About PDES
Pressure ejection is a convenient method for applying both ionic and non-ionic solutions from micropipettes. First, it can apply to almost all solutions. Second, the amount of the ejected solution can be monitored by viewing the tip of the micropipette under a microscope. npi PDES units are designed for pressure ejection of drugs in physiological and pharmacological studies. PDES systems can are equipped with pressure outputs ( Pmax = 4 bar (58 psi) or 2 bar (29 psi)) for drug application with micropipettes. Analog or digital timers and a remote control unit facilitate the use of these instruments. They are available with one or two application channels. One channel instruments can also be equipped with a retain channel. All PDES units can be operated with internal valves as well as with external valves to reduce the minimal application time to less than one millisecond.
Each channel consists of a precision pressure regulator, pressure display, electronically controlled valves, control electronics, and a regulated power supply. Ejection of drugs can be activated manually or through a TTL input. The operational status is indicated by a red / green LED. Each system is equipped with a monitor BNC connector that reflects the opening time of the pressure valve. In digital systems the pressure is monitored at a BNC connector as well (1 V / bar or 0.1 V / psi).
Features
- High pressure output for fine tipped micropipettes
- Low-range pressure output for large tipped pipettes
- Analog or digital timers
- Anaolg or digital manometers
- Remote control available
- One or two channels versions (one channel versions can be upgraded)
- External valves for fast applications available (< 1 ms)
- System with holding pressure available
Also available as module for the EPMS-07 system.
Ordering
The various configurations of PDES systems are reflected in the part number
PDES-0X-(U)Y(E)-M-LA-Z
where:
X = number of channels (1 or 2)
U = upgrade
Y = type of timer (T=analog; D=digital)
E = configuration with external valve(s), blank = configuration with internal valve(s)
M = module
LA = configuration with digital display(s), blank = configuration with analog display(s)
Z = maximum pressure (2 bar [29 psi] or 4 bar [58 psi])
External valve options:
- PDES-0X-BOX (for “slow” valves [ca. 10 ms])
where:
X = number of channels (1 or 2)
- PDES-EHM (for “fast” microJECT valves [<1 ms])
for one channel
Choose your model
Timer – digital or analog:
The analog timer is suitable for rough timing adjustments, in the standard configuration it goes down to 1 ms.
The digital timer can be set to specific values very easily and repeatedly. The minimum time is 100 µs, but there is no valve which can switch that fast. You will need this last digit to distinguish between e.g. 3.6 or 3.8 ms.
Independent of which timer is used, all systems can be directly TTL triggered, e.g. from a data acquisition system. So if you use the intstrument in this mode, you can go for the analog timer and save money.
Valves – internal or external
With TTL input, the switching time of the valve limits pulse lenght and the time between pulses. The internal and standard external valves have switching times of ~10 ms (i.e. it takes ~10 ms for the valve to open completely and ~10 ms to close completely).
But valve switching times are only one part of the story. The length and diameter of the tubing from the valve to the pipette (i.e. the volume to be set under pressure) largely define the rise time of a pressure pulse at the pipette tip. Therefore the external valve speeds up the system already, although using the same valve (>100 ms with internal valve, >20 ms with external valve).
With the fast external valve, the µJECT, this volume is further decreased, since the valve output and the pipette input are in close vicinity (a few mm). With this pulse times of ~1 ms are achievable.
For very local applications (µm range) a fast application is necessary. If you want to do bulk loading, a slower system might be fine for you.
Manometer – digital or analog
Choosing between the analog and digital manometer is largely a personal preference. While the digital manometer is slightly more expensive than the analog manometer, it offers an additional BNC output where the actual pressure can be monitored e.g. by a data acquisition system.
Special - PDES-DXH
In the PDES-DXH the second channel is replaced by a HOLDING channel. This allows application of a small holding pressure in between the application pulses. The holding pressure counter balances the capilarry forces which would otherwise push bath solution from into the pipette.
There are rare cases where a vacuum must be applied in order to prevent application liquid from exiting the pipette. A very convenient way to do so is the use of ALA’s 2PK+ presssure/vacuum controller.
