Calibration of the SIET

Model of a Diffusional Point Source and the Non-invasive Scanning Ion-selective Electrode Technique, SIET

Predicted and observed µVolt difference curves for diffusion of protons (left) and potassium (right) from a point source:

Predictive equation for dV, the µV difference at a point in space, r µ from a point source:

                                            eff = efficiency of the measure
           S K dr                             r = distance to point source
  dV = eff ------- / (Cb + K/r) ,   where:   dr = oscillation distance
            z r2                              K = slope of [ion] curve
                                             Cb = background [ion]
                                              S = Nernst coeficient
                                              z = unit charge on the ion

This calibration curve allows one to estimate the efficiency, eff, of the electrode which can be used to turn any µV difference measured with a similar electrode into an observed flux of that ion in the space arround a cell or tissue.

Ion flux, J, emanating from a distant (µm) point source:
Observed and predicted values for 2 LIXs proton (left) and potassium (right).

Predictive equation for ionic flux, J_o:

                              D = diffusion coeficient for the ion (cm-2 sec-1)
  Jo  =  - D dC/dr ,  where  dC = concentration differential
                             dr = oscillation differential

Ion	Do	i	Nernst slope	LIX	t90	Hz	eff%
K+	19.6	+1	58	K IB	<1s.	0.3	70%
H+	93.7	+1	58	H IIA	~0.6s	0.3	80%
Ca++	7.9	+2	29	Ca IIA	<5s	0.3	50%
Mg++	7.1	+2	29	Mg IV	<30s	0.25	30%
Cl-	-20.3	-1	-58

D is expressed as 10⁶D/cm² sec^-1.
Nernst Slope, S, is expressed in mV.

If you have questions about calibrating the various vibrating probes or the University of Massachusetts Vibrating Probe Facility, email its PI, Joe Kunkel