Carbonate ISE

Many double-charged anions, such as sulfate, hydrophosphate, oxalate etc., are highly widespread in natural sources and at the same time lack any convenient technique for their determination. Therefore, development of ion-selective electrodes (ISEs), responsive to these anions, is of great practical importance. However, for a long time all attempts directed toward creation of such electrodes were unsuccessful (except for carbonate ISEs based on trifluoroacetylbenzene derivatives), and only in recent years this field has shown significant progress. 

New polymer membrane-based ISEs for nitrate and carbonate exhibit detection limits and selectivities that may be applicable for ocean measurements. In addition, a number of these ISEs can be used as internal transducers for the design of useful potentiometric gas sensors. For example, dissolved C02 can be detected potentiometrically by using either a glass membrane electrode or a polymer-based carbonate ISE, in conjunction with an appropriate reference electrode, behind an outer gas permeable membrane. Novel differential pC02 sensors based on two polymer membrane-type pH sensors have also been developed recently. 

It is possible to use a carbonate ISE in samples prediluted with base to convert all forms of C02 into carbonates or to use the C02 gas electrode or pH electrode for the measurement of total C02 evolved after addition of acid (e.g., Dade-Behringer prev. Dade). 

Carbonate ISEs have been studied using molecular tweezer compounds [21 ] capable of being incorporated into PVC membranes to give electrodes that can measure physiological levels of carbonate in serum with reasonable selectivity over other interferent compounds likely to be present. This method has also been shown to give accurate measurements of oceanic carbon dioxide levels with real samples [22]. 

Fig. 14 Setup of a novel potentiometric non-Severinghaus concept. The pC02 is determined by the potential difference between a carbonate ISE and a pH electrode. Both electrodes are directly immersed in the sample solution without the use of a separating membrane. Adapted from [46] with permission...

Fig. 15 Left Calibration curve of a conventional Severinghaus sensor (SH) and a novel non-Severinghaus sensor measuring the potential difference between a pH glass electrode and a carbonate ISE as a function of log(pC02/Po) [46]. Reproduced from [46] with permission. Right Comparison of the response characteristics of both CO2 sensors - the SH and the new pC02 electrode arrangement. Measured in 0.1 M Tris-H2S04, pH 8.0 buffer solution for the following PCO2 (A) 0.0004 atm, (B) 0.0066 atm, (O 0.0655 atm [46]...

Ion Selective Electrodes Technique. Ion selective (ISE) methods, based on a direct potentiometric technique (7) (see Electroanalytical techniques), are routinely used in clinical chemistry to measure pH, sodium, potassium, carbon dioxide, calcium, lithium, and chloride levels in biological fluids. 

The electrolytes Na", and Cl are second only to glucose in being the most frequently run hospital tests. Many clinical chemistry analyzers now contain an ISE module for electrolyte analysis. Most commonly the module will consist of a Na -glass electrode, a valinomycin/PVC electrode, a Ag/AgCl pellet or a quaternary ammonium ion/PVC electrode and a reference electrode. A selective electrode for the bicarbonate ion continues to elude workers in the field. An indirect measurement of HCOf must be made. The sample is usually reacted with acid to evolve carbon dioxide gas which is measured with a traditional Severinghaus type CO2 electrode. Alternatively, the sample is treated with base to convert HCO to CO3 and a carbonate ion-selective electrode is used In this manner, the complete primary electrolyte profile is obtained electrochemically. 

Ulis A., Rosenberg Y., Burstein L., Peled E. Degradation of Carbon-Supported Tin Alloys in LiPF6EC DEC. Proceedings of Joint (ECS ISE) International Meeting 2001 2-7 September San Francisco, 2 Abstract No. 225, 2001. 

Clinical chemistry, particularly the determination of the biologically relevant electrolytes in physiological fluids, remains the key area of ISEs application [15], as billions of routine measurements with ISEs are performed each year all over the world [16], The concentration ranges for the most important physiological ions detectable in blood fluids with polymeric ISEs are shown in Table 4.1. Sensors for pH and for ionized calcium, potassium and sodium are approved by the International Federation of Clinical Chemistry (IFCC) and implemented into commercially available clinical analyzers [17], Moreover, magnesium, lithium, and chloride ions are also widely detected by corresponding ISEs in blood liquids, urine, hemodialysis solutions, and elsewhere. Sensors for the determination of physiologically relevant polyions (heparin and protamine), dissolved carbon dioxide, phosphates, and other blood analytes, intensively studied over the years, are on their way to replace less reliable and/or awkward analytical procedures for blood analysis (see below). 

A nitrate-selective potentiometric MIP chemosensor has been devised [197, 198]. For preparation of this chemosensor, a polypyrrole film was deposited by pyrrole electropolymerization on a glassy carbon electrode (GCE) in aqueous solution of the nitrate template. Potentiostatic conditions of electropolymerization used were optimized for enhanced affinity of the resulting MIP film towards this template. In effect, selectivity of the chemosensor towards nitrate was much higher than that to the interfering perchlorate ( o3 cio4 = 5.7 x 10-2) or iodide ( N03, r = x 10 2) anion. Moreover, with the use of this MIP chemosensor the selectivity of the nitrate detection has been improved, as compared to those of commercial ISEs, by four orders of magnitude at the linear concentration range of 50 pM to 0.5 M and LOD for nitrate of (20 10) pM [197]. 

LAB 11 Laboratory for analysis of unfiltered water samples, stream sediment and floodplain sediment samples. Ion chromatography (IC) is used for Cf, Br, N03% N02, P043, S042 and ion specific electrode (ISE) for F and Total Organic Carbon (TOC) in water. X-Ray fluorescence spectrometry (XRF) analyses for over 30 elements is used for stream sediment and floodplain sediment samples. To be nominated (suggestion British Geological Survey). 

Photograph of porous carbon-contacted ISE.42 (Reprinted with permission from C.-Z. Lai et al., Anal. Chem. 2007, 79,4621—4626. Copyright 2007 American Chemical Society.)... 

Six mycotoxins, penitrems A—F [(16a)—(16f)], derived from tryptophan (with loss of the side-chain) and a diterpene unit (with loss of a carbon atom), have been isolated from Penicillium crustosum iSe of these, penitrem A was first isolated15/in 1968 from P. cyclopium, and penitrems B and C in 197l15 from a micro-organism originally presumed to be P. palitans, but now classified as P. crustosum. The occurrence of penitrem A in P. cyclopium has recently been confirmed, and the presence of penitrem B was also demonstrated.156... 

Using platinum electrodes (167, 238) requires +0.6 V versus SCE to oxidize H2O2. However, this potential precludes selective measurements of uric acid because it is also oxidized at the electrode surface (167). Thus, to improve the selectivity, bienzyme amperometric devices using a redox mediator (hexa-cyanoferrate) have been constructed (239). The enzymes uricase and peroxid ise are immobilized together and the hexacyanoferrate(III) is measured at 0.0 V versus Ag/AgCl. Alternatively, a carbon dioxide selective electrode is used for the detection of the enzymatically liberated CO2 (240, 241). 

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