EMRP - Tracebioactivity

• Research unit: METAS
• Project number: 5237.08.FP.059

Key words (German)

Ionenselektive Elektroden, Biosensoren, Elektrolyte, chemische Aktivität, Aktivitätsskala

Key words (English)

Ion-selective electrodes, biosensors, electrolytes, chemical activity, activity scale.

Short description (German)

Der frei verfügbare Stoffmengenanteil (chemische Aktivität) von physiologisch relevanten Ionen und neutralen Substanzen in Lösungen ist eine zentrale Grösse in der klinischen Chemie. Mittels ionenselektiven Elektroden und Biosensoren können chemische Aktivitäten von Elektrolytionen und gelöste neutrale Substanzen direkt bestimmt werden. Diese Methoden werden in der klinischen Analytik routinemässig eingesetzt, z.B. bei Blutdialyse, Herzoperationen oder der Behandlung von Diabetes. Weitere Anwendungsgebiete neben der Labormedizin sind die Biotechnologie und die Umwelttechnik. Obwohl chemische Sensoren empfindlich auf die chemische Aktivität reagieren, werden die Messresultate ausschliesslich in Gehalte umgerechnet. Die verwendeten fixen, empirischen Faktoren zur Umrechung von Aktivitäten in Gehalte können falsche negative oder falsche positive Resultate liefern. Die elektroanalytische Chemie kann hier einen wichtigen Beitrag zur Rückverfolgbarkeit von chemischen Aktivitätsmessungen leisten. Gravimetrisch hergestellte Lösungen mit berechneten Aktivitäten, gemäss einem international vereinbarten semi-empirischen Modell, soll die Aktivitätsbasis bilden, mit der die chemische Aktivität unbekannter Lösungen bestimmt werden kann. Eine neu aufzubauende, international abgestützte Aktivitätsskala für Elektrolytionen muss dabei mit der heutigen Konvention der Aktivitätsskala von Wasserstoff-Ionen (pH) im Einklang stehen.

Die Primärnormale am METAS zur Messung der chemischen Aktivität von Elektrolytionen (Potentiometrie mit ionen-selektiven Elektroden) und weiteren biologisch relevanten Substanzen (Amperometrie mit Biosensoren) werden soweit weiterentwickelt, dass entsprechende international anerkannte Dienstleistungen für die Messung der chemischen Aktivität durch das Labor Elektrochemie angeboten werden können. Das Projekt umfasst zudem die notwendigen Arbeiten zur Bereitstellung des Normals und der Kalibration für die Aktivitätsmessung von Glukose als wichtigsten Vertreter einer neutralen Substanz und Treibstoff in den Zellen aller höher entwickelten Lebewesen.

Short description (English)

The freely available amount of substance content (chemical activity) of physiological relevant ions and neutral substances in solutions are an important quantity in clinical chemistry. With ion-selective electrodes and biosensors chemical activities of electrolyte ions and neutral substances can be determined directly. These methods are regularly used in clinical diagnostics, such as haemodialysis, cardiac surgery and for the treatment of diabetes. Additional fields of applications are bio- and environmental technology. Although chemical sensors react to the chemical activity, measurement results are exclusively converted to amount of substance content. The applied fixed, empirical factors for the conversion of chemical activities to amount of substance content may result in false negative or false positive results. The electro-analytical chemistry can add here an important contribution to the traceability of chemical activity measurements. Gravimetrically prepared solutions with calculated activities according to an internationally agreed semi-empirical model will allow building up an activity basis used to determine the chemical activity of unknown solutions. A newly built up activity scale for electrolyte ions has to be in accordance with the established convention of the activity scale of hydrogen ions (pH).

 

The two primary standards at METAS for the determination of the chemical activity of electrolyte ions (potentiometry with ion-selective electrodes) and further biological relevant substance (amperometry with biosensors) will be further developed to the stage where internationaly accepted services for the measurement of chemical activity can be offered. The project also includes the necessary work to establish the standard and calibration procedure for the activity measurements of glucose as the most important representative of neutral substances and fuel for all cells of higher developed organisms.

This project is partly funded by the European Community’s Seventh Framework Programme, ERA-NET Plus under Grant Agreement No 217257.

Project aims (German)

International anerkannte Normale und die darauf basierenden Dienstleitungen sind entwickelt für:

• die Bestimmung der chemischen Aktivität (Gehalt) der Elektrolytionen Na⁺, K⁺, Ca²⁺, Mg²⁺ und Cl^- im physiologischen Bereich;
• die Bestimmung der chemischen Aktivität (Gehalt) von Glukose.

Project aims (English)

Internationally recognised standards and calibration services are developed for:

• the determination of the chemical activity (amount of substance content) of the electrolyte ions Na+, K+, Ca2+, Mg2+ und Cl- in the physiological range;
• the determination of the chemical activity (amount of substance content) of glucose.

Abstract (English)

In a first stage the partners selected and chemically characterised four high purity materials carefully. The now metrologically sufficiently well known materials were subsequently used to gravimetrically prepare mixtures of known composition. The unknown activities, that is the free biological active part of the ions in these complex calibration mixtures were calculated based on well established and accepted scientific model calculations (Pitzer’s semi-emprirical approach). Measurement systems - that are instruments and calibration standards, as well as measurement methods - that are defined procedures for signal acquisitions and software for data evaluations, were developed in order to quantify the chemical ion activity in samples. The work also included the metrologically sound evaluation of the measurement uncertainty of the values for the estimated measurands. As each of the ions in question has its own characteristics the sensors systems used to selectively register the ion signals had to be optimised for each type of ion independently. An international intercomparison on the present level of comparability in ion activity measurements among NMI’s and expert laboratories was organised and completed (cf. EURAMET project no. 1165).

An amperometric flow measurement system based on a GOD-biosensors for glucose activity measurements was developed and tested successfully for water based buffer  systems. In real world samples the matrix interferences from proteins still remain a metrologically insufficiently solved problem, that is indicated by drifting signals. Well defined solutions with physiological electrolyte composition that are buffered and have known SI-traceable glucose values were developed and are available for calibration purposes.

Transfer and application (English)

Correct measurements in clinical chemistry are of fundamental importance in medicine as a whole and for every individual patient. Traceable measurements are legally required in Europe and are obligatory in many countries for this reason. The methods developed in this project shall be used as reference points for traceability used by clinical test laboratories in Europe for the benefit of the patients and cost reduction in health care.

1. METAS is now able to offer SI-traceable standards and calibrations for the ion activity and the concentration (or content) of the main serum electrolyte ions Na+, K+, Mg2+, Ca2+ und Cl- in the physiological range.
2. METAS offers SI-traceable standards and calibration of instruments for the concentration (or content) of glucose in serum material as a service.

Currently, internationally accepted standards based on primary methods linking to the clinically active forms of elements are not available. The method developed in the project provide such tools. This comprises reference methods species like doubly charged calcium ions. Such health status markers are essential in diagnosis of critical diseases like e.g. heart attack and depression. 

The results can be used to calibrate and compare new and additional measurement systems in the medical diagnostic field. Such new tools will help to improve medical decisions in coherence with the requirements of an evidence based medicine.

Engagement with external bodies and stakeholders
A number of decision makers such as the joint committee for traceability in laboratory medicine (JCTLM), the international federation of clinical chemists (IFCC), the medical diagnostic industry as well as relevant national associations have been informed about the higher order reference standards and procedures developed within the workpackage.

The expected impact in the medical diagnostic field is promising, but cannot yet be quantified. If the IFCC promotes the activity scale similar to pH the medical diagnoses of the electrolyte status will be much better defined.
METAS has applied at JCTLM for the acceptance of new reference measurement procedures. A number of stakeholders from diagnostic instrument manufacturers as well as national associations involved in medical diagnostic have been contacted and the new opportunities were offered and explained. A one day symposium for the regulators and national decision makers in the health field was organised at METAS on 2011-06-06 in order to discuss the current status and future opportunities in the clinical analytical field of Switzerland.

PTB one of our project partners is in contact with MHH (Medizinische Hochschule Hannover) a German leading health clinic for preliminary test measurements for activity of doubly charged ions in comparison with atomic emission spectrometric measurements. A combined flow through measurement system consisting of ISE’s and a pH electrode may show its suitability in a future reference measurement procedure for blood serum.

The two Swiss proficiency testing centres (MQ Zürich and CSCQ Geneva working according to the rules imposed by QUALAB) received reference values for electrolyte concentration values for one such comparison in 2011. Some severe deviations became visible as the consensus values defined did not agree with the SI-traceable reference values using the Rilibäk tolerance limits.

For these analytes traceability was established as required by the IVDD 98/79/EG which is part of the Swiss medical prodcuts ordinance MepV (MepV Art. 4b) and higher order reference standards as well as procedures for their measurement are available for medical diagnostic purposes.

The knowledge gained for glucose measurement was used to calibrate reference measurement instruments for two industrial POCT-instrument manufacturer from abroad.

Traceability of concentration and activity values for certain analytes in serum can now be offered to interested customers from the clinical field as a service.

Publications / Results (English)

Information on results were published in well recognised peer reviewed  journals (Electroanalysis, Chimia) as well as in house organs from PTB and METAS. Several oral presentations were given and posters were shown on occasion of international conferences (Chemical Sensors Forum 2008, CIA 2009, 25th PSI Electrochemistry Symposium 2009, ESEAC 2010 13th International Conference on Electroanalysis,  ANAKON 2011, Matrafüred Conference 2008 and 2011). The outcome of the international intercomparison that was organised as a practical test for the measurement of the ion activity measurement in complex electrolytes will soon be published.  A preliminary report on the results from all participants has been prepared.

S. Wunderli, H. Andres,
Metrological Aspects of Activity Measurements in Mixed Electrolytes by Ion-Selective Electrodes,
Electroanalysis, (2008), 20(3), 324-330.

S. Wunderli, H. Andres,
Metrological Aspects of Glucose Measurements by Biosensors,
Electroanalysis, (2009), 21(17), 1984-1991.

D.Berdat, H.Andres, S.Wunderli
Development of Suitable ISE Measurement Procedures for SI-traceable Chemical Activity Determination,
Chimia, (2009), 63(10), 670-67.

An additional final publication is in preparation together with our project partners.