Optodes in clinical chemistry: potential and limitations

Clinica Chimica Acta, 1970

Revista Romana de Medicina de Laborator

Clinical Chemistry and Laboratory Medicine, 2000

This paper will familiarize the reader with the terms used to describe the behavior of ion-selective electrodes, particularly in relation to their use in clinical chemistry for determination of blood electrolyte cations. It serves as an introduction to a series of papers dealing with important cations in blood, namely calcium, sodium, and potassium. The detailed relationships between the ion activity determined by means of ion-selective electrode potentiometry in undiluted specimens, and the total substance concentration measured by flame atomic-emission spectrometry are described by flow chart and equations. Adoption of a convention for reporting results is recommended.

Clinical Chemistry, 1974

analyzer, in which ion-selective electrodes are used to measure sodium, potassium, and chloride in serum, was assessed in a clinical sethng. Day-to-day precision, evaluated by replicate analysis of serum pools, yielded the following coefficients of variation for sodium, potassium, and chloride, respectively: 0.99%, 1.39%, and 0.67%. Values for chloride in both commercial control sera and aqueous standards were linearly related to concentration over a range of at least 10-220 mmol/liter; however, results with the potassium and sodium electrodes showed slight curvilinearity over the range 0-24 and 10-220 mmol/liter, respectively.

The advent of ion-selective electrodes made possible the potentiometry of sodium in serum and plasma. These methods were based on dilution of serum, as done in flame photometry, and the results were identical. Analysis of whole blood precludes dilution and so "direct" potentiometry was developed. Results by this technique are variable but tend to compensate for the spurious hyponatremias found by the "indirect" dilution methods due to displacement of volume by lipids and protein. However, there is no unambiguous theoretical basis on which to choose between the various direct ion-selective-electrode techniques and instruments. As an alternative, I propose use of current indirect methods, with numerical correction for the shift in normal sodium values in the presence of abnormal lipid and (or) protein. A table was constructed for making such corrections.

Analytica Chimica Acta, 1999

An optrode for continuous monitoring of potassium to be used in whole blood was realized. Several commercial chromoionophores have been tried and composition of the membrane has been optimized in order to obtain the highest sensitivity around pH 7.4 and maximum light stability. The sensor is sensitive to pH but a simple equation relates absorbance and the value (pH + log K) and it was used in real experiments with cow whole blood.

Clinical Chemistry and Laboratory Medicine, 2000

Laboratory Robotics and Automation, 1998

A simple and reliable multichannel potentiometric analyzer for fully automatic determination of pH and concentration of sodium, potassium, calcium, and chloride ions in serum, and whole blood samples is described. The analyzer consists of five ion-selective electrodes (ISEs) as electrochemical sensors for selected ions. A flow-through homemade design of ISEs is developed, and the measuring instrument is interfaced to an IBM compatible PC by an analog-to-digital (A/D) converter interface card and peripheral devices control card in order to develop an easy to use, reliable, and virtually maintenance-free potentiometric analyzer. The analytical performance of the described analyzer is compared with the performance of some commercial laboratory Correspondence to: Stjepan Milardović. analyzers frequently used in clinical laboratories. The comparison study showed good correlation between results obtained by the developed and described instrument and those obtained using commercial analyzers. The range of correlation coefficients found in comparison with different commercial analyzers were pH (r ‫ס‬ 0.85-0.97), potassium (r ‫ס‬ 0.97-0.98), sodium (r ‫ס‬ 0.78-0.94) and chloride (r ‫ס‬ 0.87); the poorest correlation was found for calcium concentration determination (r ‫ס‬ 0.68-0.77). ᭧

Analytica Chimica Acta, 1976

4 new, continuous method has been developed for calibration and measurement with ion-selective electrodes. The electrode is immersed into a solution diluted with respect to one of the components which influence the potential of the electrode. The change of potential is followed as a function of diluent volume or dilution time and the results can be used to establish the calibration curve or selectivity data or to determine an unknown concentration value.

Sensors and Actuators B: Chemical, 2008

A conventional flatbed scanner is used to acquire the analytical parameters for quantitative determination in one-shot optical sensors based on ionophore-chromoionophore chemistry. Variables affecting the acquisition of the images and treatment were studied. The analytical parameter, an estimated reflection density, is obtained from an area of the sensing zone of the disposable sensor using the average luminosity of the best channel that fits the sensor theoretical model. The fit of the experimental results to the theoretical sigmoidal model and the precision of the results, in terms of relative standard deviation (R.S.D.%), are used to optimize the scanner variables. In order to improve the reliability and validity of the results we worked with scanner color management. Applying this methodology, we tried to make color measurements as independent as possible from the particular scanner used. Furthermore, the perceptual stimulus, that is, the color sensor response, is preserved and enhanced across this imaging treatment without any loss of information. Using this scanner protocol for measurement and the relation between digital output of the color scanner and the concentration of potassium into the sensing zone it is possible to analyze potassium between 6.58 × 10 −6 and 10 −2 M with a precision, expressed as R.S.D. of loga K + , ranging from 0.45 to 1.80%. These results are good when compared to the same procedure using a DAD spectrophotometer in which the concentration range is 1.31 × 10 −5 and 0.1 M and the precision range between 3.31 and 7.66%. semiquantitative determination in fish . The determination of iron (III) based on the colorimetric spot-test with thiocianate or povidone-iodine antiseptic agents [13], using a hand-scanner in both cases, is improved by linearizing the responses by means of a principal component analysis. Immunochromatographic procedures have been quantitatively evaluated with flatbed scanners using carbon black particles , gold nanoparticles or sulforhodamine B-loaded liposomes [16] as a label.

Fresenius' Journal of Analytical Chemistry, 2001

The influence of several ion-selective electrode properties on electrode response and selectivity at low concentration levels has been investigated experimentally. The properties investigated were the composition of inner electrode solution, the composition of the membrane, the presence of interfering ions in the sample, and the thickness of diffusion layer in the sample solution. All the results obtained confirmed theoretical considerations.

Analytical and Bioanalytical Chemistry, 2006

In this work, ion-selective electrodes for calcium ion were investigated. Two ionophores were used in the membranes: ETH 1001 and ETH 129. An internal filling solution buffered for primary ion was used that allowed the lower detection limit to be decreased down to 10 −8.8 M. Theoretical and experimental electrode characteristics pertaining to both primary and interfering ions are discussed. Better behavior was obtained with the electrode prepared with ETH 129 in the membrane. This electrode would be the most likely candidate for obtaining a low Ca 2+ detection limit in measurements performed with high K + , Na + , Mg 2+ background, which is found inside the cells of living organisms, for example. The potentiometric response of the electrode in solutions containing main and interfering ions is in good agreement with simulated curves obtained using the Nernst-Planck-Poisson (NPP) model.

Critical care and resuscitation : journal of the Australasian Academy of Critical Care Medicine, 2005

OBJECTIVE Ion selective electrodes (ISE) measure electrolytes by two different technologies, direct and indirect. We wished to investigate the effect of total plasma protein concentration on the plasma sodium, potassium and chloride measurements by indirect ISE compared with measurements by direct ISE. METHODS The evaluation of the objective was performed in a tertiary care hospital on patient blood samples sent to the pathology laboratory for general chemistry analysis. To determine the degree of difference between the two ISE measurements, 195 lithium heparin plasma samples were measured and the results were separated into three groups (65 samples in each group) depending on the protein concentration (e.g. total plasma protein concentration less than, greater than and within the reference range between 62-83 g/L). The samples were analysed over a 40 day period on a Hitachi Modular ISE system - indirect ISE (Roche Australia) and Bayer Rapidlab 865 Blood Gas Analyser - direct ISE (B...

Clinica Chimica Acta, 2003

The understanding of the most important sources of error in potentiometric blood analyser which might contribute to better instruments measurement repeatability is very often marginalized in fabrications and daily operation of some commercial blood analysers. In this paper ISEs-potentiometric measurements were performed and validated in Clinical Institute of Laboratory Diagnosis of the Zagreb University School of Medicine and Clinical Hospital Centre, using a carefully designed and constructed fully automated (computerised) homemade ISE-based blood electrolyte analyser constructed with an in-line fivechannel flow-through measuring cell. The influence of electrolyte concentration of the salt bridge is reported. Special attention has been paid to the reference electrode design, and constructions which can operate in open liquid junction and membrane restricted liquid junction modes are described. D

Analytica Chimica Acta, 1984

A new method is proposed for the determination of selectivity coefficients of ion-selective electrodes. A reference solution of the primary ion is used and potential changes are measured after adding either the primary ion or secondary ion. Increasing concentrations of the secondary ion are added to provide the same potential change as obtained for a fixed added concentration of the primary ion. The ratio of the primary-tosecondary ion concentrations for this potential change represents the selectivity coefficient. This method is illustrated by the use of a sodium glass electrode and a potassium valinomycin electrode. Results obtained are compared with those from conventional determinations of selectivity coefficients. The advantages of this method are discussed.