Liquid Waveguide Capillary Cells (LWCC) are fiber optic cells that combine an increased optical pathlength (50–500cm) with small sample volumes (125–1250µL). 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. According to Beer’s Law the absorbance signal is proportional to chemical concentration and light path length. Compared with a standard 1 cm cell, a 1mAU signal is enhanced fifty-fold with a 50cm cell to 50mAU, using WPI’s patented aqueous waveguide technology*. The LWCC can be connected directly to a pump or can even be filled using a syringe. Based on fiber optics, the LWCC is designed for use with WPI’s Tidas I or SpectraUSB spectrophotometer systems. Further, modular sample systems can be assembled using SpectraUSB spectrometer modules and WPI’s range of UV/VIS light sources D2H and FO-6000

These spectra in the image below show the optimal detection limits for LWCCs of varying pathlength.

Applications

LWCCs have been used in a variety of applications, such as liquid chromatography, stopped-flow and colormetric detection, drinking water analysis, as well as environmental and oceanographic monitoring systems. WPI’s Liquid Waveguide Capillary Cells are made of fused silica tubing with an outer coating of a low refractive index polymer. This results in high signal stability and easy removal of air bubbles trapped in the sensor cell due to the hydrophilic character of the cell wall.

These unique instruments were invented, patented and optimized by WPI during years of research in this field.* They feature a number of advantages over conventional absorbance cells and flow cell arrangements. Designed for use with fiber optics, they require only small sample volumes and have a high optical throughput.

* Related Patents

• 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

LWCC Key Features

Pathlength, internal volume and wavelength range (measured with ultrapure water and a Tidas II spectrophotometer) are key features of the LWCC. The chart below shows the various LWCCs side by side.

	Pathlength [cm]	Internal Volume [µL]	Wavelength Range [nm] measured with Tidas II
LWCC-3050	50	125	230-800
LWCC-3100	100	250	230-730
LWCC-3250	250	625	250-730
LWCC-3500	500	1250	280-730