diode-array detector
/ DY-ohd uh-RAY dee-TEK-tor /
A traditional spectrophotometer reads one colour at a time, like a person checking a row of mailboxes key by key. A diode-array detector instead has hundreds of tiny light sensors lined up side by side, so it reads every colour at once — like glancing at the whole row of mailboxes in a single look.
It is a detector made of a long row (an array) of photodiodes, each catching a different narrow band of wavelengths after the light has passed through the sample and been spread out by a grating. Because all wavelengths land simultaneously, the instrument captures a full absorption spectrum in a fraction of a second.
This speed is its great strength: it lets an analyst record a whole spectrum almost instantly, ideal for fast-changing samples or as a detector at the end of a chromatography column. The trade-off is that individual diodes are small, so the wavelength resolution is usually a little coarser than a slow scanning instrument's.
As peaks elute from an HPLC column, a diode-array detector grabs a full UV spectrum of each one on the fly, helping confirm a peak's identity as well as measure its size.
Capturing a whole spectrum per peak adds identity to a chromatography run.
In a diode-array instrument the dispersing grating sits after the sample, not before it, so there is no scanning monochromator slit in front of the cell.