Liquid Waveguide Capillary Cells

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.

• Optical sample flow cell that combines an increased optical pathlength with a small sample volume
• Measure liquids in a continuous flow or using discrete samples
• Connects with 600 µm 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

Typical optical pathlengths of cuvettes and flow cells are between 0.2 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 to 500 cm) with small sample volumes ranging from 2.4 µl to about 3 ml. Compared with a standard 1 cm cell, a 1 mAU signal is enhanced one hundred fold with a 100 cm flowcell to 100 mAU.

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.

Benefits:
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
Applications:
Trace detection of nutrients (nitrite, nitrate, phosphate, iron) in seawater
Environmental and oceanographic monitoring
Drinking water analysis
Colored dissolved organic matter (CDOM)
Process control

LWCC Properties:
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 1 ml/min
LWCC has been operated at 100 to 200 psi without observed malfunction
Maximum hydrostatic pressure the LWCC can withstand has not been established