Computer aided spectral analysis

Ethylene. Reactions occurring in mixtures containing 03 and C2H4 in the ppm concentration range in air have been examined by Su et al. [123] and by the authors group [124]. A major product, previously unidentified (compound X), was detected, and the kinetic and spectroscopic characterization of this compound was attempted. The representative spectral data and the results of the computer-aided data analysis are illustrated in Figures 14-16. 

Sodium valproate was not sufficiently volatile for mass spectral analysis. The mass spectrum of valproic acid as shown in Figure 5 was obtained using an Associated Electrical Industries Model MS-902 Mass Spectrometer with the ionization electron beam energy at 70 eV. High resolution data were compiled and tabulated with the aid of an on-line PDP-11 Computer. 

MALDI quadrupole ion trap mass spectrometry has also been used to localize and identify the post-translational modifications on the Sindai virus [18]. The polymerase associated protein (P protein) from this virus is reported in the literature to be highly phosphorylated. In vitro studies have detected phosphorylation in different regions of the protein, while a single phosphorylation site was found in the in vivo studies. Mass spectral data, along with computer-aided analysis, enabled the identification and localization of two phosphorylation sites. 

Systems where computer-aided interpretation of spectral data is used in order to identify the structure of organic compounds will find their main application in fields where samples have to be routinely analyzed without knowledge of their origin, e. g. in the fields of forensic chemistry, analysis of metabolites, and environmental pollution. 

Spectral databases of all known carbohydrate structures are undoubtedly useful for the identification of the carbohydrates at hand. Most of the oligosaccharide structures contained in the SweetDB are appended with H- and/or C-NMR spectra. Computer Aided Spectrum Evaluation of Regular Polysaccharides (CASPER) at htq) //www.casper.organ.su.se/casper/ is a tool for the analysis of the primary structures of oligosaccharides and for polysaccharides with repeating units based on NMR spectroscopy... 

Two separate teams, those of Wolfgang Bremser and Henk van t Klooster, were chosen to cover the subject of spectral databases, computer-aided library search systems and expert systems for structure analysis. 

The identification of compounds comprising more than 1 wt% in the oils can be also carried out by C-NMR and computer-aided analysis. " The chemical shift of each carbon in the experimental spectrum can be compared with those of the spectra of pure compounds. These spectra are listed in the laboratory spectral database, which contains approximately 350 spectra of mono-, sesqui-, and diterpenes, as well as in the hterature data. Each compound can be unambiguously identified, taking into account the number of identified carbons, the number of overlapped signals, as well as the difference between the chemical shift of each resonance in the mixture and in the reference. 

Mass spectrometry (electron impact, field desorption, and chemical ionization ) in principal provides either a completely different, alternative method for peptide sequencing or a valuable supplement to the standard method. Applications have, however, been relatively few so far. Further studies on the mass spectral patterns obtained from model compounds have been reported. These should allow inter alia distinctions to be made between a- and y-glutamyl peptides and between leucyl and isoleucyl residues. Sequence studies on myoglobin from the bottle-nosed dolphin were facilitated by a computer comparison method. In this method, a peptide was either deuteroacetylated and deuteropermethylated or subjected to one step of the Edman degradation, followed by deuteroacetylation and deuteropermethylation. Comparison of the mass spectra of these derivatives aided the analysis.""... 

Vibrational spectroscopy should be used whenever chemical specificity and selectivity are needed. As an identification tool, IR has no close spectroscopic competitor. Commercial laboratories have thousands of spectra filed on computers, and seek and identify programs have been written to aid in the identification process [5,6]. All of the identification procedures are based on the assumption that the compound is pure, but routine samples are seldom pure. Therefore, it is advisable to ascertain the purity of the sample before spectral analysis is undertaken. For polymer samples, additives such as fillers, antioxidants, lubricants, and mold release agents can generate spectral interferences [7]. However, except for fillers and plasticizers, the process and stabilizer additives generally amount to 1% by weight of total polymer and contribute very little to the total spectrum. 

Woodruff and co-workers introduced the expert system PAIRS [67], a program that is able to analyze IR spectra in the same manner as a spectroscopist would. Chalmers and co-workers [68] used an approach for automated interpretation of Fourier Transform Raman spectra of complex polymers. Andreev and Argirov developed the expert system EXPIRS [69] for the interpretation of IR spectra. EXPIRS provides a hierarchical organization of the characteristic groups that are recognized by peak detection in discrete ames. Penchev et al. [70] recently introduced a computer system that performs searches in spectral libraries and systematic analysis of mixture spectra. It is able to classify IR spectra with the aid of linear discriminant analysis, artificial neural networks, and the method of fe-nearest neighbors. 

The El source has been the most widely used ion source over the past 60 years and continues to be the method of choice for the analysis (either qualitative or quantitative) of small- to medium-sized volatile organic compounds. The inherent reproducibility of the mass spectra has enabled the assembly of large spectral libraries. Computers associated with current generation instruments can efficiently (in a few seconds) search an unknown mass spectrum against tens of thousands of reference spectra in order to aid in the identification of an analyte. The general scheme of an El source includes the introduction of the vaporized analyte molecules into the ionization chamber, exposure of those molecules... 

To aid in the analysis of NMR spectra, computer programs have been developed which solve the nuclear-spin secular equation.12 The input to these programs is the observed spectral data and initial guesses for the chemical shifts and coupling constants by an iterative process, accurate parameters are calculated. Programs are available from the Quantum Chemistry Program Exchange (Section 1.21). 

Many modern scanners have a computer-controlled motor-driven monochromator that allovre automatic recording of in situ absorption and fluorescence excitation spectra. These spectra can aid compound identification by comparison with stored standard spectra, test for identity by superimposition of spectra from different zones on a plate, and check zone purity by superimposition of spectra from different areas of a single zone. The spectral maximum determined from the in situ spectrum is usually the optimal wavelength for scanning standard and sample areas for quantitative analysis. 

The acquisition of the spectral information from each single spark separately is now possible with advanced measurement systems, using integration in a small capacitor and rapid computer-controlled readout combined with storage in a multichannel analyzer. With the aid of statistical analysis, sparks with outlier signals can be rejected and the precision improved accordingly. Furthermore, pulse differential height analysis enables discrimination between a number of elements such... 

Spectroscopic methods can provide fast, non-destructive analytical measurements that can replace conventional analytical methods in many cases. The non-destructive nature of optical measurements makes them very attractive for stability testing. In the future, spectroscopic methods will be increasingly used for pharmaceutical stability analysis. This chapter will focus on quantitative analysis of pharmaceutical products. The second section of the chapter will provide an overview of basic vibrational spectroscopy and modern spectroscopic technology. The third section of this chapter is an introduction to multivariate analysis (MVA) and chemometrics. MVA is essential for the quantitative analysis of NIR and in many cases Raman spectral data. Growth in MVA has been aided by the availability of high quality software and powerful personal computers. Section 11.4 is a review of the qualification of NIR and Raman spectrometers. The criteria for NIR and Raman equipment qualification are described in USP chapters <1119> and < 1120>. The relevant highlights of the new USP chapter on analytical instrument qualification <1058> are also covered. Section 11.5 is a discussion of method validation for quantitative analytical methods based on multivariate statistics. Based on the USP chapter for NIR <1119>, the discussion of method validation for chemometric-based methods is also appropriate for Raman spectroscopy. The criteria for these MVA-based methods are the same as traditional analytical methods accuracy, precision, linearity, specificity, and robustness however, the ways they are described and evaluated can be different. 

Spectrophotometers can measure the spectral reflection of a sample and represent it graphically by means of computer peripherals. Spectrophotometers are a useful aid in the analysis and synthesis of color samples. All colorimeters enable calculation of the total color difference with the CIELAB color difference formula. 

The main analytical instrumentation in the vehicle is a benchtop GC/MS by Hewlett Packard, HP 5890 GC/5970 MSB (mass selective detector). A basic configuration for analyzing liquid samples includes a heated injection port and a capillary fused-silica column interfaced directly to the MS via a heated transfer line. The MS is a quadrupole design operated under vacuum provided by a diffusion pump and backed by a mechanical rotary pump. System operation and data analysis are performed by a Pentium-level personal computer loaded with proprietary software and a NBS spectral library to aid with identification of unknowns. Depending on the mission, a simpler installation may consist of a GC equipped with an appropriate detector such as the electron capture detector (ECD). 

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