Target capturing techniques

Fluid samples may be collected downhole at near-reservoir conditions, or at surface. Subsurface samples are more expensive to collect, since they require downhole sampling tools, but are more likely to capture a representative sample, since they are targeted at collecting a single phase fluid. A surface sample is inevitably a two phase sample which requires recombining to recreate the reservoir fluid. Both sampling techniques face the same problem of trying to capture a representative sample (i.e. the correct proportion of gas to oil) when the pressure falls below the bubble point. 

However, luminescence-based detection techniques often require a high number of steps. Consider ELISA as an example. As a first step, the sample is introduced into a 96-well plate an antibody targeting the antigen of interest has been immobilized to the wells of the plate. After a rinse, the wells contain the antibody and any bound antigen. However, although the antigen has been isolated, the protocol is nowhere near completion. The remaining steps include another antibody (different from the first) to form a sandwich assay, a secondary antibody with an enzymatic label, and a substrate that is luminescent when activated by the enzyme. Finally, the sample is analyzed by relatively expensive detection optics to determine the amount of analyte that was captured in the assay. The steps are illustrated in Fig. 14.1a. 

Affinity capture-release electrospray ionization mass spectrometry (ACESIMS) is another recently introduced technique for quantification of proteins, and to date has most often been applied to clinical enzymology.60 The product conjugates of the enzymatic reaction between the synthetic substrate and targeted enzyme are captured by immobilized affinity reagents, purified, released into solution, and analyzed by ESI-MS. 

Mass-spectroscopic technique has also been used with non-fissile targets after pile or cyclotron bombardment to determine the mass-numbers of radioactive nuclides. In one case, the branching ratios of certain isotopes for and electron capture decay (where different elements are produced by the two routes) were determined from the amount of the stable end-products of radioactive decay, using the mass-spectrometer to identify the isotopes concerned and to correct for any stable impurities of the elements concerned (98). For some purposes, mass-spectroscopic separations could be very valuable technically such as the... 

Finally, there are custom two-step quantitation methods such as chromatography or ELISA that require a capture step for isolating the protein and then a quantitation step based on a standard curve of the purified target protein. The preliminary capture step may also concentrate the protein for increased sensitivity. These techniques are typically not available in a commercial kit form and may require extensive method development. They are more labor intensive and complex than the colorimetric or absorbance-based assays. In addition, recovery of the protein from and reproducibility of the capture step complicate validation. Despite these disadvantages, the custom two-step quantitation methods are essential in situations requiring protein specificity. 

Pervaporation may certainly play an important role for replacement of evaporative techniques as well as aroma-recovery processes based on solvent extraction, in particular when the labelling natural is considered crucial. Some of the most relevant technical challenges discussed herein have to be addressed in order to render organophilic pervaporation a competitive process (Fig. 19.4). In particular, the way of capturing the target aromas from the permeate stream has to be reanalysed in terms of minimising energy consumption and labour-intensive operations. 

---