Laboratory procedures desorption

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

Lee and Chau [66] have discussed the development and certification of a sediment reference material for total polychlorobiphenyls. Alford Stevens et al. [49] in an inter-laboratory study on the determination of polychlorobiphenyls in environmentally contaminated sediments showed the mean relative standard deviation of measured polychlorobiphenyl concentrations was 34%, despite efforts to eliminate procedural variations. Eganhouse and Gosset [67] have discussed the sources and magnitude of bias associated with the determination of polychlorobiphenyls in environmental sediments. Heilman [30] studied the adsorption and desorption of polychlorobiphenyl on sediments. 

Generally, there is no simple and easy theoretical procedure which can provide exact or nearly precise quantitative predictions of what and how much will be adsorbed/desorbed by any solid phase over a period of time [9, 136-139]. Understanding sorption/desorption characteristics of any solid phase materials requires two main laboratory experimental techniques (a) batch equilibrium testing, and (b) continuous solid phase column-leaching testing. These involve... 

As a partial compromise between the use of on-site instrumental analysis and laboratory analysis, a passive sampler can be immersed into the soil (at a specified depth or at several depths) to collect the evolved gases that are adsorbed onto a solid-phase support. The sampler is then removed to the laboratory, where the gases are transferred by Curie point desorption, directly into the ion source of an interfaced quadrupole mass spectrometer. This procedure has its origin in the petroleum exploration industry, and the samplers can be used at a considerable range of depths (Einhom et al., 1992). 

The tubes for solvent desorption are typically constructed of glass tubing, with both ends flame-sealed and containing two sections of suitable sorbent. The first section contains the adsorbent for the sample and the second section a back-up to test for breakthrough. Packed tubes are commercially available, alternatively empty tubes can be packed in the laboratory. The commercial sorbent tubes for solvent desorption, for example XAD glass tubes, are assumed to be clean but their cleanliness must, regardless of the assurances of the manufacturers, be checked by analyzing a minimum of five blank tubes by the same desorption and analytical procedures as used for the real samples. 

Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF)-mass spectrometry (MS) is now routinely used in many laboratories for the rapid and sensitive identification of proteins by peptide mass fingerprinting (PMF). We describe a simple protocol that can be performed in a standard biochemistry laboratory, whereby proteins separated by one- or two-dimensional gel electrophoresis can be identified at femtomole levels. The procedure involves excision of the spot or band from the gel, washing and de-stain-ing, reduction and alkylation, in-gel trypsin digestion, MALDI-TOF MS of the tryptic peptides, and database searching of the PMF data. Up to 96 protein samples can easily be manually processed at one time by this method. 

Developments in mass spectrometry technology, together with the availability of extensive DNA and protein sequence databases and software tools for data mining, has made possible rapid and sensitive mass spectrometry-based procedures for protein identification. Two basic types of mass spectrometers are commonly used for this purpose Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF) mass spectrometry (MS) and electrospray ionization (ESI)-MS. MALDI-TOF instruments are now quite common in biochemistry laboratories and are very simple to use, requiring no special training. ESI instruments, usually coupled to capillary/nanoLC systems, are more complex and require expert operators. We will therefore focus on the use of MALDI-... 

Adsorption Method Iodine separation by the platinum adsorption technique was first reported by Toth (1961) and Lin et al. (1963). Oak Ridge National Laboratory has adopted an adsorption procedure (Case and Acree, 1966) for the purification of I produced from fission by a distillation process. In 1966, in comparison with other methods of L Baker (1966) has concluded that the adsorption technique is the most efficient and economical method. In this method, a metallic Pt plate or felt is used to adsorb carrier-free iodine from an acidic solution containing target materials. The Pt plate or felt with iodine activity is then removed from the solution and thoroughly washed with water. The activity is then desorbed in a slightly basic solution. Application of electrical current could enhance the desorption process. Nearly quantitatively the adsorbed iodine activity can be desorbed from the Pt surfaces. 

Numerous procedures, by a variety of different instruments, are available to quantify the amount of thallium present in hair, blood, tissue, saliva, and urine (for reviews, see [9,81]). Instrumentation used includes emission spectrography, flame and flameless atomic absorption spectroscopy (AAS), voltammetry, neutron activation analysis, and field desorption mass spectroscopy [13,17,82-90]. Field desorption mass spectroscopy when combined with stable isotope dilution can detect fentomole quantities and has value in that no tissue preparation (other than homogenization) is required [65,82,89], The use of these two methods, however, is restricted to specialized laboratories. 

The high-performance thin-layer chromatography-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HPTLC-MALDI-TOF-MS) procedure was found to be robust because disintegrating pieces of the layer material, which might damage the MS, were not observed even under routine laboratory conditions. 

Several mass spectrometric techniques including fast atom bombardment (FAB), plasma desorption (PD), matrix-assisted laser desorption/ionization (MALDI), and electrospray (ES) mass spectrometry (MS) are presently available for the analysis of peptides and proteins (Roepstorff and Richter, 1992). Of these techniques, mainly PDMS has gained footing in protein laboratories because the instrumentation is relatively cheap and simple to operate and because, taking advantage of a nitrocellulose matrix, it is compatible with most procedures in protein chemistry (Cotter, 1988 Roepstorff, 1989). Provided that the proper care is taken in the sample preparation procedure most peptides and small proteins (up to 10 kDa) are on a routine basis amenable to analysis by PDMS. Molecular mass information can be obtained with an accuracy of 0.1% or better. Structural information can be gained by application of successive biochemical or chemical procedures to the sample. 

In 1996 we described (1) the successful application of Matrix-Assisted-Laser-Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS) for characterizing hemicelluloses isolated from wood and pulps. Since then this approach has been improved considerably (2,3) and several different procedures for wood and pulp constituents have been reported (3-8). In the present article, a selection of our previously reported analytical procedures are discussed together with some hitherto unpublished results from our laboratory. 

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