A novel approach to high pressure flow digestion

Abstract

A new high pressure flow digestion system has been developed for sample digestion at a pressure of up to 40 bar and a temperature of about 230 C. The reaction with acids takes place in a PFA tube and is heated by microwave radiation in a multimode cavity. As the PFA tube cannot withstand the harsh digestion conditions without support, it is placed inside a coiled glass tube pressurized by 40 bar nitrogen thus forming an autoclave. Corrosion of system components by acid fumes and related sample contamination is circumvented by establishing a slow but steady flow of the high pressure nitrogen countercurrent to the sample flow. The presented system does not constrain the selection of the digestion reagent. Acid cocktails of nitric acid with hydrochloric and/or hydrofluoric acid as well as hydrogen peroxide were successfully used for the digestion of various samples. The method accuracy was validated with five certified reference materials (BCR 62, DORM-2, NIST SRM 1515, NIST SRM 1567, NIST SRM 1568) and good agreement between the determined and the certified values was obtained for Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES) for analyte quantification. The flow digestion of the CRMs resulted in clear solutions with residual carbon concentrations (RCC) between 11 and 40%. Spike recoveries of Al,

High pressure microwave-assisted flow digestion system using a large volume reactor-feasibility for further analysis by inductively coupled plasma-based techniques

“…1) a pressurized autoclave. 14 It is important to note, that the liquid volume heated inside the microwave cavity could be easily doubled by winding a second layer of PFA tube on to the coil former. 1) and four 16.4 mm diameter PEEK rods (G in Fig.…”

“…14 The residual acid concentration in the digested samples was determined by manual titration with 0.10 mol L À1 NaOH (Roth, Karlsruhe, Germany) using phenolphthalein as indicator. 14 The residual acid concentration in the digested samples was determined by manual titration with 0.10 mol L À1 NaOH (Roth, Karlsruhe, Germany) using phenolphthalein as indicator.…”

“…When performed in closed vessels analyte losses and contamination are avoided, a fast and efficient digestion is promoted and reagent consumption and waste generation is reduced. Based on the applied pressure during digestion, they can be broadly classied as ambient pressure, 5-9 medium pressure (<25 bar) [10][11][12] or high pressure (>25 bar) [13][14][15] ow digestion systems. These procedures are time consuming anddespite the fast heating stepadd signicantly to the total time required for the digestion step.…”

“…1,4 Different types of microwave-assisted ow digestion systems have been described in literature. Based on the applied pressure during digestion, they can be broadly classied as ambient pressure, [5][6][7][8][9] medium pressure (<25 bar) [10][11][12] or high pressure (>25 bar) [13][14][15] ow digestion systems. Another classication can be made based on the ow regime during digestion, distinguishing between continuous ow [5][6][7][10][11][12][13][14][15] and stopped ow 8,9,16 systems.…”

“…Based on the applied pressure during digestion, they can be broadly classied as ambient pressure, [5][6][7][8][9] medium pressure (<25 bar) [10][11][12] or high pressure (>25 bar) [13][14][15] ow digestion systems. Another classication can be made based on the ow regime during digestion, distinguishing between continuous ow [5][6][7][10][11][12][13][14][15] and stopped ow 8,9,16 systems. The main shortcoming of ambient and medium pressure systems is the lower digestion temperature, whichin combination with the short residence time inside the heated zonecauses inefficient digestion especially for solid samples.…”