Quantitative analysis using representative methods

Quantitative analysis using FAB is not straightforward, as with all ionisation techniques that use a direct insertion probe. While the goal of the exercise is to determine the bulk concentration of the analyte in the FAB matrix, FAB is instead measuring the concentration of the analyte in the surface of the matrix. The analyte surface concentration is not only a function of bulk analyte concentration, but is also affected by such factors as temperature, pressure, ionic strength, pH, FAB matrix, and sample matrix. With FAB and FTB/LSIMS the sample signal often dies away when the matrix, rather than the sample, is consumed therefore, one cannot be sure that the ion signal obtained represents the entire sample. External standard FAB quantitation methods are of questionable accuracy, and even simple internal standard methods can be trusted only where the analyte is found in a well-controlled sample matrix or is separated from its sample matrix prior to FAB analysis. Therefore, labelled internal standards and isotope dilution methods have become the norm for FAB quantitation. 

The enzyme-linked immunosorbent assay (ELISA or EIA) is one of the most commonly utilized methods used in protein detection and analysis. An ELISA can provide quantitative information about antigen or antibody concentrations in solution by comparing the results of an unknown sample assay to a calibration curve based on known standard concentrations of the antibody or antigen of interest. Although, there are many variations in how ELISA may be performed, three of the most commonly used representative methods are discussed here (Fig. 1). The choice of which ELISA technique is used often depends on the nature of the antigen or antibody of interest, the availability of appropriate binding pairs, and the specificity of only the antigen of interest to a monoclonal antibody. 

In this section, we apply the phase-change rule and the loop method to some representative photochemical systems. The discussion is illustiative, no comprehensive coverage is intended. It is hoped that the examples are sufficient to help others in applying the method to other systems. This section is divided into two parts in the first, loops are constructed and a qualitative discussion of the photochemical consequences is presented. In the second, the method is used for an in-depth, quantitative analysis of one system—photolysis of 1,4-cyclohexadiene. 

There are two general types of aerosol source apportionment methods dispersion models and receptor models. Receptor models are divided into microscopic methods and chemical methods. Chemical mass balance, principal component factor analysis, target transformation factor analysis, etc. are all based on the same mathematical model and simply represent different approaches to solution of the fundamental receptor model equation. All require conservation of mass, as well as source composition information for qualitative analysis and a mass balance for a quantitative analysis. Each interpretive approach to the receptor model yields unique information useful in establishing the credibility of a study s final results. Source apportionment sutdies using the receptor model should include interpretation of the chemical data set by both multivariate methods. 

Quantitation. The organic species identified by the GC-MS analyses were quantitated by GC analysis using internal and external standardization methods. Pure compounds representative of the various compound classes identified by GC-MS were selected as standards and methylated. A specific amount of each standard was co-injected with each sample to confirm the GC-MS identifications. For quantitation purposes, each standard was injected onto the gas chromatograph prior to and following sample analyses. The response factor of each standard was calculated under analytical conditions identical to those of the sample analyses. 

The use of SRM methods for quantitative bioanalysis represents increased dimensions of mass spectrometry analysis. SRM methods that use APCI-LC/MS/MS for the quantitative analysis of an antipsychotic agent, clozapine, in human plasma were described by Dear and co-workers (Dear et al., 1998). Preclinical development studies of clozapine in rats and dogs used HPLC with fluorescence detection (FLD). With this method, a better limit of quantitation (LOQ) of 1 ng/mL was obtained. As the compound moved into the clinical stages of development, a more sensitive method of analysis was required to obtain rapid metabolic information in support of drug safety evaluation studies. A standard LC/MS/MS method is used for the quantitative analysis of clozapine (I) and four metabolites (II-V) in human plasma (Figure 6.34). 

Abstract The aim of the present chapter is to present the current research and potential applications of chemoinformatics tools in food chemistry. First, the importance and variety of molecular descriptors and physicochemical properties is delineated, and then a survey and chemical space analysis of representative databases with emphasis on food-related ones is presented. A brief description of methods commonly used in molecular design, followed by examples in food chemistry are presented, such methods include similarity searching, pharmacophore modeling, quantitative... 

Coincident with this new technique for procurement of human bone biopsies was the development of quantitive methods of bone analysis.12 These methods include histochemical analysis of both decalcified and unde-calcified42 48 bone sections, microradiography,44 tetracycline labeling45 and autoradiography.42 The latter two techniques require administration of a tetracycline antibiotic or isotopic tracer prior to procurement of the biopsy. Undecalcified thin sections, prepared with the use of a Jung microtome after the bone core is fixed, dehydrated and embedded in methacrylate,45 are analyzed by intersect and point count methods46 47 which permit three-dimensional assessment.48 49 Tetracycline antibiotics deposit in vivo in sites of bone formation constituting markers which can be studied in undecalcified sections by fluorescence microscopy.45 47 This represents the safest and best tissue time marker for microscopic measurement of bone formation dynamics. 

---