Metrological Aspects of Activity Measurements in Mixed Electrolytes by Ion‐Selective Electrodes

Wunderli, Samuel; Andres, Hanspeter

doi:10.1002/elan.200704051

Cited by 4 publications

(8 citation statements)

References 28 publications

(14 reference statements)

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“…(5). [2] The uncertainty in E J is generally considered as a major source of bias in ISE measurements, whereas the uncertainty of the dynamic term is usually not considered. [30,31] …”

Section: Potentiometric Measurementsmentioning

confidence: 99%

“…[38] The parameters ij (0) , ij (1) and ij (2) are specific for each electrolyte. They are obtained through fitting of isothermal or isobaric thermodynamic data available for aqueous solutions of the considered electrolyte.…”

Section: The Pitzer Semi-empirical Ion Interaction Modelmentioning

confidence: 99%

“…, ij (2) , α 1 , α 2 and C ij φ from literature tables or from the Pitzer database. [38] The parameters ij (0) , ij (1) and ij (2) are specific for each electrolyte.…”

Section: The Pitzer Semi-empirical Ion Interaction Modelmentioning

confidence: 99%

“…1, is an improved version of previously described work. [2] The electric valve drives K-6 (KNAUER, Berlin, Germany) have been adapted and allow us to perform runs of up to 18 solutions sequentially with three switchable valve blocks of six entries. A METAS calibrated potentiometer with six measurement channels (C-CIT) allows us to perform multichannel detections with PFA flow modules in which the membranes are clamped and up to six working electrodes (in our experiments four electrodes were connected).…”

Section: Mass Of Pure Electrolyte Components Forming the Mixturementioning

confidence: 99%

“…[1] For this purpose, considerable efforts are carried out by international institutes to promote and give guidance on measurement comparisons and metrological traceability using appropriate certified reference materials. [2] The legal requirements for products manufactured and marketed in Europe, stated in the 'In Vitro Diagnos-tic Medical Directive' (98/79/EC), demand that the traceability of values that are assigned to calibrators and control materials must be assured with reference measurement procedures and/or available reference materials of a higher order. [3][4][5] The Joint Committee for Traceability in Laboratory Medicine (JCTLM), an assembly established by the International Committee of Weights and Measures (CIPM), the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC), and the International Laboratory Accreditation Cooperation (ILAC), recommends specially qualified laboratories and metrological institutions to assign reference values to standards.…”

Section: Introductionmentioning

confidence: 99%

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Development of Suitable ISE Measurement Procedures for SI-Traceable Chemical Activity Determination

Berdat¹,

Andres²,

Wunderli³

2009

Chimia

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In clinical chemistry and medical diagnostics, the reliability of the results obtained by numerous testing protocols has a major impact on the critical decision-making processes. Considerable efforts are made by international institutes to promote and give guidance on measurement comparisons and metrological traceability using appropriate certified reference materials. The concentration values or amount of substance contents are usually assigned to chemical analytical results. In contrast, the most relevant quantity is the activity of ions in clinical chemistry. Activity corresponds to the available biologically active part of these components in a mixture. Many measurement methods and instruments currently in use do not differentiate between the total substance concentration and its biologically active component. In physiological solutions, such as blood plasma, the chemical activity makes a clear difference between ion or substrate concentration. Ion selective electrodes (ISE) are widely used to directly measure the activity of ions. Measurement by means of ion-selective electrodes is a standard method in point of care testing units (POCT) for continuous monitoring for e.g. haemodialysis, cardiac surgery and in intensive care units. A metrological approach to ISE potentiometric measurements is proposed, to determine the activity with their uncertainty. A prerequisite is to develop an activity calibration scale for complex electrolyte solutions with known and traceable ion activities.

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“…(5). [2] The uncertainty in E J is generally considered as a major source of bias in ISE measurements, whereas the uncertainty of the dynamic term is usually not considered. [30,31] …”

Section: Potentiometric Measurementsmentioning

confidence: 99%

Section: The Pitzer Semi-empirical Ion Interaction Modelmentioning

confidence: 99%

“…, ij (2) , α 1 , α 2 and C ij φ from literature tables or from the Pitzer database. [38] The parameters ij (0) , ij (1) and ij (2) are specific for each electrolyte.…”

Section: The Pitzer Semi-empirical Ion Interaction Modelmentioning

confidence: 99%

Section: Mass Of Pure Electrolyte Components Forming the Mixturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Development of Suitable ISE Measurement Procedures for SI-Traceable Chemical Activity Determination

Berdat¹,

Andres²,

Wunderli³

2009

Chimia

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Metrological Aspects of Glucose Measurements by Biosensors

Wunderli

Andres

2009

Electroanalysis

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In a chronoamperometric measurement the chemical activity of glucose is directly determined using a glucose sensitive biosensor based on glucose oxidase and an efficient mediator. Within the physiological range of 2 mmol kg À1 and 10 mmol kg À1 glucose in aqueous solutions behaves almost ideally and the chemical activity equals the glucose molality, the amount of glucose per unit mass of water, within the estimated measurement uncertainty. In physiological samples the equality between chemical activity and glucose molality is destroyed and has to be corrected for. Gravimetrically prepared mixtures of high purity glucose in buffered aqueous solutions are used as standards for calibration of the chronoamperometric measurement setup. Based on the model equation for the measurand aqueous or physiological sample, all significant sources of uncertainty are identified, their magnitude estimated from published and experimental data and finally combined to give the uncertainty in the reported value of the glucose molality. It is found, that the combined uncertainty of the glucose molality comprises mainly uncertainty contributions from the nonideal behavior, the chronoamperometric measurement setup, from the purity of glucose used and from the chemical composition of the test sample. The expanded uncertainty is below 2% rel., the glucose content determined by the bioelectrochemical measurements thus competes well with todays considered most accurate reference method Isotope Dilution Mass Spectrometry. Advantageous of the presented electroanalytical method is the direct measure of the glucose molality without prior sample preparation and dilution.

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