High pressure flow cell

As well as the CIR-type cells discussed above, the ATR technique has also been employed in other types of HP IR cell. An alternative arrangement to a cylindrical crystal inserted through the autoclave body (Figure 3.8) is to embed the ATR crystal in the base or wall of the autoclave. This approach was used in the HP IR cell developed by Wolf et al., illustrated in Figure 3.9 [43]. An ATR crystal is mounted in the bottom of the reactor, which can operate at pressures up to 200 bar and can be adapted to give a high pressure flow-cell. 

Automation 10 [A 10] High-pressure Flow Cell for Optical Microscopic Observations... 

Fig. 7.17. High-pressure flow-cells. (A) Cell for voltammetric measurements in water-in-CO, microemulsions a working electrode, b reference electrode, c supercritical fluid inlet, d supercritical fluid outlet, e sample port, f Teflon O-ring. (B) Fibre optic-assisted cell for fluorimetric measurements. (Reproduced with permission of the American Chemical Society.)...

Fluorescence spectrometry is a powerful analytical tool by virtue of its high sensitivity however, the usual presence of emission and excitation spectral interferences calls for additional sample pretreatments. This technique has been used in combination with SFE mainly in the determination of PAHs, which possess well-known luminescence properties. Screening these compounds from soil entailed the use of a high-pressure flow-cell such as that of Fig. 7.17B and allowed the extraction and determination of five individual PAHs in soil with relative standard deviations less than 5% also, it provided qualitative and semi-quantitative information from the screening of natural soil samples [113]. 

Carbon dioxide is transparent to below 190 nm, making it an ideal fluid for use with ultraviolet (UV) detectors. It can be used with acetonitrile above 195 nm and with methanol above 205 nm. The UV-vis detectors used in SFC are standard HPLC detectors in every way except for high pressure flow cells. Double tapered windows (45° bevels with matching seals) balance the stress and allow cells to be built that withstand more than 600 bar. The operator needs to be sure that the data collection rate is set fast enough to not round off the faster peaks experienced in SFC. 

Figure 2. Micro CIRCLE high-pressure flow cell. (Photograph courtesy of Spectra-Tech, Inc.)...

The flow method ts the simplest and the most straightforward. In the flow method, the solvent fluid is supplied to a compressor by a pressure cylinder. At the desired pressure, the fluid passes into the thermostatted extractor cell that contains the solute present in appropriate matrix (e.g., multiple layer of glass wool). The fluid dissolves the solute in the extractor and, on expansion through a heated metering valve, precipitates solute into a series of collection vessels to be measured gravimetrically. The volume of the decompressed fluid is totaled by a wet or dry gas test meter. Static or equilibrium solubility measurement methods are used to eliminate the need to sample the supercritical fluid solution. A high-pressure flow cell is placed in the flow circuit to monitor the dissolution process by spectrophotometry. 

Pumps operated in a flow eontrol mode with pressure controlled by a backpressure regulator mounted downstream from the column (except for packed capillary columns). UV detector with a high-pressure flow cell or evaporative light-scattering detector for compounds lacking a chromophore... 

RS Addleman, JW Hills, CM Wai. A high pressure flow cell for on-hne absorption, Raman, and time resolved laser induced fluorescence spectroscopy in supercritical fluids. Rev Sci Instrum 69(9) 3127-3131, 1998. 

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