croiontophoresis Current Programmer
WORLD PRECISION INSTRUMENTS
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Table of Contents
1.0
Introduction ...................................................................................................1
2.0
Specifications ................................................................................................1
3.0
Controls ........................................................................................................2
4.0
Operation
4.1
Preliminary Instrument Check .....................................................3
4.2
Single Channel ............................................................................3
4.3
Dual Channel, Hold-Eject ............................................................4
4.4
Auto Operation ............................................................................4
4.5
Compliance Alarms .....................................................................5
4.6
Battery Replacement ...................................................................5
5.0
Application Note and References .................................................................6
References ..............................................................................................................9
Warranty ................................................................................................................12
Copyright © 2000 by World Precision Instruments, Inc. All rights reserved. No part of this publication may
be reproduced or translated into any language, in any form, without prior written permission of World
Precision Instruments, Inc. Model 260 Microiontophoresis Current Programmer
WORLD PRECISION INSTRUMENTS
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1.0 Introduction
The Model 260 Microiontophoresis Current Programmer is a floating, battery-
operated instrument designed for the electroiontophoresis of dyes, drugs and
charged substances from micropipettes. Two identical battery operated current
generators are available. In ordinary use, the two current generators are operated
in parallel providing two distinct currents; one for preventing substances in the
micropipette from outward diffusion (the retain or hold current) and the second for
the active ejection of charged material. For pipettes with submicron tips, a hold
current may not be necessary if there is little outward diffusion of pipette material.
Model 260 is powered by four standard 9 volt transistor batteries. Their life
expectancy can be considerably improved if the user remembers to turn off the
power switch when the instrument is not in use.
2.0 Specifications (each channel)
Current Range .....................................................0 to 100 nanoamperes
0 to 1000 nanoamperes
Maximum Output Voltage (compliance) ...............100 volts
Operating Modes .................................................Manual or Auto (external control)
Auto Input (external control
for current on/off) ....................................+5 volts
Auto Input Resistance ..........................................1.5 KOhms, approx.
Auto Input Delay ..................................................< 100 microseconds
Output Polarity NORMAL .....................................red terminal, positive
Current Meter Error ..............................................+/- 2% max.
Power ...................................................................Two 9 volt alkaline cells Model 260 Microiontophoresis Current Programmer
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3.0 Controls (each channel)
POWER ON/OFF ....................................Instrument power switch. To maximize
battery life, turn power OFF when the
channel is not in use.
CURRENT LEVEL .................................This control varies the current amplitude
as indicated on the ammeter. To prevent
accidental current flow via \he output
terminals place the OUTPUT switch in the
PRESET position while adjusting current
amplitude.
CURRENT RANGE ...............................Selects either 100 or 1000 nanoampere
current range
MODE SELECT ......................................MANUAL operation allows the user to
apply a DC current when the OUTPUT
switch is changed from PRESET to
ENABLE. AUTO operation requires the
user to apply a +5 volt command potential
to initiate the flow of current.
OUTPUT POLARITY NORMAL .............indicates that the red output connector is
positive with respect to the black
connector. INVERT reverses connector
polarity.
AUTO INPUT ..........................................If the MODE SELECT switch is in the
AUTO position the AUTO INPUT
connector controls current turn-on. Five
volts positive with respect to the outer
connector shell will maintain current for as
long as this voltage is applied. The
CURRENT LEVEL control continues to
dictate the actual current amplitude.
OUTPUT .................................................In the PRESET position, the red and black
current output terminals are disconnected
from the current generating circuit.
ENABLE connects the output terminals to
the current source. If the OUTPUT switch
is in the PRESET mode current cannot
flow out of the instrument in either
MANUAL or AUTO operating modes. Model 260 Microiontophoresis Current Programmer
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CHAS GND .............................................This green binding post is connected to the
chassis or metallic enclosure of the
instrument. It should normally be
connected by the user to the ground point
of his recording system.

4.0 Operation
4.1 Preliminary Instrument Check
Switch the OUTPUT switch to PRESET on either channel. This disconnects the red
and black output terminals and internally short circuits the output of the current
generator. Switch the MODE SWITCH to MANUAL. Turn on the POWER switch
located just below the current indicating ammeter. Notice that as the CURRENT
LEVEL control is rotated, the ammeter reading will change accordingly. Switch
current ranges and note the similar ammeter behavior. Note that one may easily
reach and exceed the ammeters maximum reading. If one cannot reach and
exceed full scale on the ammeter, the transistor batteries may need
replacement. If the OUTPUT switch is changed from PRESET to ENABLE at any
current setting an audible alarm will sound and a red lamp on the front panel will
light to indicate that the output current pathway is an open circuit.(At very low
nanoampere current settings, the alarm may take several seconds to be activated.)
Check the performance of both channels in the manner indicated above. Ground
the CHAS GND green binding post to assure low noise. The instrument is now
ready to use.
4.2 Single Channel Operation
Model 260 contains two completely independent floating,battery operated current
generators which may be operated independently or in parallel connection. As an
independent current generator the user need only connect his external electrode
pair to the red and black output terminals of channel 1 (HOLD) or 2 (EJECT). While
making these connections and any preliminary control adjustments, the
OUTPUT switch should be in the PRESET position. This will prevent any
accidental current flow. Proceed to set the CURRENT RANGE and CURRENT
LEVEL controls. For currents below 100 nanoamperes the 100 nanoampere range
is recommended because one may adjust these low current values with better
resolution in the lower current range.
Adjust he CURRENT LEVEL control until the required DC current value is observed
on the channel ammeter. Select the OUTPUT POLARITY desired. NORMAL yields Model 260 Microiontophoresis Current Programmer
WORLD PRECISION INSTRUMENTS
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a positive potential at the red output terminal. Switching the OUTPUT switch from
PRESET to ENABLE releases the required current from the output terminals. To
halt current flow, return to the PRESET mode.

4.3 Two Channel Operation, Hold-Eject
As will be described in section 5.0 the electrophoretic release of charged
substances from micropipettes often requires the use of a second current to counter
the outward diffusion of material from the delivery pipette. This current has been
referred to in the literature as backing, holding or retaining current. One causes a
small current to flow in a direction that will offset the spontaneous leakage of the
active agent from the pipette until it is required.
Connect a shorting wire or jumper to tie the red OUTPUT terminals of the HOLD
channel and the EJECT channel together. Connect an identical jumper wire
between the black OUTPUT terminals. This effectively connects the two current
generating channels in parallel. Current does not flow from one channel into the
other but will sum algebraically in the common electrode pathway if both channels
are operating simultaneously. Place both channels in the PRESET mode to prevent
accidental current flow during set up. Set the polarity and current amplitude on the
HOLD channel to retain the active agent in the electrode. Now set the polarity and
amplitude of the current in the EJECT channel. Two operating procedures are
possible:
1. One may leave the hold current on at all times and effect ejection by
superimposing the larger eject current by operating the PRESET/ENABLE switch
on the EJECT channel. Thus the ejection current will swamp the smaller hold
current. One must then algebraically add the hold current to the eject current to
compute the actual ejection current. For example, if the hold\ current had been -5
nanoamperes and the eject current were +50 nanoamperes, the effective ejection
current is +45 nanoamperes. This method has the advantage that one need only
operate a single PRESET/ENABLE switch o