AL a
b
Figure 1 – a) Schematic view of system and dilution module. b) System: 1) educt pumps, 2) microreactor, 3) MRA, 4) multiport valve, 5) solvent car- rier module (microannular gear pump and mass flow controller), 6) dilu- tion pump, 7) compensation pump, 8) mass analyzer, 9) heating/cooling module, 10) communication module.
microreactor flowed through the MRA, and then a portion of the output stream split off and entered the dilution flow. The amount of output stream sent to the dilution flow was determined by the split factor set on the device, which governs the switching frequency (0.2 Hz–2 Hz) and aliquot volume (22, 100 and 300 nL). Dilution ratios up to 100,000 are possible by changing the split factor and dilution flow rate.
Because microreactor output can be varied to monitor different reac- tion stages, input to the MRA can be altered as well. For stable dilutions, the split amount should be stable to different input flow conditions. However, initial testing showed strong dependence of the signal intensity (peak area) of the diluted solution on the microreactor flow rate, espe- cially below 3 mL/min (Figure 2a). This unexpected influence of flow rate variation on the splitter impacts the dilution. The signal intensity of the diluted flow shows higher stability with microreactor flow rates greater than 3 mL/min; thus an additional pump (G1310A, Agilent Technologies) was added. This isocratic pump is activated when the flow does not reach 3 mL/min. In turn, the dilution flow rate is reduced, corresponding to the added portion to the main stream. This dilution process is automatic so that the split factor, dilution flow rate and compensation flow rate are automatically selected based on the dilution ratio and reaction stages set by the user. For example, with a dilution ratio of 1:100, if the micro- reactor flow rate is 4 mL/min (>3 mL/min), a split factor of 1 and dilution flow rate of 1 mL/min are selected. When the microreactor flow rate is 1 mL/min (<3 mL/min), the compensation flow is 3 – 1 = 2 mL/min. In this case, the original solution is diluted by 66.7%, the required dilution ratio now being only 1:33. Therefore, the dilution flow is reduced to 0.33 mL/min
AMERICAN LABORATORY 37 JANUARY/FEBRUARY 2017
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