Analytical target profile

Recommendation Dilute the standard solutions twice with blank solutions prepared from each of the blank samples. Impurities in the blank samples reduce the thermal decomposition of the target analytes in the injection port and stabilize the profiles of ionization and fragmentation of the target analytes. 

Modifiers can be used very effectively in on-line SFE-GC to determine the concentration levels of the respective analytes. This presents an advantage in terms of the use of modifiers in SFE, since they appear as solvent peaks in GC separations and do not interfere with the target analyte determination. Although online SFE-GC is a simple technique, its applicability to real-life samples is limited compared to off-line SFE-GC. As a result, on-line SFE-GC requires suitable sample selection and appropriate setting of extraction conditions. If the goal is to determine the profile or matrix composition of a sample, it is required to use the fluid at the maximum solubility. For trace analysis it is best to choose a condition that separates the analytes from the matrix without interference. However, present SFE-GC techniques are not useful for samples... 

Spectrofluorometry underpins all luminescent techniques for characterizing the target analyte and the associated sample matrix. LIF occurs from the vacuum UV through the NIR range, but is most common between 250 nm and 800 nm. A typical fluorescent profile contains an absorption spectrum and an emission spectrum as depicted in Figure 11.3. Spectrofluorometric excitation profiling at emission maxima and syn-chronons scanning are common methods to characterize a fluorophore. 

Organic acid analysis could be performed in other biological specimens [14, 22] when targeting specific analyte(s) in previously diagnosed patients, or fetuses at risk for a specific condition. Plasma/serum profiling is not helpful in the laboratory evaluation of patients without a specific diagnosis, and should be avoided [2]. 

On the other hand, the SIM analysis of a predefined set of analytes (Fig. 3.1.4a) require visual inspection, but only to exclude unexpected interferences in the signal of a target compound. For the purpose of detecting unexpected interferences, it is necessary, and is also a CAP accreditation requirement, to monitor at least two ion species per compound (Fig. 3.1.4b and c), so as to recognize artificial variations in the intensity ratios between two ion chromatograms. Figure 3.1.5 shows examples of characteristic organic acid profiles in patients with selected conditions [32]. 

Lipid analyses include both global profiling of the main lipid classes and targeted methods for specific lipid classes which are usually not covered by the global methods due to their low concentrations (e.g., eicosanoids, steroids), instability, or other physicochemical features. Different analytical methods are typically needed for these two approaches. 

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