What are the applications of microwave digestion systems?

Microwave Introduction

Microwaves are a type of electromagnetic wave, with frequencies ranging from 300MHz to 300GHz, corresponding to wavelengths between 100cm and 1mm—falling between far infrared and radio waves. Within the microwave spectrum, the 1-25cm band is specifically used for radar, while the rest is employed for telecommunications transmission. To prevent interference from civilian microwave power with radio communications, broadcasting, television, and radar, international regulations set the frequency for industrial, scientific research, and household civilian microwaves at ±50MHz around 2450MHz. Consequently, the frequency used by microwave digestion instruments is primarily 2450MHz, and the same applies to household microwave ovens.

Microwave Characteristics

Metals do not absorb microwave radiation; instead, they reflect it. This includes metals like copper, iron, and aluminum. When metals, such as stainless steel plates, are used as the cavity in a microwave oven, they reflect the waves back and forth, thereby heating the contents. It is not advisable to place metal containers inside a microwave oven, as the reflected microwaves can damage the magnetron.

(2) Insulators can pass through microwaves, absorbing almost no microwave energy. Materials such as glass, ceramics, plastics, quartz, and paper are transparent to microwaves, allowing them to penetrate and propagate through. These substances do not absorb microwave energy, or absorb it minimally. The strength of a material's absorption of microwaves is essentially related to its complex dielectric constant, meaning the higher the loss factor, the greater its ability to absorb microwaves [2]. Most containers for household microwave ovens are made of plastic. Materials used for microwave-sealed digestion of samples include polytetrafluoroethylene and engineering plastics.

(3) Polar molecules, such as water and acids (which are high-loss factor materials), absorb microwave energy. These molecules possess a permanent dipole moment, meaning the center of positive and negative charges does not align. In a microwave field, polar molecules rapidly change orientation with the frequency of the microwaves, rotating back and forth, causing them to collide and rub against each other. This process absorbs microwave energy, resulting in an increase in temperature. The food we consume, which contains moisture, has strong polar molecules, allowing it to be heated in a microwave oven.

Microwave Digestion Apparatus Usage

The microwave digestion instrument can rapidly and efficiently digest and determine the Chemical Oxygen Demand (CODcr), Total Phosphorus (TP), and Total Nitrogen (TN) in various surface waters, domestic wastewater, and industrial wastewater.

Microwave Digesters are widely used by various environmental protection departments, water resource management authorities, and public health departments for water quality assessment and management.

Microwave organic synthesis is set to replace traditional synthesis methods due to its absolute application advantages. More and more laboratories are adopting microwave sample processing systems for the preparation of samples for analyzers such as atomic absorption spectrometers, atomic fluorescence spectrometers, inductively coupled plasma emission spectrometers, inductively coupled plasma mass spectrometers, high-performance liquid chromatographs, and gas chromatographs, as these methods are time-consuming, labor-intensive, and heavily polluting.