Liquid Pumping Methods

The liquid pumping in the microfluidic chip is mostly achieved by using electro-osmotic flow (EOF) [324]. Other liquid pumping methods have also been employed for microfluidic flow. Flow has been employed for fraction collection and generation of concentration gradient. Laminar flow in the microfluidic channel allows liquid-liquid extraction and microfabrication to occur within the channels. Moreover, valving and mixing are needed in order to achieve a better flow control. All these microfluidic flow operations are further described in subsequent sections. 

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Bushings in vertical pumps are normally lubricated by the liquid pumped. Alternative methods of lubrication shall be proposed if the pumped liquid is not suitable. 

High-pressure processes require suitable liquid pumps, gas compressors, agitators, extruders and other machinery components. High-pressure production methods are generally expensive to develop, to design, to build, to operate, and to maintain. Their application will only be successful if clear advantages can be achieved with respect to the product quality and the costs in general. 

Schubert et al. [72] developed and validated a liquid chromatographic method for the determination of omeprazole in powder for injection and in pellets. The analyses were performed at room temperature on a reversed-phase Ci8 column of 250 mm x 4.6 mm (5 /im). The mobile phase, composed of methanol-water (90 10) was pumped at a constant flow-rate of 1.5 ml/min. Detection was performed on a UV detector at 301 nm. The method was validated in terms of linearity, precision, accuracy, and ruggedness. 

The thermal effect is exploited to produce liquid pumping. For instance, a thermocapillary pump was constructed. The pumping method is based on surface-tension change due to local heating created by heaters fabricated on a Si-Pyrex chip. This method was used to pump reagents to perform successive PCR, gel electrophoresis, and detection [392,393],... 

A similar PDMS valve control layer was used to achieve rotary liquid pumping for PCR [357]. In another report, a similar valving method was used to deliver cells and to introduce reagents for cell reactions. Solutions were pumped at 5-60 Hz to achieve a linear flow rate of 300-1000 pm/s [368]. 

Panderi and Parissi-Poulou developed a microbore liquid chromatographic method for the simultaneous determination of benazepril hydrochloride and hydrochlorothiazide in pharmaceutical dosage forms [30]. The use of a BDS C-18 microbore analytical column was found to result in substantial reduction in solvent consumption and in increased sensitivity. The mobile phase consisted of a mixture of 25 mM sodium dihydrogen phosphate buffer (pH 4.8) and acetonitrile (11 9 v/v), pumped at a flow rate of 0.4 mL/min. Detection was effected at 250 nm using an ultraviolet absorbance detector. The intra- and inter-day relative standard deviation values were less than 1.25% (n = 5), while the relative percentage error was less than 0.9% (n = 5). The detection limits obtained according to the IUPAC definition were 0.88 and 0.58 pg/mL for benazepril hydrochloride and hydrochlorothiazide, respectively. The method was applied to the quality control of commercial tablets and content uniformity test, and proved to be suitable for rapid and reliable analysis. 

Flash evaporation is another liquid vaporisation method as shown in Figure 3.6. By using a micropump (e.g. syringe pump, peristaltic pump), the amount of liquid can be accurately metered. When the liquid precursor is injected into the heat exchanger, it is immediately vaporised into gas, which in turn is introduced into the... 

A characteristic feature of ESI is that the sample can be pumped into the mass analyser continuously. MALDI, on the other hand, is a pulsed method which requires a dry sample. Thus, ESI-MS can be coupled directly to liquid separation methods such as RP-HPLC (section 2.3.1) and CE (section 3.3). As the sample emerges from the separation column it is directly pumped into the electrospray chamber. As outlined earlier, MALDI-TOE is capable of separating... 

The active site responsible for the aerobic oxidation of alcohols over Pd/AljO, catalysts has long been debated [96-lOOj. Many reports claim that the active site for this catalyst material is the metallic palladium based on electrochemical studies of these catalysts [100, 101]. On the contrary, there are reports that claim that palladium oxide is the active site for the oxidation reaction and the metalhc palladium has a lesser catalytic activity [96,97). In this section, we present examples on how in situ XAS combined with other analytical techniques such as ATR-IR, DRIFTS, and mass spectroscopic methods have been used to study the nature of the actual active site for the supported palladium catalysts for the selective aerobic oxidation of benzylic alcohols. Initially, we present examples that claim that palladium in its metallic state is the active site for this selective aerobic oxidation, followed by some recent examples where researchers have reported that ojddic palladium is the active site for this reaction. Examples where in situ spectroscopic methods have been utilized to arrive at the conclusion are presented here. For this purpose, a spectroscopic reaction cell, acting as a continuous flow reactor, has been equipped with X-ray transparent windows and then charged with the catalyst material. A liquid pump is used to feed the reactants and solvent mixture into the reaction cell, which can be heated by an oven. The reaction was monitored by a transmission flow-through IR cell. A detailed description of the experimental setup and procedure can be found elsewhere [100]. Figure 12.10 shows the obtained XAS results as well as the online product analysis by FTIR for a Pd/AljOj catalyst during the aerobic oxidation of benzyl alcohol. 

A dilatometer can be used in a driiihoie to obtain data reiating to the deformabiiity of a rock mass (Fig. 7.19). These instruments range up to about 300 mm in diameter and over 1 m in length and can exert pressures of up to 20 MPa on the drillhole walls. Diamentral strains can be measured either directly along two perpendicular diameters or by measuring the amount of liquid pumped into the instrument. The last method is less accurate and is only used when the rock is very deformable. 

Backward-feed multiple-effect evaporators. In the backward-feed operation shown in Fig. 8.2-4 for a triple-effect evaporator, the fresh feed enters the last and coldest effect and continues on until the concentrated product leaves the first effect. This method of reverse feed is advantageous when the fresh feed is cold, since a smaller amount of liquid must be heated to the higher temperatures in the second and first effects. However, liquid pumps... 

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