Waters 2998, Operator'S Manual

Page: 15 / 122

Detector optics 1-3
Calculating absorbance
The detector computes absorbance by subtracting the dark current (see “Dark
current” on page 1-9 ) from the reference spectrum (reference energy) and the
acquired spectrum (sample energy). Absorbance is based on the principles of
Beer’s law.
Beer’s law
The Beer-Lambert law (commonly called Beer’s law) describes the
relationship between the quantity of light of a particular wavelength arriving
Window Used to help minimize air infiltration into the lamp
housing.
Filter flag/shutter Flag positions for measuring open (sample) and
blocked (dark) beam energies and a third for
wavelength verification.
Flow cell Houses the segment of the flow path (containing eluent
and sample) through which the polychromatic light
beam passes.
Spectrograph
mirror and mask
The mirror focuses light transmitted through the flow
cell onto the slit at the entrance to the spectrographic
portion of the optics. The mirror mask defines the size
of the beam at the grating.
Slit Determines wavelength resolution and intensity of
light striking the photodiodes. The width of the slit is
50 µm.
Grating Disperses light into bands of wavelengths and focuses
them onto the plane of the photodiode array.
Order filter Reduces the contribution of second-order diffraction of
UV light (less than 370 nm) to the light intensity
observed at visible wavelengths (greater than 370).
Photodiode array A linear array of 512 photodiodes. The diode width
(50 µm), together with a 50-µm slit, yields single
wavelength resolution of 1.2 nm.
Optics assembly components (Continued)
Component Function