Analyte enrichment

Basically, two methods are available for concentrating organic compounds from seawater solvent extraction and sorption onto a solid adsorbent. 

The advantages and disadvantages of solvent extraction have been discussed in the second edition of this book. It becomes inconvenient when large volumes have to be extracted, as is necessary for determinations of organochlorine compoimds in seawater other more suitable methods being available it will not be discussed here. 

Various materials have been used to adsorb organochlorine compounds from natinal waters. They include activated charcoal urethane foam plugs polyurethane foam coated with adsorbents a porous polymer (Tenax GC) a mixture of activated chmcoal powder, MgO powder and refined diatomaceous earth Carbowax4000 and n-undecane on Chromo-sorb DMCS Serdolit and Amberlite XAD resins (references were given in the second edition). The last material has been used most successfully (IOC, 1993). The use of XAD resin has been described in some detail by Dawson (1976). Problems initially encountered with cleaning of this adsorbent have been solved in the meantime. Extremely low blank values can now be obtained for XAD-2 columns. Their use allows reliable determinations of CBs present in seawater at levels as low as 0.005-0.1 pg/L. 

The advantages of using XAD-2 resin, as we see them today, are the large volumes that can be processed per unit time (90L/h, Le., 5 bed volumes/min), and the use of several extractors in series, if necessary. The extraction efficiency of a single column is 70-90 %, if the capacity of the column is not exceeded (Schulz, 1990). This is in good agreement with the results of another study (Gomez-Belinchon etal., 1988). 

Procedures for cleaning the resin, blank determination and analyte desorption are described in Chapter 18. A simpler version of the extractor shown in Fig. 18-la may also be used it was described by Ehrhardt (1987) and is shown in Fig. 22-2. 

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The composition, properties and size (weight, volume) of the sample material to be analyzed are important aspects for analytical method development and for analyte enrichment vs depletion of sample matrix. 

Future efforts in the field of environmental analysis will be focused on several fronts, including analyte enrichment and measurement, on-line and on-site techniques, multi-residue methodology, direct injection of aqueous samples into LC/MS/MS... 

This sorption material was suggested by Peraniemi et al. [2] for analytical enrichments of phosphate and arsenate. The activated carbon was shaken with a solution of Zr0(N03)2 as described in [2] and a final concentration of 28 mg Zr per g activated carbon was yield. 

The particle-beam interface is an analyte-enrichment interface in which the column effluent is pneumatically nebulized into a near atmospheric-pressure desolvation chamber connected to a momentum separator, where the high-mass analytes are preferentially directed to the MS ion source while the low-mass solvent molecules are efficiently pumped away (71, 72). With this interface, mobile phase flow rates within the range O.l-l.O ml/min can be applied (73). Since the mobile phase solvent is removed prior to introduction of the analyte molecules into the ion source, both EI and CI techniques can be used with this interface. 

Antibodies are extremely versatile weapons of the immune system, but also useful tools for science in general, as well as for laboratory and clinical medicine, agriculture, and biotechnology. They were a great discovery for analytical chemistry as antibodies can be easily applied to sample analysis without any analyte enrichment, purification, or pre-treatment usually required with standard methods based on liquid or gas chromatography and mass spectrometry (MS). 

Lanza F, Sellergren B (2001) Molecularly imprinted extraction materials for highly selective sample cleanup and analyte enrichment. Adv Chromatogr 41 137-173... 

Jonsson, J.A., P. Lovkvist, G. Audunsson, and G. Nilve. 1993. Mass transfer kinetics for analytical enrichment and sample preparation using supported liquid membranes in a flow system with stagnant acceptor liquid. Anal. Chim. Acta 111 9-24. 

There are many similarities to the case of Marie and Pierre Curie, and their experience with the manufacturing of radium, to draw from the successful discovery of rhenium the emphasis on the analytical enrichment procedure, the determination to produce weighable samples, the art of taking patents and mastering the production of the new element and, last but not least, the writing of a monograph on... 

Even a technique of higher detection power as ET-AAS may require some sort of previous analyte enrichment for difficult elements. In the determination of As and Se in mineral waters described by Hudnik and Gomiscek [23], coprecipitation of both elements on hydrated Fe(III) oxide was employed to improve LoDs, otherwise impaired by matrix effects. A graphite tube furnace was the atomization cell, with the atomic vapor sampled with element electrodeless discharge lamps. After treatment of the sample with Fe(III) solution at the appropriate pH, the oxide precipitate was filtered and dissolved and the solution volume reduced to 5 mL of 0.2 M H2SO4. Ten-microliter volume aliquots of sample and standard solutions were injected into the furnace. Reported LoDs were 0.2 and 0.5 p,g l-1 for As and Se, respectively. 

Sample preparation also includes certain matrix separation steps (e.g., by ion exchange, extraction chromatography and others), analyte enrichment (by co-precipitation and also ion exchange, e.g., Pu separation is performed using TEVA resin ) and preconcentration steps (e.g., by evaporation of solvent) off line or on line by high performance liquid chromatography (HPLC) or capillary electrophoresis (CE) in order to improve the detection limits and avoid disturbing interference problems in ICP-MS. 

Ultrasonic nebulization is known to provide a higher analyte transport efficiency than pneumatic nebulization (normally 8-15 times higher) this results in improved sensitivity and lower detection limits, which is especially important for the analysis of species at trace or ultratrace levels [31-35]. Ultrasound-assisted generation of smaller drops and the use of a desolvation system to remove most of the solvent load allow the production of fine, dry analyte-enriched aerosol for insertion into a detection system some authors, however, ascribe most of the sensitivity increase of USNs to the desoivation system aione [36]. 

Analyte Enrichment factor for anthracene MIP Enrichment factor for chrysene MIP... 

MIP sensor elements are also suitable for the analysis of multicomponent samples. The cost-effective, miniaturised, non-covalent MIP sensor arrays, when combined with computational data evaluation, make weak artificial recognition phenomena highly applicable for smart sensors. In comparison to gas or liquid chromatography, the results with mass-sensitive MIP sensors are faster and cheaper to obtain [32]. For effective on-line monitoring, the ideal MIP sensor or actuator should allow reversible analyte enrichment without dependencies on intermediate washing procedures (with organic solvents, for example). 

Three objectives determined the developments throughout the past 30 years the ability to couple conventional LC columns to a mass spectrometer, the ability to achieve analyte enrichment in order to enable electron ionization (El). 

The use of semi-permeable silicone rabber membranes for on-line analyte-enrichment in LC-MS was described in 1974 by Westover et al. [53]. Polycyclic aromatic hydrocarbons were analysed by MS after evaporation of the reversed-phase LC column effluent and passage of the vapom through a membrane-based solvent-separator. This system, designed by Jones et al. [54], is limited to the analysis of non-polar analytes which are sufficiently volatile at 250°C, the maximum operating temperature of the membrane. 

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