A cuvette works well with a focused beam of light traveling straight through a clear sample to the detector. Thus,
It is successful ONLY when the sample is clear
It is successful ONLY in measuring the portion of the sample the focused light beam passes through
It is successful ONLY within a narrow dynamic range
Which means it is only useful with samples you produce in the laboratory, devoid of any natural or desired environment, diluted to a range useful to the spectrophotometer, and costing you a small fortune in time, consumables and talent to create.
The integrating cavity method works by diffusing the measurement light to fill the integrating cavity. The consequences are all to the good:
All of the sample is involved measurement
All of the erstwhile lost or scattered light is prevented from escape and is thus captured
We produce cavities of various volumes which result in sensitivity from 0.001 to 100 absorbance units/ centimeter, thus for samples from the most dilute suspension to whole milk and beyond.
Core to a “CLARiTY” spectrometer is the DSPC – DeSa Suspension Presentation Chamber – which houses an integrating cavity.
An integrating cavity is a filled integrating sphere, first developed in the 1950s by a group of oceanographers who were looking to obtain the longest possible pathlength in order to achieve the highest possible sensitivity. In their paper was the offhand remark: ‘scatter by small particulates didn’t matter.’ In 2008, Dr. Richard DeSa found this line while researching a means to study living cells, which are obviously packed with light scattering particles.1
Inserting solids into the DSPC can be done directly or using a test tube for ease of sample entry and removal.
A suspension-filled integrating cavity, shown external to the completed DSPC. Most are 8 mL, but larger and smaller cavities are available to support a breadth of sample types and effective pathlengths.
A standard cuvette next to the integrating cavity.
A DSPC next to the integrating cavity.
Various size integrating cavities are available to support a variety of sample types.
1 Applied Optics, 1992: “… an integrating cavity is completely filled with an absorbing sample, which generally will be considered to be an aqueous suspension or solution. Because the diffuse reflecting cavity walls have high reflectivity, the effective absorption length in the sample is many times the diameter of the integrating cavity…this integrating cavity concept is especially sensitive to small absorptions.” Another way to think of an integrating cavity is as a bright white room without windows, just two small doors. All of the measurement light, which enters through one door, and all of what would be scattered light, stays within this room, bouncing off the reflective walls, until it escapes through the second door to the detector.
This short video shows exactly what happens inside the OLIS DSPC.
DSPCs are available for a variety of uses. Each can be easily removed and replaced with a different one.
Integrating Cavity (DSPC)
(a.) Samples can be pipetted into the cavity (highest sensitivity, research lab method)
(b). Samples can be dropped into the cavity (think tissue, root system, other solids,
including electrodes for spectroelectrochemistry)
(c). A test tube holding the sample can be loaded into the cavity (middle sensitivity, QC lab method; also, think actinometry)
(d.) A flow-through cavity can be used (highest absorbance samples, i.e., ferment, milk,
The dynamic range of one CLARiTY spectrophotometer is determined by the cavity within its DSPC. Using the right DSPC extends the dynamic range of the CLARiTY spectrophotometer. It takes moments to exchange one DSPC to another and you can always add another in future, should your interests expand.
~50 uL protein in a low absorbing solvent will be measured using a 9 mL DSPC with roughly 30 cm pathlength; here, the expected dynamic range is nominally 0.001-1 Abs/cm.
2 mL test tubes are useful for samples with absorbances 0.1 to 2 Abs/cm
Flow-through (FT-)DSPCs are available in five different pathlengths, from 5 mm to 0.2 mm for absorbance work from nominally 5-100 absorbance units/ centimeter!
Apparent absorbance is collected. Optionally convert to absorbance/ centimeter using math we provide.
See the papers by the oceanographers, Javorfi, and others who prepared the way for the CLARiTY here.
Quantum Northwest produces the Peltier DSPCs for Olis instruments.