Waters ACQUITY UPC2 Manuale operativo
ACQUITY UPC2
Photodiode Array Detector
Overview and Maintenance Guide
Revision A
Copyright © Waters Corporation 2012
All rights reserved
ii
Copyright notice
© 2012 WATERS CORPORATION. PRINTED IN THE UNITED STATES OF
AMERICA AND IN IRELAND. ALL RIGHTS RESERVED. THIS DOCUMENT OR
PARTS THEREOF MAY NOT BE REPRODUCED IN ANY FORM WITHOUT THE
WRITTEN PERMISSION OF THE PUBLISHER.
The information in this document is subject to change without notice and should not be
construed as a commitment by Waters Corporation. Waters Corporation assumes no
responsibility for any errors that may appear in this document. This document is believed
to be complete and accurate at the time of publication. In no event shall Waters
Corporation be liable for incidental or consequential damages in connection with, or
arising from, its use. For the most recent revision of this document, consult the Waters
Web site (waters.com).
Table of Contents iii
Copyright notice ...................................................................................................................... ii
Overview
Detector optics .................................................................................................................... 1
Calculating absorbance....................................................................................................... 4
Flow cell operating principles ............................................................................................ 6
Detector capabilities ......................................................................................................... 16
Preparing the detector ......................................................................................................... 17
Installing the detector .......................................................................................................... 18
Plumbing the detector .......................................................................................................... 21
Installing the multi-detector drip tray ............................................................................... 24
Making Ethernet connections ............................................................................................. 25
I/O signal connector.......................................................................................................... 26
Connecting to the electricity source ................................................................................... 26
Starting the detector ............................................................................................................ 27
Monitoring detector LEDs................................................................................................ 29
About the detector control panel....................................................................................... 30
Using a cuvette ...................................................................................................................... 31
Shutting down the detector ................................................................................................. 34
Maintaining the detector ..................................................................................................... 34
Contacting Waters technical service ................................................................................. 34
Maintenance considerations.............................................................................................. 35
Proper operating procedures ............................................................................................. 36
Maintaining the leak sensor .............................................................................................. 37
Replacing the detector’s leak sensor................................................................................. 42
Maintaining the flow cell.................................................................................................. 44
Replacing the lamp ........................................................................................................... 49
Reading lamp energy ........................................................................................................ 52
Replacing the fuses ........................................................................................................... 52
Table of Contents
iv Table of Contents
Cleaning the instrument’s exterior.................................................................................... 53
Spectral contrast theory ...................................................................................................... 54
Comparing absorbance spectra ......................................................................................... 54
Representing spectra as vectors ........................................................................................ 55
Spectral contrast angles .................................................................................................... 57
Undesirable effects ........................................................................................................... 60
Error messages and troubleshooting .................................................................................. 64
Startup error messages...................................................................................................... 64
Error messages preventing operation................................................................................ 67
Detector troubleshooting .................................................................................................. 70
Specifications ........................................................................................................................ 72
ACQUITY UPC2PDA detector specifications ................................................................ 72
Solvent considerations ......................................................................................................... 74
Solvent miscibility ............................................................................................................ 75
UV cutoffs for common solvents...................................................................................... 75
Overview 1
Overview
The Waters ACQUITY UltraPerformance Convergence Chromatography
(ACQUITY UPC2™) photodiode array (PDA) detector is an ultraviolet- and
visible-wavelength (UV/Vis) spectrophotometer designed for use in the
ACQUITY UPC2system. Empower™ or MassLynx™ software can control the
detector for LC/MS and LC applications.
With a photodiode array of 512 photodiodes and an optical resolution of
1.2 nm, the detector operates within the range 190 to 800 nm.
To use the detector’s operating software effectively, you must understand the
principles that underlie operation of its optics and electronics.
Detector optics
The light path through the optics assembly of the detector is shown in the
following figure.
2
Optics assembly light path:
The following table describes the optics assembly components.
Optics assembly components:
Component Function
Filter flag Influences the light entering the flow cell. These are
the flag settings:
• Shutter – Prevents light from entering the flow cell.
In the shutter position, dark counts are measured at
each pixel and subsequently subtracted from
observed signal counts to give true signal counts.
• Open – Allows light to pass into the flow cell. It is
the normal setting when performing runs.
• Erbium – Inserts an erbium filter into the light
beam that allows the wavelength calibration to be
checked or updated.
TP02819
Grating
Photodiode
array
Spectrograph
mirror and
mask
Slit (50-µm)
Flow cell
Window
Filter Flag
Lamp and
lamp optics
M1 mirror
Order filter
Overview 3
Flow cell Houses the segment of the flow path (containing eluent
and sample) through which the polychromatic light
beam passes.
Grating Blazed, holographic diffraction grating that disperses
light into bands of wavelengths and focuses them onto
the plane of the photodiode array.
Lamp and lamp
optics
Focuses light from the high-brightness deuterium (D2)
source lamp and, via a mirror, redirects the light
through a beam splitter and then to the flow cell.
M1 mirror Off-axis, ellipsoidal mirror that projects light from the
lamp into the flow cell.
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 nm).
Photodiode array An array of 512-pixel photodiodes arranged linearly.
The diode width (50-μm), together with a 50-μm slit,
yield single wavelength resolution of 1.2 nm.
Slit Determines wavelength resolution and intensity of
light striking the photodiodes. The width of the slit is
50 μm.
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.
Window Used to help minimize air infiltration into the lamp
housing.
Optics assembly components: (Continued)
Component Function
4
Calculating absorbance
The detector computes absorbance by subtracting the dark current (see “Dark
current” on page 14) and reference spectrum from the acquired spectrum.
Absorbance is based on the principles of Beer’s law.
Beer’s law
The relationship between the quantity of light of a particular wavelength
arriving at the photodiode and the concentration of the sample passing
through the flow cell is described by the Beer-Lambert law (commonly called
Beer’s law).
Beer’s law is expressed as:
A= lc
where
A= dimensionless quantity measured in absorbance units
= constant of proportionality, known as the molar extinction coefficient
l= path length, in centimeters (1.0 cm in the detector’s normal flow cell)
c= concentration, in moles per liter
Beer’s law applies only to well-equilibrated dilute solutions. It assumes that
the refractive index of the sample remains constant, that the light is
monochromatic, and that no stray light reaches the detector element. As
concentration increases, the chemical and instrumental requirements of
Beer’s law can be violated, resulting in a deviation from (absorbance versus
concentration) linearity.
Overview 5
Absorbance as a function of concentration:
Concentration
Absorbance
Ideal
Actual
Working range
Background absorbance
6
Flow cell operating principles
The Waters TaperSlit™ flow cell used in the detector renders the detector
baseline essentially insensitive to changes in mobile phase refractive index
(RI). RI changes occur during gradient separations or result from temperature
or pump-induced pressure fluctuations.
To achieve RI immunity, a combination of a spherical mirror, a lens at the
entrance of the flow cell, and a taper to the internal bore of the flow cell
prevents light rays from striking the internal walls of the flow cell. The
Waters TaperSlit flow cell, so-called because of the shape of the flow cell exit
face, matches the shape of the spectrograph slit. Compared with a
conventional flow cell with a cylindrical shape, the detector achieves higher
light throughput for a given spectral resolution with the TaperSlit cell design.
Comparison of flow cell characteristics:
Resolving spectral data
Together with photodiode spacing, the detector’s 50-μm-wide slit determines
the intensity and bandwidth of the light that strikes the photodiode array.
Variations in intensity and bandwidth provide the means to distinguish
among similar spectra.
Window
Window
UV light
Conventional flow cell:
TaperSlit analytical flow cell:
Window
Lens
UV light
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