Since it is desirable to automate the entire assay protocol, including sample preparation steps, both sample dissolution and digestion have been frequently attempted to be automated on line  FI as well as in SI mode. Yet regrettably, only the batch technique is, in my opinion, practical and provides reliable way  for dissolution  of samples digestion of such compounds as e.g. polyphosphates.

Recently summarized  papers on sample dissolution (Cerdá & Estela 2008) reveal the difficulties of inserting slurries, and their subsequent dissolution at elevated temperatures, using microwave-assisted heating with mixtures of aggressive reagents (e.g. HCl + HF + HNO3). The samples must be finely powdered and processed at a sampling rate of only 10s/ hour, while channel blockage must be carefully avoided.

The  pioneering efforts in this field should indeed be applauded, but presently, the use of on line dissolution and in some cases also of on line decomposition is not reliable enough to be used in a routine laboratory for serial assays.

Digestion and Dissolution
The alternative, batch digestion practical, safe and efficient. Samples are digested automatically and simultaneously in parallel, unattended, for any desired length of time, and with minimum reagent consumption. Once dissolved, samples can be loaded into an autosampler, split for assays for different analytes, and processed  at a high sampling frequency either by FI or by SI.

On-Line Sample Pretreatment: Dissolution and Digestion. V.Cerdá and J.M.Estela. Chapter 6 in Advances in FIA and Related Techniques. S.D. Kolev and I.D. McKelvie Ed. Elsevier Amsterdam 2008