Flow Injection Tutorial

Versatility of pFI in LOV format is its key advantage, when compared to continuous flow FI. This is because in order to accommodate different assays, cFI manifold must be physically reconfigured, while miniSIA instrument accommodates the assays by flow programming. Briefly, in the traditional continuous Flow Injection: Volume of the injected sample is adjusted by changing volume of the injection loop.

Concentration of reagent in sample/reagent mixture is adjusted by changing diameter of peristaltic tubing that feeds reagent into the confluence point. Incubation time is adjusted by changing the length of reaction coil(s) between injector and detector.

In pFI-LOV format the key parameters are controlled by software. Volume of injected sample is adjusted by selecting sample volume aspirated into holding coil Concentration of reagent in sample/reagent mixture is adjusted by flowrates generated by pumps. Incubation timeis adjusted by selecting the length of stop flow period.

Reproducibility of assays performed in the pFI-LOV mode varies between rsd 1.1 % (1.2.34.) for nitrite assay, to rsd. 3.3% (1.2.38.) for nitrate assay, the latter being based on complex microfluidic manipulations. This level of precision is in agreement with precision of spectrophotometry (Christian 2014) used here as detection technique.

Versatility and applications of programmable FI are documented in the following publications:

“Redesigning flow injection after 40 years of development: flow programming” J. Ruzicka, Talanta 176, (2018), 437.

“Programmable flow injection. Principle, methodology and application for trace analysis of iron in sea water matrix” M. Hatta, Ch. I. Measures, J. Ruzicka, Talanta 178 (2018) 698.

“Determination of traces of phosphate in sea water automated by programmable flow injection: Surfactant enhancement of the phosphomolybdenum blue response” M. Hatta, Ch. I. Measures, J. Ruzicka, Talanta 191 (2019) 333.

In summary, advantages of flow programming makes pFI-LOV an attractive methodology for many applications, with the exception of serial assays of a large number of samples, where sampling frequency is of importance. The reason is that pFI-LOV cannot at present exceed rate of about 100 samples/hour due to software limitation, that requires about 15 seconds per sampling cycle for controlling instrument and data evaluation. On the other hand pFI-LOV is a powerful research tool for investigation and optimization of reagent based assays, as illustrated in the publications listed above and in Section 1.5.