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Agilent 8453 Diode Array
Spectrophotometer
HP 8452A Diode Array
Spectrophotometer
Specifications:
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Single, collimated (parallel)
beam that allows greater flexibility in your selection of cuvettes
and accessories
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Diode array detector with
different options
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UV-Vis instrument for
ultraviolet and visible range 190 nm to 820nm
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low
noise lamp with low power requirements.
- HP-IB communication protocol for flexibility in selecting
present and future controllers
Diode arrays are assemblies of individual photo diodes in a linear
array. Self-scanned arrays have the read-out electronics included on
the chip with the array. When read out, all elements of the array must
be read out in series. The array has 1024 elements. Light of all
wavelengths falls on the diode-array and is measured simultaneously,
that is, data acquisition is done in parallel. speed is the best known
advantage of diode-array spectroscopy. Data is acquired in parallel,
the detectors are read-out by "electronic scanning", and
microprocessors and computers are used to process data; Measurements
are made at different wavelengths at the same time. Conventional
spectrophotometers can make multi-wavelength measurements but there is
a time differential between each measurement.
The diagram below illustrates what happens in a diode array
spectrophotometer. First, a light source generates light at a specific
wavelength or wavelengths. Normally, a UV/Vis spectrophotometers
utilize two light
sources: a deuterium arc lamp for consistent intensity in the UV range
(190 to 380 nm) and a tungsten- halogen lamp for consistent intensity
in the visible spectrum (380 to about 800 nm). Some spectrophotometers
use xenon flash lamps, which offer decent intensity over the UV and
visible regions.
The entrance slit, dispersion device,
and exit slit are referred to as the monochromator. Light passing
through the monochromator exits as a band. The width of this
band of light at half the maximum
intensity is the spectral bandwidth. Bandwidth comes in to play with
regard to accuracy, since the accuracy of
any absorbance measurement is dependent on the ratio of the spectral
bandwidth to the natural bandwidth of the
substance being measured. The natural bandwidth is the width of the
absorption band of the sample at half the absorption maximum.
As a rule, a ratio between spectral
bandwidth and natural bandwidth of 0.1 or less will generate
absorbance measurements 99.5 percent
accurate or better.
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Agilent 8453 Diode Array Spectrophotometer
The Agilent
8453 UV-Visible value system is a current model
economical system for UV-visible spectroscopy
based on a photo diode array detector. It is ideally suited
for performing general-purpose spectroscopy tasks in chemical,
biochemical or environmental labs Included with the system are a
small form factor PC and a flat panel
monitor. Single beam 190 to 1100 nm, 1-nm slit
width, diode array detection, Deuterium and Tungsten lamps.
The Agilent 8453 UV-visible Pharma capable
system is an industry-specific solution for UV-visible spectroscopy
that is based on the reliable Agilent 8453 spectrophotometer with
dedicated Windows-based software running on a PC.
Other system components can be
chosen to provide an optimum price/performance configuration for
both QA/QC and research laboratories in the pharmaceutical industry.
The Agilent ChemStation Security Pack software module -
can be purchased at additional cost -to
helps laboratories comply with the U.S. Food and Drug
Administration's ruling on electronic data records and signatures
(FDA 21 CFR Part 11).
HP 8452A Diode Array Spectrophotometer
The HP 8452A Diode-Array Spectrophotometer
is a single-beam, microprocessor-controlled spectrophotometer.
Visible/UV - range of 190 to 820 nm with 2 nm resolution. It is used
when speed of measurement is essential. It is faster, more sensitive
and some believe it has more precision than
a conventional spectrometer due to the photo diode-array detection
system.
With its diode array technology, the
spectrophotometer is much faster then conventional instruments; with
more precision, more sensitivity and more reproducible results.
The spectrophotometer can be controlled
from a computer equipped with HP UV-Vis software. It can also be
equipped with accessories which include special cell holders,
peristaltic pumps, auto sampler, a multicell transport, a Peltier
temperature control accessory, and valve unit and valve – pump
controller. All accessories are extra and they are not included with
system.
Our basic system ships
with computer, software, and a singel cell holder.
We have UV-Visible Software Rev. A
running on Windows 95
$ Ordering Information
Ready to buy or learn more
about this instrument?
Please
click here
& fill out our contact page
or contact our knowledgeable sales force at
763-712-8717 / 800-745-2710 for more information.
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The source light is then directed to
a dispersion device that causes different wavelengths of light to be
dispersed at different angles. Two common dispersion devices used in
UV/Vis spectrophotometers are prisms and
holographic gratings. The angle of dispersion with a prism, however,
can be nonlinear and sensitive to changes in temperature.
Holographic gratings are glass blanks with narrow ruled grooves. The
grating itself is usually coated with aluminum to create a
reflecting source. Holographic gratings eliminate nonlinear
dispersion and are not temperature sensitive. They do require
filters, though, since light is reflected in different orders with
overlapping wavelengths.
Once the light has been passed
through the dispersion device and the sample of interest it reaches
a detector. Detectors in UV/Vis
spectrophotometers come in a variety of shapes and sizes.
Photomultiplier tubes are common; they provide good
sensitivity throughout the UV/Visible spectral
range and are highly sensitive at low light levels.
Photodiodes have seen increasing use as detectors
in spectrophotometers, bringing to
the table a wider dynamic range. A photodiode is generally made
up of a semiconductor and a capacitor to charge the semiconductor.
As light hits the semiconductor, electrons
flow through it, thereby lowering the charge on the capacitor. The
intensity of light of the sample is
proportional to the amount of charge needed to recharge the
capacitor at predetermined intervals. As
opposed to having single photodiodes, some spectrophotometers are
composed of a photodiode array. Here,
several photodiode detectors are arranged on a silicon crystal. The
advantage of an array is the ability to do side-by-side
readings, thus increasing speed.
In a conventional spectrophotometer,
polychromatic light from the monochromator is transmitted
through the sample, and the sample absorbance is determined
by comparing the intensity of the light
hitting the detector with just a sample blank with the intensity of
light hitting the detector with the sample
in place. With a diode array spectrophotometer, polychromatic light
passes through the sample and is focused
on the entrance slit of the polychromator (the entrance slit and
dispersion device). The light is then
dispersed onto the diode array with each diode measuring a portion
of the spectrum.
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