Triangular-wave controlled amplitude-modulated flow analysis for extending dynamic range to saturated signals.

We have applied our amplitude-modulated flow analysis concept to extend the dynamic range to saturated analytical signals. Sample solution, the flow rate F of which is periodically varied with a triangular control signal V, is merged with a reagent solution delivered at a constant flow rate F. While the total flow rate F is kept constant, a diluent with F-(F + F) flow rate is aspirated from the third channel. The analytical signal V obtained downstream is processed by fast Fourier transform to obtain the amplitudes of the wave components in V. When the sample concentration C is low, V shows a triangular profile like V; the sum of the amplitudes ΣA is proportional to C. When C is high, V shows a trapezoidal profile because of the V saturation. A linear calibration curve can also be obtained for such saturated signals by plotting CΣA against C. The proof of the concept is validated by applying it to spectrophotometric determinations of a dye (Methylene Blue) and colored complexes of Fe - phenanthroline and Fe - Tiron.