Parallel four-channel

The only solution to the count rate problem is multimodule operation. Splitting the light into several detectors connected to independent TCSPC modules proportionally increases the counting capability. Of course, multimodule operation also increases the system cost and can cause space and power supply problems in the host computer. These problems have at least partially been solved since packages of relatively small and cost-efficient TCSPC modules are available. A fully parallel four-channel package (SPC-134, Becker Hickl, Berlin) is shown in Fig. 3.16. 

The final structure design of the four-channel YI sensor is shown in Fig. 10.7 top-view (a), cross-section perpendicular to output channels (b), and side-view along the optical path (c). The distance between the mutually parallel output branches of the first Y-junction is chosen as D = 160 pm and the length of the splitting section is Ls, it 10 mm. 

Figure 9. SPR sensor with four parallel sensing channels (provided hy S. Lolas, Biacore AB.)...

Performing parallel analysis of compound libraries offers many potential advantages over serial-based LC/MS analytical methods, the most obvious of which is dramatically increased compound analysis throughput. Using singlechannel HPLC-based purification systems, routine sample throughput of up to 192 reaction mixtures per 24-hour day was reported [64]. With parallel HPLC systems, it has been reported that the theoretical throughput increases to 384 samples per day for a two-channel system and to 768 samples per day for a four-channel system. 

A schematic of a commercially available system that was conflgured in our laboratory for parallel analysis and purification is shown in Figure 11-9. This four-channel parallel LC/MS purification system consists of a binary HPLC system, an autosampler configured with four injection, a multichannel UV detector, a quadrupole mass spectrometer equipped with an MUX ion source which monitors four flow streams simultaneously, and four independently... 

Figure 5.12 Four-channel multiplexed electrospray for four-channel parallel LC-MS, available from Waters. Reprinted with courtesy from Waters.

At the same time, the bioanalysis of LOR and DCL in rat, rabbit, mouse, and dog plasma was reported by others [64]. In order to get more rehable toxicology data, the bioanalysis in these four preclinical species is done simultaneously instead of on separate days. The sample pretreatment was SPE in a 96-well plate format, using a Tomtec Quadra hquid handling system and an Empore Cig 96-well extraction disk plate. Fom-channel parallel LC was done with four 100x2-mm-lD Cg colunms (5 pm) and a mobile phase of 85% methanol in 25 mmol/1 aqueous AmOAc (adjusted to pH 3.5). The mobile phase was delivered at a flow-rate of 800 pl/min and split into 200 pl/min over each of the four colunms. A multi-injector system was apphed with four injection needles. A post-column spht was applied to deliver 60 pEmin per column to a four-channel multiplexed ESI source (Ch. 5.5.3). The interspray step time was 50 ms. Positive-ion ESI-MS was performed in SRM mode with a dwell time of 50 ms for each of the four transitions, i.e., LOR, DCL, and their [DJ-ILIS, with 20 ms interchannel delay. The total cycle time was thus 1.24 s. The LOQ was 1 ng/ml for both analytes. QC samples showed precision ranging from 1 to 16% and accuracy from -8.44 to 10.5%. The interspray crosstalk was less than 0.08% at concentrations as high as 1000 ng/ml. 

The incorporation of four-column parallel F-HPLC coupled with a multichannel MS interface increased the speed both for sample analysis and sample demixing [56]. A 5 min analysis method for baseline separation of five components of M-79a-d was applied to four-channel parallel LC-MS analysis (see Scheme 13.18 and Figure 13.2). Four mixture samples containing a total of 20 compounds could be separated in 5 min, which dramatically improves the efficiency of FMS. 

The MS instrumentation is the most expensive part of the LC-MS system, hence efforts to improve the throughput of the LC-MS analysis often involve the use of parallel multiple columns that feed into a single mass spectrometer. Zeng and Kassel [99] developed an automated parallel analytical/preparative LC-MS workstation to increase the throughput for the characterization and purification of combinatorial libraries. The system incorporates two columns operated in parallel for both LC-MS analytical and preparative LC-MS purifications. A multiple-sprayer ESI interface was designed to support flows from multiple columns. The system is under complete software control and delivers the crude samples to the two HPLC columns from a single autosampler. The authors demonstrated characterization of more than 200 compounds per instrument per day, and purification of more than 200 compounds per instrument per night. De Biasi et al. [100] described a four-channel multiplexed... 

An ideal propulsion system should ensure reproducible flow rates on a short-term (hours) and long-term (days) basis, multi-channel capability (at least four parallel pumping channels to provide system versatility), resistance to aggressive reagents and solvents, readily adjustable flow rates and low initial investment and running costs [7]. The maintenance of a consistent flow is essential to obtain good analytical reproducibility. Flow rates are typically in the 0.2—5.0 mL min-1 range so that the system operates under low pressure, normally lower than 10 psi [0.689 bar]. The number of channels used depends on the manifold complexity. 

SPR is a representative physical phenomenon that is widely utilized for label-free characterization of molecules on thin metal films. The basic principle and operation of SPR has been described in more detail in several review articles [77, 78]. The reports on SPR-based immune sensors have steeply increased for detection of analytes with low molecular weights in recent years. SPR detection in microfluidic systems can provide various advantages. Immunoreactions are completed within a short time due to small sample volumes down to the nanolitre scale. Kim et al. developed a simple and versatile miniaturized SPR immunosensor enabling parallel analyses of multiple analytes [79]. Their SPR sensor was claimed to exhibit good stability and reusability for 40 cycles and more than 35 days. Feltis et al. demonstrated a low-cost handheld SPR-based immunosensor for the toxin Ricin [80]. Springer et al. reported a dispersion-free microfluidic system with a four-channel SPR sensor platform, which considerably improved the response time and sensitivity [81]. The sensor was able to detect short sequences of nucleic acids down to a femtomole level for 4 min. Waswa et al. demonstrated the immunological detection of E. coli 0157 H7 in milk, apple juice, and meat juice extracted from... 

SPR detection is highly adaptable to multiplexed configurations in miniaturized formats. The flow cells in the original Biacore systems had four measuring spots positioned within a few millimeters (Fig. 19). Prototype systems with eight parallel flow channels have also been described and applied to food analysis apphcations [64]. 

Fig. 3.16 Package of four fully parallel TCSPC channels...

Fig. 5.94 Efficiency versus count rate for a single TCSPC channel (a) and a system of four parallel TCSPC channels (b). Dead time 100 ns...

A system with four parallel TCSPC channels can be used up to 40 MHz detector count rate. When this count rate is compared to the count rates of other time-resolved detection techniques, the high efficiency of TCSPC must be taken into account. Consider a gated image intensifier that is operated at a gate width of 100 to 200 ps, i.e. at a time resolution equivalent to a mediocre TCSPC system. The short gate width then results in an efficiency of 0.05 to 0.1. A four-channel TCSPC system operated at 40 MHz has an efficiency of 50%. The 40 MHz detector count rate of the TCSPC system therefore corresponds to an input count rate of 200 to 400 MHz in the image intensifier. 

Multi-channel capability, providing at least four parallel pumping channels to ensure high versatility. 

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