Computer-controlled pump systems, liquid

A versatile Laser-SNMS instrument consists of a versatile microfocus ion gun, a sputtering ion gun, a liquid metal ion gun, a pulsed flood electron gun, a resonant laser system consisting of a pulsed Nd YAG laser pumping two dye lasers, a non-resonant laser system consisting of a high-power excimer or Nd YAG laser, a computer-controlled high-resolution sample manipulator on which samples can be cooled or heated, a video and electron imaging system, a vacuum lock for sample introduction, and a TOF mass spectrometer. 

This paper describes work on equipment and instrumentation aimed at a computer-assisted lab-scale resin prep, facility. The approach has been to focus on hardware modules which could be developed and used incrementally on route to system integration. Thus, a primary split of process parameters was made into heat transfer and temperature control, and mass transfer and agitation. In the first of these the paper reports work on a range of temperature measurement, indicators and control units. On the mass transfer side most attention has been on liquid delivery systems with a little work on stirrer drives. Following a general analysis of different pump types the paper describes a programmable micro-computer multi-pump unit and gives results of its use. 

In addition to the basic control loops, all processes have instrumentation that (1) sounds alarms to alert the operator to any abnormal or unsafe condition, and (2) shuts down the process if unsafe conditions are detected or equipment fails. For example, if a compressor motor overloads and the electrical control system on the motor shuts down the motor, the rest of the process will usually have to be shut down immediately. This type of instrumentation is called an interlock. It either shuts a control valve completely or drives the control valve wide open. Other examples of conditions that can interlock a process down include failure of a feed or reflux pump, detection of high pressure or temperature in a vessel, and indication of high or low liquid level in a tank or column base. Interlocks are usually achieved by pressure, mechanical, or electrical switches. They can be included in the computer software in a computer control system, but they are usually hard-wired for reliability and redundancy. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

Figure 16 pictures a high-pressure autoclave set up as a CSTR. In this arrangement the introduction of the substrate is done using an HPLC pump. The liquid level in the reactor is kept constant using a liquid level controller (A) which is monitored by the computer. When the liquid input reaches a set level an exit valve (B) is opened to drain some of the reaction liquid to maintain the liquid level in the reactor. With such a system there is no need for a second pump to remove the product stream. 

Current Development. Following success of the prototype IPU a second more comprehensive facility was commissioned. This is capable of up to four pumps of mixed peristalitic or diaphragm types, each linked to specific feed vessels on individual balances. The whole is interfaced to an IBM AT computer (see Figure 7) which in addition to Intelligent liquid additions, has the capacity to absorb modules from the work on temperature control and stirring in a full multi-tasking computer-assisted system, as mentioned above. 

A test system, controlled by personal computer (PC), was developed to evaluate the performance of the sensors. A schematic of this system is shown in Figure 3. The signals from the sensors were amplified by a multi-channel electrometer and acquired by a 16 bit analog to digital data acquisition board at a resolution of 0.0145 mV/bit. The test fixture provided the electrical and fluid interface to the sensor substrate. It contained channels which directed the sample, reference and calibrator solutions over the sensors. These channels combined down stream of the sensors to form the liquid junction as shown in Figure 1. Contact probes were used to make electrical connection to the substrate. Fluids were drawn through the test fixture by a peristaltic pump driven by a stepper motor and flow of the different fluids was controlled by the pinch valves. 

Descriptive model and its division into parts. The first steps in the model construction are related to Fig. 3.7. The pump PA assures simultaneously the suspension transport and the necessary transmembrane pressure. The excessive accumulation of the solid in the retentate is controlled by its permanent removal as a concentrated suspension from the reservoir RZ. The clear liquid (permeate) flow rate and the solid concentration in the exit suspension are permanently measured and these values are transferred to the control and command computer CE. The instantaneous values of the operation pressure and input rate of fresh suspension are established by the computer (this works with software based on the mathematical model of the process) and corrected with the command execution system CSE. 

The complete system can be controlled by a computer with special software designed for this type of analysis and is available from PS Analytical (UK) as a Touchstone Package (PSA 30.0). The carrier liquid and sample plug is transported using a multiroller peristaltic pump at a rate predetermined to suit the analysis of interest. Silicone tubing of 0.8 to 1.0 mm internal diameter is normally used and is found to be best for most organic solvents. A sample loop used for injection is usually in the volume range of 150 to 500 pi with an internal diameter 0.8-1.0 mm and is made of solvent resistant plastic. The best volume of loop is predetermined for a particular sample and analyte concentration. 

SEC was performed according to the method of Chin et al. (1994). A Shodex KW802.5 SEC column (Waters Corp., Milford, MA., USA) was used and a Waters liquid chromatography system consisting of the following components was used for the analysis Waters 501 high pressure pump. Waters 717 autosampler, InterAction column temperature control oven, Waters 484 UV/VIS detector, and Waters Millenium 2.0 computer software package. 

The HPLC equipment is a Perkin-Elmer Nelson Model 1022 Plus Chromatograph, connected to a Perkin-Ehner series 200 LC Pump, a LC295 UV/VIS detector, a 7125 BIO injector with a 20-pL loop, and a Canberra Packard Elow Scintillation Analyzer 500 TR Series, with a 0.5-mL flow cell. The system is interfaced with a Compaq Prolinea 5100 computer, using a Canberra Packard ELO-ONE software for system control and data processing. The RP-HPLC columns are Pecosphere Ci8, 5 jam, 30 X 3 mm i.d. (SGE Inc.), with a 5- im C18 guard column (SGE Inc.). Mobile phase is a mixture of methanol water acetic acid (85 15 0.1), and the elution of metabolites is done at a constant flow rate of 0.8 mL/min. Absorbance values are measured at 204 nm. Liquid scintillation cocktail (Ultima Ho M, Canberra Packard) is mixed with the eluent at a 1 2 (eluent(LSC) ratio. Retention times of AEA and arachodonic acid (AA) are 3.2 and 4.5 min, respectively. The concentration of AA is calculated from radioactivity of peak area, and FAAH specific activity is expressed as pmol AA released/min/mg protein. 

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