Table 2 Advantages and disadvantages of ultraviolet spectrophotometric methods for the determination of the minor component presented in different fixed-dose pharmaceutical combinations
Methods | Advantages | Disadvantages |
|---|---|---|
Methods based on signal enhancing | ||
Zero-crossing derivative | -Raises resolution of overlapped spectra in binary mixture. | -Amplifies signal to noise ratio. -Demands choosing a suitable wavelength increment for proceeding derivative -Demands selecting zero-crossing point. |
Area under the curve correction | -Raises sensitivity, more than absorption correction method -Easier calculations than traditional (AUC) | -Requires extended spectrum of one of the components than the other. |
Chemometric methods | ||
Continuous wavelet transform as a pre-processing tool in partial least-squares | Collects more analytical data from the full matrix spectrum of drugs mixture tested, enabling each component in the mixture to be calculated successfully. | Several steps were required to complete the separation process successfully. The need to special software (Matlab) |
Partial least-squares (PLS) | In PLS, both the data in the absorption matrix and the concentration matrix are used and this provides a more stable model as it eliminates noise from both absorption and concentration data. | Need Matlab program connected with UV-spectra device |
Partial least squares with regression model updating | Considered as a robust analytical method despite spectral data noise and missing data. | Need Matlab program connected with UV-spectra device |
Artificial neural networks (ANN) | Obtaining the relationships between independent variables, allowing all drugs to be calculated in extended nonlinear range. | Need Matlab program connected with UV-spectra device |
Methods based on geometrical relationship of standard addition | ||
H-Point standard addition | -Determines binary mixture with large difference in its components signal | -Required choosing two wavelengths where the interfering component has the same absorbance -Many graphical representations and tests are needed |
Ratio H-point standard addition | -Determines binary mixture with large difference in its components signal -No need for any considerations upon selecting the wavelengths | -Required normalized spectrum for division |
Geometrical amplitude modulation | -Applicability to partial and sever overlapped spectra | -The need ofiso-absorption point or extended spectrum of the major component. -The need of normalized spectrum for division -Many tests are needed. |
Geometrical induced amplitude modulation | -Applicability to partial and sever overlapped spectra -No need for iso-absorption point or extended spectrum of the major component. | The need of normalized spectrum for division - Many tests are needed |
Methods based on geometrical relationship of standard addition | ||
Compensated area under the curve | -Determines binary mixture with large variance in its components signal | -Calibration curve is required for every mixture |
Derivative compensation ratio | -Determines binary mixture with large variance in its components signal -Raises resolution of overlapped spectra in binary mixture | -Calibration curve is needed for every mixture -Needs for choosing a suitable wavelength increment for proceeding derivative |
Methods based on ratio spectra | ||
Ratio difference | Cancels derivative step which improve signal to noise ratio | -Requires tests to choose the best concentration for dividing. -The need of standard spectrum of the interfering substance for the dividing process |
Ratio subtraction | -Regains the zero order spectra of the interfering substances | -Require extended spectrum of one of the components than the other -Incapables to determine the extended component |
Derivative ratio–zero-crossing | -Applies to determine compounds in ternary mixture | -Requires tests to choose the best concentration for dividing. -Needs standard spectrum of interfering substance for the dividing process -Needs selecting zero-crossing point |
Derivative ratio | -Applies to determine compounds in ternary mixture. -No necessity for zero-crossing point | -Requires tests to choose the best concentration for dividing -Needs choosing a suitable wavelength increment for proceeding derivative -Needs standard spectrum of the interfering substance for the dividing process. |
Double divisor ratio spectra derivative | -Applies to determine compounds in ternary mixture. -No necessity for zero-crossing point | -Requires tests to choose the best concentration for dividing -Needs choosing a suitable wavelength increment for proceeding derivative. -Needs standard spectrum of the two interfering substances for the dividing process |
Area under curve of derivative ratio | -Cancels interference of the major compounds -Raises sensitivity | -Requires tests to choose the best concentration for dividing -Needs standard spectrum of the interfering substance for the dividing process |
Successive derivative of ratio spectra | -Applies to determine compounds in ternary mixture | -Requires extended spectrum of one of the components in the ternary mixture - Requires tests to choose the best concentration for dividing. -Needs standard spectrum of the interfering substance for the dividing process |
Extended ratio subtraction | -Regains the zero order spectra of the interfering substances | -Requires extended spectrum of one of the components -Un appropriates for determining low concentrations of the more extended substance -Needs standard spectrum of the none extended substance for the dividing processspectrum as a divisor -Requires tests to choose the best concentration could be used as a divisor |
Constant center | -Regains the zero order spectra of the interfering substances -Applicability to partial and sever overlapped spectra | -Needs standard spectrum of the interfering substance for the dividing process -Requires tests to choose the best concentration for dividing |
Amplitude modulation | -Eliminates the step of selecting the best divisor concentration. -Getting the concentration of both substances by one regression equation | -Requires extended spectrum of one of the components -The need of normalized spectrum for dividing process |
Absorption subtraction | -Getting the concentration of both substances by one regression equation | -Demands the calculation of absorption factor. |
Amplitude summation | -The drafts in the isosbestic point in derivative step may able to correct interference from some additives | -Demands the calculation of response factor. -Amplifies signal to noise ratio. -Requires choosing a suitable wavelength increment for proceeding derivative |
Absorptivity centering | -Regains the zero order spectra of the interfering substances -Applicability to partial and sever overlapped spectra | -Demands the calculation of two factors -The need of normalized spectrum for dividing process -Requires many steps to apply it |
Derivative subtraction coupled with constant multiplication | -Regains the zero order spectra of the interfering substances | -Requires extended spectrum of one of the components -Requires tests to choose the best concentration for dividing |
-Constant multiplication coupled with spectrum subtraction | -Regains the zero order spectra of the interfering substances | -Require extended spectrum of one of the components -Requires standard solutions of the interfering compound to be used as a divisor. -Requires tests to choose the best concentration could be used as a divisor |
Constant center coupled with spectrum subtraction | -Regains the zero order spectra of the interfering substances -Applicability to partial and sever overlapped spectra | -Requires standard solutions of the interfering compound to be used as a divisor. -Requires tests to choose the best concentration for dividing |
Mean centering | The transformed signals are evaluated at the highest peak point, for optimum maximum sensitivity, levels De-noising and raising the signal to noise ratio | Coding of algorithms (special sequence in Matlab®) |
Continuous wavelet transform | Many different wavelets family are often used for CWT analysis as they allow the separation of phase and amplitude components associated with the signal. | Several experiments were required to find the suitable wavelet family to complete the separation process successfully |
Methods based on sample enrichment by sample spiking (standard addition ) or spectrum addition technique | ||
Sample spiking (standard addition) | -Determines low concentration of minor component when eviating from Beer’s law | Depending on one standard added for determination |
Spectrum addition | -Determines low concentration of minor component when deviating from Beer’s law -More accurate results comparing to sample spiking (standard addition) | -Depending on one standard spectrum for determination. |