The Complete Handbook of Spectrometers

Chapter 1: Understanding Spectrometers

Every day, in laboratories and industrial plants around the world, a spectrometer answers a simple, powerful question: "What is this material made of, and how much of each component is in it?" This is not a rhetorical question, but a practical one. An incoming shipment of polymer pellets could be a high-grade resin worth thousands of dollars, or it could be a cheaper blend with different additives that will fail midway through an extrusion process. A pharmaceutical company needs to verify that a batch of pills contains exactly 10 mg of the active ingredient, not 9 or 11. A farmer testing soil needs to know the precise concentration of nitrogen and phosphorus to adjust fertilizer application and avoid waste. In each case, the answer comes from a spectrometer—a tool that, at its heart, is an exquisitely precise observer of light.

To understand what a spectrometer does, we must first accept a basic fact: "light" is more than what we can see. It is an electromagnetic wave, propagating through space at a speed of about 300 million meters per second. Its wavelength—the distance between wave crests—determines its character. The visible spectrum that your eyes can detect is just a tiny sliver of this radiant energy range, running from approximately 400 to 700 nanometers for violet to red light. This narrow band turns out to be of limited use for analytical chemistry. What is far more useful is the invisible light just beyond the visible range. Ultraviolet (UV)