Quartz flow cells

Figure 5.2 shows a typical droplet stream with the last connected droplet indicated by a thin, horizontal cursor line and the stream charge collar shown as dark rectangles on each side of the droplet stream. In this view the stream flows downward and the quartz flow cell and laser optics are located out of the frame, above. 

Two UV detectors are also available from Laboratory Data Control, the UV Monitor and the Duo Monitor. The UV Monitor (Fig.3.45) consists of an optical unit anda control unit. The optical unit contains the UV source (low-pressure mercury lamp), sample, reference cells and photodetector. The control unit is connected by cable to the optical unit and may be located at a distance of up to 25 ft. The dual quartz flow cells (path-length, 10 mm diameter, 1 mm) each have a capacity of 8 (i 1. Double-beam linear-absorbance measurements may be made at either 254 nm or 280 nm. The absorbance ranges vary from 0.01 to 0.64 optical density units full scale (ODFS). The minimum detectable absorbance (equivalent to the noise) is 0.001 optical density units (OD). The drift of the photometer is usually less than 0.002 OD/h. With this system, it is possible to monitor continuously and quantitatively the absorbance at 254 or 280 nm of one liquid stream or the differential absorbance between two streams. The absorbance readout is linear and is directly related to the concentration in accordance with Beer s law. In the 280 nm mode, the 254-nm light is converted by a phosphor into a band with a maximum at 280 nm. This light is then passed to a photodetector which is sensitized for a response at 280 nm. The Duo Monitor (Fig.3.46) is a dual-wavelength continuous-flow detector with which effluents can be monitored simultaneously at 254 nm and 280 nm. The system consists of two modules, and the principle of operation is based on a modification of the 280-nm conversion kit for the UV Monitor. Light of 254-nm wavelength from a low-pressure mercury lamp is partially converted by the phosphor into a band at 280 nm. 

Thacker [24] reported the design of a miniature flow fluorimeter for liquid chromatography. The body of the fluorimeter was machined from a block of aluminium and contained a low-pressure mercury lamp, an excitation filter, a quartz flow cell, an emission filter, a photomultiplier tube and a photoconducter in order to compensate for fluctuations in lamp intensity. Fluorescence was examined at a direction perpendicular to that of the excitation light. The cell was small enough for it to be attached directly to the end of the column with a minimum dead volume. 

The Cr-catalysts were dried at 50 C for 8 h and granulated. The size fraction of 0.16-0.40 mm was loaded in a quartz flow cell with Suprasil window for DRS and a side arm for ESR. The samples were subsequently dried at 90 °C during 16 h followed by calcination at 550 °C during 6 h in an oxygen stream. DRS spectra were recorded on these calcined samples. The samples were dien contacted during 30 min. with a Nj-stream saturated with hydrochloric acid, ethanol, propanol, water, ammonia at room temperature and with carbon monoxide, hydrogen, dichloromethane at 400 °C and ethylene at 100 C. After each treatment, DRS spectra were taken. 

Fig. 2.9 Schematic representation of hexagonal flow cell. Hexagonal Reactor with 10 cm sides. The central quartz tube is kept as provision for simultaneous irradiation with UV light...

A spiral coil of Teflon, or a spiral groove on a stainless steel surface covered with quartz, is used as a flow cell in the CL detector. These cells are placed in front of a photomultiplier tube (PMT), which detects photons emitted by the CL reaction. The cell volumes are generally in the range of 60-120 J.L. 

A joining part of the spiral coil or the quartz part that is in contact with stainless steel in the flow cell might not withstand high levels of pressure (generally smaller than 10 kg/cm2) hence careful operation to prevent excess flow is... 

Figure 3.7 — (A) Cross-sectional view of the McPherson stopped-flow mixer unit. The outer aluminum housing (a) and quartz windows b) are press-fitted with three bolts. Mixing occurs at e, where the streams meet at 90° to each other one stream is in the figure plane and the other normal to it. The immobilized enzyme reactor is placed inside d. With the reactor in place, the observation cell is 1.75 cm in length. The dashed arrow represents the lightpath inside the cell. (B) Flow-cell used to accommodate enzymes on CPG. (Reproduced from [48] and [49] with permission of Elsevier Science Publishers).

Figure 5.23 — Flow-through ionophore-based sensor for the determination of lithium in serum. (A) Mechanism involved in the sensor response (symbol meanings as in Fig. 5.20). (B) Diffuse reflectance flow-cell (a) upper stainless steel cell body (A) silicon rubber packing (c) quartz glass window (d) Teflon spacer (0.05 mm thickness) (e) hydrophobic surface mirror (/) lower stainless steel cell body. For details, see text. (Reproduced from [90] with permission of the American Chemical Society).

The detector inlet usually passes through a coiled stainless steel tubing heat exchanger and into the flow cell. The flow cell is the most complicated part in the system. The body is stainless steel or quartz, windows are quartz, and, if it can be taken apart for cleaning, there is usually a Teflon gasket between the stainless steel body and the quartz window. Finally, we move out of the flow cell into the wide-diameter Teflon tubing of the outlet tubing and into a backpressure device in the waste vessel. 

Advantages of the technique are its relatively low cost combined with quickness and ease of operation. One can work with dilute solutions (indeed they are usually a prerequisite) and water is a good solvent as it does not absorb in the UVMsible range. Quartz cells are required for observation of absorptions in the UV range, otherwise glass or plastic (for aqueous solutions) can be used for visible frequencies. Flow cells are available for coupling to separation equipment and absorption can either be monitored at a fixed wavelength for detection of a specific compound or class of compounds, or, if a diode array is available, a complete spectrum can be recorded for each fraction on-line. 

A portion of the exiting stream of the molten blend is diverted into the Flow Cell , where Nomarsky reflection microscopy is carried out in a thin slit, the bottom plate of which is reflective polished steel and the top is a quartz window. The microscope, the rapid image data acquisition device, and analyzer are capable of producing dispersion data down to sizes of one micrometer. The TSMEE is shown schematically for both the (M-M) and DMM) modes in Fig. 11.31 (119-121). 

---