Solvent-free sample preparation

While the solvent-free sample preparation is useful for generating MALDl spectra for some polymers, the mechanism underlying the success of the method seems to contradict the conventional wisdom that, in MALDl, analyte molecules should be well incorporated into matrix crystals. It has been shown recently, however, that in favorable cases such as large accessible surface areas-as would be generated in samples consisting of layers of many small matrix crystals-the adsorption of analyte at the matrix crystal surface suffices for the generation of MALDl spectra [87]. However, at present this method appears to be limited to the analysis of relatively low mass polymers (i.e., 30 000 Da). 

If an analyte is definitely insoluble or only soluble in solvents that are not acceptable for the standard MALDI sample preparation technique, it can alternatively be ground together with the solid matrix, preferably in a vibrating ball mill. The resulting fine powder is then spread onto the target. To avoid contamination, nonadherent material should be gently blown away from the target before insertion into the ion source. [103,108,109] 

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Principles and Characteristics Solid-phase microextraction (SPME) is a patented microscale adsorp-tion/desorption technique developed by Pawliszyn et al. [525-531], which represents a recent development in sample preparation and sample concentration. In SPME analytes partition from a sample into a polymeric stationary phase that is thin-coated on a fused-silica rod (typically 1 cm x 100 p,m). Several configurations of SPME have been proposed including fibre, tubing, stirrer/fan, etc. SPME was introduced as a solvent-free sample preparation technique for GC. 

Solid-phase microextraction eliminates many of the drawbacks of other sample preparation techniques, such as headspace, purge and trap, LLE, SPE, or simultaneous distillation/extraction techniques, including excessive preparation time or extravagant use of high-purity organic solvents. SPME ranks amongst other solvent-free sample preparation methods, notably SBSE (Section 3.5.3) and PT (Section 4.2.2) which essentially operate at room temperature, and DHS (Section 4.2.2),... 

It needs to be pointed out, that the investigation of some technically important polymers like polyolefines has not been very successful so far. Owing to their inert nature they are difficult to dissolve and also difficult to ionize. Typically one needs for the ionization process some heterogeneities or double bonds in the polymer. For some insoluble substances a solvent-free sample preparation method has been developed that allows a characterization by MALDI-TOF mass spectrometry [93]. 

For standard MALDI sample preparation, the analyte should be soluble to about 0.1 mg ml in some solvent. If an analyte is completely insoluble, solvent-free sample preparation may alternatively be applied (Chap. 10.4.3). The analyte may be neutral or ionic. Solutions containing metal salts, e.g., from buffers or excess of non-complexated metals, may cause a confusingly large number of signals due to multiple proton/metal exchange and adduct ion formation even complete suppression of the analyte can occur. The mass range of MALDI is theoretically almost unlimited in practice, limits can be as low as 3000 u, e.g., with polyethylene, or as high as 300,000 u in case of antibodies. 

Prans, J.K. Vietzke, J.-P. Strassner, M. Rapp, C. Hintze, U. Konig, W.A. Characterization of Low Molecular Weight Hydrocarbon Oligomers by Laser Desorp-tion/Ionization-TOF-MS Using a Solvent-Free Sample Preparation Method. Rapid... 

Trimpin, S. Grimsdale, A.C. Rader, H.J. Mullen, K. Characterization of an Insoluble Poly(9,9-Diphenyl-2,7-Fluorene) by Solvent-Free Sample Preparation for MALDI-TOF-MS. Anal. Chem. 2002, 74, 3777-3782. 

Solid-phase microextraction (SPME), a new solvent-free sample preparation technique, was invented by C. Arthur and J. Pawliszyn in 1990. This method was mainly applied for the extraction of volatile and semivolatile organic pollutants in water samples. However, since 1995, SPME has been developed to various biological samples, such as whole blood, plasma, urine, hair, and breath, in order to extract drags and poisons in forensic field. The main advantages of SPME are high sensitivity, solventless, small sample volume, simplicity, and rapidity (Liu et al., 1998). 

Analytical methods for the analysis of volatile compounds in the environment have been extensively reviewed.85 87 159 160 The volatility of this class of compounds—industrial solvents, emissions from the petrochemical industry and from combustion engines—suggests that GC should be used for their determination. Solvent-free sample preparation techniques, such as P T (dynamic HS), static HS, and SPME or SBSE, in which the analytes are isolated from the aqueous matrix and simultaneously preconcentrated, are preferred. They also have the advantage that extraction solvents that could interfere with early-eluting, volatile analytes are avoided. If solvent extraction of volatile compounds... 

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. 

Solvent-free sample preparation techniques attract widespread attention to reduce the use of toxic organic solvents. Solid-phase microextraction (SPME) is a solvent-free technique for sample preparation that can integrate sampling, extraction, concentration, and sample introduction into single step, resulting in high sample throughput. 

Matrix assisted laser desorption ionisation (MALDI) is an important technique for characterisation and fingerprinting of large molecules. However, solvents used at sample preparation have a negative effect on the quahty of the fingerprint. Work is therefore performed on development of solvent free sample preparation methods for characterisation of synthetic polymers [61]. 

Matz, G., Loogk, M., and Lennemann, F., Online gas chromatography-mass spectrometry for process monitoring using solvent free sample preparation, J. Chromatogr. A, 819, 51-60, 1998. 

Flame Photometric Detector (PFPD) or an ICP-MS. The various sample treatment steps, liberation of the compounds, their derivatization and preconcentration via headspace on to a SPME phase, all occur in the same vial, hmiting contamination and loss risks. SPME is a solvent-free sample preparation method in which a fused-sUica fiber coated with a polymeric organic stationary phase is used to extract organic compounds directly from aqueous or gaseous samples.Further GC separation of the compounds and MS, FPD, or ICP-MS detection allows very sensitive determinations. This method will be further referred to as the SPME method. 

Solvent-free sample preparation. Solvent-free sample preparation is a relatively new approach termed solvent-free or solvent-less MALDI [56]. In this approach, the matrix, sample, and a salt are mixed together in an appropriate proportion and ground with either a mortar and pestle or a ball mill. The dry mixture is applied to the MALDI target with a double-sided sticky tape. The solvent-free procedure is more universal because it may also be used with insoluble analytes. 

Trimpin, S., Rouhanipour, A., Az, R., Rader, H.J., and Mullen, K. (2001) New aspects in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry a universal solvent-free sample preparation. 

Solid-phase microextraction (SPME) was introduced in the early 1990s by Arthur and Pawliszyn. SPME is a simple solvent-free sample preparation method for GC and LC. The extraction is based on the partitioning of the analyte between the organic phase on the fused silica fiber and the matrix. Many factors such as pH, temperature, salt concentration, and stirring affect the equilibrium constant and the equihbration time. Fiber lifetime is a significant issue. SPME fiber is quite sensitive to complex matrix such as... 

Edwards et al. [51] developed a solvent-free sample preparation method for carbonaceous pitches derived from anthracene and petroleum. A high molecular weight fraction of a petroleum pitch gave a LD mass spectrum with maximum ion intensity at about ni/z 900 and extended to an upper mass of at least m/z 2000. 

SPE is an exhaustive and almost solvent-free sample preparation technique. Typically, a tube is filled with a sorbent, which can be porous particles or a polymerized monolith. Various interactions are used to extract analytes from complex samples. Many of the commercially available SPE systems are for single use, but some, like RAM (restricted access materials) and MIP (molecular imprinted polymers), are typically obtained as reusable extraction devices. As will be discussed in detail, the extraction sorbents mainly function as normal phase, reversed phase, cation exchange, anion exchange, or a combination of these. 

Solid-phase microextraction (SPME) is a solvent-free sample preparation technique. The volume of the extraction phase is very small compared to the sample volume. The extraction is not exhaustive, but is based on equilibrium between the sample and the extraction phase, which is located on a fiber. SPME involves an adsorption step of the analyte, from a gas headspace or in a liquid sample (direct immersion), and a desorption step, which often is coupled directly with injection in the analytical system. Although SPME is mainly used in combination with GC, it has also been automated for HPLC. Eigure 9.10 shows a schematic representation of an SPME device. 

Solid-phase microextraction (SPME), first described by Pawliszyn and coworkers [157-161], is a recent upcoming sample preparation method for phenolic and other organic compounds from water and air samples. It is a novel solvent-free sample preparation technique. SPME has advantage of simplicity, low cost, and rapid extraction. It has been successfully coupled with various techniques such as GC, HPLC, CE, and MS. 

LPME proved to be an extremely simple, low cost, and virtually solvent-free sample-preparation technique, which provides a high degree of selectivity and enrichment by additionally eliminating the possibility of carryover between runs [219-225]. LPME overcomes the drawback of the droplet fall. An alternative LPME was performed in a hollow fiber of 2 cm, which is sealed and immersed in the sample to extract the analytes. With this approach, higher enrichment factors are obtained for penta- and hexachloro-benzene and can be used for slurry, real environmental, and biological samples [226]. 

Trimpin S, Rader HJ, Mullen K. Investigations of theoretical principles for MALDl-MS derived from solvent-free sample preparation. Part 1. Preorganization. Int J Mass Spec 2006 25 13-21. 

Trends in MALDI-ToFMS research are search for new matrices, solvent-free sample preparation, advances in analyser design (oaToF-MS, Q-ToFMS, QITMS, QIT-ToF, ToF-ToF), and (on-line) coupling to other (pre)separation techniques. 

Solvent-free separation using IMS-MS when combined with solvent-free sample preparation and appropriate ionization methods provides TSA that are independent of analyte solubility and is applicable to complex mixtures. A new ionization method, LSI, which operates at AP with laser ablation of samples prepared in a MALDI matrix, has been effectively interfaced with a SYNAPT G2 IMS-MS instrument. Early results show separation of protein mixtures and that protein ion structures from LSI and ESI are similar. Further, a new matrix allows LSI multiply charged ion formation to be extended to solvent-free matrix preparations. Thus TSA by LSI-IMS-MS is a new approach to tissue imaging at high spatial resolution on high-end mass spectrometers such as the SYNAPT G2 and Orbitrap instruments. LSI has... 

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