Closed Vessel Digestion System

What is the Closed Vessel Digestion System?

A closed vessel digestion system seals sample and acid in a pressure-rated container and heats it to dissolve difficult matrices. It retains volatiles and is used where open digestion would lose analytes.

Overview

A closed vessel digestion system uses sealed, pressure-rated vessels that are heated in a block, oven or microwave cavity. The sealed environment raises the boiling point of the acid mixture above atmospheric conditions, so decomposition is faster and more complete, and volatile elements remain in solution. Vessels are commonly made from PTFE-TFM with a pressure-relief mechanism or a rupture disc, and a liner may be used for trace work. Temperature and pressure are monitored, and vessels are cooled before opening. The low blank and full recovery of volatile elements make the technique suitable for trace analysis, though cycle times are longer than open block digestion.

How does it work?

Digestion breaks down a sample matrix so that the analytes of interest enter solution in a measurable form. In block digestion, tubes or vessels are heated on a temperature-controlled aluminium block and acid is added, often with reflux. In Kjeldahl digestion, the sample is heated with sulfuric acid and a catalyst to convert nitrogen compounds to ammonium sulfate. In closed-vessel and microwave digestion, acid and sample are sealed in a pressure-rated vessel and heated rapidly, so higher temperatures are reached, volatiles are retained and less acid and time are needed. Reagent choice, temperature, pressure and time determine completeness, and the resulting digest is diluted and filtered before measurement.

What are the key features?

• Sealed pressure-rated vessels
• Higher boiling point for complete digestion
• Retention of volatile elements
• Low reagent blank for trace analysis
• Pressure relief for safety

What are the technical specifications?

A typical closed vessel digestion system configuration offers max temperature of Up to 200 °C, max pressure of Up to 60 bar, vessel volume of 50–100 mL, vessel material of PTFE-TFM with liner option, vessel positions of 6–24 and pressure relief of Rupture disc or vent valve. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Closed Vessel Digestion System is used in trace metal analysis of environmental samples, volatile element determination, geological and refractory material digestion and food and biological trace analysis. Across the wider Digesters class, laboratories also deploy it for environmental soil, sediment and sludge analysis, food and feed elemental analysis and metals and alloy trace analysis.

Which standards and certifications apply?

Relevant standards and methods include EPA 3051A, EPA 3050B, EPA 200.2, ISO 11466 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Add acids in a fume hood and use the protective equipment specified for the reagent, including face and eye protection, gloves and an acid-resistant apron. Do not exceed the rated temperature or pressure of the vessels, and allow closed vessels to cool before opening to avoid acid spray. Digest a reagent blank and, where required, a certified reference material to verify recovery and completeness. Check vessels for scratches and damage, and replace them on schedule, since worn vessels may fail. Follow the applicable method, such as EPA 3051A, EPA 3050B, ISO 11466 or the Kjeldahl procedure, and record all temperatures, times and reagent volumes.

How do I select the right Closed Vessel Digestion System?

Select a closed vessel digestion system when volatiles must be retained or when a low blank is required for trace analysis. Confirm the temperature and pressure ratings suit the method, the vessel material is compatible with the acids, and the pressure relief is adequate. In an RFQ state the sample matrix, analytes, acid mixture and throughput.

How does it compare with other Digesters variants?

Choose a digester according to the sample matrix, the analytes and the required detection limits. Block digestion suits routine, high-throughput work with simple matrices and volatile analytes that are retained, such as nitrogen and some metals. Kjeldahl systems are specific to nitrogen and protein determination. Closed-vessel and microwave digestion suit difficult matrices, volatile elements and low detection limits, because they reach higher temperatures and retain volatiles. Automated systems add reagent dosing, heating programmes and cooling for reproducibility. Confirm the vessel material and pressure rating suit the acids used, the temperature reaches the method requirement, and the throughput matches the workload.