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INTRODUCTION
The UltraPath 2 sampling system is a unique high-performance spectrophotometer offering
user-selectable optical path lengths of 10, 50 and 200 cm. Designed for the detection of low
absorbing species in solution, UltraPath 2 is an ideal tool for any study requiring precise and
highly sensitive spectroscopic determination of analytes, either in the lab or in the field. The
instrument operates in the wavelength range of 220 to 720 nm (UPUV-2) and has an
exceptional dynamic range allowing reliable absorbance measurements between 5
μ
AU/cm to
1 AU/cm to be routinely made.
The UltraPath system was developed by WPI under a collaborative agreement with NASA
(Stennis Space Center) for the spectroscopic determination of colored dissolved organic matter
(CDOM) in seawater and freshwater environments. It was designed for use in the laboratory
and in the field (
i.e.
, at sea). CDOM concentrations vary significantly between open ocean
samples with low CDOM (
e.g.
, 0.007 m-1 at 380 nm), and high CDOM freshwater environments
(
e.g.
, 10-20 m-1 at 380 nm).
To address these problems the design requirements of UltraPath mandated the development
of a rugged portable system capable of highly sensitive measurements across a wide dynamic
range.
The UltraPath 2 sample cell has three optical pathlengths contained within a single sample cell
(10 cm, 50 cm and 200 cm). The pathlengths are user selectable, offering a very high sensitivity
and an extended dynamic range for VIS and UV absorbance measurements. The fluid path of
the sample cell is optimized to produce a laminar flow that is virtually free of interference from
trapped air bubbles and adherence of dissolved substances to the cell wall. In particular, the
design greatly minimizes the problems commonly found with flow cells of long optical
pathlengths: the risk of trapping dust particles, fibers or particulate matter inside the cell.
