Integrated illumination-detection flow cell for liquid chromatography
A liquid chromatography flow cell including an integrated light source and an integrated detection chamber. The integrated light source includes a plurality of light emitting diodes (LEDs), wherein each LED emits light of a specific wavelength. The light emitted from the integrated light source is directed to pass through a sample in a flow chamber of the flow cell without any optical conditioning, and the light not absorbed by the sample flows out of the flow chamber directly into the integrated detection chamber, where an intensity of the unabsorbed light is measured by detectors coupled to the integrated chamber.
1. A method, comprising:
activating one light emitting diode (LED) from a plurality of LEDs integrated within a flow cell;
adjusting an output of the one LED based on a signal from a reference photodiode adjacent to the one LED, the output of the one LED travelling along a light path to one of a plurality of coupling optics, wherein each of the plurality of coupling optics is positioned between each LED and a first optically transparent wall of the flow cell, and after passing through one of the plurality of coupling optics, the output of the one LED passing through the first optically transparent wall of the flow cell into a sample chamber of the flow cell; and
detecting an amount of light transmitted through the sample chamber through a second optically transparent wall of the flow cell, opposite the first optically transparent wall, via one or more photodetectors coupled to a detection chamber integrated with the flow cell;
wherein the reference photodiode detects a portion of light from the one LED that is reflected from the one of the plurality of coupling optics; and
wherein the one LED and the reference photodiode adjacent to the one LED are positioned on a bottom surface within the flow cell.
2. The method of claim 1 , wherein each of the plurality of LEDs emits light of a different wavelength, and wherein each LED of the plurality of LEDs has a corresponding reference photodiode, each of the corresponding reference photodiodes detecting corresponding portions of light from each corresponding LED that are reflected from the one of the plurality of coupling optics.
3. The method of claim 2 , wherein each of the corresponding reference photodiodes is integrated within the flow cell and adjacent to the corresponding LED.
4. The method of claim 1 , wherein the detection chamber is an integrating chamber, and a bottom surface of the detection chamber is at least partially comprised of the second optically transparent wall, wherein the integrating chamber fully collects wide dispersion light exiting the second optically transparent wall, and wherein the signal from the reference photodiode is based on the portion of light detected by the reference photodiode.
5. The method of claim 1 , further comprising determining an absorbance of a sample within the sample chamber based on the detected amount of light transmitted through the sample chamber, and wherein a first bottom surface of the reference photodiode and a second bottom surface of the one LED lie on a same horizontal plane within the flow cell.
6. The method of claim 1 , wherein adjusting the output of the one LED based on the signal from the reference photodiode adjacent to the one LED includes modulating the output of the one LED so that an amount of light measured by the reference photodiode remains constant.
7. The method of claim 1 , further comprising adjusting the output level of the one LED based on a signal measured by the one or more photodetectors based on a signal-to-noise ratio.