Unique wavelengths

Spectra can be obtained as either absorption spectra, in which the material of interest absorbs unique wavelengths of radiation, or emission spectra, where... 

Unlike the previous techniques, sensitivity is not an issue for AAA. There are few interfering substances because the method involves hydrolysis, derivatization, and chromatography with detection at a unique wavelength. Most excipients will not affect the hydrolysis step, but one has to be careful to ensure that the amino acids used to quantitate the protein are not destroyed. In addition, it must be determined if the excipients interfere with the derivatization chemistry or the chromatography. A BSA standard in the same buffer formulation is routinely run in parallel to the target protein to ensure the accuracy of the method. 

Obtain a UV scan of analyte Scan from 200 nm to 400 nm, looking for max or a unique wavelength appropriate for analysis. Generally, selectivity increases with wavelength. 

As with MID on MS, the more wavelengths that are simultaneously monitored, the greater is the likelihood of valid identification. Another analytical technique is the formation of derivatives which are fluorescent or absorb UV radiation at unique wavelengths. The compound of interest may be derivatized and injected onto the HPLC system the column separates the reactants and then passes them through the detector. The compound may also be derivatized "post column" as done by amino acid analyzers. The de-rivatizing reactant is metered to mix with the column effluent and is then sent to the detector. Ideally, only the derivatized products should be detectable. 

Near-infrared spectroscopy has been used to quantitate sulfathiazole Form-I and Form-Ill in binary physical mixtures in which one form was the dominant component.81 The spectra of each form exhibited sufficient differences that unique wavelengths of absorbance were easily attributable to each form. Excellent linearity in calculated versus actual compositions were obtained over the concentration range of 0-5% for either Form-I in Form-Ill, or for Form-Ill in Form-I. After considering appropriate calibration models, a limit of quantitation of approximately 0.3% was ultimately deduced. 

The existence of an isosbestic point is not proof of the presence of only two components. There may be a third component with e = 0 at this particular wavelength. The absence of an isosbestic point, however, is definite proof of the presence of a third component, provided the possibility of deviation from Beer s law in the two-component system can be dismissed. For a two-component system, the isosbestic point is a unique wavelength for quantitative determination of the total amount of two absorbing species in mutual equilibrium. 

An atomic absorption spectrometer requires a lamp of unique wavelength (e.g. b or d nm) for each exciting element [2]. The wavelengths of elements are... 

There are multiple types of molecular vibrations that absorb at unique wavelengths or frequencies of near-infrared energy depending upon the bond type. Several normal (or normal mode) types of molecular vibrations active within the NIR region are illustrated in the following figures. Each of these types of vibrations has a unique frequency where absorption occurs. The location of these frequencies and the associated molecular structures (spectra-structure correlations) are the purpose of this book. 

---