Study of Cobalt(III) Corrole as the Neutral Ionophore for Nitrite and Nitrate Detection via Polymeric Membrane Electrodes

Cobalt(III) 5,10,15‐tris(4‐ tert ‐butylphenyl) corrole was synthesized and incorporated into plasticized poly(vinyl chloride) membranes and studied as a neutral carrier ionophore via potentiometry. This cobalt(III) complex has binding affinity to nitrite, and the resulting membrane electrode yields reversible and Nernstian response toward nitrite. Enhanced nitrite selectivity is observed over other anions, including lipophilic anions such as thiocyanate and perchlorate when an appropriate amount of lipophilic cationic sites are added to the membrane phase. Detection limit to nitrite is ca. 5 µM. Using tributylphosphate as the plasticizer with the cobalt(III) corrole species yields electrodes with enhanced nitrate selectivity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102049/1/2579_ftp.pd

Quantitative Determination of High Charge Density Polyanion Contaminants in Biomedical Heparin Preparations Using Potentiometric Polyanion Sensors

Quantification of oversulfated chondroitin sulfate (OSCS) in biomedical heparin preparations is achieved using a recently described potentiometric polyanion sensor-based approach operated in a kinetic mode of analysis. This is accomplished by adjusting the concentration of the test sample to a range where the OSCS level is low enough for the sensor not to achieve a full and rapid equilibrium phase boundary potential change at the membrane/sample interface upon exposure to the heparin sample. Using this method, the OSCS wt% determined within heparin samples containing OSCS are shown to be in good agreement with those determined by an accepted NMR method.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64540/1/26_ftp.pd

Polyion Detection via All‐solid‐contact Paper‐based Polyion‐sensitive Polymeric Membrane Electrodes

The first all‐solid‐contact paper‐based single‐use polyion‐sensitive ion‐selective electrodes (ISEs) are described. These polyion‐sensitive ISEs are fabricated using cellulose filter paper coated with a carbon ink conductive layer. A polyanion sensing membrane is cast on a section of the coated paper and the sensor is insulated, resulting in a disposable, single‐use device. Various polyanions are shown to yield large negative potentiometric responses when using these disposable devices for direct polyanion detection. These new sensors are further demonstrated to be useful in indirect polycation detection when polycations (i. e., polyquaterniums (PQs)) are titrated with polyanionic dextran sulfate (DS). Titrations monitored using these paper‐based, all‐solid‐contact devices yield endpoints proportional to the given PQ concentration present in the test sample.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151253/1/elan201900155.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151253/2/elan201900155_am.pd

In vitro platelet adhesion on polymeric surfaces with varying fluxes of continuous nitric oxide release

Nitric oxide (NO) is released by endothelial cells that line the inner walls of healthy blood vessels at fluxes ranging from 0.5 × 10 −10 to 4.0 × 10 −10 mol cm −2 min −1 , and this continuous NO release contributes to the extraordinary thromboresistance of the intact endothelium. To improve the biocompatibility of blood-contacting devices, a biomimetic approach to release/generate NO at polymer/blood interfaces has been pursued recently (with NO donors or NO generating catalysts doped within polymeric coatings) and this concept has been shown to be effective in preventing platelet adhesion/activation via several in vivo animal studies. However, there are no reports to date describing any quantitative in vitro assay to evaluate the blood compatibilities of such NO release/generating polymers with controlled NO fluxes. Such a methodology is desired to provide a preliminary assessment of any new NO-releasing material, in terms of the effectiveness of given NO fluxes and NO donor amounts on platelet activity before the more complex and costly in vivo testing is carried out. In this article, we report the use of a lactate dehydrogenase assay to study in vitro platelet adhesion on such NO-releasing polymer surfaces with varying NO fluxes. Reduced platelet adhesion was found to correlate with increasing NO fluxes. The highest NO flux tested, 7.05 (±0.25) × 10 −10 mol cm −2 min −1 , effectively reduced platelet adhesion to nearly 20% of its original level (from 14.0 (±2.1) × 10 5 cells cm −2 to 2.96 (±0.18) × 10 5 cells cm −2 ) compared to the control polymer coating without NO release capability. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56095/1/31105_ftp.pd

Continuous monitoring of gas-phase species at trace levels with electrochemical detectors : Part 2. Detection of chlorine and hydrogen chloride

A detection system for the continuous and simultaneous measurement of gas-phase chlorine and hydrogen chloride in the low parts per billion (109) by volume (ppbv) range is described. Both gases are trapped through the walls of a microporous polypropylene tube into an appropriate flowing recipient buffer. The buffer then flows through two electrochemical detectors placed in series downstream from the sampling tube. Chloride ions from gas-phase hydrogen chloride are detected potentiometrically with an Ag/AgCl working electrode. Chlorine is detected biamperometrically (at 0.1 V) via its oxidation of added iodide ions to form triiodide. In a continuous-flow measurement mode, detection of chloride and hydrogen chloride at levels as low as 0.75 and 2.1 ppbv, respectively, is possible. Use of a 2-min stopped-flow/flow-injection arrangement results in a three-fold improvement in detection limits. The selectivity of each detector with respect to carbon dioxide, sulfur dioxide, nitrogen dioxide and hydrogen sulfide is also examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29210/1/0000264.pd

Anion selective optical sensing with metalloporphyrin-doped polymeric films

Metalloporphyrins (Mn(III) and In(III)] are investigated as active polymer film components in the design of reversible anion-selective optical sensors. The optical measurements are made by casting thin plasticized polymer films (PVC, polyurethane, etc.) containing the given metalloporphyrins on glass plates. When bathed in aqueous test solutions, the optical response of such films is based upon the selective extraction of anions by metalloporphyrins into the organic membrane phase. Changes in optical absorbance occur via either of two mechanisms. For films based on Mn(III) tetraphenylporphyrins, the porphyrin itself can serve simultaneously as the ionophore and chromophore for the detection of iodide ions. In this instance, direct ligation of iodide as an axial ligand of the central (Mn(III) results in a change in the molar absorptivitiy of the soret band of the porphyrin. In the case of In(III) octaethylporphyrin, the incorporation of an appropriate pH-indicator dye along with the metalloporphyrin is required to achieve films with optical selectivity toward nitrite and chloride. The analytical characteristics of these porphyrin-based films with respect to anion response time, dynamic measurement range, and reproducibility, are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30442/1/0000065.pd

Immobilization of proteins on gold coated porous membranes via an activated self-assembled monolayer of thioctic acid

A new methodology for efficient protein (e.g., antibodies, enzymes, etc.) immobilization on microporous nylon membranes for use in a variety of bioanalytical systems is introduced. The method utilizes an activated self-assembled monolayer (SAM) of thioctic acid on gold coated forms of the membranes. Via a carbodiimide mediated reaction, the protein is anchored to the gold surface through an amide bond with the terminal carboxyl group of the adsorbed thioctic acid. The immobilization efficiency is high (∼95% for a monoclonal immunoglobulin G(IgG) and the surface bound protein appears to be stable enough to resist any displacement by other proteins in a matrix as complex as serum. Immunological activity of immobilized antibody is retained as demonstrated via use of such membrances in colorimetric ELISA for human chorionic gonadatropin (hCG). The high protein immobilization efficiency, the high tensile strength of microporous nylon membranes, and the excellent electrochemical characteristics of gold make this approach very attractive for preparing biomembranes that should be useful in affinity chromatography, electrochemical immunosensing systems, flow-through enzyme reactors, etc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41622/1/604_2005_Article_BF01244890.pd

Membrane-dialyzer injection loop for enhancing the selectivity of anion-responsive liquid-membrane electrodes in flow systems Part 2. A selective sensing system for salicylate

An electrode-based flow-injection system suitable for the direct determination of salicylic acid is described. The system utilizez a tubular polymer membrrane electrode based on manganese(III) tetraphenylporphyrin chloride to sense salicylate ions formed in a recipient buffer solution held within the upper channel of a flow-through membrane dialyzer assembly. Samples containing salicylic acid are manually intoduced into the lower channel of the dialysis unit, in which a thin silicone rubber membrane separates the two channels. The analyte is trapped across the membrane as salicylate ions within a static layer of an appropriate recipient buffer. After a fixed trapping time, the recipient plug is flushed to the electrode in a conventional flow-injection manner. Peak potentials observed are logarithmically related to the salicylic acid concentrations in the original sample. Without the dialysis unit, the electrode response to salicylate is nearly Nernstian over the range 2 x 10-6-10-2 M. In the complete flow/dialysis system, near Nernstian response was achieved for 10-4-10-2 M salicylate with a 2-min trapping time. Detection limits can be altered by changing the trapping time. Anionic salicylate can be determined by acidifying the sample. The resulting system offers very high selectivity for salicylate (as salicylic acid) over most inorganic and organic anions normally found in blood. Preliminary studies demonstrate the practical application of this system for the determination of salicylate in serum.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26342/1/0000429.pd

Continuous-flow enzymatic determination of creatinine with improved on-line removal of endogenous ammonia

A new continuous-flow automated enzymatic method suitable for the direct determination of creatinine in physiological samples is described. The proposed system utilizes an on-line gas predialysis unit in conjuction with a flow-through enzyme reactor coil and a potentiometric ammonia detector. The enzyme reactor contains immobilized creatinine iminohydrolase (EC 3.5.4.21) which converts creatinine to ammonia and N-methylhydantoin. Ammonia liberated from this reaction is detected downstream with the membrane electrode-based detector. The novel gas predialysis unit effectively removes>99.8% of endogenous ammonia (up to 1 mM) present in the sample. Thus, final peak potentials recorded by the electrode detector are directly proportional to the logarithm of creatinine concentrations present. The method is shown to be precise (<3%), selective, and capable of accurately determining creatinine in serum and urine samples containing abnormally high endogenous ammonia levels. Determinations of creatinine in serum samples (n = 30) using this new method correlate well with an existing Technicon AutoAnalyzer colorimetric method (r = 0.996).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26866/1/0000431.pd

Replacement ion chromatography with potentiometric detection using a potassium-selective membrane electrode

The use of a simple potassium-selective membrane electrode as a detector in replacement ion chromatography of both cations and anions is examined. For cation chromatography, separated alkali metal ions are detected in the effluent of a suppressed chromatographic system by replacement with potassium ions via cation-exchange tubing bathed in potassium chloride solution. Subsequent downstream potentiometric measurement of the exchanged potassium ions is made with a wall-jet type valinomycin-based polymer membrane electrode. The same replacement stage and potentiometric detector can be used for anion chromatography, in which case counter hydrogen ions in the effluent are the cationic species replaced by potassium. The detection capabilities of the method are shown to depend on a number of factors, including the lengths of suppressor and replacement ion-exchange tubing, the nature and concentration of the bathing electrolytes in the suppressor and replacement stages and the system flow-rates. Under optimized experimental conditions, it is shown that the membrane electrode-based ion replacement scheme can rival the conventional conductivity methods for the detection of separated ions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28129/1/0000579.pd