Single-beam advantages

Some spectrophotometers are single-beam instruments, and some are double-beam instruments. In a double-beam instrument the light beam emerging from the monochromator is split into two beams at some point between the monochromator and the detector. The double-beam design provides certain advantages that we will discuss shortly. 

What are the advantages of a double-beam instrument over a single-beam instrument ... 

How does a single-beam atomic absorption instrument differ from a double-beam instrument What advantages does one offer over the other ... 

Replacement of the conventional incoherent light source with a laser has allowed CD measurements to be made on extremely small samples, such as those encountered in capillary electrophoresis. In addition, the unique spatial properties of the laser are utilized to advantage in thermal lens spectroscopy. TL detection of CD, either via a single beam, or a differentially configured arrangement, has demonstrated significant improvements in the measurement SNR. Application to HPLC detection, or time-resolved studies, are currently under investigation. 

A further advantage of spectrophotometers is the ready availability of a number of low-cost instruments with sufficient accuracy and reproductivity for dyebath analysis. Much of the work in the current study was carried out on a single-beam grating spectrophotometer costing approximately 2,000. The computations necessary in the analysis can be conveniently carried out on low-cost desk calculators or microprocessors. The calculations necessary for a four-dye mixture (or three dyes plus background) can be handled on a system costing less than 1,000. The least-squares fit of 16 points of the absorption spectrum can be carried out on a 3,000 minicomputer. Development of these low-cost instrument-minicomputer systems is largely responsible for consideration of dyebath reuse as a practical reality for the textile industry. 

Forward optic spectrophotometers are either singlebeam or double-beam spectrophotometers. The singlebeam instruments can be either very simple or expensive depending on the sophistication desired or needed. Simple single-beam instruments have poor stability and excessive drift. These advantages are eliminated in systems equipped with a high-resolution monochromator with adjustable slits, controlled by microprocessors for rapid data acquisition and evaluation of data. 

Although less common, fast scanning single-beam dispersive instruments are available, replacing the complexity of the interferometer with the economy of the monochromator. These instruments can provide speed and resolution comparable to the FTIR instruments but lack the multiplex advantage that decreases noise for low-level measurements. 

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