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Microwave Digestion – Fiber Optic Temperature Solutions

posted by Rugged Monitoring on 2020-07-06

Microwave digestion is one of the most commonly used industrial technique for sample preparation during Atomic Absorption (AA) and Inductively Coupled Plasma (ICP) analyses. In microwave digestion, the combination of the sample matrix (components other than the analyte of interest) and acid is heated up to 260°C in a pressurized container. Microwave heating under high pressure breaks the sample molecules faster and dilutes them into a solution.

The other advantage of microwave assisted digestion is that the sample is heated evenly within the shortest possible time. This avoids the loss of test elements in vapor and provides the best quality samples for further analysis.

Microwave assisted digestion requires less acid which reduces the risk of contamination from external sources. Temperature and pressure monitoring are essential for safe and efficient microwave digestion.

Relevance of Temperature Monitoring during Microwave Assisted Digestion

Accurate temperature monitoring and control becomes very important in microwave assisted digestion because of the rapidly changing temperatures during the process. The various kinds of test samples require varying temperature for digestion. In the absence of an adequate temperature setting and control, the digestion results may not be accurate and reliable.

Many times, researchers also face issues related to the overflow of the sample liquid from the digestion reactors. The overflow is the result of inaccurate temperature measurement and lack of control. The overflow spoils the microwave, forces the researchers to repeat the sample preparation and increases the time necessary to prepare the sample. 

Most of the microwaves for digestion systems come with built-in temperature sensors for monitoring and control over the digestion process. However, the infrared sensors used in the microwaves have significant limitations such as the accuracy and speed of measurement. Due to these limitations, fiber optic temperature sensors have been proved to be the most suitable for microwave assisted digestion.

Fiber Optic Temperature Sensors for Microwave Digestion

One interesting fact about fiber optic temperature sensors is that they can survive aggressive acids, temperatures ranging up to 260°C and they have excellent insulation capacity (dielectric properties). 

Fiber optic temperature sensors are the safest sensors to measure temperature under radiofrequency and microwave environments. The sensors can be installed inside the microwave digestion reactors to measure the direct sample temperature during the digestion process. Unlike metal sensors, these sensors do not create sparks inside of microwaves.

The high accuracy and fast responsiveness of fiber optic temperature sensors make them the ideal choice for temperature monitoring and control in microwave assisted digestion. A fiber optic temperature sensor is installed in the reference digestion reactor to provide closed loop temperature feedback. This temperature feedback is used to control the speed of microwave heating. 

As a manufacturer, we have industrialized the Gallium Arsenide (GaAs) fiber optic sensing technology as a temperature monitoring solution. We provide a wide range of fiber optic temperature sensors such as LSENS-P, LSENS-T and LSENS-R which are chemically inert and immune to microwave environments. Due to lower thermal mass, these sensors are fast, responsive and accurate.

Our fiber optic temperature sensors are corrosion resistant and do not contaminate the digestion samples. The sensors are designed for measuring temperature under the high-pressure environment of the microwave digestion reactor. The customized mounting options are being provided to customers based on their microwave design.

Rugged Monitoring also provides customized and small sized fiber optic temperature monitors that can be installed into the microwave control box. The sensors and monitors are designed to last up to 15 years and do not require calibration over time.


We understand the benefits of microwave assisted digestion and the importance of adequate temperature control during the digestion process. It is critical to monitor the temperature during the ramp up & hold time within the microwave environment and even during the cooling process. Due to the high concentration of acid, the environment inside the microwave digestion unit could be hazardous. 

Fiber optic temperature sensors have significant advantages compared to infrared sensors. They can measure sample temperatures faster and more accurately. Unlike other technologies, the fiber optic temperature sensors provide direct temperature measurement of the digestion sample. We provide high-quality fiber optic temperature sensors and monitoring systems that meet the requirements for microwave digestion, extraction, and synthesis applications.