We propose a novel concept of flow-based analysis for spectrophotometric speciation based on flow rate modulation and fast Fourier transform (FFT). A redox reagent solution's and a sample solution's flow rates are varied by sinusoidal control signals with periods of T and 0.5T, respectively. Both solutions are merged with a color reagent, while the total flow rate is held constant. Downstream, the absorbance of the mixed solution is measured and acquired as the detector output voltage (V_d). The V_d is analyzed by FFT with the window's time length of T. One species that directly reacts with the color reagent contributes only to the amplitude (A₂) of the second harmonic wave component in V_d. The other species that needs the redox conversion before the coloration contributes to the amplitude (A₁) of the fundamental wave component, in addition to A₂. The former species+' concentration can be estimated from A₂ by taking the latter's contribution to A₂ into account. The latter species’ concentration can be determined only from A₁. The proposed concept was demonstrated by applying it to the speciation of Fe²⁺ and Fe³⁺ by an o-phenanthroline spectrophotometry, where Fe³⁺ was reduced to Fe²⁺ by L-ascorbic acid before the coloration.

我们提出了一种新的基于流的分析概念，用于基于流率调制和快速傅里叶变换（FFT）的分光光度分析。氧化还原试剂溶液和样品溶液的流速分别通过周期为T和0.5 T的正弦控制信号而变化。两种溶液均与着色试剂合并，而总流速保持恒定。在下游，测量混合溶液的吸光度，并将其作为检测器输出电压（V _d）来获取。的V _d是由FFT用的窗口的时间长度分析Ť。直接与色剂反应的一种物质仅对振幅有贡献（A ₂）在所述第二谐波分量的V _d。除A ₂以外，在着色前还需要进行氧化还原转换的其他种类也有助于基波成分的振幅（A ₁）。前者+的浓度可通过考虑后者对A ₂的贡献来从A ₂估算。后者的浓度只能由A ₁确定。通过邻菲咯啉分光光度法将其应用于Fe ²⁺和Fe ³⁺的形态进行了证明。着色前，L-抗坏血酸将³⁺还原为Fe ²⁺。