Analytes thermolabile

Several qualifying features for polymer extract analysis are summarised in Table 2.11. Quantitative separation of polymer and (thermolabile and/or volatile) additives without decomposition of the analyte(s) is difficult for thermoplasts, but even more difficult for... 

The conditions in PHWE are typically harsh and, therefore, the method is not suitable for thermolabile compounds. Analytes may also react with each other or with the water molecules during the extraction. From an analytical point of view the most salient negative factors of SWE in the continuous mode are co-extraction of undesirable components of the matrix (usually polar components) and dilution of the analyte in the extract. This calls for a clean-up and concentration step prior to individual separation and detection of the target compounds. 

Table 3.45 lists the main characteristics of SPME. The technique is sensitive, reduces analyte loss and can successfully be applied to the analysis of both polar and nonpolar volatile and nonvolatile analytes from solid or liquid and in the gas phase [535]. Room temperature operation of SPME favours thermolabile compounds (only heating during injection into GC). Method... 

Three major difficulties have been generally met in directly combining LC with MS. The first concerns the ionization of nonvolatile and/or thermolabile analytes. The second is related to the mobile-phase incompatibility as result of the frequent use of nonvolatile mobile-phase buffers and additives in LC. The third is due to the apparent flow rate incompatibility as expressed in the need to introduce a mobile phase eluting from the column at a flow rate of 1 ml/min into the high vacuum of the MS. 

Atmospheric MAE system This second technique employs solvents with low dielectric constants. Such solvents are essentially microwave-transparent they thus absorb very little energy, and extraction can therefore be performed in open vessels. The temperature of the sample increases during extraction because it usually contains water and other components with high dielectric constants the process is thereby enhanced. Because extraction conditions are milder, this mode of operation can be used to extract thermolabile analytes. 

The temperature of the medium can have a strong influence on the rate of digestion. In the case of thermolabile analytes, operation over very short periods of time or circulation of thermostatted cold water in the tank may be alternative means of controlling the temperature. 

Many microwave extractions can reach maximum recovery in 10 to 20 minutes. Longer extraction time is not necessary and may lead to the decomposition of thermolabile analytes. It was reported that the recovery of sulfonylurea from soil was not affected by extraction time in the range 5 to 30 minutes [79], Similar observation was made in the extraction of PAHs from soils and sediments [6], In the extraction of PAHs and LAHs (linear aliphatic hydrocarbons) from marine sediments, the extraction time was found to be dependent on the irradiation power and the number of samples extracted per run [81], When the irradiation power was 500 W, the extraction time varied from 6 minutes for one sample to 18 minutes for eight samples [74], The recovery of OCPs from spiked marine sediments increased from 30% at 5 and 10 minutes to 60% at 20 minutes and to 74 to 99% at 30 minutes [82],... 

At that time the mass spectrometric ionization techniques of electron ionization (El) [1] and chemical ionization (Cl) [2] required the analyte molecules to be present in the gas phase and were thus suitable only for volatile compounds or for samples subjected to derivatization to make them volatile. Moreover, the field desorption (FD) ionization method [3], which allows the ionization of non-volatile molecules with masses up to 5000 Da, was a delicate technique that required an experienced operator [4], This limited considerably the field of application of mass spectrometry of large non-volatile biological molecules that are often thermolabile. 

In addition to common organic solvents, supercritical fluids (scf s) can be used for a great variety of extraction processes [158 165], Supercritical fluid extraction (SFE), mostly carried out with SC-CO2 as eluant, has many advantages compared to extractions with conventional solvents. The solvent strength of a supercritical fluid can easily be controlled by the pressure and temperature used for the extraction at a constant temperature, extraction at lower pressures will favour less polar analytes, while extraction at higher pressures will favour more polar and higher molar mass analytes. As supercritical fluids such as CO2 and N2O have low critical temperatures (tc = 31 °C and 36 °C, respectively), SFE can be performed at moderate temperatures to extract thermolabile compounds. Typical industrial applications using SC-CO2 include caffeine extraction from coffee beans [158] as well as fat and oil extraction from plant and animal tissues [165]. For some physical properties of supercritical solvents, see Section 3.2. 

The ability of USAL to operate under ambient conditions with respect to temperature and pressure ensures stability of thermolabile analytes. 

Temperature is a key variable in most analytical processes. In microwave-assisted processes, it plays a prominent role and affects the rate of some reactions, the degradation of thermolabile species and the solubilization of some substances, among others. A number of devices have been developed for monitoring or even controlling the temperature, some of which are commented on in Section 5.3. 

MS is a universal detector for LC Analysis of thermolabile analytes, not amenable to GC-MS Analysis of nonvolatile analytes Avoid analyte derivatization MS affords a low detection limit (<10g) Identification of the analytes Assessment of peak purity... 

When LC is coupled with MS, three major problems generally arise. The first concerns the ionization of nonvolatile and/or thermolabile analytes. As MS operation is based on magnetic and electric fields that exert... 

The table shows one of a variety of possible test configurations the EU requires at least 6 months of data before marketing. Clinical trial (CT) products do not require long shelf lives and therefore testing can be limited. For some thermolabile products the temperature range may be lower, or testing at higher temperatures may be terminated quickly. A full analytical profile should be determined for all samples if possible. 

Several compounds have also been extracted from flowers such as magnolia (26,27), lavender (28), crimson glory fresh flowers (29), and chamomile (30), for which SFE both at the analytical and preparative scale offered considerable advantages over the traditional methods such as steam distillation, Soxhlet extraction, and maceration. Using CO2, extractions were performed in a shorter time (30 min by SFE versus 6 h by Soxhlet and 3 days by maceration) and under mild conditions, thus minimizing degradation of thermolabile components (e.g., matricine) and increasing the yield of volatile analytes (31). 

The interface must be able to get rid of the liquid mobile phase, convert the relatively involatile and/or thermally labile analytes into a gas and transfer the gas from atmospheric conditions to a high vacuum. Compared to GC-MS, different ionisation methods must be used for these kinds of analytes (liquid phase, nonvolatile, thermolabile) as El and Cl are not suitable. However, in most cases the capillary is inserted directly into the ion source and, in this case, the ionisation source becomes the interface suitable ionisation sources are described below. 

Long extraction time Large solvent volume Clean up step needed Thermolabile analytes are altered... 

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