Primary filters

Instruments for the measurement of fluorescence are known as fluorimeters or spectrofluorimeters. The essential parts of a simple fluorimeter are shown in Fig. 18.1. The light from a mercury-vapour lamp (or other source of ultraviolet light) is passed through a condensing lens, a primary filter (to permit the light band required for excitation to pass), a sample container, a secondary filter (selected to absorb the primary radiant energy but transmit the fluorescent... 

Procedure. Measure the fluorescence of each of the above solutions at 445 nm, using that containing 62.0 mL of the dilute quinine solution as standard for the fluorimeter. Use LF2 or an equivalent primary filter (/cx = 350 nm) and gelatin as the secondary filter if using a simple fluorimeter. 

Figure 5.25 — Flow-through ion-selective optrode based on a multilayer lipidic membrane prepared by the Langmuir-Blodgett method. (A) Cross-sectional view of the composite six-layer membrane (four layers of arachidic acid/ valinomycin covered by an arachidic acid and rhodamine dye bilayer). (B) Optical arrangement integrated with the sensor, which is connected to a flow system. LS light source Ml and M2 excitation and emission monochromator, respectively FI and F2 primary filters M mirror LB lipid-sensitive membrane in a glass platelet FC flow-cell A amplifier D display P peristaltic pump. (Reproduced from [107] with permission of the Royal Society of Chemistry).

Fig. 3.53. Diagram of the cell assembly of the Fluoro Monitor. S, Source F, primary filter C, and C sample and reference cells F, secondary Alter D, and D, elements of the dual photocell B, light...

Fig. 2.46. Basic principle of a venting filter for in situ integrity tests. Arrangement of the sterile venting filters for in-line sterilization and integrity tests (I tests). The integrity tests are carried out following the water intrusion method (WIT). In this figure, WIT is carried out only at the primary filter. The secondary filter is installed as a back-up filter (police filter). 1, Primary filter with a 0.22 pm cartridge 2, secondary filter with a 0.22 pm cartridge the secondary filter can be sterilized independent-...

The primary choice in this assessment is whether to utilize a biochemical or biophysical screen as the primary filter. Although it seems like an either/or choice, this is a false dichotomy. The most successful fragment screens obtain orthogonal data, i.e. both biochemical and biophysical data in parallel or in quick succession. With orthogonal data, the probability of false positives (or negatives) is reduced. Most commonly biochemical and biophysical data are obtained. However, all the different biochemical and biophysical screens can be considered orthogonal. We would recommend that if two biophysical methods are to be used at least one should be a direct method (discussed below). As is noted many times in this book, rapid iterations among the various data sources are the key to a successful process. 

In the more modern fluorescence microscopes the primary filter has been replaced by a system of mirrors (the Ploem illuminator in the Leitz microscope) which serves a similar function. 

Applying this procedure to investigation of the metabolic stability of CYP2D6, we were able to find a model to correctly classify metabolically stable and unstable compounds. This model was trained using a set of 129 compounds from the Bio-Print [31] database. Drug-likeness and solubility properties were used as primary filter in order to eliminate unattractive compounds and all those compounds classified as not soluble, which are always classified as metabolically stable. The data-... 

Level 1 Primary filters only (e.g, EN779 G4 filters)... 

In cake filtration (Figure 22.1b), solids and liquid are separated by filter medium, which retains the solids as a cake and permits the liquid to pass through under pressure, vacuum, or centrifugal forces. At the start of filtration, some particles may pass through the medium, and the filtrate may be turbid. Once the cake is formed, it becomes the primary filter medium and particles finer than the openings of the medium can be separated. 

Describe the instrumentation required for fluorescence analysis. What is a primary filter A secondary filter ... 

Filters may be divided into two basic types, depending on the method of the filtration material recovery — primary and secondary. Primary filters work under conditions of a continuous regeneration of the filtration material (input dust concentrations in g m ), and secondary filters operate with periodic exchanges of the filtration material after clogging (input concentrations in mg m ). 

Figure 9.3. Schematic diagram (top view) of the components of a fluorometer (filter fluorometer or spectrofluorometer). The source is a mercury-arc or xenon-arc lamp. The excitation grating or primary filter transmits only a portion of the radiation emitted by the source. Most of the exciting radiation passes through the sample cell without being absorbed. The radiation absorbed causes the sample to fluoresce in all directions, but only the emission that passes through the aperture or slit and through the secondary filter or fluorescence grating is measured by the phototube, or photomultiplier. The output of the detector is either measured on a meter or plotted on a recorder. From G. H. Schenk, Absorption of Light and Ultraviolet Radiation, Boston Allyn and Bacon, 1973, p 260, by permission of the publisher.

Selecting a Secondary Filter and Measuring Emission. After penetrating the aperture, the emitted luminescence passes through a secondary filter or fluorescence grating that eliminates any scattered radiation. The bandwidths of the primary and secondary fitters should not overlap. For example, if a 7-60 primary filter were used, then the secondary filter chosen should not transmit below about 400 nm a good choice would be the so-called 2A secondary filter shown in Figure 9.5B. 

If A absorbs ultraviolet radiation in a spectral region where B does not, then the grating or primary filter that selects the excitation wavelength can be adjusted so that only A is excited. Then only A will emit fluorescence and the detector will measure only emission from A. 

Another problem was to choose the most efficient method of exciting salicylic acid, which has only one useful excitation band (at 308 nm). One approach was to use a special phosphor-lamp source emitting between 270 and 340 nm with a peak at 306 nm this gave good sensitivity for salicylic acid. Another approach was to use the somewhat weak 313 nm line emitted by a low-pressure mercury-arc lamp, selected with a combination primary filter consisting of the 7-54 filter along with a plastic filter used to cut out the 254-nm mercury line. This procedure essentially excited only the salicylic acid, not ASA. In both cases, a sharp-cut filter with 37% T at 465 nm was used to exclude any possible emission by ASA. 

Monel and lined carbon steel are standard materials of construction for filter vessels. Linings are similar to those used in primary filters. Figure 7.60 shows a typical vertical-tank vertical-leaf filter. The stream to be filtered enters the body of the tank. A bottom connection is shown, but there are other options. The leaves are arranged vertically, and flow is from the outside to the inside of the leaves. Filtrate collects in a pipe at the bottom this also serves as support for the filter elements. The tank also has drain, vent, and compressed air connections. The detail shows one type of assembly that can simply be lifted from the effluent pipe. O-rings supply the seals. 

---