Application Guide

Quartz Cuvettes for Protein Quantification: A280, Bradford & BCA

Protein quantification runs at two very different wavelengths, and that single fact determines which cuvette you need. Direct UV absorbance at 280 nm requires quartz — no plastic or optical glass transmits there. Bradford and BCA assays read in the visible (562–595 nm), where glass and disposable plastic also work. This guide covers both, with the path length and volume trade-offs that matter when samples are precious.

1. Why A280 Needs Quartz

Proteins absorb UV at 280 nm through their aromatic residues — tryptophan and tyrosine primarily, with a smaller contribution from phenylalanine and disulfide bonds. Measuring there directly is fast, reagent-free, and the sample is recoverable, which matters when the protein is the product and not just the analyte.

But 280 nm is deep UV. Disposable polystyrene cuvettes cut off around 340 nm and optical glass around 340 nm as well — both are opaque at 280 nm. Only fused silica transmits there. JGS1 synthetic fused silica covers 200–2,500 nm, so a quartz cell handles A280 and every visible assay on the same instrument.

2. Direct UV (A280) vs Colorimetric Assays

Method	Wavelength	Cuvette material	Sample recoverable?
A280 direct UV	280 nm	Quartz (required)	Yes
Bradford	595 nm	Quartz, glass or plastic	No
BCA	562 nm	Quartz, glass or plastic	No
Lowry	650–750 nm	Quartz, glass or plastic	No

3. Choosing Path Length for Protein

Beer-Lambert linearity holds roughly between 0.1 and 1.0 absorbance units. Outside that window your numbers drift, and no amount of cuvette quality fixes it.

Dilute samples (<0.1 AU at 10 mm) — stay at the standard 10 mm path rather than concentrating.
Concentrated samples (>1.0 AU at 10 mm) — switch to a short path cell (1–5 mm) instead of diluting. This keeps the reading in range and avoids pipetting error.
Unknown concentration — measure at 10 mm first, then pick the path length that lands you between 0.1 and 1.0 AU.

4. Volume: Micro and Sub-Micro Cells

A standard 10 mm macro cell needs roughly 3.5 mL; a semi-micro around 1–1.5 mL. Purified protein rarely comes in those quantities. Micro and sub-micro cells with a masked (black-walled) chamber bring the working volume down to 50–500 µL while keeping the 10 mm path the instrument expects, because the light beam is narrowed rather than the path shortened.

If your sample volume is the binding constraint rather than concentration, this is the first specification to change.

5. Recommended Cells

A280 work — JGS1 quartz macro cells, 10 mm. Transmission to 200 nm means 280 nm sits in a flat, low-noise part of the curve.
Limited sample — micro and semi-micro quartz cells (black-walled versions available).
Very concentrated — short path length cells, 1–5 mm.
Bradford / BCA only — quartz still preferred for reuse and solvent resistance, but optical glass is an acceptable economy option.

6. Practical Notes

Blank with the same buffer the protein is in — buffer absorbance is not zero at 280 nm.
Detergents (SDS, Triton) absorb strongly below 280 nm and will distort A280. Use a detergent-compatible colorimetric assay instead.
Rinse protein residue promptly; dried protein film is the most common cause of a drifting baseline. See the cleaning protocol.
Verify your cell at the wavelength you actually use — a cell certified at 600 nm tells you nothing about 280 nm.

Need a quartz cell verified at 280 nm?
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Protein Quantification Cuvettes — Frequently Asked Questions

Which cuvette should I use for protein quantification?

For Bradford, BCA or Lowry assays use standard 10 mm cells for normal volumes, or micro / ultra-micro cuvettes (down to ~35 µL) when sample is limited. UV A280 readings require quartz. Micro cuvettes.

Quartz vs disposable plastic cuvettes for protein assays?

Disposable PS/PMMA cells are fine for visible-range colorimetric assays, but quartz is required for UV A280 measurements and for organic solvents that attack plastic. Quartz vs glass/plastic.

Cuvette or microplate for protein assays?

Microplates suit high-throughput screening; a cuvette gives a single, accurate reference reading with a fixed 10 mm path and is better for method setup and verification.