Monte Carlo simulation for the prediction of precision of absorbance measurements with a miniature CCD spectrometer

Abstract

The precision characteristics of the absorbance measurements obtained with a low-cost miniature spectrometer incorporating an array detector were evaluated. Uncertainties in absorbance measurements were due to a combination of non-uniform light intensity and detector response over the wavelength range examined (350-850 nm), in conjunction with the digitization of the intensity indications and the intrinsic noise of the detecting elements. The precision characteristics are presented as contour plots displaying the expected RSD% of absorbances on the absorbance versus wavelength plane. The minimum RSD% for the spectrometer configuration tested was observed within the 0.2-1.5 absorbance units and 500-750 nm wavelength range. Without invoking signal enhancement features of the data-acquisition program (scan average, higher integration times, smoothing based on averaging the signal detected by adjacent pixels), the attainable precision within this range was 0.4-0.8%. A computer program based on Monte Carlo simulations was developed for the prediction of absorbance precision characteristics under various conditions of measurements.

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“…[5,6] As per Beer-Lambert law, an accurate UV spectrophotometric analysis of dissolution aliquots requires UV absorbance in the range of 0.2-1.0 to achieve linear correlation coefficient close to 0.999 (Beer Lambert's law). [7] Hence, when using an online auto analyzer, one of the major aspects to be accounted is the dilution factor required to obtain drug concentration in Beer-Lambert range. Every drug has its unique property in terms of wavelength maxima (λ max ), and its corresponding absorbance value at selected λ max .…”

Uncertainty in CCD detectors with and without cooling devices when used for molecular fluorescence measurements

“…In the last few years, charge-coupled devices (CCDs) have been increasingly used for light measurements, either as portable detectors or for ow methods, chromatography, etc. [15][16][17] Most of the time, they are used for absorbance measurements, 18,19 but also they are suitable for luminescence or Raman measurements due to their high quantum yield; however, uncertainty studies are scarce in the latter case. 20 Owing to the low detector signal during uorescence measurements, it can be expected that uncertainty will depend greatly on background noise (eqn (1)), that is, on dark noise, reset noise, read-out noise and non-uniformity; 21 no one of these depends on the signal, but they depend strongly on detector temperature (T det ).…”

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

“…The leader work on the subject 8 was up-dated recently for diode-array and photomultiplier spectrophotometers, 9 showing that the main source of uncertainty in these detectors comes from the statistical variance in the photon arrival rate. However, not many studies on the characteristics and performance of CCDs as detectors seem to have been accomplished and very few uncertainty studies can be found: 10 they mainly refer to CCDs as detectors for luminescence, Raman, reflectance, etc., and deal with the handling of signals to improve the S/N (average, integration time, binning, 3 etc.). Nevertheless, the characteristics of CCDs, when they are used as detectors for absorbance, may differ from those when they are used for Raman, luminescence, etc.…”