Instrumental determination

There are a variety of analytical methodologies developed for the analysis of emerging contaminants selected for this chapter. In almost all cases, the instrumental analysis is based on the use of GC or LC coupled to MS or MS-MS. The selection of one or another technique depends primarily on the physicochemical properties of the compounds. We summarize the more recently developed methodologies for each of the families (Table 1). 

GC-MS is applied in some methods for the analysis of pharmaceuticals in sludge [45, 109]. However, this technique can only be successfully applied for a limited number of nonpolar and volatile pharmaceutical compounds, while analysis of polar pharmaceuticals requires a time-consuming and often irreproducible deriva-tization. Consequently, LC-MS is the preferred technique in many laboratories. Some other detection techniques are also employed, such as diode array (DAD) and electrochemical (ED) and fluorescence detection (ELD). In the case of fluoroquinolones, ELD is still the favored technique. 

A similar situation exists for the case of estrogens, which have also been analyzed by GC or LC coupled to MS or MS-MS. However, LC-MS offers the advantages, as compared to GC-MS, of not requiring prior compound derivatiza-tion and allowing the analysis of both free and conjugated estrogens in a single run. 

GC-MS operated in electron impact (El) mode was only sporadically used for the determination of some UV filters such as 4-MBC, EHMC, and OC. Separation was achieved on a 60 m x 0.25 mm i.d. DB-5 column, with 0.25-pm film thickness. For quantification of the compounds, data acquisition was performed in selected ion monitoring (SIM) mode recording three characteristic ions per compound. GC-MS allowed the differentiation between the two isomers (cis/trans) for 4-MBC and EHMC. 

HBCD can be determined by GC-MS, using methods similar to those developed for PBDE determinations. As the response factors of the three diastereomers do not appear to differ very much, HBCD can be quantified as total HBCD. However, the different isomers have not so far been separated by this technique. Moreover, because isomers of HBCD are thermally labile (it is known that HBCD decomposition takes place between 240°C and 270°C), elution from a GC column usually results in a broad, diffuse peak. In addition, a number of chromatographic peaks corresponding to different breakdown products were detected. These peaks could interfere with some BFR congeners (e.g., BDE-99) [102,110]. TBBPA can be also determined by GC-MS however, a derivatization step must be carried out prior to injection on the GC system. 

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The time resolution of the instrument determines the wavenumber-dependent sensitivity of the Fourier-transformed, frequency-domain spectrum. A typical response of our spectrometer is 23 fs, and a Gaussian function having a half width... 

Most modern methods of analysis to determine pesticide residues in food commodities, whether a multi-residue method (MRM) or a single-residue method (SRM), can be broken down into three or four basic steps sample processing, sample extraction, extract cleanup (optional) and instrumental determination. 

Traditionally, the analysis of BFRs has been developed using GC as the principal separation technique, due to the volatility of these compounds. However, GC analysis of some BFR compounds, such as HBCD or TBBPA, presented some drawbacks. That because, in recent years, methods employing LC-MS and LC-MS-MS have been developed offering good results. Guerra et al. [112] presented an overview of current analytical methods for selected BFRs, focusing on instrumental determination using LC-MS. Table 1 summarizes different LC-MS methods found in the literature for the analysis of different BFRs. 

Regarding the instrumental determination, developed methodologies are based on the use of mass spectrometry (MS), either coupled to gas chromatography (GC) or... 

Namiesnik et al. [33] have reviewed the analysis of soils and sediments for organic contaminants. They discuss methods of sample preparation and isolation-preconcentration prior to instrumental determination. Compound classes discussed include volatile organic compounds, polychlorobiphenyls, polyaromatic compounds, pesticides and polychlorodibenzo-p-dioxins and polychlorodibenzofurans. 

Using one of your standards and the Spectronic 20, or other single-beam visible spectrophotometer, obtain an absorption (or transmittance) spectrum of the Fe-o-phenanthroline complex ion (instructor will demonstrate use of instrument). Determine the wavelength of maximum absorbance from the spectrum and use this wavelength to obtain absorbance readings of all the solutions. (Use the blank for the 100% transmittance setting.)... 

ISO 9370, Plastics - Instrumental determination of radiant exposure in weathering tests - General guidance and basic test method, 1997. 

The general requirements for accelerated weathering apparatus are given in ISO 4892-1 [29], whilst ISO 4892 Parts 2-4 [26-28] deal more specifically with xenon arcs, fluorescent tubes and carbon arcs respectively. ISO 4892 refers to ISO 9370 [30] (Instrumental determination of radiant exposure in weathering tests), and CIE publication 85 (Solar spectral irradiance) [31]. 

Many automated instruments measure enzyme activity using fixed time colorimetric methods. Some, however, can be classed as reaction rate analysers, e.g. the centrifugal analysers, and these instruments determine the reaction rate from either the initial slope of the reaction curve or from repeat measurements at fixed intervals. In both methods the slope of the line is taken to represent the activity of the enzyme. 

Eigure 6.2, shows a specific example of the use of the H4IIE-EROD assay for purified SPMD extracts. After purification of SPMD extracts. Gale et al. (2000) showed that H4IIE-determined TEQs were well correlated with instrumentally-determined TEQs. 

Differential scanning calorimetry is primarily used to determine changes in proteins as a function of temperature. The instrument used is a thermal analysis system, for example a Mettler DSC model 821e. The instrument coupled with a computer can quickly provide a thermal analysis of the protein solution and a control solution (no protein). The instrument contains two pans with separate heaters underneath each pan, one for the protein solution and one for the control solution that contains no protein. Each pan is heated at a predetermined equal rate. The pan with the protein will take more heat to keep the temperature of this pan increasing at the same rate of the control pan. The DSC instrument determines the amount of heat (energy) the sample pan heater has to put out to keep the rates equal. The computer graphs the temperature as a function of the difference in heat output from both pans. Through a series of equations, the heat capacity (Cp) can be determined (Freire 1995). 

A classical food residue analysis based on chromatography include the following steps (i) sampling (ii) sample preparation/subsampling (iii) extraction (iv) clean-up (v) chromatographic separation and (vi) instrumental determination. 

The final stage of the residue analysis procedures involves the chromatographic separation and instrumental determination. Where chromatographic properties of some food residues are affected by sample matrix, calibration solutions should be prepared in sample matrix. The choice of instrument depends on the physicochemical properties of the analyte(s) and the sensitivity required. As the majority of residues are relatively volatile, GC has proved to be an excellent technique for pesticides and drug residues determination and is by far the most widely used. Thermal conductivity, flame ionization, and, in certain applications, electron capture and nitrogen phosphorus detectors (NPD) were popular in GC analysis. In current residue GC methods, the universality, selectivity, and specificity of the mass spectrometer (MS) in combination with electron-impact ionization (El) is by far preferred. 

ASTM D-5373. Standard Test Methods for Instrumental Determination of Carbon, Hydrogen, and Nitrogen in Laboratory Samples of Coal and Coke. 

Despite the remarkable sensitivity of modern instrumental detection techniques, analysis of environmental water samples nearly always requires enrichment of the analytes. This, together with separation from the matrix, are the two main functions of sample preparation appropriate sample preparation techniques address both issues at the same time, while striving to impose as few restrictions as possible on the subsequent instrumental determination (separation and detection). Sample preparation is strongly dependent on the nature of the analyte and the matrix, particularly with regard to its volatility and polarity. Figure 13.8 gives a general overview of common sample preparation (enrichment) techniques for aqueous and other matrices. 

The visual appearance of a commercial sugar product has long been used as an index of the impurities contained. Despite a general advancement in instrumentation, determination of the perceptual color is still frequently the primary control in the manufacture of white or near-colorless sugar products. This situation is shared by cane-sugar refineries and beet-sugar factories a similar state of affairs exists in the production... 

Two areas of research, psychophysics and sensory evaluation, have made recent contributions to the understanding of oral sensations of heat derived from peppers. Psychophysical studies have characterized observer s responses to heat from spice-derived compounds, focussing on such aspects as time-intensity functions, areas of oral stimulation, correlation with evoked salivary flow, interactions with basic tastes, and effects of sequential stimulation. Sensory evaluation of the heat level of ground red pepper has recently been advanced by the validation of a new method which solves many of the problems inherent in the previous Scoville procedure. The new method is based on anchored graphic rating by panels Who are trained with physical reference standards. The procedure has shown excellent reliability, fine discriminations among samples, and high correlations with instrumental determinations of capsaicinoid content of pepper samples. 

The new sensory method shows excellent correlation with instrumental determination of capsaicinoid content of red pepper samples, and can be converted to Scoville units for universal understanding. 

Fig.4.28 (a, b)IR spectra of (a) Form 1 and (b) Form 2 of ranitidine hydrochloride. The spectra are very similar (though not identical) in many respects, with one particularly distinguishing band at 1045 cm in the spectrum of Form 2. (From Cholerton et al. 1984, with permission.) Detail of the (c) Form 1 and (d) Form 2 FTIR spectra of the two polymorphs of ranitidine hydrochloride, including the instrument-determined location of individual peaks. (FromForster et al. 1998, with permission.)... 

The type of measurement instrument determines the degree of precision possible. 

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