Bio-Rad MicroPulser™ Electroporator - Manual (Page 27)

Electrical Problem Possible cause and solution
Verify the display LED shows a reading
between “5.50” and “6.50”.
If problems persists, contact Bio-Rad.
1. Instrument shows “Arc” on Arcing in the cuvette is the result either of an
display LED actual arc occurring or of medium that is too
conductive. An actual arc will occur usually only
at high voltage (>1500V). If media is too
conductive, the display LED may show “Arc”
even though an actual arc has not occurred. The
limit of conductivity depends on the voltage,
electrode gap, and sample volume, but under
standard conditions, solutions of 10 meq or higher
(< 600 ohms resistance) will certainly indicate
“Arc”.
To determine whether an actual arc has occurred
or the media is too conductive, look at the cuvette
while pulsing the sample again. If a small spark
occurs across the electrodes, an arc has
occurred. If no spark is observed, lower the voltage
and re-pulse the sample. Continue lowering and
re-pulsing the sample until a pulse occurs.
Check the time constant; if the time constant is
low (< 3 msec), the sample is too conductive.
There are several causes of excessive conductivity:
1. Washing and resuspending cells in a buffer too
high in ionic strength.
2. Insufficient washing of the cells—salts from the
growth medium are not completely removed;
the cells should be washed at least three to
four times with non-conductive solution.
3. Lysed cells in the preparation—cell contents
contribute to conductivity.
4. DNA solution too high in salt; for example, CsCl
carried over from plasmid preparation, or
residual salts from ethanol precipitation or liga-
tion.
Electroporation with cuvettes above 0 °C: reducing
sample temperature increases sample resistance.
2. Wrong time constant. Samples electroporated in the Micropulser
should have a time constant close to 5 msec. If
the time constant is much shorter than the
expected value (
e.g., 3 msec instead of 5 msec),
the sample is too conductive. The
probable reasons for this are listed above under
“arcing”. Correct the problem of high conductivity
by additional washing of the cells, or by removal
of salts from the DNA preparation.
3. Sample does not “twitch”. This may mean that the pulse is not reaching the
sample. Check the connections between the
MicroPulser and sample chamber. Check to see
that the contacts in the base of the sample
chamber are not broken.
4. Instrument displays “no” on The manual setting is used and the voltage is set
front panel. to 0.00. Use the “Raise” button to select a voltage
between 0.02 and 3.00 kV.
5. Instrument displays “err” on Turn instrument off, then on again.
front panel. If problem persists, contact Bio-Rad.
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