SPE performance

A 96-well SPE system for the simultaneous extraction of drugs and metabolites in biological matrices developed by Wu and coworkers (Simpson et al, 1998) is shown in Figure 6.39. In this approach, smaller elution volumes (75-200 FL) are used to improve SPE performance. This volume reduction allowed for the direct injection of samples without any evaporation and reconstitution. The collection plate that contains the elution fraction is loaded to an autosampler that is compatible with 96-well plates, thereby, eliminating the transfer to injection vials. This quantitative process improvement led to an improved analytical performance, considerable savings in time, and reduced cost. 

Solid-phase extraction (SPE) can be used to separate an organic analyte from the aqueous phase and to concentrate the analyte in a few milliliters of solvent. SPE also can be used to clean up a sample matrix and remove concomitant contaminants from the analyte. In some cleanups the analyte is absorbed onto the solid phase and the interferences pass through unretained. In the opposite cleanup strategy the solid phase retains the interferences and allows the analyte to pass through the cartridge with the mobile phase. In some environmental application, SPE performs all three roles—extraction, concentration, and cleanup. 

ME A series 2-7 were prepared to test SPE performance as a function of hydrophobic properties of the MEA. GDL with different polytetrafluoroethylene (P IPE) loading were used with MEA 2-A, and hydrophilic GDL were used with MEA 6 and 7.While pressing the first series of MEA, the carbon cloth adhered to the PTEE liner on the hot press. This was attributed to the extra layer of Nafion placed on the carbon cloth before pressing. To avoid this problem, the Nafion content in subsequent inks was increased to 0.8g. 

MEAs 10 and 11 were assembled, tested, and compared to MEAs 6-8 to check the effect of catalyst loading on SPE performance, and the results are presented in Figure 8.4 below. 

Effects of Different Carbon-Based GDL Components on SPE Performance... 

MEAs tested so far, had established that use of Ft/C catalysts on the anode reduced the performance of the SPE electrolyzer. In addition flow rate had been optimized, trends with temperature were observed, the effect of using alternative proton conducting membrane on SPE performance, and a suitable carbon-based GDL had been demonstrated. The use of a titanium fiber based GDL was identified as an option to optimize SPE performance via judicious selection of material components that make up the system. MEA 42 was assembled using a proton conducting membrane from GEEC (GEEC 117), commercial iridium oxide catalyst on the anode and titanium fibers GDL on both anode and cathode side. In contrast, MEA 51 was made with a homemade iridium oxide catalyst on the anode, Bekinit GDL on the anode and... 

The System is built by using three independent modules (SPE, SEE and GC) in Such a way that it can be assembled to perform experiments in the on-line coupled mode (SPE-SEE, SEE-GC, SPE-GC and SPE-SEE-GC) or as independent units (GC, SPE, and SEE). This means that if we want to use the system for standard GC, there will be no problems, with the same applying for both SPE and SEE. 

Figure 11.18 Schematic diagram of an in-line SPE unit for CE using (a) polyester wool frits to hold the sorbent, or (b) a paiticle-loaded membrane. Reprinted from Journal of Capillary Electrophoresis, 2, A. J. Tomlinson and S. Naylor, Enhanced performance membrane preconcenti ation-capillary electrophoresis-mass spectiometi y (mPC-CE-MS) in conjunction with ti ansient isotachophoresis for analysis of peptide mixtures, pp 225-233, 1995, with permission from ISC Teclmical Publications Inc.

Although most of the reactions are performed in liquid state - which is the simplest reaction medium - a combination of solid-phase extraction (SPE) and reaction... 

Hinds, A. A., S. P. T. Smith, and E. K. Morton, A comparison of the performance, cost and environmental effects of diesel-based and low-toxicity oil mud Systems, SPE 11891, Offshore Europe 1983 Conference, Aberdeen, September, 1983. 

Knox, D. W. J., and J. M. Milne, Measurement-while-drilling tool performance, SPE 16523, Offshore Europe 1987 Conference, Aberdeen, Proceedings Vol. 1, September 1987. 

Rosato, D. V., Design Features that Influence Part Performance, SPE-IMD Newsletter, Issue 46,1997. 

ECD = electron capture detector GC = gas chromatography HPLC = high-performance liquid chromatography MC = microcoulometric detector MS = mass spectrometry NICI = negative ion chemical ionization RSD = relative standard deviation SPE = solid phase extraction... 

The role of the distribution of species in solution in determining the CdS film composition and structure was studied by Rieke and Bentjen [244], who performed equilibrium analysis of the cadmium-amine-hydroxide system to predict the spe-ciation in solution. The focus was on the formation of Cd(OH)2 and Cd(NH3) species due to their importance in film growfh. If was concluded fhat for deposition of high-quality, adherent, phase-pure CdS films, a surface cafalytically active toward thiourea decomposition is desirable. The Cd(OH)2 film was thought to be responsible for this effect. 

Whilst for the analysis of plant material for cannabinoids both GC and HPLC are commonly used, in analytical procedures the employment of GC-based methods prevails for human forensic samples. Nonetheless, the usage of HPLC becomes more and more of interest in this field especially in combination with MS [115-120]. Besides the usage of deuterated samples as internal standards Fisher et al. [121] describe the use of a dibrominated THC-COOH (see 7.5). The usage of Thermospray-MS and electrochemical detection provide good performance and can replace the still-used conventional UV detector. Another advantage in the employment of HPLC rather than GC could be the integration of SPE cartridges, which are needed for sample preparation in the HPLC-system. 

L. S. Boak, G. M. Graham, and K. S. Sorbie. The influence of divalent cations on the performance of BaS04 scale inhibitor species. In Proceedings Volume, pages 643-648. SPE Oilfield Chem Int Symp (Houston, TX, 2/16-2/19), 1999. 

K. M. Cowan and L. Eoff. Surfactants Additives to improve the performance properties of cement. In Proceedings Volume, pages 317-327. SPE Oilfield Chem Int Symp (New Orleans, LA, 3/2-3Z5), 1993. 

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