Capillary instrumentation

For all capillary instruments the time t needed for a certain volume V of the solution to flow through a thin capillary of length l and radius R is measured. Assuming a laminar flow, the Hagen-Poisseuille equation can be applied, leading to... 

The pK screening methodology was further standardized and optimized for high-throughput measurements. Current developments are the use of a commercially available 96 capillary instrument including the corresponding evaluation software, the use of commercially available separation kits and pressure-assisted CE to shorten the run times. 

Precision of the assay was evaluated for day-to-day, capillary-to-capillary, instrument-to-instrument, and the results are shown in Table 5. 

S12. Swerdlow, H., Jones, B. J., etal., Fully automated DNA reaction and analysis in a fluidic capillary instrument. Anal. Chem. 69(5), 848-855 (1997). 

All glass capillary viscometers should be calibrated carefully (21). The standard method is to determine the efflux time of distilled water at 20°C. Unfortunately, because of its low viscosity, water can be used only to standardize small capillary instruments. However, a calibrated viscometer can be used to determine the viscosity of a higher viscosity liquid, such as a mineral oil. This oil can then be used to calibrate a viscometer with a larger capillary. Another method is to calibrate directly with two or more certified standard oils differing in viscosity by a factor of approximately five. Such oils are useful for calibrating virtually all types of viscometers. Because viscosity is temperature-dependent, particularly in the case of standard oils, temperature control must be extremely good for accurate calibration. 

This brings me back to methods development. Running a 96-capillary instrument with a poorly constructed method presents the opportunity to perform 96 horrible separations simultaneously. 

Ramseier A, von Heeren F, Thormann W. Analysis of fluorescein isothiocyanate derivatized amphetamine and analogs in human urine by capillary electrophoresis in chip-based and fused-silica capillary instrumentation. Electrophoresis 1998 19 2967-2975. 

Capillary electrophoresis is an exciting, new, high resolution separation technique useful for the determination of drugs and their metabolites in body fluids. The first commercial capillary electrophoresis instruments began to emerge on the market in 1988. Today approximately a dozen companies manufacture electrokinetic capillary instrumentation, with many of these fully automated, that comprise auto samplers with computerized data evaluation.f Capillary electrophoresis involves the electrophoretic separations of minute quantities of molecules in solution according to their different velocities in an applied electrical field. The velocity of these molecules... 

Fig. 1 Multiple-capillary instrument employing the sheath-flow technique. Key 14, capillary 18, capillary outlet 20, capillary inlet 22, buffer well 24, microtiter plate 26, quartz chamber 36, laser 38, laser beam 40, lens 58, fluidic stream. The electrodes are not shown nor is the device for delivering the sheath fluid. (Reprinted in part from U.S. Patent No. 5,741,412, Figure 1.)...

A number of viscometers have been developed for securing viscosity data at temperatures as low as 0 °C (58,59). The most popular instruments in current use are the cone plate (ASTM D3205), parallel plate, and capillary instruments (ASTM D2171 and ASTM D2170). The cone plate can be used for the determination of viscosities in the range of 10 to over 109 Pa-s (1010 P) at temperatures of 0—70°C and at shear rates from 10-3 to 102 s-1. Capillary viscometers are commonly used for the determination of viscosities at 60 —135°C. 

Obviously, designs of capillary gas chromatographs must be more carefully executed than those of packed column instmments. The chief reasons for this are the very low flow-rates used and the overall small volumes of capillary columns. Under such circumstances, the units connecting the column to either the inlet or detector parts must virtually be absent of any dead volumes. Inlet systems with clean geometry are also required to introduce the sample as the narrowest possible band into the first column section. A constant dilemma of the manufacturers of modern instruments has been whether to design universal instruments or those usable just for certain column types. It seems now that the production of dedicated capillary instruments is becoming common. Alternatively, instruments can be provided with multiple inlet and detector capabilities. Numerous laboratories also successfully modified the earlier versions of instruments into capillary gas chromatographs. 

As mentioned earlier, viscometric manipulations are simplified considerably by using a capillary instrument of the Ubbelohde type, as modified by Davis and Elliott, rather than one of the Ostwald or Fenske t3q)e. This viscometer has a side arm at the base of the capillary which breaks the liquid flow to form a suspended level, and also reduces kinetic-energy corrections. The latter are very important, but can be made negligible by careful viscometer design. Kinetic-energy corrections are inversely proportional to the flow time, and so the viscometer should be designed so that solvent flow-times of 150-200 seconds are achieved. Full details of viscometric techniques can be found elsewhere. ... 

Consequently, the rheological measurements of MPSs should be carried out such that the dimension of the flow channel is significantly larger than the size of the flow element. For example, the relative viscosity, jjr, of diluted spherical suspensions measured in a capillary instrument depends on the (d/D) factor, where 7) is the sphere diameter and d that of the capillary—for d 107), the error is around 1% [Happel and Brenner, 1983]. Thus, if 1% error is acceptable, the size of the dispersion should be at least 10 times smaller than the characteristic dimension of the measuring device (e.g., diameter of a capillary in capillary viscometers, distance between stationary and rotating cylinders or plates). Following this recommendation is not always possible, which lead to the decline and fall of continuum mechanics [Tanner, 2009]. 

As the chapter quotation indicates, almost the first thing Cou-ette did after he built his famous rotational rheometer was to compare its results to those from Poiseuille s capillary instrument. If we do our measurements right and make the appropriate corrections, all the instruments shown in Figure 5.1.2 should give the same value of the viscosity. The major theme of Chapters 5-9 is determining what it takes to get absolute material function data. We will see how well this can be done by comparing results (for G, t],, etc.) by the different shear methods at the end of Chapter 6. 

The most common capillary instrument in the polymer industry is not a rheometer but an indexer. The quality of nearly every batch of thermoplastic made in the world is controlled by melt index. Because it is so widely used and has all the essential features of a capillary rheometer, and because rheologists ate often asked to compare their results to melt index values, we need to examine it here. 

Flow curves - Melt rheological properties of PES were evaluated on a capillary instrument attached to a Shimadzu Universal Materials Testing Machine model AG-IOTA. Viscosity curves measured at 315, 330 and 350°C and for shear rates ranging from 10 to 10000 1/s are presented in Figure 1. A typical pseudo-plastic behavior can be seen. That is, the melt viscosities of PES decrease with the increase of apparent shear rates. 

Pressure-driven rheometers, particularly capillary instruments, are the rheological work-horses of the plastics industry, as they are relatively simple and easy to use, even for melts at high temperatures. In most capillary rheometers, the flow is generated by a piston moving in a... 

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