Ionophores concentration range

At present the plastic membrane with ionophore ETH 2137 is used. The introduction of ionophore ETH 2137 generated a stable selectivity towards sodium ion allowing for numerical correction of sodium influence using the values of independently measured sodium. Thus a complete procedure covering therapeutic concentration range of lithium (which should be <1.2mmol/L) is available. 

In electrically driven guinea-pig atria, callipeltin A induces a positive inotropic effect at concentrations ranging between 0.7 and 2.5 jlM [108,109]. Callipeltin A appears to display an Na-ionophore action, since resting aorta responded to callipeltin A in a dose-dependent manner, with EC50 at 0.44 p,M, which was not inhibited by common calcium channel blockers. Callipeltin A also increased Na efflux of Na-loaded erythrocytes, with EC50 at 0.51 p,M [110]. 

Sodium permeabilities were found to be 62, 82, 126 and 158 ni /sec for 15, 22.5, 30 and 37.5 yM monensin respectively and lithium permeabilities were 12 uid 33 ni /sec for 400 and 800 yM monensin respectively. Thus, the permeabilities extrapolated to 1 yM of monensin for Ihe same don and lipid concentration are for Na 4.0 0.4 m /sec, for Li 0.035 4 0.005 nn sec. These results show that within the concentration range studied the sodium transport rate increases fairly linearly with the ionophore concentration, indicating that the dominant transporting species is a 1 1 complex of the sodium ionophore. The much higher value obtained for sodium either indicates that the complex association-dissociation processes determine the overall rate of transport or reflects the difference in the binding constants for these two ions. 

The determination of U ions (as uranyl) using a macrocylic N-subsstituted amide (26) as the ionophore was reported by Shamsipiu et al. in 2002. The ISE in question was based on (26). It displayed a Nemstian response (29.2 mV per decade) with a DL of 3.5 x 10 M and was found to operate over a wide concentration range (from 5.0 x 10 to 1.5 X 10 M). Gratifyingly, this system displayed good selectivity for luanyl ions and was subject to almost negligible interference from other cations (e.g., alkali, alkaline earth, transition, and heavy metal ions). ... 

Including also the Ag+-selective ionophore SS-Ag-II in the modification trials revealed that the Au membranes could only be modified in one step with all components dissolved in methanol and the optimal composition of the modifying solution was SS-Ag-II/MDSA/PFT at a total concentration of 0.2 mM, and molar ratios of 11 10 1, respectively. The calibration curves for Ag+ revealed detection limits in the lower nanomolar concentration range associated with fast and drift-free Nernstian potential responses (Figure 22.9b). 

A cyclic aza-oxa-cycloalkane, 7,13-bis( -octyl)-l,4,10-trioxa-7,13-diazacyclo-pentadecane (LI), was characterized and its interaction with anionic surfactants studied. Different PVC membrane anionic surfactant-selective electrodes were prepared using LI as ionophore and o-NPOE, bis(2-ethylhexyl) sebacate (BEHS) or DBP as plasticizers. The PVC-based membrane electrode containing o-NPOE as plasticizer showed a Nemstian response with a slope of 57.7 0.2 mV decade for lauryl sulfate (LS) in a concentration range from 3.3 x 10 to 6.7 x 10 mol L with a detection limit of 2.2 x 10 mol L The fabricated electrode was used for the determination of anionic surfactants in several mixtures, and the results obtained were compared to those found using a commercially available electrode. A similar ligand (7-methyl-7,13-di-octyl-l,4,10-trioxa-13-aza-7-azonia-cyclopentadecane)... 

Doses range from 6 to 33 ppm ia the diet, but very htde if any ionophore can be measured ia the circulation after feeding. Monensia is absorbed from the gut, metabolized by the Hver, and excreted iato the bile and back iato the gut. Thus tissue and blood concentrations are very low. Over 20 metabohtes of monensia, which have Htde or ao biological activity, have beea ideatified (47,55). 

It has been long believed that a lithium ion-selective electrode would render obsolete the flame photometer in the clinical laboratory. Lithium is administered to manic depressive psychiatric patients. Since the therapeutic range (0.5-1.5 mM) is quite close to the toxic range (>2 mM), it must be closely monitored. Most of the iono-phores propo d to date have not met the Li" /Na selectivity required for an interference-free assay. However, it has been reported that calibration in the presence of 140 mMNa permitted the analysis of Li in serum The errors observed are due to fluctuations in the Na concentrations in the sample. More selective ionophores would certainly improve the accuracy of this method. 

In biomedical applications, the ranges of ion concentration are higher by several orders of magnitude. For instance, the abovementioned calcium probes for living cells cannot be used because the dissociation constant is so low that they would be saturated. Special attention is thus to be paid to the ionophore moiety to achieve proper selectivity and efficiency of binding. For instance, at present there is a need for a selective fluorescent probe for the determination of calcium in blood which could work in the millimolar range in aqueous solutions so that optodes with immobilized probes on the tip could be made for continuous monitoring calcium in blood vessels. 

---