SFM-3 BioLogic Stopped-Flow Module

The BioLogic stopped-flow module (SFM), consists of a mechanical subsystem and a motor power supply (MPS). The SFM-3 mechanical sub-system consists of three machined syringes, one valve block with (3) 3-way valves, with the possibility to include one or two mixers and one ageing loop. All SFM syringes, valves, delay lines and cuvettes are enclosed in a water jacket to allow temperature regulation of the reactants containers. The syringe plungers of the SFM are driven by stepping motors via ball screws.

The mechanical part of the SFM module is carefully constructed. The parts in contact with the sample and the buffers are all machined out of materials selected for their inert characteristics: stainless steel, Teflon, Kel-F, VITON, EPDM, PEEK and quartz.

Millisecond dead time can be achieved with the SFM due to the combined effects of high performance control of the stepping motors, and low dead volumes.

Ageing lines of various volumes can be used in the SFM. The ageing line(s) of the instrument can be replaced and secured in a few minutes.

The syringes of the SFM are driven by independent stepping-motors. The stepping-motors are of hybrid technology with 200 steps per revolution and 4 phases, each phase being powered by a constant current supply (2.9 A per phase). The power supply of each motor is microprocessor controlled. A complex impulse sequence enables micro-positioning of the motor's rotor with an accuracy equivalent to 1/32 of the mechanical step. This gives an effective number of steps of 6400 per revolution, or a volume quantification of 0.14 µl per micro-step (µ-step), when standard (20 ml) syringes are used.

With the damping produced by the rotor inertia, this results in an almost continuous, linear movement of the syringe even at very low flow rates. The motors can be activated manually or automatically. The manual mode is mainly used to refill or wash the syringes; the syringes can be driven independently and their speed adjusted using the microcomputer with a very simple menu. The automatic mode is used for actual experiments.

The motor impulses are counted in the positive direction (refilling), or negative direction (emptying), so that the contents of each syringe can be continuously displayed. Zero volume corresponds to the uppermost position of the syringe and referencing the zero volume position can be done using the keyboard of the microcomputer.

The movements of the syringes are completely controlled by the microprocessor, which eliminates the need for a stop syringe. Thus, the stop artifact present in most conventional stopped-flow systems is absent in the SFM. The observation system can be synchronized with the syringe "start" or "stop" by using the trigger pulses available on the front panel of the MPS unit. The independent control of each syringe allows a high versatility of the injection sequence. It is possible to make an injection of one syringe only, unequal filling of the syringes, variable ageing times, variable concentration , variable mixing ratios and other complicated actions with only a few keystrokes.