The need for sample pretreatment

Chemical Analysis Second Edition Francis and Annick Rouessac 

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Also, subcritical (hot/liquid) water can be used as a mobile phase for packed-column RPLC with solute detection by means of FID [942]. In the multidimensional on-line PHWE-LC-GC-FTD/MS scheme, the solid sample is extracted with hot pressurised water (without the need for sample pretreatment), and the analytes are trapped in a solid-phase trap [943]. The trap is eluted with a nitrogen flow, and the analytes are carried on to a LC column for cleanup, and separated on a GC column using the on-column interface. The closed PHWE-LC-GC system is suitable for many kinds of sample matrices and analytes. The main benefit of the system is that the concentration step is highly efficient, so that the sensitivity is about 800 times better than that obtained with traditional methods [944]. Because small sample amounts are required (10 mg), special attention has to be paid to the homogeneity of the sample. The system is... 

Spectrometric methods are usually recommended by pharmacopoeias for the assay of pharmaceutical products.55 These require both a separation step and a calibration graph. The resolution of a spectrometric method used for assay of a ternary or quaternary mixture of drugs is not good when a certain, well-known calibration graph is used. To obtain the maximum reliability for data processing it is necessary to use the PLS methodology222 because it eliminates the need for sample pretreatment. This model represents essentially an optimization method that can be applied to the problem of the experimental design. 

The bioaerosol mass spectrometer (BAMS) is an instrument designed specifically for real-time, automated detection of select airborne bioagents without the need for sample pretreatment, cleaning, or chemical derivatization. The development of the BAMS is the result of the collaborative effort of a research division... 

TRXF was used to determine the trace elements in samples of lecithin, insulin, procaine, and tryptophan in an attempt to develop elemental fingerprints that could be used to determine the origin of the sample [80]. It was reported that through the use of matrix-independent sample preparation and an internal standard, one could use TXRF to facilitate characterization of the samples without the need for extensive pretreatment. In another work, a study was made of the capability of TXRF for the determination of trace elements in pharmaceutical substances with and without preconcentration [81]. 

It has been demonstrated that ILMs are suitable for qualitative and quantitative analyses of low-molecular weight compounds of biological interest, for example, carbohydrates, vitamins and amino acids [38], and glycolipids [40]. ILMs were further used for fhe direct analysis of alkaloids, anesthetics and antibiotics, separated by thin-layer chromatography (TLC) [46]. For this purpose, the ILM was spotted onto the fractions on the TLC-plates and the complete plate was measured in MALDI MS without the need for additional pretreatment of the TLC-samples. The mass deviation inherently caused by the inhomogeneous surface of fhe TLC-plafe was balanced by using the... 

Inject the dialysates immediately there is no need for sample pretreatment because the dialysis procedure excludes large molecules from the samples. 

RMs represent an important tool for demonstrating the traceability of analytical measurements to given references. One should keep in mind that the traceability of chemical analyses is often more difficult to demonstrate than for physical measurements. This is due to major differences in the measurement processes (e.g., matrix influence on chemical analyses, various analytical problems linked to the analytes and the methods used, need for sample pretreatment, etc.). Contrary to physical measurements, the calibrants and CRMs used for chemical analyses are not only used for instrument calibration but also for a variety of other purposes (e.g., method validation). In terms of traceability, the theory implies that the certified values of a substance in a CRM should be traceable to the amoimt of the given substance expressed according to the relevant SI unit, i.e., the mol. Since there is no reference mol , this traceability can be established only in relation to the mass SI unit, i.e., the kg. 

Although SPME was applied initially for the analysis of relatively volatile environmental pollutants in waters, rapid developments have enabled SPME to be successfully applied for the analysis of pesticides in water, wine and more complex food samples such as honey, fruit juice and pears, vegetables and strawberries. With food samples, most analysts recognize the need for some sample pretreatment in order to minimize matrix effects. The matrix can affect the SPME efficiency, resulting in a reduced recovery of pesticides. The most common method is simply to dilute the sample or sample extract with water. Simpltcio and Boas comminuted pears in water prior to the determination of pesticides. Volante et al. extracted over 100 pesticides... 

SPE offers many advantages over LLE, as shown in Table 3.44. The main disadvantage is the need for method development. There will never be a universal SPE method because the sample pretreatment depends strongly on the analytical demand. 

Recent trends in pesticide analysis in food aims for reduced sample pretreatments or simplified methodologies (as QuEChERS approaches), the use of online purification processes, the use of new adsorbents (such as molecular imprinted polymers (MIPs) and nanomaterials) for the extraction and clean-up processes, and focused on the development of large multiresidue methods, most of them based on LC-MS/ MS. In spite of the relevant role of LC-MS/MS, GC-MS-based methods still play an important role in pesticide analysis in food. Despite the development achieved in the immunochemical approaches, the need for multi-residue methods has supported the development and use of instrumental techniques. 

Identifying pharmaceuticals, whether APIs or excipients used to manufacture products, and the end products themselves is among the routine tests needed to control pharmaceutical manufacturing processes. Pharmacopoeias have compiled a wide range of analytical methods for the identification of pharmaceutical APIs and usually several tests for a product are recommended. The process can be labor-intensive and time-consuming with these conventional methods. This has raised the need for alternative, faster methods also ensuring reliable identification. Of the four spectroscopic techniques reviewed in this book, IR and Raman spectroscopy are suitable for the unequivocal identification of pharmaceuticals as their spectra are compound-specific no two compounds other than pairs of enantiomers or oligomers possess the same IR spectrum. However, IR spectrometry is confronted with some practical constraints such as the need to pretreat the sample. The introduction of substantial instrumental improvements and the spread of attenuated total reflectance (ATR) and IR microscopy techniques have considerably expanded the scope of IR spectroscopy in the pharmaceutical field. Raman spectroscopy,... 

Utilizing direct chromatographic analysis whenever possible, as it permits analytes in a sample to be determined without the need for pretreatment or sample preparation... 

Silica gels were deuterated by pumping D20 at equilibrium vapour pressure over the sample. Time and temperature of both the adsorption and evacuation step were varied. The continuous flow of D20 vapour overcomes the need for repeating the procedure in several reaction cycles. The spectrum of silica gel, pretreated at 473 K under vacuum, before and after room temperature deuteration is shown in figure 3.5. Optimal exchange was observed if the adsorption was performed for 1 h at room temperature and the evacuation at the same temperature as pretreatment. 

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