Sodium sensor linearity

A potassium-ion-selective, dendritic, fluorescing chemosensor, bearing three crown ether moieties in the periphery, shows a linear increase in fluorescence intensity with increasing potassium concentration (in acetonitrile). An important criterion for potassium chemosensors is their mode of action (selectivity) in the presence of large amounts of sodium. The tris-crown ether sensor shown in Fig. 8.16 is able to detect very small traces of potassium ions, even if large quantities of sodium ions are present in the same solution - such as in body fluids [55]. 

Sodium, potassium and chloride sensors were evaluated using undiluted serum specimens with no sample pretreatment of any kind. The performance data set, summarized by Table II, comprises a minimum of 8 sensors and 60 samples. The bicarbonate assays were performed separately on serum specimens buffered at pH 9.0. Clinical efficacy is normally judged by the response linearity, precision and... 

A potassium opto-sensor was recently described [75] for the continuous determination of electrolytes. Certain fluorescent dyes respond to an electric potential at the interface between the aqueous and lipid phases. This potential is created by the neutral ion carrier. The lipid layer is formed on a glass support by the Langmuir-Blodgett thin-fllm technique. This layer incorporates Rhodamine B as a dye and valinomycin as the carrier. The lipid membrane is made of arachidic acid. The fluorescence intensity decreases when this layer is exposed to potassium ions (linearity between 0.01 and 10 mM). This optode is also sensitive to sodium ions [76]. The selectivity factor of potassium in comparison with sodium ions varies from 10 - to 10 , and in relation to ammonium ions by 10. Interferences can be compensated for by a reference optode. However, better selectivity is obtained with new lipid membrane compositions (octadecan-l-ol-valinomycin) [77]. Tetralayers (Figure 17-9) give a maximum response for K". The K /Na selectivity is about 10 in a wide range (0.01-100 mM). 

The first system, devised in the University of Porto, Portugal, was a sensor array for the measurement of creatinine in urine [18]. It consisted of a creatinine iminohydrolase enzyme immobilized by entrapment using a chitosan membrane onto a nonactin ISE. Catalytic hydrolysis by the enzyme generated ammonium ion which was then directly detected. The system was completed with ISEs for ammonium, potassium, sodium and calcium which allowed to correct for any endogenous ammonium (by the first ISE) or for alkaline and alkaline-earth interference in the ammonium-based biosensor (the other three). Linear response ranges were between 0.1 and 10 mM, what permitted the resolution of the multicomponent determination by PLS method. Comparison with reference Jaffe method showed a satisfactory correlation, although the slope of obtained vs. reference values was rather low the obtained value was 0.87, whereas theoretical value should be 1.0. 

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