Detection hyphenated techniques

In the mass balance approach, all impurities are quantified and subtracted from the absolute value of 100%. This approach will result in a purity value that, if all impurities are accounted for, is more accurate than the external or internal standard methods. However, the ability to identify all impurities in a given drug substance may require the use of hyphenated detection techniques and could be extremely costly to complete on a regular basis. Therefore, a related approach, called Area Normalization, is often used where the majority of the impurities can be identified and quantified in a single chromatogram. In the simplest case, all of the impurities would be assumed to have the same relative response... 

When the rows of a data matrix follow a certain pattern, e.g. the appearance and disappearance of compounds as a function of time, a fixed-size window EFA is applicable. This is the case, for instance, for data sets generated by hyphenated measurement techniques such as HPLC with DAD. Fixed-size window EFA [22] can be applied for detecting the presence of minor compounds (< 1 %) and for the resolution of a data set into its components (pure spectra and elution profiles). 

In the case of the low abundance of some compounds, there are difficulties with signal overlap. To overcome these difficulties, there have been developments involving NMR hyphenation with techniques such as HPLC and mass spectrometry. In LC/NMR methods of analysis, NMR is used as the detector following LC separation and this technique is capable of detecting low concentrations in the nanogram range. This technique has been reported for the detection and identification of flavanoids in fruit juices and the characterization of sugars in wine [17]. 

Transient signals are typically obtained in atomic spectrometry when samples are introduced by flow injection techniques or when the spectrometer is used as an element-specific detector in hyphenated techniques. Inductively coupled plasma mass spectrometry has nowadays become the detection technique of choice for multielement-specific detection in speciation as it allows multielemental... 

Hyphenated chromatographic techniques of various types (e.g., HRGC/HRGC and HPLC/HRGC) are being used in conjunction with a variety of detectors to improve detectability, increase specificity, and reduce cleanup costs for routine analysis. Vuruls et al. (1992) reported ng/L quantitation for aqueous atrazine samples by LC/GC/MS. 

The nutritional, chemical, biological, and toxicological properties of a chemical element are known to be critically dependent on the form in which it occurs in food. The recognition of this fact has spurred the development of species-selective (speciation) analytical methods for food additives and contaminants. According to the IUPAC s dehnition, speciation analysis deals with the analytical activities of identification and/or measurement of the quantities of one or more individual chemical species in a given sample [1], The analytical approach is usually based on the combination of a chromatographic separation technique with an element-specif>c detection technique. The former ensures that the analyte compound leaves the column unaccompanied by other species of the analyte element, whereas the latter enables a sensitive and specil>c detection of the target element. Coupled (also called hyphenated) techniques have become a fundamental tool for speciation analysis and have been discussed in many published reviews [2D6]. 

The possibility of combining separation and detection techniques gives origin to the so-called hyphenated-techniques , analytical systems able to answer these questions. Well described approaches on the subject are in the special issue of Spectrochimica Acta devoted to Speciation [111]. 

The mass spectrometric detector is often coupled to GC to provide a very sensitive separation and detection instrument in one. This system is discussed in more detail in the section on hyphenated (hybrid) techniques. 

The molecular information that FTIR detection offers that MS, the other common hyphenated GC technique, cannot, includes elucidation of aromatic ring substitution (for example, with di-substitution, ortho, meta, or para), cis or trans or geminal substitution on a carbon-carbon double bond, the arrangement of rings in PAHs (benz[a]anthracene versus chrysene or triphenylene or benzo(c]phenan-threne or tetracene for the four-ring ortho-fused PAHs), aUcyl-chain branching isomers, and alcohols, which often shows in the MS as the easily dehydrated product aUcene [84]. 

Mass spectrometry (MS) is one of the most powerful detection techniques employed in environmental screening due to the intrinsic structural information and high sensitivity it provides. With the advent of effective interfaces, soft ionization modes (electrospray ionization, ESI, and atmospheric pressure chemical ionization, APCI) and increased affordability of CE-MS instruments, the hyphenated technique has become widespread. 

For convenience, the book is organized into three parts and 15 chapters. Part I has five chapters that provide a detailed description of the instrumentation aspects of mass spectrometry. Topics in this section include modes of ionization (Chapter 2), mass analysis and ion detection (Chapter 3), tandem mass spectrometry (Chapter 4), and hyphenated separation techniques (Chapter 5). Mass... 

The variety of methods for the determination of chromium species may be classified into two fundamental categories species-selective, direct measurements and nonselective detection combined with species-selective separation methods. In the case of chromium, two strategies can be distinguished for the later approach simultaneous separation and determination of both species or determination of one species and the total chromium concentration, obtaining the result for the second species by calculation through difference . Since such an indirect approach involves some risk due to cumulative errors, it is nowadays avoided whenever possible. Such and other problems can often be prevented by techniques combining a selective separation technique online with a sensitive detection technique, creating a very powerful hyphenated technique . 

Metalloid compounds are usually determined by flowing-stream techniques hyphenated with hydride generation (HG)-atomic absorption or atomic fluorescence spectrometry. The continuous operation mode inherent to flow injection is specially suited for the latter detection technique as the tetrahyd-roborate reagent is a potential source of hydrogen for supporting the flame. Analyte preconcentration is frequently needed to detect the typical levels of metalloid species found in water matrices. In this context, cold trap collection of generated hydrides, sorbent extraction microcolumn methods, sorption... 

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