of single-line flow-injection systems without chemical reaction on the output signal : Part 1. Dispersion Characteristics of the Main Sections of the Flow System

Single-line flow-injection systems with valve, hydrodynamic, syringe or delta-function injection of the analyte are considered. Appropriate equations for calculating the Peclet numbers of their main sections (i.e., the fore-section, the injection section, the reactor, the measurement cell, and the after-section) are described. Two types of reactor with different dispersion characteristics (i.e., straight tube and coiled tube reactors) are considered. The detector is assumed to measure one of three concentrations: (1) the mean concentration in the cross-section of the flow situated in the middle of the measurement cell; (2) the average integral concentration in the whole volume of the measurement cell; or (3) the average integral surface concentration at the inner walls of the measurement cell. Equations for calculating the Laplace transform of the surface and the integral surface concentration, and for the mean and the variance of the corresponding concentration curves are derived. The conclusions made can be used to investigate the influence of the main parameters of single-line flow-injection systems on sample throughput by simulation of the mathematical models.     

Rapid flow-injection sandwich-type immunoassays of proteins using an immobilized antibody reactor and adenosine deaminase-antibody conjugates

A rapid flow-injection sandwich enzyme immunoassay suitable for the direct determination of proteins in biological samples is described. The proposed system utilizes highly active adenosine deaminase—antibody conjugates in conjunction with a flow-through immunoreactor and an ammonium ion-selective potentiometric detector. After appropriate sample/reagent injection steps, the enzyme activity bound to the reactor is measured by diverting a coninuously flowing stream of substrate (adenosine) through the packed immunocolumn and detecting liberated ammonium ions downstream with a tubular ammonium ion-selective electrode. The bound enzyme activity is directly proportional to the concentration of analyte in the original sample. By using non-equilibrium flow-rates of sample and reagent slugs, a single protein assay takes less than 12 min, including regeneration of the reactor. The proposed method is shown to be selective, reproducible and capable of determining accurately the model protein (human IgC) at sub-μg ml^?1 concentrations.     

Urea Biosensor Based on Electrochromic Properties of Prussian Blue

Prussian blue (PB) is an electrochromic material, which can be used as a signal transducer in the formation of optical urea biosensors. The previous researches in electrochromic properties of PB demonstrated the optical PB response to ammonium ions, which occurs when ammonium ions are interacting with PB layer at a constant 0.2 V vs Ag|AgCl|KCl_sat potential. In this work PB optical dependence on ammonium ions concentration was applied in the formation of electrochromic urea biosensor. Biosensor was formed by modifying the optically transparent indium tin oxide (ITO) coated glass electrode (glass/ITO) with Prussian blue layer and immobilizing urease (glass/ITO/PB‐urease). Calibration curve showed the linear dependency (R²=0.995) between the change of maximal absorbance (ΔA) and urea concentration in concentration range varying from 3 mM to 30 mM. The highest sensitivity (4 ΔA M^?1) of glass/ITO/PB‐urease biosensor is in the concentration range from 7 mM to 30 mM. It was determined that working principle of the glass/ITO/PB‐urease biosensor is not related to pH changes occurring during enzymatic hydrolysis of urea.     

Amperometric detection of simple carbohydrates at platinum electrodes in alkaline solutions by application of a triple-pulse potential waveform

The response of ten simple carbohydrates was investigated voltammetrically at platinum electrodes in 0.10 M sodium hydroxide by application of a conventional linear sweep waveform and a triple-pulse waveform. Linear-sweep data were interpreted to suggest that electrochemical reactions of the carbohydrates involve oxidation of adsorbed hydrogen atoms produced by surface-catalyzed dehydrogenation of the adsorbed carbohydrate. The triple-pulse measurement technique was evaluated for a flow-injection system by introducing 100-μl samples into a stream of 0.1 M NaOH with a flow rate of 0.375 ml min^-1, and measuring the peak current. Peak currents for ten carbohydrates at 0.5 mM ranged from 17 to 42 μa and a detection limit of 0.01 mM was evaluated for dextrose. Calibration plots of reciprocal peak current (I^-1_p) vs. reciprocal of concentration (C^-1) were linear for dextrose and sorbitol concentrations between 0.1 and 1.0 mM.     

Simultaneous flow-injection analysis of three components with on-line dialyzers in series. Determination of sodium, potassium and chloride in blood serum

A fast and reliable fully automated three-component flow-injection procedure for the simultaneous determination of sodium, potassium and chloride in blood serum is described. A single sample injection (100-mul blood serum) is directed to two different channels by using two dialyzers in series. To avoid interferences and blocking of the fine jet of the atomizer, sodium and potassium are dialyzed by the first dialyzer before measurement by AES with a flame photometer. A second dialyzer in series is used to eliminate interferences and for automated dilution before the dialyzed chloride is measured by UV/VIS spectrophotometry at 485 nm. The results obtained for the sodium, potassium and chloride in blood serum at a sampling rate of 106 samples per hour compared well with data obtained by standard methods.     

Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethylenebis(triphenylphosphoniu) cation

Cobalt (0–10 μg) may be determined spectrophotometrically at 625 nm after flow-injection extraction into chloroform of the ion associate ethylenebis(triphenylphosphonium) tetrathiocyanatocobaltate(II). The carrier stream contained 10% (w/v) ammonium fluoride and the reagent stream contained 0.5% (w/v) ethylenebis (triphenylphosphonium) bromide and 5% (w/v) ammonium thiocyanate. The injection rate was 20 h^?1. The calibration graph is linear up to 20 μg ml^?1 and detection limit is 0.23 μg ml^?1 cobalt, based on injection volumes of 500 μl. The system has been applied to the determination of cobalt in a range of tool steels.     

Determination of potassium in sea-water by capillary isotachophoresis

Summary A new analytical procedure for the determination of potassium in sea-water was developed using capillary isotachophoresis and ion-exchange. After the sea-water sample was passed through the column packed with an ammonium form cation-exchange resin, sodium ion was removed with 2×10^–2 mol/l ammonium chloride solution and then potassium ion was eluted with 3×10^–1 mol/l ammonium chloride solution. Simultaneous determination of potassium and sodium ions was performed with a newly developed electrolyte system; the leading electrolyte was 5 mmol/l cesium hydroxide containing 2 mmol/l 18-crown-6, 0.01% hydroxypropyl methylcellulose (HPMC) and 70% methanol; the terminating electrolyte was 5 mmol/l tetrabutylammonium bromide containing 0.01% HPMC and 70% methanol. A large amount of ammonium in the eluate did not interfere with the isotachophoretic measurement of potassium and sodium ions. A linear working curve was obtained for artificial sea-water samples containing up to 700 mg/l potassium ion. The proposed method was applied to the determination of potassium in surface and bottom sea-water samples.

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Kaliumbestimmung in Meereswasser durch Capillar-Isotachophorese