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  • Chemistry
  • Health Assessment and Safety

General Information

Matrix:Serum / Plasma
Application:Insurance Risk Assessment, Wellness
Turnaround Time:Daily
Analytical - Method:An Ion-Selective Electrode (ISE) makes use of the unique properties of certain membrane materials to develop an electrical potential (electromotive force, EMF) for the measurements of ions in solution. The electrode has a selective membrane in contact with both the test solution and an internal filling solution. The internal filling solution contains the test ion at a fixed concentration. Because of the particular nature of the membrane, the test ions will closely associate with the membrane on each side. The membrane EMF is determined by difference in concentration of the test ion in the test solution and the internal filling solution. The EMF develops according to the Nernst equation for a specific ion in solution: (1) E = E0 + RT / nF x In (f x Ct) / (f x Ci) Where: E = electrode EMF E0 = standard EMF R = constant T = temperature n = charge of the ion F = Faraday’s constant In = natural logarithm (base e) f = activity coefficient Ct = ion concentration in test solution Ci = ion concentration in internal filling solution For sodium, potassium and chloride, which all carry a single charge, R, T, n, and F are combined into a single value representing the slope (S). For determination on a cobas c 111 ISE unit where the sample is diluted 1:6, the ionic strength and therefore the activity coefficients are essentially constant. The concentration of the test ion in the internal filling solution is also constant. These constants may be combined into the E0 term. The value of E0 is also specific for the type of reference electrode used. Equation (1) can hence be rewritten to reflect these conditions: (2) E = EI0 + S x In (Ct) The complete measurement system for a particular ion includes the ISE, a reference electrode and electronic circuits to measure and process the EMF to give the test ion concentration. The sodium and potassium electrodes are based on neutral carriers and the chloride electrode is based on an ion exchanger.
Reportable - Test Results Type:Quantitative
Units - Conventional:mmol/L

Specimen Information

Minimum Volume:300 µL
Preferred Volume:500 µL
Rejection Criteria:Improper labeling, improper sample handling, and wrong sample type.
Collection Instructions:See "Blood Collection"
Collection Patient Preparation:NA
Container:Serum or plasma, free from hemolysis. The only acceptable anticoagulant is lithium heparin. For sodium and chloride determinations serum is the specimen of choice.