Liquid Waveguide Capillary Cell, 50 cm pathlength
Microliter Sample Volume - Exceptional Sensitivity
- Optical sample flow cell that combines an increased optical pathlength (50cm) with a small sample volume (125 µL).
- Measure liquids in a continuous flow or using discrete samples
- Connects with 600um core optical fibers to fiber optic spectrometers and light sources via SMA terminations
- Efficient measurement of low-volume or low-concentration (ppb-ppt) aqueous samples.
- Functions with most liquids(with the exception of perfluorinated solvents) having a refractive index ≥ 1.30
- Absorbance measurements can be performed in the UV, VIS, and NIR ranges to detect low sample concentrations in a lab or process environment.
- Adapts to most fiber optic detection systems via SMA terminations
- Efficient measurement of low-volume or low-concentration (ppb-ppt) aqueous samples
- Functions with most liquids (with the exception of perfluorinated solvents) having a refractive index ≥ 1.30
- Absorbance measurements can be performed in the UV, VIS, and NIR ranges
- 20 years of manufacturing experience
- Low UV drift
Note: WPI offers the LWCC Start-up Kit (KITLWCC) includes two 1 meter fiber optic cables (505195), Sample Injector Assembly (58006) MiniStar™ Peristaltic Pump (MiniStar), and Waveguide Cleaning Kit (501609)
- Similar to optical fibers, light is confined with the (liquid) core of an LWCC by total internal reflection at the core/wall interface
- Made from fused silica tubing with an outer coating of a low refractive index polymer.
Pressure and Flow Rate
Flow is proportional to pressure and to the fourth power of the diameter of the fluid capillary, as well as the reciprocal to the length of the capillary and fluid viscosity
- 1 m of 55 μm ID waveguide requires approximately 1.5 PSI for water flow of 1mL/min
- LWCC has been operated at 100 to 200 PSI without observed malfunction
- Maximum hydrostatic pressure the LWCC can withstand has not been established
- Trace detection of nutrients (nitrite, nitrate, phosphate, iron) in seawater
- Environmental and oceanographic monitoring
- Drinking water analysis
- Colored dissolved organic matter (CDOM)
- Process control
UV/VIS/NIR absorbance spectroscopy is governed by Beer’s Law, where the absorbance signal is proportional to chemical concentration, light path length and the compound’s specific molar absorption coefficient. Typical optical pathlengths of cuvettes and flow cells are between 0.2cm and 10 cm. Longer pathlengths are difficult to achieve due to mechanical constraints. Liquid Waveguide Capillary Cells (LWCCs) fill this gap. LWCCs are fiber optic flow cells that combine an increased optical pathlength (10–500 cm) with small sample volumes ranging from 2.4 µL to about 3mL. Compared with a standard 1cm cell, a 1 mAU signal is enhanced one hundred fold with a 100 cm flow cell to 100 mAU, using WPI’s patented aqueous waveguide technology.*
They can be connected via optical fibers to a spectrophotometer with fiber optic capabilities. Ultra-sensitive absorbance measurements can be performed in the ultraviolet (UV), visible (VIS) and near-infrared (NIR) to detect low sample concentrations in a laboratory or process control environment.
Your sample is the core of a light guide
WPI’s Liquid Waveguide Capillary Cells are made of fused silica tubing with an outer coating of a low refractive index polymer. Your liquid sample is guided through the capillary and represents the core of the waveguide. The hydrophilic character of the fused silica capillary inner wall results in high signal stability and easy removal of air bubbles trapped in the flow cell. However, the transmission of the LWCC is mainly dependent on the intrinsic attenuation of the sample liquid.
The LWCC-3xxx series of flow cells uses traditional HPLC type 10-32 coned port fittings with 1/32 inch tubing for liquid connection and 500 µm SMA fiber optic adapters for light input and output. The LWCC-4xxx series of flow cells uses 1/4-28 flangeless flat bottom fittings with 0.125" tubing 600 µm SMA fiber optic adapters.
Liquid can be pumped into the flow cells using (in the simplest case) a sample injector (58006) and a ministar peristaltic pump (MINISTAR). The LWCC may be connected directly to a fluid injection analysis (FIA) system or to a gas segmented fluid injection analysis (GFIA) system via a debubbler.
For routing discrete measurements, WPI’s LWCC Injection system (89372) may be used when the sample is injected into a constant flow via an injection loop of 3–4 times the internal flow cell volume to ensure a stable baseline and avoid the introduction of micro air bubbles into the flow cell.
LWCCs have been used in a variety of applications such as liquid chromatography, stopped-flow and colorimetric detection, drinking water analysis, as well as environmental and oceanographic monitoring systems.
Micro Chemical Analysis Employing Flow Through Detectors, 1995, U.S. Patent No. 5,444,807.
Aqueous Fluid Core Waveguide, 1996, U.S. Patent No. 5,507,447.
Long Capillary Waveguide Raman Cell, 1997, U.S. Patent No. 5,604,587.
Chemical Sensing Techniques Employing Liquid-Core Optical Fibers, U.S. Patent No. 6,016,372
These spectra show the optimal detection limits for LWCCs of varying pathlength.
An illustration of a complete WPI long pathlength liquid absorbance system for trace detection.
Typical LWCC setup includes an injection system, a pump, and a spectrophotometer.
|Optical Pathlength||50 cm||100 cm||250 cm||500 cm||10 cm||50 cm||100 cm|
|Internal Volume||125 µL||250 µL||625 µL||1250 µL||0.31 mL||1.57 mL||3.1 mL|
|Fiber Connection||600 µm SMA||600µm SMA|
|Maximum Pressure||100 PSI|
|Wetted Material||PEEK, Fused Silica, PTFE|
|Liquid Input||Standard 10-32 Coned Port Fitting|
* Referenced using coupled 500µm fibers
** Measured using ASTM E685-93
*** A one-meter waveguide of 550µm internal diameter requires approximately 1.5PSI for water flow of 1.0mL/min.
When comparing light throughput versus wavelength of three fiber optic cables, the greater the diameter of the cable, the better the LWCC performance up to 600µm which is the input diameter of the SMA connector.
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Long Pathlength Ensures Significant Increase of Sensitivity