Wide band-pass filter

A hexapole assembly of rods (poles) is built similarly to the quadrupole, but now there are three sets of opposed rods evenly spaced around a central axis. The hexapole cannot act as a mass filter by applying a DC field and is used only in its all-RF mode. It is therefore a wide band-pass filter and is used to collimate an ion beam. (Like-charged particles repel each other, and an electrically charged beam will tend to spread apart because of mutual repulsion of ions unless steps are taken to reduce the effect.)... 

Figure 20-10 Transmission spectra of interference filters, (a) Wide band-pass filter has 90% transmission in the 3-to 5-gm wavelength range but <0.01% transmittance outside this range, (b) Narrow band-pass filter has a transmission width of 0.1 u.m centered at 4 u.m. [Courtesy Barr Associates, Westford, MA]...

Grating and prism spectrophotometers should recover the theoretical ab-sorptivities shown in Table 3 interference-filter photometers typically produce lower values, and glass-filter photometers produce lower values still. As ageneral rule, the wider the band-pass of die filter, the lower the absorptivity. In any case, even filter photometers should show constant absorptivities with time. Because many automated enzyme assays do not use a standard but rely on the absorptivity of the chromophore to determine the activity, low values of the absorptivity owing to a wide band-pass filter will yield lower enzyme activities. 

Generally, filter fluorimeters are more sensitive than those with monochromators. However, they lack scaiming options and hence cannot be used for investigations related to molecular structure. Nevertheless, for a number of routine analyses filter instruments are quite satisfactory. If a filter fluorimeter is used, the excitation filter should be a narrow band filter (+5nm) centred at 325 nm. On the emission side, a wide band pass filter ( 10-20 nm) centred at 420 nm should be used. Scanning fluorimeters should have excitation and emission monochromators with slit widths of 5 nm or smaller. 

A wide band-pass filter can be formed by simply cascading a high-pass and low-pass filter so that... 

Solution filters. They are both short-wavelength cut-off or wide band-pass filters (a and c in Fig. 4.2), mainly constituted by aqueous solutions of inorganic compounds. Several of them, which cover the wavelength interval between 200 and 650 nm, have been described in detail in [2] and references therein. It is however to be noted that some of these filters may undergo thermal or photochemical reactions, so that a periodic control of their absorbance is recommended. 

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