A simplified measurement procedure and portable electronic photometer for disposable sensors based on ionophore-chromoionophore chemistry for potassium determination

Abstract

A field-portable photometer for potassium determination with disposable sensors has been developed. It can be applied to routine water and beverage analysis. The disposable sensor is based on ionophore-chromoionophore chemistry. A colour change in the sensing film is detected by measuring the transmitted intensity with a solid state photodetector. Optical excitation at 660 nm is emitted by a light-emitting diode (LED). Negative feedback for LED bias and thermal correction were included to improve system stability. Additionally, a measurement procedure is presented, characterized and validated for in situ photometer use and real-time results. This simplified procedure is based on prior preparation of the disposable sensor in its acidic form and on the use of an absorbance ratio as analytical parameter. The only requirement for analysis is prior equilibration with a buffered sample solution for 3 min and absorbance measurement before and after equilibration. Good sensitivity in the concentration range 5 muM to 100 mM and very good repetitively and stability were achieved that are comparable to those obtained with bulkier analytical instrumentation. Given the compact size, low weight, rapid response and low energy requirement of the electronic photometer developed here, this measurement system is suitable for potassium determination in the field.

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field

“…In previous studies, 24 we reported on the use of an absorbance ratio, namely, A / A reference , as the analytical parameter instead of the ␣ value in order to simplify the analytical methodology and shorten the analysis time with respect to eliminating some calibrating solutions ͑acid, base, or buffer͒. In the case of cations, such as potassium, we proposed the ratio A / A HC +, which is A / A HCl since full protonation of the membrane is obtained with HCl.…”

“…The detection limit of the procedure calculated from the average A buffer / A HCl value using the same procedure indicated above gave a value of 5 M or 0.19 mg l −1 . 24 The trueness of the procedure for potassium was demonstrated in the same way used for nitrate. The regression line obtained ͑y = 0.9849x − 1.0901; r 2 = 0.9939͒ shows that the slope did not differ from the unity and the intercept did not differ from zero, thus the results obtained show no statistical differences between both sets.…”

“…Additionally, we used one-shot sensors pretreated with acid in the case of cations or with base in the case of anions, in such a way that the direct absorbance measurement of the membrane without reaction with any solution and subsequent equilibration with sample solution produces the analytical parameter. Preparations of membranes 23,25 and pretreated membranes 24,28 are given in previous reports.…”

“…Everything, from the one-shot sensor to the signal processing electronics, has also been designed with the aim of applying a novel measurement procedure to dissolve analytes in natural waters and beverages simply and with enough sensitivity and repeatability for in situ measurement at low cost. As examples of one-shot sensors to be used along with the measurement procedure described here, we have selected two ionophore-based membranes for potassium 23,24 and nitrate 25 previously reported by us for the analysis of these species in water.…”

State-of-the-Art of (Bio)Chemical Sensor Developments in Analytical Spanish Groups

“…The one-shot sensor used in these papers is a potassium sensor, previously developed and characterized by the Capitán-Vallvey group [222], based on lipophilized Nilo Blue as the chromoionophore changing its color from violet to blue when the potassium concentration increases. Several detection techniques were used to acquire the analytical parameters, such as a conventional flatbed scanner [223], transflectance and chromaticity systems [224], and transmitted intensity with a solid state photodetector due to color change in the sensing film [225] for quantitative determination of potassium. Potassium sensing films were produced on a polyester substrate with PVC, 2-nitrophenyloctyl ether (NPOE), dibenzo-18-crown-6-ether (DB18C6), the chromoionophore N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine (ETH 5294) and potassium tetrakis (4-chlorophenyl) borate (TCPB).…”