Separation-detection combined methods

In Table 3 are summarized the combined separation-detection methods used for end analysis in this chapter. 

In addition, chromatographic separation combined with detection methods, such as neutron activation analysis (NAA) and ICP-MS, was also reported for chemical speciation analysis of iodine in water (Hou et at, 1999b Reifenhauser and Heumann, 1990 Schwehr and Santschi, 2003). In... 

For single-carbon-number AOS samples, analyses can be performed satisfactorily using just the GC method. For multicarbon-number AOS samples that have high sultone content (about 50 ppm), the LC method provides adequate resolution and sensitivity. However, for multicarbon-number AOS samples containing normal sultone levels and for AES samples, the combined LC-GC method is necessary to obtain the required separation and detection levels. Additionally, the combined method is advantageous in eliminating interferences in the LC method that are sometimes observed with AOS samples that have been bleached. 

Note When combined with thin-layer chromatographic separation the reagent provides a specific detection method for nitrate and nitrite. The color development is often completed within a few minutes on silica gel plates. In the absence of ammonia vapor traces of oxides of nitrogen in the laboratory atmosphere can slowly cause the background to become reddish-brown. The simultaneous presence of the following ions in the chromatogram zones interferes with the detection of nitrate/nitrite I , 10J, IO4, MoO and H2PO2. 

Several methods are available for the analysis of trichloroethylene in biological media. The method of choice depends on the nature of the sample matrix cost of analysis required precision, accuracy, and detection limit and turnaround time of the method. The main analytical method used to analyze for the presence of trichloroethylene and its metabolites, trichloroethanol and TCA, in biological samples is separation by gas chromatography (GC) combined with detection by mass spectrometry (MS) or electron capture detection (ECD). Trichloroethylene and/or its metabolites have been detected in exhaled air, blood, urine, breast milk, and tissues. Details on sample preparation, analytical method, and sensitivity and accuracy of selected methods are provided in Table 6-1. 

Separation and detection methods Very refined chromatographic and electrophoretic separation techniques have been developed for metallothioneins. The detection is commonly based on the retention time and UV detection. Other researchers measured the element with e.g. ICP-MS to quantify the compotmd. Combination with electrospray MS-MS leads to the unequivocal identification of the species. 

The spectrum of new analytical techniques includes superior separation techniques and sophisticated detection methods. Most of the novel instruments are hyphenated, where the separation and detection elements are combined, allowing efficient use of materials sometimes available only in minute quantities. The hyphenated techniques also significantly increase the information content of the analysis. Recent developments in separation sciences are directed towards micro-analytical techniques, including capillary gas chromatography, microbore high performance liquid chromatography, and capillary electrophoresis. 

It is important that any method for surfactant analysis maintains the same oligomer distribution in the extracted samples. LLE and SPE are generally combined with chromatographic methods for separation and resolution of non-ionic surfactants into their ethoxamers. An alternative is the use of SPME-HPLC, recently reported by Chen and Pawliszyn [141]. Alkylphenol ethoxylate surfactants such as Triton X-100 and various Rexol grades in water were determined by means of SPME-NPLC-UV (at 220 nm) [142]. Detection limits for individual alkylphenol ethoxamers were at low ppb level. 

Principles and Characteristics In some cases, analysis using an appropriate combination of a single separation and detection method is not satisfactory, and it becomes necessary to utilise a combination of separation methods and/or multidetector monitoring. This approach is termed multidimensional, or coupled chromatography and is meant to describe a specific sequential combination of chromatographic procedures. 

Hyphenated techniques like combination of optical detection methods based on reflectometry or refractometry and separation techniques are of future interest. The same is valid for the intention to couple SPR or RIfS with mass spectrometry like MALDI33. 

In analytical chemistry there is an ever-increasing demand for rapid, sensitive, low-cost, and selective detection methods. When POCL has been employed as a detection method in combination with separation techniques, it has been shown to meet many of these requirements. Since 1977, when the first application dealing with detection of fluorophores was published [60], numerous articles have appeared in the literature [6-8], However, significant problems are still encountered with derivatization reactions, as outlined earlier. Consequently, improvements in the efficiency of labeling reactions will ultimately lead to significant improvements in the detection of these analytes by the POCL reaction. A promising trend is to apply this sensitive chemistry in other techniques, e.g., in supercritical fluid chromatography [186] and capillary electrophoresis [56-59], An alter-... 

See Selectivity, above, and Table 21.9. Industrial problems usually generate samples with complex matrices and many potential interferences. Selective analytical methods or sample preparation are normally required. Separation techniques are quite commonly used. In the average industrial analytical lab, the most numerous instruments are usually gas or liquid chromatographs because they combine separation with detection. 

Many separation and detection methods applied in combination with liquid chromatography (LC) that are described in the literature for the determination of surfactants are not specific to the detection of these compounds at trace levels. Even ultraviolet (UV) spectra obtained from diode array detectors often give only limited information. Furthermore, non-reproducible retention behaviour as well as coelution interference effects are frequently observed during the separation of surfactant-containing extracts. This is recognised, however, only in those cases where specific detection methods such as mass spectrometry (MS) are applied. 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

Various gas chromatographic techniques combined with plentiful detection methods were used to separate and quantify volatile V-nitrosamines. Preconcentration methods were usually applied for separating these compounds. Thus, a method was developed for determination of V-nitrosodimethylamine (278a) in minced fish or frankfurters, based on SPE followed by GC-CLD-TEA RSD was 0.56 to 2.25%569. This method has been adopted by AOAC. A similar GC method using NPD was described for the determination of 278a in fish products570. Steam distillation can also be used to isolate volatile... 

The hyphenation of CE and NMR combines a powerful separation technique with an information-rich detection method. Although compared with LC-NMR, CE-NMR is still in its infancy it has the potential to impact a variety of applications in pharmaceutical, food chemistry, forensics, environmental, and natural products analysis because of the high information content and low sample requirements of this method [82-84]. In addition to standard capillary electrophoresis separations, two CE variants have become increasingly important in CE-NMR, capillary electrochromatography and capillary isotachophoresis, both of which will be described later in this section. 

Separation of dibenzothiophene derivatives from petroleum oil fractions has been achieved by integrated approaches in which fractionating processes such as isothermal distillation, vacuum fractionation, and molecular distillation have been combined with spectroscopic methods including mass spectrometry and NMR spectroscopy. " Dibenzothiophenes have also been concentrated in sharp chromatographic fractions obtained, for example, by, alumina gel percolation, and have been detected by gas chromatography. Gas chromatography has also been used to... 

The elution character of the FFF techniques allows for it to be used in combination with other methods for further on-line or off-line characterization of the analytes (see Figure 12.1). FFF can be hyphenated with selective detection systems like mass spectrometry, multiangle laser scattering and can be combined with different separation techniques in multidimensional modes. In Figure 12.3, the trend in the number of published papers is reported. 

EC detection methods have often been considered incompatible with electrophoresis because the combination of high voltages applied for electrophoretic separation and sensitive electrodes is seen as a conflict. However, traditional capillary electrophoresis takes advantage of many of them and with appropriate designs of the detector cell the separation voltage does not interfere with the EC measurement. On the other hand, there are several reports in which this interference is taken as a benefit for generating new detection approaches (see Sections 34.1.3.1 and 34.1.3.2) [52-54],... 

By the late 1990s and into the 2000s, a number of additional groups became involved in automated fluidic separations for radiochemical analysis, especially as a front end for ICP-MS. Published journal articles on fluidic separations for radio-metric or mass spectrometric detection are summarized in Tables 9.1 through 9.5. The majority of such studies have used extraction chromatographic separations, and these will be the main focus of the remainder of this chapter. Section 9.4 describes methods that combine separation and detection. Section 9.5 describes a fully automated system that combines sample preparation, separation, and detection. 

Reversed phase is the most used separation technique and in combination with fluorescence detection (FD) it is a good choice for analysis of for example, PAH (Hansen et al., 1991) in indoor samples (Jensen, Kofoed-Sorensen and Clausen, 2005a). The FD is a relatively specific and sensitive detection method that uses both an excitation and an emission (fluorescence) wave length and requires, of course, that the target compounds are fluorescent FD reduces the risk of interference. 

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