Vessel Inserts

Vessel-inside-vessel technology was developed by Milestone in the late 90s. Vessel-inside-vessel technology uses a smaller secondary vessel inside the primary microwave vessel. The secondary vessel contains the sample and digestion reagents, and the primary vessel contains the solution required to achieve accurate temperature monitoring. This configuration reduces the amount of acid required for digestion to near stoichiometric quantities, which reduces the dilution factor and increases the detection limit.

The use of vessel-inside-vessel technology is also used for the processing of larger organic sample sizes. This is accomplished by controlling the reaction kinetics and lowering the pressure inside the microwave vessel. Controlling reaction kinetics is especially important when trying to digest large quantities of organic material. The use of vessel-inside-vessel technology helps to control these exothermal reactions by providing a heat sink for the energy liberated during oxidization. This is accomplished by placing water in the outer microwave vessel. The water draws the heat away from the reaction mixture, slowing down the reaction kinetics and preventing a runaway reaction. A variety of inserts are available from Milestone, in different materials (Quartz or TFM) and with different sizes and shapes, to accomplish all application requirements.

Milestone offers both quartz vessels and insert options for the SK-15 and MAXI-44. Quartz is the ultimate vessel material for ultra-trace analysis, since it can be cleaned more effectively, and has lower background levels than even extra high purity TFM.
Optional inserts, available in quartz and high purity TFM, fit inside the standard TFM vessels of the High pressure SK-15 rotor, and expand the application range of the Ethos UP beyond any other microwave system thanks to Milestone’s exclusive “vessel-in-vessel” technology. The quartz inserts are especially effective for difficult organics such as polymers and oils, since these samples can sometimes stick to Teflon walls and damage them during heating. Quartz inserts also enable higher weights of difficult organics (up to 1g) to be digested without causing the vessel to vent. The inserts sit in a water/H2O2 mixture, which produces O2 during heating, which in turn converts CO2 and NOx produced during digestion to HNO3, greatly reducing pressure build up in the vessel. An additional benefit is that as little as 1 mL HNO3 is used, which reduces reagent blank and allows analysis at lower dilution levels, improving detection limits.

35 mL Quartz and Extra High Purity TFM Inserts

Designed for ultratrace analysis, these inserts are manufactured from extra high purity TFM or quartz for the lowest possible blank contribution. Maximum temperature is 300°C. These inserts fit inside standard 100 mL vessels and can only be used with the SK-15 rotor.

Microsampling Inserts

TFM and quartz microsampling inserts (3mL or 6mL) are designed for use with very small sample sizes and increase the capacity of a 15 position rotor to 45 positions. Maximum temperature is 300°C. Microsampling inserts fit inside standard 100 mL vessels and can only be used with the SK rotors.


  • Less acid volume
  • Higher sample amount
  • Lower dilution factor
  • Increased method detection limit
  • Less surface contamination
  • Lower analytical blank