D E M O U N T A B L E L I Q U I D C E L L
OPER ATION AND USER MANUAL
Introduction
The Spectral Systems Demountable Liquid
Cell is an ideal accessory for the analysis of
liquids when a wide range of component
concentrations is encountered and when the
sample type varies frequently. The pathlength
of the analysis is defined by your choice of
spacer included with the accessory. Spacers
are composed of Teflon® which is inert and
compatible with all sample types.
Spectral Systems offers a complete
selection of window materials for analysis in
the mid-, near- and far-infrared spectral
regions and to provide compatibility with
organic and aqueous solvents. All windows
offered for our Demountable Liquid Cell are
edge rounded and finished for exceptional
durability and improved seal.
Maximum Sampling Pathlength Flexibility• Easy spacer change for flexible sampling pathlength
• Complete selection of window materials for all sample types
• Standard rectangular slide mount configuration to fit your FT-IR spectrometer
S PECI F I C AT I O NS
Plate Geometry Rectangular
Plate Dimensions 2.0" W × 3.0" H
IR Beam Port Dimension 9.5 × 21 mm
Spacer Thickness, mm 0.015, 0.025, 0.050, 0.10, 0.20, 0.50, 1.0
Nominal Pathlength Spacer thickness
Seal Type Friction, Teflon
Fill Port Type Luer Lock
Window Dimensions 32 × 3.0 mm circular
Window Flatness λ/5 at 10.6 micron (Except KRS-5 and Polyethylene)
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Unpacking Your Product
The Demountable Liquid Cell will be packaged
in a plastic storage container. If IR windows
are ordered with the cell they will be
packaged separately. When the IR windows
are not in use they should be stored in a low
humidity environment such as a desiccator
to protect the long-term integrity of the IR
windows.
What’s included?
• Cell holder (base and cap)
• Needle plate with Luer Lock fittings
• Alignment pins
• Teflon gasket
• Teflon o-ring
• 2 Teflon stoppers for cell
• 2 each of 0.015, 0.025, 0.050, 0.10, 0.20,
0.50 and 1.0 mm Teflon spacers
Assembling the Cell
The Demountable Liquid Cell is easily
assembled with your choice of spacer
thickness which provides the nominal
infrared sampling pathlength.
In Figure 1 we show the assembly process;
1. Lay the Demountable Liquid Cell (DLC)
base onto a flat working surface and
install a Teflon o-ring into the DLC base.
2. Gently install an undrilled window into the
DLC base.
3. Install your choice of Teflon spacer over
the undrilled window.
4. Install a drilled window over the Teflon
spacer with the drill holes oriented left/
right with respect to the length of the DLC.
5. Insert alignment pins one each into the
drill holes of the drilled window.
6. Install the drilled Teflon apacer over the
alignment pins and over the drilled window.
7. Install the needle plate over the alignment
pins and over the drilled Teflon spacer
fitting the needle plate alignment pin into
the slot of the DLC base.
8. Install the optional aluminum o-ring
(only if using 2 mm thick windows) over
the needle plate. The optional aluminum
o-ring is not used with the standard 3 mm
thick windows.
9. Install the DLC cap onto the DLC base and
turn to begin seal of the cell. Slowly
continue finger/hand turning until tight.
10. Pull the alignment pins out of the needle
plate and your Demountable Liquid Cell
is ready to use.
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Figure 1. Demountable Liquid Cell (DLC) assembly
Determining Cell Pathlength
The nominal cell pathlength of your
Demountable Liquid Cell is determined by
the thickness of your choice of Teflon spacer.
You can determine its precise pathlength by
using the following procedure.
1. Collect an open beam background
spectrum on your FT-IR
2. Collect the spectrum of the empty cell.
The resulting spectrum will exhibit a
fringing pattern resulting from the
reflection of the IR beam between the
opposing surfaces of the open cell.
3. Select a region of the spectrum where
the fringing pattern is distinct – free of
interference (water bands, etc.) and note
beginning and ending point values in cm-1
for a significant number of fringes. Figure 2
shows the spectrum of a 0.1 mm
Demountable Liquid Cell.
4. The pathlength of the cell can be
calculated from the following equation1:
Pathlength = 10 N/2(λ1 – λ2)
Where;
Pathlength = value in mm
N = number of fringes between λ1 and λ2
λ1 = starting value in cm-1 for measurement
λ2 = ending value in cm-1 for measurement
In the example shown in Figure 2, λ1 =
2534.38 cm-1, λ2 = 1138.93 cm-1 and N = 29.
From this we calculate the actual pathlength
to be 0.104 mm.
Note: In order to exhibit the spectral fringing pattern described above sufficient spectral resolution must be selected. See required values in Table 1.
Figure 2. Spectrum of 0.1 mm pathlength Demountable Liquid Cell
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Minimum Spectral Resolution Required
CELL MINIMUM PATHLENGTH SPECTR AL (mm) RESOLUTION (cm -1)
10 0.25
5 0.5
1 2.5
0.5 5.0
Table 1. Minimum spectral resolution required for measuring fringe pattern
Sampling Procedures
Samples measured in the Demountable
Liquid Cell are generally a component in a
base liquid, for example an additive in fuel
for a combustion engine. Generally the
pathlength of the liquid cell is chosen to
optimize the absorbance of the component
which needs to be measured. Often the
components of interest are at low concen-
trations within the base liquid; parts per
million (ppm) and low percentage levels are
typical. Therefore, we generally need to
choose longer pathlength cells to “see” and
measure these low concentration levels. The
primary absorbance bands from the base
liquid generally are out of the linear range of
the spectrometer and therefore cannot be
used to internally calibrate the pathlength of
the measurement. The Demountable Liquid
Cell is ideal for “finding” the appropriate cell
pathlength for the quantitative analysis.
When this is completed it may be beneficial
to move to a fixed cell path cell offered by
our Super-Sealed™ Liquid Cell. In some sample
measurements weakly absorbing bands of
the base liquid can be used as a measure of
the liquid cell pathlength. In these cases the
absorbance of the component of interest
can be ratioed to an absorbance band of the
base liquid to determine concentration and a
fixed pathlength cell aids in the precision of
the quantitative measurements.
Using the Demountable Liquid Cell
The assembled Demountable Liquid Cell is
configured with two Luer Lock ports for
connection with Luer Lock style syringes. It
is very important to use proper procedure
for filling the cell.
• Gently connect a Luer Lock style syringe
with your liquid sample onto one of the
Luer Lock fittings of the cell.
• Gently connect an empty Luer Lock style
syringe onto the other Luer Lock fittings
of the cell.
• Filling the cell must be pull via the empty
syringe to prevent damage to the cell.
• Slowly pull the plunger of the empty
syringe upward to draw the liquid into
the cell as shown in Figure 3.
• Remove the Teflon stoppers and install
one each Teflon stoppers into the
Luer Lock ports to seal the liquid
sample in the cell. Examine the
filled cell to ensure liquid
maintains fill in the cell and
that no bubbles are present.
• To remove sample from the
flow cell, remove the Teflon
stoppers from the Luer Lock
fittings and install an empty
glass syringe onto the lower
port and slowly pull the
plunger in the out direction
to remove the sample.
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Figure 3. Filling the Demountable Liquid Cell
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Cleaning and Storing the Liquid Cell
Before storing the liquid flow cell after use it
is important to remove all sample residue to
prevent long-term damage to the cell.
• Pull a suitable cleaning solvent through
the cell using the following method;
• Install a Luer Lock glass syringe with
solvent onto the lower port of the
Demountable Liquid Cell. Install an empty
glass syringe onto the upper port of the
cell. Gently pull the plunger of the upper
syringe out to draw the solvent into the
cell. It is recommended this be done three
times using three times the volume (each
time) of the liquid cell to completely
remove sample residue.
• Store the Demountable Liquid Cell in a
desiccator to protect the long-term
integrity of the IR windows. Alternately,
disassemble the cell and store the IR
windows in a desiccator.
Product Configurations
The Demountable Liquid Cell is available
with your selection of window materials.
Table 2 shows a complete list of Spectral
Systems part numbers for these configurations.
Each of the window materials have of
course unique properties and capabilities
relative to spectral range and water
solubility. For your convenience we have
listed some of these properties for each of
the materials in Table 3.
Safety Precautions
It is essential to utilize safe laboratory
procedures when using the Demountable
Liquid Cell. Safety protective eyeglasses and
laboratory gloves are required.
Follow proper cell flowing and emptying
procedures as outlined in Sampling
Procedures. Failure to do this may cause
liquid flow cell damage and or exposure to
the liquid sample.
Make sure your sample is compatible with
the window material of the flow cell. Failure
to do this may cause liquid flow cell damage
and or exposure to the liquid sample.
Maintenance
When IR sampling is completed with the
Demountable Liquid Cell, empty and clean
the cell as detailed in Sampling Procedures.
The cell and or windows should be stored in
a desiccator to prevent damage to hygro-
scopic IR windows.
If any damage to the cell is detected, please
contact Spectral Systems for assistance.
References:
1. Conley, Robert T., Infrared Spectroscopy
(Allyn & Bacon, 1966).
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Part Numbers List for Demountable Liquid Cell Windows
WINDOW UNDRILLED DRILLED MATERIAL PART NO. PART NO.
BaF2 915-3716 915-3717
CaF2 920-3716 920-3717
CsI 935-3716 935-3717
Ge 940-3716 940-3717
IR-Quartz 965-3716 965-3717
KBr 945-3716 945-3717
KRS-5 950-3716 950-3717
NaCl 955-3716 955-3717
Polyethylene 957-3716 957-3717
Si 960-3716 960-3717
ZnSe 975-3716 975-3717
ZnS 971-3716 971-3717
Table 2. Special versions of these windows are also available from Spectral Systems. Versions with specialized coatings to increase IR throughput and versions with window wedging to improve performance for high-resolution measurements are available. Please contact us for more information for your requirements.
Spectral Range and Solubility for Demountable Liquid Cell Windows
SHORT LONG WINDOW WAVELENGTH, WAVELENGTH, SOLUBILITY, MATERIAL CM-1 CM-1 G/100 G
BaF2 66,600 782 0.17
CaF2 79,500 1025 0.0017
CsI 42,000 172 44
Ge 5,500 574 0
IR Quartz 50,000 2,677 0
KBr 48,800 388 53
KRS-5 17,900 232 7.4
NaCl 52,600 584 36
Polyethylene 700 ~0 0
Si 8,900 969 0
ZnSe 15,000 508 0
ZnS 17,000 722 0
Table 3. Spectral range and water solubility for Demountable Liquid Cells where SWL = highest wavenumber, LWL = lowest wavenumber and Solubility is the value at room temperature.
Replacement Spacers for Demountable Liquid Cells
SPACER THICKNESS PART NO.
0.015 097-3713
0.025 097-3714
0.050 097-3715
0.10 097-3716
0.20 097-3717
0.50 097-3718
1.0 097-3719
Spacers include 12 each. Spacers are composed of Teflon which is compatible with organic and aqueous solvents.
Replacement Parts and Options for Demountable Liquid Cells
DESCRIP TION PART NO.
Teflon Stoppers (12 each) 097-3711
Teflon Gaskets (12 each) 097-3712
Teflon O-Rings (12 each) 097-3737
Aluminum O-Rings (12 each) 097-3723
Needle Plate 097-3727
Alignment Pins (12 each) 097-3709
Glass Syringe, 1 mL 097-3801
Glass Syringe, 5 mL 097-3805
Glass Syringe, 10 mL 097-3810
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