Pre-treatment of samples

For the analysis of solid tissue samples such as muscle, kidney, or liver, a representative liquid sample first has to be obtained. Fluids can be simply collected by the fluid expression technique (Section 5.2.4). To improve detection limits for certain compounds and provide an alternative method for samples where the fluid cannot be obtained by expression alone. Stead et al. described a solvent extraction method applicable for the generic recovery of antimicrobial compounds from a wide variety of matrices. A comparison of the fluid expression and solvent extraction techniques in combination with the 

TABLE 5.3 Comparison of Fluid Expression (Garlic Press) versus Generic Solvent Extraction in Combination with PremiTest Using Tissue Fortified with Various Antimicrobial Compounds 

Antibiotic Compound EU MRL (p.g/kg) in Porcine Muscle PremiTest Limit Detection in Porcine Muscle (p.g/kg) Fluid Expression Solvent Extraction  

Notation Less than sign indicates that a strong positive response was recorded at the denoted concentration. The actual hmit of detection will be, by definition, lower than this value. 

PremiTest was performed in porcine tissue fortified with a wide range of antimicrobial compounds. The use of a solvent extraction was found to generate lower detection capabilities, especially for the weaker inhibitors (e.g., the tetracycline class) compared to the fluid expression approach (Table 5.3). 

---

Air-dry samples have been studied using the methods of scanning electron microscopy, X-ray microanalysis, thermal analysis and X-ray diffraction. The latter two methods are crucial for conclusions regarding thermal pre-treatment of samples to be exploited in power sources. 

ISO 11464 (1994) Soil quality - Pre-treatment of samples for physico-chemical analysis. 

ISO/FDIS 14507 (2002) Soil quality — Pre-treatment of samples for determination of organic contaminants. 

Application of chemical methods to the pre-treatment of samples before chromatographic separation... 

Infrared spectroscopy is a versatile experimental technique and it is relatively easy to obtain spectra from biological samples either in solution or in the soUd state. You have already studied the principles of infrared spectroscopy and the instrumentation required to produce the spectra. In this present chapter we shall study how samples can be introduced into the instrument, the equipment required to obtain spectra and the pre-treatment of samples. 

SBSE presents a series of advantages over the rest of extraction techniques is solvent-free (environmental friendly) could be completely automated don t requires pre-treatment of samples (reduces analytical errors) and presents greater sensitivity than SPME, reaching lower detection and quantitation limits. However, it presents two clear disadvantages compared with the other extraction techniques PDMS is the only phase commercially available to date, limiting the extraction of polar substances and a specific thermal desorption unit is required for optimize the process (Castro et al., 2008). The increase of the extraction yields for the recovery of polar compoimds could be carry out by in-site derivatization. Recently, other phases under development were referred, namely those based on the sol-gel technology, restricted access materials and molecular imprinted polymers (Prieto et al., 2010). 

As an explanation for some additional contradictions, the authors refer to the importance of the pre-treatment of samples before analysis. This is considered in greater detail in Chapter III. 

The flow rate is critical in on-line stripping methods, as it controls the dispersion between the sample and the carrier solution. This factor and the deposition time contribute to the amount of analyte deposited on the electrode surface. With respect to the reaction coil length, it has to be sufficiently long for loading and pre-treatment of sample previous to the deposition step. In addition, for total As determination the chemical parameters such as reduction time and reducer concentration must guarantee the complete reduction of the As(V) contained in the sample to As(III). 

---