Electroporation Q - (Jul/18/2013 )

Hi,
Its quiet technical question.
If I run Biorad Micropulser Electroporator without cuvette it shows 1.8kV, in 6.4mSec.
I = V / R

For air
I = 1.8 * 10^6/3.3*10^16 = 0.54 * 10^-10 Amp


For Iron
I = 1.8* 10^6/ 1.0* 10^10-7 = 1.8 * 10^13
Amp
Does it means mentioned current is passing in as per medium?

with medium current will pass in 5.6 mSec but with air 6.4mSec why is there so small difference in time of current passing.


Thanks.

I don't know how good your EE background is, but here goes. The circuit in question is an RC circuit, formed by a charged capacitor (the value is chosen on the front panel). This capacitor is charged with a DC supply at the requested voltage. The capacitor is then switched (mechanically) across a resistor (also set by a front panel switch, or permanently chosen in some cases). The cuvette is in parallel to the resistor. If the cuvette is empty, the RC time constant is the product of the resistance and capacitance chosen. As the cuvette material is lower resistance, it parallels the resistance of the resistor, lowering the effective resistance. The time constant goes down. So, if you have an open circuit (empty cuvette) you have one time constant. If you have a pure water cuvette, practically the same thing happens. If you have a salty water cuvette, then it has resistance low relative the chosen resistor, and you get a significant change in the time constant.

So, nothing much changes until you get a cuvette conductance sufficiently large relative to the resistor conductance.

Thanks for pretty classic answer.

I see you are talking about http://hughestech.com/rc_calculator/.

My question remains. As in case of absence of cuvette resistance is high( But its 6.4msec) so time should be quiet high as compare to empty cuvette/ cuvette with bacterial sample(5.6mSec).
Why time difference so less (6.4msec- 5.6mSec= 0.8mSec) as air resistance is much higher than cuvette material? Does air ionize or something allowing resistance of air to lower?

I think, if you look at the set up of a cuvette, there isn't a complete circuit unless the cuvette is filled with a conductive medium (e.g. electroporation buffer), if you use an empty cuvette, this is essentially equivalent to using no cuvette, so the time constants will be similar.

Yes empty cuvette is like no cuvette. Saw reading with no cuvette, not empty cuvette ( too expensive too try). Used slash in my previous post empty as I thought from post#2 that empty cuvette carries electricity. I observed cuvette, Electrodes are not connected.