Edge Collective
UV Spectrophotometry
Designing a DIY UV SpectrophotometerQuick links
Background
Kearns et al have been working to develop lower-cost methods of testing that leverage a particular feature of biochar (and similar filters): some contaminants adbsorb much more easily than others. It turns out that the presence of one class of more weakly-adsorbed contaminants -- dissolved organic matter -- is relatively easy to assess with a lower-cost laboratory method: UV spectrophotometry.
The details of this approach are laid out in a 2020 article by Kearns et al:
- "Biochar Water Treatment for Control of Organic Micropollutants with UVA Surrogate Monitoring" -- https://www.liebertpub.com/doi/full/10.1089/ees.2020.0173 | PDF | local PDF
And specific instructions for performing the UV absorbance test are laid out in the supplementary section, here:
Further: while commercial UV spectrophotometers used in such tests are usually over $2000, there are several designs available for DIY forms of the instrument, costing under $100 in parts. We found one design to be particularly simple and well-characterized:
- "An accurate, precise, and affordable light emitting diode spectrophotometer for drinking water and other testing with limited resources" -- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6988917/
Our aim is to build a working prototype of this UV spectrophotometer, compare its performance to similar commercial instruments used in a laboratory, and then see if such an instrument might be easy to build and use in a community workshop setting.
Misc notes
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Josh Kearns substack piece on Kearns et. al, "Leveraging DOM UV absorbance and fluorescence to accurately predict and monitor short-chain PFAS removal by fixed-bed carbon adsorbers"
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Analog Devices article by L. Orozco, "Synchronous Detectors Facilitate Precision Low-Level Measurements"
Sun Mar 3 08:35:31 PM EST 2024
Building the circuit
Precision voltage to current converter
Adafruit 4-pin jumper cable here
Adafruit 4-pin jst ph stemma here
Adafruit JST 4-pin jst ph stemma SMD here
- diagram here
Mon Mar 11 05:20:16 PM EDT 2024
LED polarity 
uv detector IN-C35PPCTGU0
datasheet here
custom footprint:
emitter v_0.1 ordered 3/11/24
detector v_0.1 ordered 3/12/24
Fri Mar 15 11:00:43 AM EDT 2024
instructrable on 555 as switch mode supply
Sat Mar 23 03:52:20 PM EDT 2024
Solder mask goof-up on UV emitter part!
Reference for UV emitter IN-C35PPCTGU0
Also: two pins on Q1 on emitter are 'flipped' -- need to fix pins -- was able to solder 'upside-down' anyway to fix
Mon Mar 25 08:17:39 PM EDT 2024
Made a quick 3d enclosure using openscad:
openscad and stl files are here
Fri Mar 29 08:57:08 PM EDT 2024
Water filtering, 1 micron
Selection at McMaster here
Nice pairing on Amazon:
Most recent prototype
Fri Apr 5 08:31:52 PM EDT 2024
Working on detector v_0.2 ...
Sub-schematic that will be moved to a 'control board':
Version 0.1 footprint assignments:
Version 0.1 pinout:
(need to add 2.5V ref)
Fri Apr 5 11:01:04 PM EDT 2024
Detector schematic:
Emitter schematic:
Revision 0.2 of emitter and detector
Sat Apr 6 10:25:06 PM EDT 2024
Edited footprint for LED (remove solder mask from center pad)
Revising mosfet pin assignment on emitter ...
2N7000 pinout:
emitter ver 0.2
Sat Apr 6 10:22:42 PM EDT 2024
board layout:
schematic:
)
board files:
detector ver 0.2
Sat Apr 6 10:22:55 PM EDT 2024
board layout:
schematic:
)
board files:
Mon Apr 15 08:18:11 PM EDT 2024
Collecting water samples and filtering through 1 um filter ...
3/4" NPT male + 3/4" barb fitting on Amazon
electric water transfer pump on Amazon
calibration of total organic carbon / uv254, EPA document pdf
'request a quote' for uva254 go here
might want to search for 'total organic carbon' (TOC)
An easy spectrophotometric acid-base titration protocol for dissolved organic matter
correlating uv254 to TOC, BOD, and COD video
Great paper on UV254 methods and applications. Note: correlations between uv254 and disinfection byproducts! references here