Column connection hardware

Install the hardware (computer, equipment, fittings, and tubings for fluid connections, columns in HPLC and GC, power cables, data flow, and instrument control cables). 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

Installation qualification establishes that the instrument is received as designed and specified, that it is properly installed in the selected environment, and that this environment is suitable for the operation and use of the instrument. During installation, one should 1) Compare the equipment, as received, with the purchase order 2) check documentation for completeness or for any damage 3) install hardware (computer, equipment, fittings and tubings for fluid connections, columns in HPLC,... 

The basic setup for 1C is as follows. A pump is used to force the eluent through the system at a fixed rate, such as 1 mL/min. In the FILL mode a small sample loop (typically 10 to 100 pL) is filled with the analytical sample. At the same time, the eluent is pumped through the rest of the system, while by-passing the sample loop. In the INJECT mode a valve is turned so that the eluent sweeps the sample from the filled sample loop into the column. A detector cell of low dead volume is placed in the system just after the column. The detector is connected to a strip-chart recorder or a data-acquisition device so that a chromatogram of the separation (signal vs. time) can be plotted automatically. A conductivity- or UV-visible detector is most often used in ion chromatography. The hardware used in IC is described in more detail in Section 1.4. 

Figure 6.4. Detailed diagram of hardware configuration for post-column addition of SPR. (1 = Conductivity detector Waters 431 detector, four electrode cell design 2 = waste line 4 x 0.009 in. stainless connected to 431 + 24 X 1/16 X 0.060 in PTFE tubing 3 = tee to 431 15 x 1/16 x 0.010 in PTFE to 431 inlet 4 = column to lee shortest 1/16 x 0.010 in PTFE from column to tee 5 = tee Unmount tee from check valve block for shortest path length 6 = analytical colunm Waters 1C PAK A or 1C PAK A HR 7 = check valve to tee 2 x 1/8 in o.d. PTFE 8 = check valve 9 = polisher column to check valve 3 x 1/8 in o.d. PTFE 10 = polisher column 8 x 25 mm containing AGI x 8, 200 mesh 11 = reservoir to polisher column 12 x 1/8 in. o.d. PTFE 12 = air supply minimum of 90 p.s.i. compressed air supply 13 = reservoir for SPR reconfigure with outlet on left side. From Ret [9] with permission.)...

The separation of various arsenic species is a good example of the application of ICP-AES detection to anion chromatography [26]. A microbore colunm 10 cm X 1.7 mm I.D. was used with a low flow rate (<100 pL/min). The column was packed with a low-capacity anion-exchange material (0.05 mequiv/g and solution containing 5 mM ammonium carbonate and 5 mM ammonium bicarbonate at pH 8.6 served as the mobile phase. The column hardware was connected directly to the inlet of the DIN-ICP-AES via a short length of 0.3 mm I.D. PEEK tubing. 

A peristaltic pump delivers the eluent and sample to the low-pressure column. Because a peristaltic pump is a flow-through device, the integrity of the sample is maintained as it is passed through the pump. However, because peristaltic pumps can only pump at a maximum of 100 psi, the columns must operate at a low backpressure. Development of a low backpressure column depends on several factors. First, the ion exchange resin must be small, uniform and efficient. The column hardware and fluid connections must be well designed and not contain flow paths that broaden the sample peaks. The column should be short so that the eluent backpressure is low. Finally, the detector must be able to operate at low (eluent) flow rates. The low eluent flow rates (approximately less than 100 pL/min) generate lower backpressures than standard flow rates. 

Some suppliers have integrated the installed analytical column in their hardware systems for identification purposes. This can be performed by a funk chip that is connectedto the column and can be recognized by the column compartment (Agilent) or by a clip that is connected to the column that is then fixed at the column compartment (Waters). 

The use of ultra-high-pressure regimes and/or flow rates in the micro- or nanoliters per minute range imposes unique requirements on LC system hardware, such as pumps, valves, injectors, connecting tubing, column construction, stationary phases, column heating systems, detection flow cells, and the detector s data collecting speed. 

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