Evaluation of a Correction for Photometric Errors in FT-IR Spectrometry Introduced by a Nonlinear Detector Response

1998 ◽  
Vol 52 (4) ◽  
pp. 565-571 ◽  
Author(s):  
Robert L. Richardson ◽  
Husheng Yang ◽  
Peter R. Griffiths
Keyword(s):  
Empirical Method ◽  
Second Order ◽  
Detector Response ◽  
Ir Spectrometry ◽  
First Order ◽  
Beer's Law ◽  
Ft Ir ◽  
Beer’S Law ◽  
First Order Correction ◽  
Phase Spectra

For strongly absorbing bands measured with a Fourier transform infrared (FT-IR) spectrometer, the effects of a nonlinear detector response must be eliminated before Beer's law linearity can be achieved. An empirical method for greatly reducing the effect of detector nonlinearity on FT-IR Beer's law spectra measured by using an FT-IR spectrometer equipped with a mercury-cadmium-telluride (MCT) detector is investigated. This first-order analytical function has been applied to correct nonlinear vapor-phase spectra and statistically evaluated for validity for spectral regions above the detector cutoff. In addition, a series of second-order functions has been evaluated to investigate the possibility that the transmittance scale is slightly nonlinear even after the first-order correction has been applied. Any improvement caused by the second-order functions was not statistically significant.

scholarly journals Estimation of Tadalafil Using Derivative Spectrophotometry in Bulk Material and in Pharmaceutical Formulation

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Zamir G. Khan ◽  
Amod S. Patil ◽  
Atul A. Shirkhedkar
Keyword(s):  
Wavelength Range ◽  
Area Under Curve ◽  
Pharmaceutical Formulation ◽  
Second Order ◽  
Order Derivative ◽  
Uv Spectrophotometry ◽  
First Order ◽  
Beer's Law ◽  
Beer’S Law ◽  
Derivative Uv Spectrophotometry

Four simple, rapid, accurate, precise, reliable, and economical UV-spectrophotometric methods have been proposed for the determination of tadalafil in bulk and in pharmaceutical formulation. “Method A” is first order derivative UV spectrophotometry using amplitude, “method B” is first order derivative UV spectrophotometry using area under curve technique, “method C” is second order derivative UV spectrophotometry using amplitude, and “method D” is second order derivative UV spectrophotometry using area under curve technique. The developed methods have shown best results in terms of linearity, accuracy, precision, and LOD and LOQ for bulk drug and marketed formulation as well. In N,N-dimethylformamide, tadalafil showed maximum absorbance at 284 nm. For “method A” amplitude was recorded at 297 nm while for “method B” area under curve was integrated in the wavelength range of 290.60–304.40 nm. For “method C” amplitude was measured at 284 nm while for “method D” area under curve was selected in the wavelength range of 280.80–286.20 nm. For methods A and B, tadalafil obeyed Lambert-Beer’s law in the range of 05–50 μg/mL while for “methods C and D”, tadalafil obeyed Lambert-Beer’s law in the range of 20–70 μg/mL, and-for “methods A, B, C, and D” the correlation coefficients were found to be > than 0.999.

scholarly journals On a theory of the second order longitudinal spherical aberra­tion for a symmetrical optical system

1920 ◽  
Vol 97 (683) ◽  
pp. 196-198
Keyword(s):  
Optical System ◽  
Spherical Aberration ◽  
Empirical Method ◽  
Second Order ◽  
Point Of View ◽  
Axial Plane ◽  
First Order ◽  
Usual Theory ◽  
Semi Empirical

1. The object of this investigation is to establish a formula for the longitudinal spherical aberration of rays which traverse a symmetrical optical system in an axial plane that shall be capable of fairly easy computation for any combination of lenses, and at the same time shall be accurate to the second order and free from certain important difficulties of convergency which occur in certain neighbourhoods when we attempt to use for the longitudinal aberration the method of aberration of successive orders. From the point of view of the optical designer, the usual theory of aberrations, which, for all practical purposes, is largely restricted to the first order, is known to give an unsatisfactory approximation. In practice, the designer adopts a semi-empirical method of tracing a number of rays through the system by means of the trigonometrical equations, a method which is laborious and lengthy, and which can at best give only incomplete informa­tion and very limited guidance for effecting improvements.

Nonlinearity of Beer's Law in Gas-Phase FT-IR Spectroscopy

2001 ◽  
Vol 55 (1) ◽  
pp. 50-54 ◽  
Author(s):  
Mikko Ahro ◽  
Jyrki Kauppinen
Keyword(s):  
Ir Spectroscopy ◽  
Gas Phase ◽  
Beer's Law ◽  
Ft Ir ◽  
Beer’S Law ◽  
Ft Ir Spectroscopy

Effects of Detector Nonlinearity on Spectra Measured on Three Commercial FT-IR Spectrometers

1998 ◽  
Vol 52 (4) ◽  
pp. 572-578 ◽  
Author(s):  
Robert L. Richardson ◽  
Husheng Yang ◽  
Peter R. Griffiths
Keyword(s):  
Flux Density ◽  
Signal To Noise Ratio ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Source Image ◽  
Empirical Correction ◽  
High Photon Flux ◽  
Beer's Law ◽  
Ft Ir ◽  
Beer’S Law

The effect of the nonlinear response of mercury-cadmium-telluride (MCT) detectors has been evaluated on three commercial Fourier transform infrared (FT-IR) spectrometers. The greater the photon flux and the photon flux density, and the smaller the area of the detector on which the source image is focused, the greater are the effects of the nonlinearity. The signal-to-noise ratio (SNR) of spectra measured with an MCT detector under conditions of high photon flux and, especially, high photon flux density is significantly less than the SNR calculated by using the manufacturer's D* value. Detector nonlinearity usually leads to negative deviations in Beer's law plots. An empirical correction algorithm has been applied to Beer's law spectra acquired with the use of photoconductive MCT detectors and has been found to work well.

Evaluation of a System for Generating Quantitatively Accurate Vapor-Phase Infrared Reference Spectra

1998 ◽  
Vol 52 (1) ◽  
pp. 143-153 ◽  
Author(s):  
Robert L. Richardson ◽  
Peter R. Griffiths
Keyword(s):  
Cadmium Telluride ◽  
Vapor Phase ◽  
Nonlinear Response ◽  
Mercury Cadmium Telluride ◽  
Detector Response ◽  
Quantitative Accuracy ◽  
Beer's Law ◽  
Certified Value ◽  
Beer’S Law ◽  
Forced Mixing

A static delivery system for generating infrared vapor-phase reference spectra has been constructed and validated for liquid analytes with polarities up to that of methanol. Several important factors that determine the accuracy of these mixtures have been identified. These include thorough degassing of the liquid analyte, maintenance of water content inside the system below a predetermined value, isolation of the pure analyte vapor before inlet of the fill gas to avoid back-flow of vapor, forced mixing to overcome the effect of excessively slow diffusional mixing of the analyte vapor and fill gas, and measurement within the linear Beer's law range for the resolution and apodization employed. To maintain Beer's law linearity, it is vital to eliminate the effect of a nonlinear response of the mercury cadmium telluride detector. In this paper, the procedure developed to ensure quantitative accuracy from statically generated gas mixtures is described. The effect of detector response linearity on photometric accuracy is discussed, along with a method of empirically correcting for this nonlinear response. The accuracy of vapor-phase samples made by this approach has been validated by comparison to the spectra of certified standards and found to be within 2% of the certified value.

The Quantitative Analysis of Absorption Spectra

1979 ◽  
Vol 33 (5) ◽  
pp. 481-487 ◽  
Author(s):  
C. L. Lin ◽  
E. Niple ◽  
J. H. Shaw ◽  
J. G. Calvert
Keyword(s):  
Absorption Spectrum ◽  
Quantitative Analysis ◽  
Standard Deviation ◽  
Absorption Spectra ◽  
Empirical Method ◽  
Wide Region ◽  
Synthetic Spectra ◽  
Beer's Law ◽  
Beer’S Law

Methods of estimating the information in an absorption spectrum concerning the amount of absorber are presented. The analysis allows a single value of the absorber amount and its standard deviation to be obtained when a wide region of the spectrum is analyzed. An empirical method of reducing the errors caused by departures from Beer's Law is demonstrated to improve the results of the analysis of synthetic spectra of N2O.

Consistency in Circle Cell FT-IR Analysis of Aqueous Solutions

1987 ◽  
Vol 41 (6) ◽  
pp. 1057-1067 ◽  
Author(s):  
Ernest H. Braue ◽  
Michael G. Pannella
Keyword(s):  
Aqueous Solutions ◽  
Practical Method ◽  
Peak Height ◽  
Chemical Effects ◽  
Beer's Law ◽  
Ft Ir ◽  
Beer’S Law ◽  
Ir Analysis ◽  
Ft Ir Spectroscopy

The CIRCLE CELL®, based on the cylindrical internal reflection technique (CIR), has become a popular FT-IR accessory because it allows for easy collection of IR spectra from aqueous solutions. In this paper we describe a detailed study of the quality of quantification possible with the use of aqueous acetone mixtures over a concentration range of 0.01 to 90% (w/w). During a period of four months, the method's sensitivity, accuracy, precision, and time stability were evaluated. With the use of a Nicolet 60SX FT-IR, an MCT-A detector, 500 scans, and a 300-s sampling delay, five sets of triplicate runs, approximately one month apart, were made at each of 10 concentrations. Our results indicate the following conclusions: (1) quantification by peak height gives better precision, whereas peak area gives a more linear response and correlation with Beer's law over a large concentration range; (2) water bands produce spectral artifacts during subtraction, (3) repositioning of the CIRCLE CELL® optical bench between runs and the micro-boat sampling cell between samples critically affects the quantification results; (4) deviations from Beer's law are caused by chemical effects and insufficient resolution errors; and (5) the reliable sensitivity limit is 0.05% w/w. These findings suggest that precise quantitative analysis of aqueous solutions is now a practical method with the use of FT-IR spectroscopy.

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