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A new FI/FTIR method for the determination of acetaminophen (paracetamol, N-acetyl-p-aminophenol) involving on-line reaction is described. The proposed method is based on the alkaline hydrolysis of the analyte to produce p-aminophenol and its oxidation reaction with potassium ferricyanide to produce p-benzoquinone-monoimine which eventually oxidizes to form pbenzoquinone. The chemistry of the reaction was studied both, in the visible and IR regions of the spectrum and the method has been developed by the application of ¯ow-injection methodology. The reaction was carried out in aqueous media and at room temperature. The micro-¯ow version of the CIRCLE 1 IR accessory, which is compatible with aqueous solutions, was used. Measurements were carried out at the OH-phenolic deformation (1274.1 cm À1) and the aromatic ring mode (1498.2 cm À1 ) infrared vibrations for the hydrolysis product, p-aminophenol. The method was applied to the determination of acetaminophen in commercial tablets, and mean detection values of 512 and 491 mg were found at 1274.1 and 1498.2 cm À1 , respectively.

No abstract

Membrane electrode assemblies (MEA) based on proton-conducting electrolyte membranes offer opportunities for the electrochemical compression of hydrogen. Mechanical hydrogen compression, which is more-mature technology, can suffer from low reliability, noise, and maintenance costs. Proton-conducting electrolyte membranes may be polymers (e.g., Nafion) or protonic-ceramics (e.g., yttrium-doped barium zirconates). Using a thermodynamics-based analysis, the paper explores technology implications for these two membrane types. The operating temperature has a dominant influence on the technology, with polymers needing low-temperature and protonic-ceramics needing elevated temperatures. Polymer membranes usually require pure hydrogen feed streams, but can compress H 2 efficiently. Reactors based on protonic-ceramics can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. However, because of the high temperature (e.g., 600 ° C) needed to enable viable proton conductivity, the efficiency of protonic-ceramic compression is significantly lower than that of polymer-membrane compression. The thermodynamics analysis suggests significant benefits associated with systems that combine protonic-ceramic reactors to reform fuels and deliver lightly compressed H 2 (e.g., 5 bar) to an electrochemical compressor using a polymer electrolyte to compress to very high pressure.

An electrochemical detector lor liquid chromatography was designed and constructed, based upon thin-layer cells with working electrodes prepared from a mixture ot Ceresin wax and graphite powder In a ratio of 1:1.3 by weight. Both twin electrode steady-state amperometry (four-electrode configuration) and simple thin-layer hydrodynamic amperometry (three-electrode configuration) were examined. A comparison of the four-electrode system with the three-electrode method showed the former to be slightly more sensitive at flow rates below 0.2 mL/mln. In addition, the four-electrode detector Is capable of selectively detecting compounds based upon their electrochemical reversibility. A strong cation exchange resin

M.B.G. wishes to express his thanks for support in the form of a Stauffer Fellowship awarded by the chemistry department. Work was also supported by a grant from the Graduate School, University of

The Reticulated Vitreous Carbon flow-through electrode Is demonstrated to be a useful detector for flow Injection analysis In both an amperometrlc and a coulometric mode of operation. A relative precision of a few ppt was achieved In the latter mode, but the sampling rate was limited to about 24 samples per hour. A liquid chromatographic internal sampling valve was used to inject the sample into the supporting electrolyte stream. With amperometric operation, sampling rates as high as 264 samples per hour were achieved with a relative precision of ±0.5%. A peak current detector is described which stores the peak current In a 10-bit A/D converter. The reduction of ferricyanide ion and the oxidation of ascorbic acid, epinephrine, and L-Dopa were investigated. Detection limits for these analytes are a few tenths of a nanogram.

A new cell design for detectlon in flowing streams incorporating a reticulated vitreous carbon (RVC) worklng electrode has been Investigated. The prlnclpal feature Is geometrlcal symmetry in the radlai direction between the working eiectrode and counterelectrode. This arrangement produced weildeflned hydrodynamlc voltammograms. The reticulated structure of the worklng electrode provides a large surfacearea-to-volume ratlo whlch allows rapld coulometric conversion without slgnlflcant band broadening when the detector is used for flow injection analysis (FIA) or hlgh-performance iiquld chromatography (HPLC). The sensltivity and detection ilmlts of several test compounds were lnvestlgated In thls cell.The sensltlvlty was found to approach the theoretlcal value of 96485 CIequlv at flow rates less than 1.0 mLImln. Detection limits were close to a picoequivalent ( S I N = 2) for the compounds studied by FIA. The residual current decays In less than 30 min to a steady-state value of approximately 1 PA. Detection at the plcoequlvalent level Is possible after thls equlilbration period. Both catecholamines and amoxlcliiln were used to characterlze thls detector for use with HPLC systems.At the present time, the most widely used controlled-potential electrolysis cells for flow streams are operated amperometrically, where the fraction of electroactive species electrolyzed is typically less than 0.1. In the case of coulometric operation, the fraction is one. The methodology of applying the perturbation signal and measuring the current response is identical for coulometric and amperometric detectors. In principle, the same cell could be operated in either mode depending on the flow rate. However, in practice, the design of coulometric cells presents some special problems, and they have not achieved the same degree of popularity as the amperometric detectors. It is generally recognized that large surface area electrodes with relatively large cell volumes are required for coulometric conversion and it is generally perceived that they are not especially well-suited for applications in areas such as liquid chromatography and flow injection analysis (FIA). Two factors, perhaps, have contributed to this secondary position for coulometric detectors. The first is the lack of widespread understanding of the nature of porous electrodes and the second is a failure to recognize that the coylometric detector is a mass flow rate sensitive device. Nevertheless, porous electrodes have been examined in excellent reviews by Newman and Tiedemann (1) and by Sioda and Keating (2). Early work on coulometric detectors was reviewed by Johnson and Larochelle (3) and some recent developments regarding both amperometric and coulametric detectors have been described by Stulik and Pacakova (4). Brunt (5) and Rucki (6) have presented general reviews of Present address: . electrochemical detectors. Weber and Purdy (7) have discussed detector design and mass transfer coefficients.The objectives of this study were to design and characterize a coulometric dete...