CCD detectors for molecular absorption spectrophotometry. A theoretical and experimental study on characteristics and performance.

Uncertainty in charge-coupled devices (CCDs) as UV-vis spectrophotometric detectors is studied here considering that it highly affects the limit of detection of analytical methods. Opposite to photomultiplier-type detectors (PMDs) and diode-array detectors (DADs), where uncertainty is mainly dependent on the photonic signal (shot noise), in CCD detectors uncertainty may come from both independent and dependent effects upon the photonic signal. Shot noise is specially important for high photonic signals in the detector (those for low absorbances) while the uncertainty that is independent of the signal is specially important for low photonic signals in the detector (those for high absorbances). That is, the main source of uncertainty is different depending on the value of the experimental measurement. On the other hand, temperature does not practically affect absorbance measurements, though it is very important for emission measurements (fluorescence, Raman, scattering, etc.). Mathematical equations for uncertainty are proposed with excellent fittings to the experimental data. The equation parameters can be experimentally determined from non-linear regression analysis and used to characterize spectrometers or to test their performance. In order to help buyers and users, some recommendations are finally given considering, among others, cooling, slit, attenuator or fiber optic assemblies.