Systems and methods for pressure differential molecular spectroscopy of compressible fluids
View Patent ↗Described herein is a spectroscopic system and method for measuring and monitoring the chemical composition and/or impurity content of a sample or sample stream using absorption light spectroscopy. Specifically, in certain embodiments, this invention relates to the use of sample pressure variation to alter the magnitude of the absorption spectrum (e.g., wavelength-dependent signal) received for the sample, thereby obviating the need for a reference or ‘zero’ sample. Rather than use a reference or ‘zero’ sample, embodiments described herein obtain a spectrum/signal from a sample-containing cell at both a first pressure and a second (different) pressure.
1. A spectroscopic system for measuring chemical composition and/or trace impurities in a compressible fluid sample, the system comprising:
an electromagnetic radiation source for generating electromagnetic radiation;
optics for directing the generated electromagnetic radiation through a sample cell containing a compressible fluid sample;
an optical detector array for receiving electromagnetic radiation from the sample cell containing the fluid sample and for generating an electrical signal indicative of spectral information associated with the fluid sample;
a pressure modulating system for varying the pressure of the fluid sample in the sample cell, thereby varying sample density; and
a processor and memory having instructions stored thereon, wherein the instructions, when executed by the processor, cause the processor to identify and/or analyze at least two absorption spectra obtained at different sample pressures in the fluid sample, thereby identifying a differential absorption spectrum for the fluid sample.
2. The spectroscopic system of claim 1 wherein the pressure modulating system comprises:
a valve assembly having a first input port, a second input port, and an output port, the valve assembly being configured to selectably permit flow (i) between the first input port and the output port and (ii) between the second input port and the output port, according to a selectable configuration of the valve assembly; and
a check valve connecting between the first input port and the second input port to allow setting of measurement pressure of the fluid sample in the sample cell.
3. The spectroscopic system of claim 2 , wherein the valve assembly comprises a three-way valve.
4. The spectroscopic system of claim 1 , wherein the sample cell is a flow cell permitting flow of the fluid sample therethrough during measurement.
5. The spectroscopic system of claim 1 , wherein the pressure modulating system allows for setting measurement pressure of the fluid sample in the sample cell at a first pressure and at a second pressure while maintaining a consistent flow rate throughout measurement.