Troubleshooting

UV-Vis Spectrophotometer Troubleshooting Guide

A practical troubleshooting guide for UV-Vis problems: noisy baselines, drift, spikes, poor repeatability — with the cell-related fixes you can try before calling service.

1. Symptom → Cause → Fix Matrix

Symptom	Most likely causes	First fix
Noisy baseline	Lamp ageing, dirty windows, air bubbles in cell	Clean cells; degas sample; check lamp hours
Baseline drift over time	Warm-up not complete, temperature change	Warm up 30 min; control lab temperature
Absorbance spikes	Air bubbles, particles in beam path, cell not seated	Tap/fill cell; check alignment; filter sample
Poor repeatability	Cell orientation, evaporation, dirty windows	Mark orientation; cover cell; clean windows
Negative readings	Blank mismatch, dirty reference cell	See negative absorbance guide
Flat/low signal	Wrong Z dimension, cell too empty	Check Z dimension; fill above beam

2. Cell Checks (5 Minutes)

Windows clean? — inspect both optical faces; clean per protocol.
Matched pair? — sample vs reference transmission should match within tolerance.
Same path length? — mixing 10 mm and 5 mm cells in one run gives nonsense.
Filled correctly? — sub-micro cells need volume above the beam; check the Z dimension.
No bubbles? — gently tap the cell after filling.

3. Instrument Checks

Warm-up 15–30 minutes before critical measurements.
Verify wavelength calibration with a holmium or didymium filter.
Check lamp age — deuterium lamps fade in the UV end first.
Run an air baseline and a water baseline to separate cell vs instrument problems.

4. When to Call It a Cell Problem

If the instrument baseline is clean with empty cells but degrades with a specific cell, the cell is the problem — usually a scratched window, etched surface or a failing glue line. Replacement is cheaper than a service call.

Suspect a cell issue? Send us a photo of the baseline and we will help diagnose.
Send us your instrument model and sample type — our engineers will reply within 1 business day with the right specification and a firm price. Contact Scuvette →

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Frequently Asked Questions

Why is my baseline drifting or not flat?

Usually the cell is dirty, scratched or has fingerprints/oil on the windows. Re-clean the cuvette, handle it by the matte side, and verify the reference (blank) is correct and matched to the sample cell.

Why are my absorbance readings noisy or not reproducible?

Common causes are air bubbles in the beam path, a smudged or scratched window, wrong path length, or using a glass cell in the UV range. Degas the sample, re-clean the cell, and confirm you are using a quartz cell for UV measurements.

How do I tell whether the problem is the cuvette or the instrument?

Run a quick cell check: swap in a known-good reference cell with the same blank, compare the same sample in two identical cells, and inspect windows under light. If the fault follows the cell, it is a cell issue; if it persists with a clean cell, check the lamp, wavelength calibration and cuvette holder alignment.

Can I reuse a cuvette after a sample precipitated inside?

Only after thorough cleaning. Precipitates (salts, proteins) leave films that raise baseline absorbance. Soak and rinse until the windows are clear under strong light; if etching or scratches remain, retire the cell from quantitative work.

Why do I get negative absorbance values?

Negative absorbance means the sample transmits more than the reference. This happens when the blank and sample are swapped, the reference cell is dirtier than the sample cell, or the cells are not matched. Re-run with a correctly prepared blank in the reference position.