Lariat crown ethers (LCEs) offer the ability to bind selectively alkali metal ions. The presence of a coordinating functionality in the sidearm chain provides a means to further tune the selectivity of LCEs. A series of four LCEs based on a 15‐crown‐5 structural motif were synthesized with variations in the coordinating functionality of the sidearm and the substitution at the carbon pivot atom. Poly(vinyl chloride) liquid‐membrane ion‐selective electrodes were prepared with each of the four ionophores, and their response patterns to various alkali metals were determined. The results of this experimentation revealed that the coordinating ability of the sidearm is more important than the substitution at the geminal group at the pivot atom. It was also demonstrated that the change of a single atom in the sidearm structure, to induce coordinating ability to the sidearm, alters the selectivity between sodium and potassium by roughly five orders of magnitude.

The analysis of very small samples by atomic emission from a hollow cathode discharge source is investigated. Subpicogram detection limits of 0.88, 0.72, 0.38, and 0.70 pg are reported for Li, Na, K, and Ca, respectively, by viewing the excitation from a very small hollow with a custom-built multichannel spectrometer. These detection limits are comparable to those from electrothermal atomic absorption, with the additional advantage of the ability to analyze nonmetals. The technique has adequate sensitivity for the analysis of microsamples of physiological fluids for Na, K, and Ca; similar methods may be successful for Mg, P, and Cl, which are of significant physiological interest. Literature of applications of the hollow cathode as an emission source is reviewed. Instrumentation, operation, and sample preparation procedures are described. Temporal profiles of the emission from very small samples deposited in the hollow and working curves are given.