Staggered-parallel samples

Certain assays may benefit from staggered parallel chromatography, for example, when (1) the same assay must be performed for a large number of samples in a short time and (2) if the analytes of interest that elute in a narrow window account for only a fraction of a chromatogram. 

In terms of sample pretreatment, the implementation of 96-well based methods for protein precipitation [97, 101-102], LLE [103-104], and SPE [95-96] greatly contributed to improving the sample throughput. For SPE, 384-well plate methodology has even been demonstrated [106]. Staggered parallel high-flow TFC-MS is another way to increase the sample throughput [113-115]. 

Fom staggered parallel columns were coupled to one ESI-MS system via a switching valve, enabhng the subsequent detection of the chromatogram from each coluum [148]. The overall run time was reduced from 4.5 to 1.65 min per sample. 

Ayrton et al. have experimented with TFC with microbore (1 mm) and capillary (0.18 mm) formats for TFC. These columns reduce the excessive amount of mobile phase required for this technology and can provide greater sensitivity for sample-limited situations. At a flow rate of 130 /zL/min, these authors demonstrated the ability to achieve sub-ng/mL quantitation for an assay based on only 2.5 /zL of plasma [76]. More recently, this group performed TFC in a parallel four-column format. MS analysis was accomplished with a multiple sprayer-ESl interface and allowed for simultaneous LC-MS/MS detection [77]. In another example. King et al. used a commercial system based on four staggered TFC systems in conjunction with a modified autosampler to demonstrate increased throughput. These authors demonstrated the ability to pass a GLP-level validation with this system [78]. 

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