Standard spectra

Comparison of the mass spectrum from a target compound (top), with the three best fits from the library of standard spectra (lower three traces). The closeness of fit of the mass spectra and the chromatographic retention time lead to a positive identification of 2, 6-dimethylheptane. 

Spectra. The abiHty to consult collections of standard spectra is cmcial in the analysis of unknown compounds. A long history of data collection efforts has been aimed at these appHcations. Among the best known of the pubHshed handbooks are the Sadtkr Spectral Data Sheets which include ir,... 

J3 4 = 3.45-4.35 J2-4 = 1.25-1.7 and J2-5 = 3.2-3.65 Hz. The technique can be used quantitatively by comparison with standard spectra of materials of known purity. C-nmr spectroscopy of thiophene and thiophene derivatives is also a valuable technique that shows well-defined patterns of spectra. C chemical shifts for thiophene, from tetramethylsilane (TMS), are 127.6, C 125.9, C 125.9, and C 127.6 ppm. 

The Sadtler Standard Spectra, Sadder Research Laboratories, Philadelphia, Pa., 1971. 

In conclusion, SSIMS spectra provide not only evidence of all the elements present, but also detailed insight into molecular composition. Quasimolecular ions can be desorbed intact up to 15000 amu, depending on the particular molecule [3.17] and on whether an effective mechanism of ionization is present. Larger molecules can be identified from fragment peak patterns which are characteristic of the particular molecules. If the identity of the material being analyzed is completely unknown, spectral interpretation can be accomplished by comparing the major peaks in the spectrum with those in a library of standard spectra. 

Visible and UV spectrophotometric techniques are most convenient for studying the polymer and various oxidation states of plutonium. The spectra of the plutonium states and the procedure for resolution of the concentrations were previously described (9 ). Changes in the relative concentrations of the oxidation states and of the polymer generally are determined from corresponding changes in the spectra and a comparison of the changes to standard spectra of the various states. These techniques have been used exclusively for studying the photochemistry of aqueous plutonium. 

This does not mean that the other techniques discussed in Part 1 are unimportant, but that they will only need to be made use of when the standard spectra do not provide sufficient information. 

The frequencies of absorption bands present gives diagnostic information on the nature of functional groups in materials as well as information from any observed frequency shifts on aspects such as hydrogen bonding and crystallinity. In many cases, spectra can be recorded non-destructively using either reflection or transmission procedures. IR spectra of small samples can also be obtained through microscopes (IR microspectrometry). Chalmers and Dent [8] discuss the theory and practice of IR spectroscopy in their book on industrial analysis with vibrational spectroscopy. Standard spectra of additives for polymeric materials include the major collection by Hummel and Scholl [9]. 

Compared to flame excitation, random fluctuations in the intensity of emitted radiation from samples excited by arc and spark discharges are considerable. For this reason instantaneous measurements are not sufficiently reliable for analytical purposes and it is necessary to measure integrated intensities over periods of up to several minutes. Modern instruments will be computer controlled and fitted with VDUs. Computer-based data handling will enable qualitative analysis by sequential examination of the spectrum for elemental lines. Peak integration may be used for quantitative analysis and peak overlay routines for comparisons with standard spectra, detection of interferences and their correction (Figure 8.4). Alternatively an instrument fitted with a poly-chromator and which has a number of fixed channels (ca. 30) enables simultaneous measurements to be made. Such instruments are called direct reading spectrometers. 

J.F. Moulder, W.M.F. Stickle, P.R.E. Sobol, and K.H.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, a Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Perkin Elmer, 1995. 

Infrared spectra of known and newly reported compounds are provided in the British Pharmacopoeia (1998) and also in Sadtler Standard Spectra published by Sadder Research Laboratories, Philadelphia (USA) is available to check the authenticity of pure drug samples. 

The fingerprint region lies between 1300-400 cm-1 which is considered to be the most valuable component of the spectra and mainly comprises of a specifically large number of unassigned vibrations. Therefore, IR-spectroscopy aids in the identification of unknown compound by comparing its spectrum with a standard spectra recorded under exactly similar experimental parameters. Thus, pharmaceutical substances that exhibit the same infrared spectra may be inferred as identical. 

Library searching is the comparison of the test spectrum with a database of standard spectra. 

SadtlerNA. 1960. Sadtler standard spectra. Philadelphia, PA Sadtler Research Lab. 

Regarding relevance, the spectral miscibility of the data obtained from these two different sources can be readily observed by doing a PCA analysis of the combined spectral data. The scatter plot of the first two PC scores obtained from PCA of such a data set for one of the process analytes is shown in Figure 12.31a. Note that there is considerable common space for the two data sources in the PC1/PC2 space, and there are some regions of this space where only samples from the old calibration strategy lie. A similar pattern is observed in the later PCs of this model. This result indicates that the on-line spectra contain some unique information, but that the on-line and injected-standard spectra are generally quite similar. 

Sadtler Standard Spectra. Sadtler Res. Lab. Inc., Philadelphia, Pennsylvania. 

Once an identification has been made, the name and registry number of the data base compound are reported to the user. If necessary, the data base spectrum can be listed or, if a CRT terminal is being used, plotted, to facilitate direct comparison of the unknown and standard spectra. 

Mineral standards were hand crushed to -1/4 inch, then ground to a fine powder in a ball mill (alumina elements) or Bleuler Model 526/LFS678 puck mill. The resultant powder was aerodynamically classified in a Bahco Model 6000 micro particle classifier and the finest fraction ( 18 throttle) was collected. A size criterion of 90% or more by weight of particles 5 micron and smaller in diameter was used for the mineral standards. Sizes were verified by Coulter Counter. Duplicate 13 mm KBr pellets were prepared and the spectra were weight-scaled by techniques similar to those reported by Painter (3) and Elliot (4). With one exception, all the mineral standard spectra were averages of spectra from duplicate pellets. The one exception was the iron sulfate spectrum, which was obtained as the difference spectrum by subtracting the spectrum of HCl-washed weathered pyrite from that of the weathered pyrite. A weight correction was applied to the difference spectrum. 

Raman, A. Kuban, B. Razvan, A. (1991) The application of infrared spectroscopy to the study of atmospheric rust systems. I. Standard spectra and illustrative applications to identify rust phases in natural atmospheric corrosion products. Corrosion Sci. 32 1295-1306... 

Chastain J, King RC Jr (1995) Handbook of X-ray photoelectron spectroscopy a reference book of standard spectra for identification and interpretation of XPD data. Physical Electronics, Eden Prairie... 

Sadtler Research Laboratories (1980) The Sadder Standard Spectra Collection, Cumulative Index, Philadelphia, PA... 

Sadtler Research Laboratories (1980) Sadder Standard Spectra, 1980 Cumulative Index (Molecular Formula Index), Philadelphia, p. 275... 

A variety of infrared methods have been available for the simple problems of verifying the purity of the initial resin components and mixtures of those components. The simplest possible test of the purity of a reactant is to compare its spectrum with a known standard. Subtractive methods may be employed to emphasize the most significant intensity changes 19). Composition analysis of the blended resins and hardeners becomes more difficult. In some cases, one may simply select characteristic isolated absorption bands for each component and estimate the composition by comparison to standard spectra of known composition 20,21). 

Sometimes, however, the exact arrangement of the carbon atoms is not immediately clear from the standard spectra and, of course, we cannot identify the quaternary carbon atoms from an HMQC spectrum. Tn these cases, further information is required about atom connectivities, and as C is so low in natural abundance, a correlation experiment is not realistically possible with unlabelled compounds. It is possible, however, to detect couplings over... 

The Sadtler Catalogue of Standard Spectra, Samuel P. Sadtler and Son, Inc. Philadelphia, Pennsylvania. 

Prepare a table of spectral data (wavelengths of major peaks and absorbance) for each pigment. Using these data and the standard spectra shown earlier in this experiment, try to assign the identity of each pigment isolated. Now that each compound is identified, is there a correlation between the experimental Rf value and polarity as determined from the structure Which pigments are more polar—those near the top or those near the bottom of the chromatogram ... 

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