Sample preparation methods Solid samples

Solid Phase Microextraction Out of the many sample preparation methods, solid phase microextraction (SPME) is one of the most frequently used. SPME is used for the determination of VOCs in liquid, gas, and solid samples. The great advantage of the method is that it combines, in one stage, the isolation and enrichment of compounds, and completely eliminates the need for organic solvents. 

Second, the properties of micro/nano friction and wear/ scratch of several representative films are introduced. These films include from organic molecular films, solid films, to multilayers. The experiments were designed reasonably to understand the behaviors of micro/nano friction and wear of the films. The sample preparation methods were also de-... 

The preponderance of analytical sample preparation methods employs some type of extraction. Traditionally, these methods were liquid-liquid, liquid-solid, and hot... 

P.D. McDonald and E.S.P. Bouvier, Solid Phase Extraction Applications Guide and Bibliography, A Resource for Sample Preparation Methods Development, Waters, Milford, MA... 

The study concluded that Once wash steps are optimized, samples prepared by solid phase extraction are cleaner than those prepared by protein precipitation. Samples prepared by extraction with a Multi-SPE plate resulted in lower LOQs than samples prepared by solvent precipitation. Drug recoveries were acceptable (>80%) for both the SPE and the solvent precipitation methods. Well-to-well reproducibility of samples was slightly better with extraction with a Multi-SPE plate. Evaporation and reconstitution, while more time-consuming, yield better chromatographic performance, allow analysis of lower concentration samples, and require optimization for good analyte recovery. 

For sample cleanup the typical methods like solid-phase extraction (SEE) and liquid—liquid extraction can be used in the same manner as they are used for HPLC. Please refer to the corresponding handbooks for a detailed background of these sample preparation methods. ... 

Pauwels, A., Wells, D.A., Covad, A., Schepens, P.J.C. (1999). Improved sample preparation method for selecte persistent organochlorine pollutants in human serum using solid-phase disk extraction with gas chromatographic analysis. J ChromatogrB 723 117-125. 

As well as typical sample preparation methods such as filtration and liquid-liquid extraction, newer developments are now extensively used. The first of these is solid-phase extraction (SPE). This is a rapid, economical, and sensitive technique that uses several different types of cartridges and disks, with a variety of sorbents. Sample preparation and concentration can be achieved in a single step. Interfering sugars can be eluted with aqueous methanol on reversed-phase columns prior to elution of flavonoids with methanol. 

Classical sample preparation methods such as distillation, soxhlet extraction are still used [839, 840], but specific techniques such as supercritical fluid extraction (SFE) [841], and increasingly in recent years, adsorption techniques such as solid phase micro-extraction (SPME) [841a] are also being used for isolation, separation, and identification of flavor and fragrance materials. 

SFE also would appear to have utility in sample preparation methods. Lopez-Avila et al. (1992) applied SFE to the recovery of a variety of analytes, including organophosphorus pesticides, from solid matrices. The unoptimized extraction from sand gave a recovery of 54% for diazinon. Supercritical trifluoromethane has been shown to extract diazinon from glass beads with a recovery of 86% (Hillmann and Bachmann 1995). Organophosphorus pesticides have also been recovered from Tenax-GC, an adsorbent used to collect diazinon during air sampling, and analyzed directly by GC (Raymer and Velez... 

The compound to be analysed, the analyte, is generally contained in a liquid or solid matrix it is rarely found in a form that allows direct measurement. Interfering species that may lead to unwanted interactions, particularly during trace analysis in the presence of abundant matrix components, have to be eliminated. As a result, analysts have long acknowledged the need for efficient and reproducible sample preparation methods. The pre-treatment process has to take into account the analyte, matrix and measurement technique chosen. This situation has led to a number of specific sample pre-treatment protocols that describe sample treatment from sampling all the way to recording of the results (Fig. 20.1). 

You need to decide the goal of an analysis before developing a chromatographic method. The key to successful chromatography is to have a clean sample. Solid-phase microextraction, purge and trap, and thermal desorption can isolate volatile components from complex matrices. After the sample preparation method has been chosen, the remaining decisions for method development are to select a detector, a column, and the injection method, in that order. 

Section 24-4 described solid-phase microextraction, purge and trap, and thermal desorption—sample preparation methods that are especially useful for gas chromatography. 

The analyte binding efficiency is matrix dependent. Some matrices, such as urine and tissue extracts, can be directly loaded onto the column, other matrices such as milk may need sample processing prior to loading onto an immunoaffinity column. The simplest sample preparation method is dilution this method has been applied to serum, liver, and kidney extracts after removal of particulates. Sometimes dilution alone is not sufficient to eliminate the matrix effect and classical sample preparation techniques (solvent/solvent extraction, solid phase extraction, etc.) will be necessary prior to immunoaffinity chromatography. We found milk often needs this type of treatment. 

Zircon, complete solid-solution behavior is observed, and a plot of the unit cell volume against x shows that Vdgard s Law is followed. When the end members are not is structural, a systematic change in the solubility range in both structures is found as A is varied, and the data have been systematized in terms of a simple, potentially predictive, structure-field map. The pervasive polymorphism of these ABO4 compounds, involving both reconstructive and displacive transformations and metastable structures produced by different sample preparation methods, indicates that the crystal structural stability of substituted compounds needs to be carefully evaluated as a function of temperature to assess the structural integrity of waste-form materials. 

The physical state of the chemical to be analyzed determines the sample preparation method. The majority of the chemicals listed in the Schedules of the CWC are liquids in room temperature. There are also gases or solids in each schedule. Some chemicals are borderline cases, which may be solids in room temperature but melt in the infrared beam, or liquids that are too volatile in the infrared beam. Table 2 summarizes some typical chemicals of each type in the Schedules. 

Figure 1. Spectra of CR using different sample preparation methods. The spectra have been measured (a) as a solid KBr disk with deficient grinding of CR (Christiansen effect visible), (b) as a solid KBr disk with CR well reground, (c) dissolving CR into acetone and deposition on a KBr disk, and (d) by cryodeposition GC/FTIR (Source M. Soderstrom, unpubhshed results)...

New perspectives for GC-ICP-MS in a variety of research areas including food sciences are in sight on the levels of both sample introduction and mass spectrometry [54], namely, sample preparation methods including MW-assisted, solid-... 

Solid Phase MicroExtraction (SPME) is a solvent-free sample preparation method based on the adsorption of analytes directly from an aqueous sample onto a coated fused-silica fiber. Headspace SPME was used in combination with gas chromatography-mass spectrometry/ selective ion monitoring (GC/MS-SIM) to analyze for TCA in wine. 

Solid-phase microextraction (SPME) was developed as an alternative to many other sample preparation methods because it uses virtually no solvents or complicated equipment. It is an adsorption/desorption device where the compounds of interest are adsorbed onto a fused-silica fiber. After a given time, the fiber is placed into a gas chromatograph (GC), where the compounds are thermally desorbed. SPME has recently been adapted for use in HPEC, where compounds that are adsorbed are desorbed using an appropriate solvent. 

SB 8-27. Challenge Problem. Zwanziger and Sarbu conducted a study to validate analytical methods and instruments. The following data are results obtained in the determination of mercury in solid wastes by atomic absorption spectroscopy using two different sample preparation methods a microwave digestion method and a traditional digestion method. 

---