In the eight years since they were last discussed in these pages, charge-transfer device (CTD) array detectors have become an invaluable tool for the analytical chemist. The broad class of CTDs includes two subclasses: charge-coupled devices (CCDs) and charge-injection devices (CIDs). CTDs absorb photons, convert them to charge carriers, and measure the carriers to create an analytical signal. These metal oxide semiconductor array detectors are no longer primarily a research tool—they are key components in commercial instrumentation. From their inception as detectors for molecular absorbance and atomic emission spec-troscopy, CTDs are now commercially available for use as detectors in nearly all areas of chemical analysis, including molecular luminescence, atomic emission spectroscopy, Raman spectroscopy, X-ray diffraction, microscopy , separations, and MS. Only a few years ago, using a CCD or CID in- volved constructing a camera controller, writing low-level interface software, and designing a cryogenic system simply to get the device running. Today, camera systems for incorporation into research instruments, complete with control hardware and software, are widely available.
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