Spectrophotometer

Overview

The spectrophotometer measures how much light a sample absorbs at each wavelength across the ultraviolet, visible, and near-infrared range. From absorbance it determines concentration, via the Beer-Lambert law, and characterizes the spectral fingerprint of a compound. It is used everywhere from nucleic-acid quantitation to reaction kinetics and quality control. This double-beam design splits the light into sample and reference paths and compares them in real time, so lamp drift and electronic noise cancel out and the measurement stays stable over a long scan.

Construction

All optics mount on a cast-aluminum Optical Bench Baseplate inside a light-tight Housing & Chassis, which keeps stray light out and holds the alignment fixed. The Light Source Assembly combines two lamps: a deuterium lamp covers the UV down to 190 nm and a tungsten-halogen lamp covers the visible and near-infrared, brought onto a single axis by a switchable source mirror so the instrument can cover the full range in one scan.

How it works

Light enters the Monochromator, a Czerny-Turner arrangement that selects a single wavelength. The entrance slit defines the input, a collimating mirror parallels the beam onto a diffraction grating that disperses it by wavelength, and a focusing mirror images the chosen color onto the exit slit. The Grating Drive rotates the grating to scan wavelength, with an optical encoder reporting its angle, while an order-sorting filter wheel blocks higher diffraction orders that would otherwise contaminate the beam.

In the Sample Compartment, a beam splitter and a rotating chopper alternate the monochromatic beam between the sample cuvette and a reference cuvette, and a shutter provides a dark reading. The two beams fall on the Detector Assembly, whose silicon photodiode array and low-noise readout convert light into current. The Main Control Board digitizes that signal with a 24-bit ADC, computes the sample/reference ratio as absorbance, and shows results on the Front-Panel Display. A calibration filter set verifies wavelength and photometric accuracy.