2-Step Acid Digestion of Different Graphite Samples for Impurity Analysis with ICP-OES and ICP-MS

Graphite is a crystalline elemental form of carbon with its atoms arranged in a hexagonal structure. It occurs naturally and is the thermodynamically most stable modification of the element carbon under standard conditions, thus highly corrosion resistant. This makes sample preparation for subsequent wet chemical element analysis a demanding challenge: significantly high target temperatures, the right mixture of acids with sufficiently high oxidation potential and durable high-performance vessels are required for a successful digestion.

Rotor 20SVT50 in Multiwave 5000 provides the already well-established SmartVent technology, but at higher pressure and temperature limits. Controlled overpressure release is a safe and convenient way to overcome temperature challenges, as target temperatures of up to 250 °C can be reached and maintained to ensure complete digestions. The SmartTemp sensor ensures quick, accurate and contactless internal temperature measurement to reliably control the digestion process.

With up to 20 samples in one single run Rotor 20SVT50 offers unrivaled efficiency. The convenient tool-free handling and the compact vessel design to ease weighing, cleaning and operation make Rotor 20SVT50 the ideal candidate for demanding samples in Multiwave 5000.

In order to demonstrate the suitability of Rotor 20SVT50 different graphite materials were digested in one single run. Afterwards the elemental concentrations were determined via ICP-OES and ICP-MS respectively.

Two-step Digestion Procedure

In some cases, the oxidation potential of the amount of acid that can be used within one digestion step is not sufficient for complete digestion and residues may remain.

An approach to overcome this issue in a safe way is a “two-step digestion procedure “: In the first digestion step the majority of the inorganic matrix will be destroyed. Residual reaction gases will be released upon careful opening after the first digestion step, before fresh oxidant is added to the mixture. A second digestion step at a higher target temperature will improve the decomposition of the remaining residues.