Potassium selective electrode

A potassium-selective electrode , and potassium-sensitive electrode or shortened potassium electrode called, is a sensor for determining the concentration , or more specifically the activity of the potassium ion (K ⁺ ) in a solution. It is one of the chemosensors and ion-selective electrodes and enables the potassium concentration to be determined quickly in a liquid or dissolved sample. It is used in analytical chemistry , in drinking or wastewater treatment and in biochemical research, especially when continuous monitoring is useful or necessary. They are also often used in clinical examinations, as the potassium concentration in body fluids such as blood or urine can be determined directly .

Although potassium self-tests are not recommended for periodic paralysis or atrial fibrillation , there are patients suffering from these diseases who report good experiences with self-tests with a potassium-selective electrode. The potassium content in the saliva is determined, as this correlates with the potassium concentration in the blood.

construction

The potassium-selective electrode becomes selective for potassium through a special membrane that is specially designed for potassium. It usually contains - especially for clinical applications - valinomycin as a carrier or transporter (ionophore) for the potassium ion. This is embedded in a matrix made of PVC (polyvinyl chloride) or silicone rubber.

Scheme of the measurement setup with an ion-selective electrode: the voltage is measured against a reference electrode with a sensitive voltmeter. For a potassium electrode, the membrane marked in red must be potassium selective.

Measuring range and cross-sensitivity of the electrode

Usual potassium-selective electrodes can be used in the range 1 · 10 ⁻⁶ mol / l to 1 mol / l.

The potassium-selective electrode not only responds to potassium ions, but also - in order of decreasing sensitivity - to cesium , rubidium , ammonium , thallium , sodium , calcium , magnesium and lithium ions . In most practical applications, such as the investigation of drinking water or biological fluids, the concentrations of rubidium, cesium and thallium are so small that the ammonium ion is usually the most problematic interfering ion, especially when its concentration is greater than that of potassium. Although the concentration of sodium in biological samples is usually high, the selectivity of the potassium electrode is usually good enough to keep the error in the potassium determination small. Calcium, magnesium or lithium are also not a problem in most cases.

Historical

Potassium-selective electrodes based on a glass electrode were known as early as the early 1960s. They were also sensitive to sodium, however. It was only after Wilhelm Simon invented an electrode based on valinomycin at ETH Zurich - it was presented in 1969 - that reliable and highly selective potassium-selective electrodes were developed. The first valinomycin potassium electrode still had a membrane, the pores of which were filled with a liquid valinomycin solution in diphenyl ether. Solid membranes soon came into use. In 1993 it was estimated that hundreds of thousands of potassium selective electrodes had been made by then.

Individual evidence

1. ^ Testing Potassium Levels with the Cardy Potassium Ion Meter. Information for Patients and Caregivers. (No longer available online.) Periodic Paralysis International, July 17, 2011, archived from the original on March 21, 2015 ; Retrieved on March 23, 2015 (English): "has given excellent results to many patients in our group who have used it" Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  
2. ↑ Support and Resources - Home Potassium Monitoring. Periodic Paralysis Association (PPA) October 13, 2013, archived from the original April 2, 2015 ; accessed on March 23, 2015 (English): "here is a way to accurately know your potassium levels in the comfort of your own home" 
3. ^ Hans R. Larsen: Potassium level monitoring with cardymeter. (PDF) Retrieved March 23, 2015 (English). 
4. ↑ Saliva to Serum Potassium Correlations. Correlation of Saliva and Human Blood Serum Potassium Results. (No longer available online.) Periodic Paralysis International, July 17, 2011, archived from the original on March 22, 2015 ; accessed on March 23, 2015 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
5. ^ Urs Oesch, Daniel Ammann, Wilhelm Simon: Ion-selective membrane electrodes for clinical use . In: Clinical Chemistry . tape 32 , no. 8 , August 1986, p. 1448-1459 , PMID 3524901 ( abstract ).
6. ^ CJ Coetzee: Inorganic Ion Exchangers as Ion-Sensors . In: JDR Thomas (Ed.): Ion-Selective Electrode Reviews . Volume 3. Pergamon Press Ltd, Oxford, 1982, pp. 105 .
7. ↑ HD Portnoy, LM Thomas, ES Gurdjian: Improved electrodes for the continuous measurement of sodium and potassium . In: Talanta . tape 9 , no. 2 , 1962, pp. 119-124 , doi : 10.1016 / 0039-9140 (62) 80034-4 .
8. ↑ E. Pungor: eulogy for Professor Wilhelm Simon's 60th Birthday . In: Microchimica Acta [Vienna] . tape 100 , no. 3-4 , 1990, pp. 129-130 , doi : 10.1007 / BF01244837 .
9. ^ ^{A b} Lavinia AR Pioda, V. Stankovaa, Wilhelm Simon: Highly Selective Potassium Ion Responsive Liquid-Membrane Electrode . In: Analytical Letters . tape 2 , no. 12 , 1969, p. 665-674 , doi : 10.1080 / 00032716908051343 .
10. ^ Erno Pretsch, Jean Thomas Clerc: Wilhelm Simon: 1929–1992 . In: CHIMIA International Journal for Chemistry . tape 47 , no. 1-2 , January 1993, pp. 25-27 .