How do I fix nonlinear absorbance in a do-it-yourself spectrophotometer?

[Tyler_J]

I’ve been trying to calibrate my DIY spectrophotometer using a series of known concentration solutions, but my absorbance readings are consistently nonlinear at the higher end. I’m wondering if the issue is my light source’s intensity or if the cuvette path length isn’t as uniform as I thought.

[OliviaXH]

I ran into that too. At the high end the curve started flattening and it felt like the detector was clipping before the signal could follow Beer’s law.

[Nora3]

The lamp tended to drift between measurements, so I’d warm it up a bit and keep the blank consistent, but those top-end points still looked off.

[Camila95]

Could be stray light from the holder or reflections off the cuvette rims. I swapped holders and cuvettes a few times and the nonlinearity didn’t vanish.

[Adam.J]

I tried swapping for cuvettes with tighter thickness tolerance and even new buffers, but the nonlinearity still showed up around absorbance near 1.0 to 1.2.

[Anthony.T]

The path length angle or how the cuvettes sit in the holder might change the actual path length a bit; a small tilt can throw off the measurement when the signal is already strong.

[Andrew_R]

One last thing I did was look at the raw signal rather than absorbance and I noticed the response isn’t linear as the lamp warmed up; it’s not a clean straight line and I’m not sure what to fix first.