The purpose of sequencing the sample zone last into the holding (A), is to position the changes of baseline, caused by reagents, past the readout of peak maximum. The SHC software protocol (B), also reduces the time during which the baseline fluctuates, by slicing the trailing edge of the peak, through applying a short burst of a high flow rate at a selected return volume (140 to 260 mcrL) (C).
The inverted sequencing yields a smooth transition of baseline to the leading edge of the peak, since there is no absorbance change at the interface between aqueous standard solution, and DI water carrier solution (C,D).
Sensitivity of the inverted sequence method follows similar pattern as of the single interface and of the sandwich sequences, the peak height increasing (D) with increasing injected sample volume, and then declining. It turns out that the sampling frequency is lower than indicated by the time span of an individual run, since the software pauses for 3 seconds between each sampling cycle.
Thus, while for return volume of 180 mcrL (blue trace C) the sampling frequency is 115 s/hr, the serial run (E) obtained at this setting has frequency of 105/s hr.
Serial Phosphate Assay
Phosphate 0 to 300 ppB and 0 to 40 ppB
2.2.27.
