Beer-Lambert Law
Transmission measurements (%T) are often used to characterize optical materials, filters, thin film coatings, lenses and other optical components. Transmission is also used to measure the concentration of chemicals in liquid or gaseous samples. Absorbance (A) is a logarithmic transform that is linear with respect to concentration (C) of the absorbing species, the optical pathlength (l) and the extinction coefficient of the chemical (e)
A = eCl or C = A/el
The basic optical setup as shown above is to send a collimated beam of light normal to the surface a planar slab of sample. The detection is on the other side. The light that is collected without the sample in this path is the reference (R), the light that gets through the sample is (S). We also measure a background level or dark measurement (D). Transmission (T) and Absorbance (A) are calculated at each wavelength as:
T = (S – D)/(R – D) A = -log10(T)
The purpose of the probes and fixtures is to provide this basic sampling geometry. The following are a variety of absorbance and transmission measurement fixtures for a variety of applications.
Illuminated Cuvette Holders – FLAME CHEM
Compact, simple, ready to use systems for measuring absorbance of samples in 1 cm. cuvettes.
The direct attach VIS-NIR light source and built in cuvette holder bolts to the front of a FLAME spectrometer. Power and control is passed through the connector on the FLAME spectrometer and the unit becomes completely controlled through software. The cuvette holder accepts all standard 1cm cuvettes (plastic or quartz styles). Outside dimensions of “1cm” cuvettes are actually 12.5 x 12.5 mm. Our beam height is 15mm. The VIS-NIR version pictured above is powered by the USB.
The UV-VIS version shown below has a miniature deuterium bulb and a tungsten halogen lamp. It can operate over the 200-1100nm range.
| Specifications | FLAME-CHEM-UV-VIS | FLAME-CHEM-VIS-NIR |
| SPECTROSCOPIC | ||
| Spectral range: | 200-850 nm | 350-1000 nm |
| Spectrometer (preconfigured): | FLAME-S-UV-VIS-ES | FLAME-S-VIS-NIR-ES |
| Detector: | Sony ILX511B linear silicon CCD array | Sony ILX511B linear silicon CCD array |
| Entrance slit: | 25 µm | 25 µm slit |
| Optical resolution: | ~1.5 nm (FWHM) | ~1.5 nm (FWHM) |
| Order-sorting filter: | 200-850 nm | 350-1000 nm |
| Focus lens for enhanced sensitivity: | Yes | Yes |
| Signal-to-noise ratio: | 250:1 | 250:1 |
| Dynamic range: | 1300:1 for a single acquisition | 1300:1 for a single acquisition |
| Integration time: | 1 ms-65 seconds | 1 ms-65 seconds |
| Stray light: | <0.10% at 435 nm | <0.05% at 600 nm |
| INTEGRATED SAMPLING SYSTEMS | ||
| Integrated sampling system: | FLAME-DA-CUV-UV-VIS | FLAME-DA-CUV-VIS-NIR |
| Light source: | Combined deuterium-tungsten halogen (200-1100 nm) | Tungsten halogen with a violet LED (~390-1000 nm) |
| Light source features: | Manual adjustment of tungsten halogen source | I2c adjustment of the tungsten halogen and LED bulbs |
| Bulb lifetime: | 800 hours (deuterium); 2,000 hours (tungsten halogen) | 2,000 hours (tungsten halogen); 45,000 hours (LED) |
| Cuvette holder: | Accepts 1 cm pathlength cuvettes | Accepts 1 cm pathlength cuvettes |
| Cuvette holder features: | Filter slot on illumination side accepts 0.5” or 12 mm filters; improved collection optics | Improved collection optics |
| ALSO RECOMMENDED | ||
| Cuvettes: | Quartz cuvettes | Plastic cuvettes |
| Interchangeable slits for spectrometer (spare): | Select from 5 µm through 200 µm width slits (FLAME-CHEM system comes with 25 µm slit) | Select from 5 µm through 200 µm width slits (FLAME-CHEM system comes with 25 µm slit) |
| Educational curricula: | Free spectroscopy curricula featuring Flame spectrometer experiments | Free spectroscopy curricula featuring Flame spectrometer experiments |
Spark and STS systems for absorbance
Fiber Optic Cuvette holders – CUV-ALL
The CUV-ALL-UV 4-way cuvette holder for 1 cm pathlength cuvettes has fiber optic couplings at each of four collimating lenses, which couple to optical fibers to illuminate, excite or read the sample. When used with Ocean Optics spectrometers and light sources, the CUV-ALL-UV measures absorbance, fluorescence, scattering or any combination of these optical phenomena. Optical accessories are available to optimize signal reflection, accommodate linear variable filters or block ambient light.
| Engineering Specifications | CUV-UV-ALL |
| Dimensions: | 147 mm x 147 mm x 40 mm overall |
| Weight: | 540 g |
| Pathlength: | 1 cm |
| Z dimension: | 15 mm |
| Filter slot: | Accepts filters up to 6.35 mm (1/4”) thickness |
| Collimating lenses: | Four 74-UV fused silica lenses (200-2000 nm) |
| Water input fittings for temperature regulation: | 3.175 mm (1/8”) NPT |
| Fiber optic termination: | SMA 905 |
| Optional fluorescence enhancement: | Add (2) 74-MSP mirror screw plugs |
| Optional adapter accessories for LVF linear variable filters: | Use LVF-CUV-ADP adapter and CVD-DIFFUSE diffuser |
CUV-UV transmission absorbance cell holder
The CUV-UV cell holder is equipped with 2 fiber optic collimating lenses (74-UV) mounted in a standard 1cm cuvette holder. The holder has a spring loaded pin for precise positioning of the cuvette. It also features a filter slot for adding spectral bandpass or other optical filters. The AL base has water channels for connection to a circulating temperature controlled water bath. The 74-UV lenses can be removed for use in other fixtures.
| Engineering Specifications | CUV-UV |
| Dimensions: | 58 mm x 140 mm x 38 mm overall |
| Weight: | 230 g |
| Pathlength: | 1 cm |
| Z dimension: | 15 mm |
| Filter slot: | Accepts filters up to 6.35 mm (1/4”) thickness |
| Collimating lenses: | Two 74-UV f/2 fused silica lenses (200-2000 nm) |
| Water input fittings for temperature regulation: | 3.175 mm (1/8”) NPT |
| Fiber optic termination: | SMA 905 |
Covers for tall (left) cuvettes and standard (right) cuvettes block ambient light. The standard cuvette cover can also be used to block light when taking a dark readings.
CUV-FL-DA
The CUV-FL-DA cuvette holder attaches to Ocean Optics light sources and couples via optical fiber to our spectrometers, creating a small-footprint system for fluorescence and relative absorbance experiments. The CUV-FL-DA is optimized for the 200-2000 nm range, holds 1 cm pathlength square cuvettes and eliminates the need for a fiber from the excitation or illumination source. A few simple adjustments allow you to use the CUV-FL-DA for absorbance.The CUV-FL-DA is well suited for fluorescence, thanks to UV-enhanced, aluminum-coated mirrors that enhance signal reflection within the sample compartment. That increased signal reflection, combined with greater signal intensity resulting from direct attachment to the excitation source, provides CUV-FL-DA users with much greater fluorescence intensity than is possible with most cuvette holders.
| Engineering Specifications | CUV-FL-DA |
| Dimensions: | 57 mm x 61 mm x 29 mm overall |
| Weight: | 80 g |
| Pathlength: | 1 cm |
| Z dimension: | 15 mm |
| Filter slot: | Accepts filters up to 6.35 mm (1/4”) thickness |
| Collimating lenses: | One of 74-UV fused silica lens (200-2000 nm) |
| Reflection mirrors: | Two (2) of UV-enhanced, aluminum-coated |
| Light source mount diameter: | 9.52 mm (3/8”) |
| Fiber optic termination: | SMA 905 |
| Item | Description | Use |
| CUV-FL-DA | Cuvette holder with four collimating lenses | Absorbance and fluorescence |
| 74-MSP | Mirror screw plugs for increasing signal collection | Fluorescence |
| CUV-COVER | Cover for sample compartment | To block ambient light |
| CUV-COVER-TALL | Cover for sample compartment (for cells taller than 58 mm) | To block ambient light |