Staggered-parallel columns

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. 

In orthorhombic a-sulfur, the modification stable at normal conditions, S8 rings are stacked to form columns. Consecutive rings are not stacked one exactly above another (as in a roll of coins), but in a staggered manner so that the column looks like a crank shaft (Fig. 11.3). This arrangement allows for a dense packing of the molecules, with columns in two mutually perpendicular directions. The columns of one direction are placed in the recesses of the perpendicular crank shafts . In S6 and in S12 the rings are stacked exactly one above another, and the rolls are bundled parallel to each other. In the structures a... 

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]. 

The use of CS techniques reduces the column equilibration time and flushes the matrix components to waste (decreases source contamination), while narrow-bore LC columns help not only with flow rates that were amenable to most atmospheric- pressure ionization (API)- interfaces but also provide increased sensitivity [28]. A change from a serial to a parallel format further increases throughput for bioanalysis, with timed injections at intervals from multiple LC systems and staggered MS detection [29-31]. 

Figure 15.24 shows expanded upflow columns operating in parallel with a single downflow column. These are staggered when put into operation. Downflow operation is used on large-volume plants, and the breakthrough curve should be steep to maximize adsorbent utilization. 

---