Lithium ion-selectivity

EXAMPLE 5-5 Calculate the error caused by sodium ion, aNa = 0.01, in the measurement of lithium, au = 0.01, using a lithium ion-selective electrode... 

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. 

K. Watanabe, E. Nakagawa, H. Yamada, H. Hisamoto and K. Suzuki, Lithium ion selective optical fiber sensor based on a novel neutral ion-ophore and a lipophilic anionic dye, Anal. Chem., 65(19) (1993) 2704-2710. 

Figure 2.1 Illustration of the monomeric primary amido complex [Li(NHMes )(tmeda)f showing the distorted trigonal planar geometry at the lithium ion. Selected bond lengths Li-NI 1.895(8) A, Li-N2 2.137(9) A and Li-N3 2.165(9)A...

K. Kimura, T. Yamashita, M. Kaneshige, and M. Yokoyama, Crowned spironaphthoxazine lithium ion-selective coloration and ion-regulated thermal stability of its colored form, J. Chem. Soc., Commun., 1992, 969-971. 

Lithium ion selective electrodes (ISEs) have been developed (67) and may he used to provide rapid serum lithium estimations at the time of contact with the patient, for example, in the lithium clinic, as well as in clinical laboratories (68). The therapeutic advantage of this procedure is that patient compliance with medication may be improved if the results of blood monitoring are obtained on the spot. Instant results also reduce the number of times a patient needs to visit the hospital or clinic, thus saving the patient inconvenience. The psychiatrist needs fewer appointments for feedback and dosage regulation (69). 

Metzger E, Aeschimann R, Egli M, et al. 3,7-Dioxa-azela-amides as ionophores for lithium ion selective hquid membrane electrodes. Helvetica Chim Acta, 1986 69 1821-8. 

A lithium ion-selective electrode gave the potentials given in the table for the following standard solutions of LiCl and three samples of unknown concentration. 

Zhukov, A. F., Erne, D., Ammann, D., Guggi, M., Pretsch, E., and Simon, W., Improved lithium ion-selective electrode based on a lipophilic diamide as neutral carrier. Anal. Chim. Acta 131, 117-122 (1981). 

Mixed Solution Method. There are various measurement methods using mixed solutions of the two ions. The. fixed interference method is commonly used. Consider, for example, the testing of a lithium ion-selective electrode in the presence of sodium ion. A lithium calibration curve is prepared in the presence of a fixed concentration of sodium, for example, 140 mM as found in blood. A plot such as that given in Figure 13.16 results. In the upper portion of the curve, the electrode responds in a Nemstian manner to the lithium ion. As the lithium concentration decreases, the electrode potential is increasingly affected by the constant background of sodium ions, and in the lower portion of the curve the electrode exhibits a mixed response to both the lithium and the sodium. When the lithium concentration is very small, the response is due solely to sodium (the baseline potential). 

Further methods for the determination of lithium have been reviewed by Birch (1999). During the late 1980 s, the lithium ion selective electrode (Li-ISE) (Xie and Christian 1986) has been developed in order to optimize lithium treatment (Phillips et al. 1989, Sim et al. 2001). This technique allows on-the-spot estimations of lithium in whole... 

Birch NJ, Johnson AM and Padgham C (1996) Backtracking serum lithium ii) clinical validation of the Lithium Ion Selective Electrode analyser (Li-ISE). J Trace Microprobe Techn 14 439-444. 

Sim JH, Lee KM, Lee JS, Cho DH, Nam Hand Cha GS (2001) Lithium ion-selective electrode with improved lifetime. Bull Korean Chem Soc 22 765 -768. 

XiE RY and Christian GD (1986) Serum lithium analysis by coated wire lithium ion selective electrodes in a flow injection analysis dialysis system. Anal Chem 58 1806-1810. 

V. P. Y. Gadzekpo, G. J. Moody, and J. D. R. Thomas, Coated-Wire Lithium Ion-Selective Electrodes Based on Polyalkoxylate Complexes. Analyst, 110 (1985) 1381. 

R. Y. Xie and G. D. Christian, Serum Lithium Analysis by Coated Wire Lithium Ion Selective Electrodes in a Flow Injection Analysis Dialysis System. Anal. Chem., 58 (1986) 1806. 

Z.-N. Zhou, R. Y. Xie, and G. D. Christian, Relation of Plasticizers and lonophore Structures on Selectivities of Lithium Ion-Selective Electrodes. Anal. Lett., 19 (1986) 1747. 

Four data subsets are provided, and they tell a consistent story. The benzaldeliyde reactions (subset 1) proceed with mediocre selectivity that is not much affected by lithium ion. Selectivity in the PhjP series is also poor... 

A 14-crown-4 derivative has also been incorporated in a PVC membrane to construct a coated-wire lithium ion-selective electrode used for the determination of lithium in blood sera, after on-line dialysis separation in a FIA system [6]. An estimation of the overall selectivity of the method over the sodium content, including that of the dialysis membrane and the electrode, resulted in a selectivity coefficient k of 1/50. This selectivity is not sufficient to overcome interferences from relatively large fluctuations in sodium contents, and corrections based on a simultaneous evaluation of the sodium content are required under such circumstances. 

THE STRUCTURES OF NONCYCLIC POLYETHER CARRIERS EXHIBITING LITHIUM ION-SELECTIVE TRANSPORT... 

So far several polyether family compounds exhibiting lithium ion-selectivity have been reported, e.g., 12-crown-4, 14-crown-4, macro-cyclic compounds having tetrahydrofuran as a chain component, cryptand [211], spherand, noncyclic diamide, and so on (2). However these are not always suitable to transport lithium ion selectively through liquid membranes. That is, these are useful as extracting agents or chemical devices for ion selective electrode (3), but are not available and... 

We have studied the synthesis of noncyclic polyether compounds and their cation transport behaviors (5), Recently, we found that the noncyclic polyether compounds containing oxytrimethylene chain units, e.g., jL, could transport lithium ion selectively as is shown in Fig. 1 and against its concentration gradient (5b, 5e). 

From a series of studies the structural significance of the oxytri-methylene chain units in polyether 1 is noted for the appearence of a high selectivity for the lithium ion (5e). In fact, the lithium ion-selectivity in the case of polyether 2, which contains two oxyethylene chain units decreased distinctly compared with the case of 1. In addition, it has been found that the selectivity and efficiency appreciably depends on the kind of the terminal group, X. 

Polyethers, 5 and i6, containing X = o-ethoxyphenyl and o-(2-phenyl-ethoxy) phenyl groups, respectively, can also exhibit lithium ion-selectivity superior to polyether (X = phenyl). It is suggested that these substituents as well as o-[3-(l-naphthyloxy)propoxy]phenyl group in 7 and 2-methylquinolyl group in play a role of a part of the hydrophobic external wall. 

When lithium chloride is added to PS-b-PMMA, the lithium ions selectively segregate to the PMMA block due to coordination with its carbonyl groups. Perpendicular orientations are easily possible when electric fields are applied,and this behavior has been attributed to an increase in dielectric contrast from ion complexation. ... 

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