What Is an Electron Capture Detector?

Electron capture detector (ECD). The electron capture detector is also an ionization detector. It is a selective, high-sensitivity detector. It only has signals for electronegative substances such as halogen, sulfur, phosphorus, and nitrogen. The stronger the electronegativity, that is, the larger the electron absorption coefficient, the higher the sensitivity of the detector, but no signal to electrically neutral (non-electronegative) substances, such as alkanes.

Electron capture detector

Electron capture detector (ECD). The electron capture detector is also an ionization detector. It is a selective, high-sensitivity detector. It only has signals for electronegative substances such as halogen, sulfur, phosphorus, and nitrogen. The stronger the electronegativity, that is, the larger the electron absorption coefficient, the higher the sensitivity of the detector.

Since the advent of ECD, people have continuously improved and perfected it to make its structure and performance more ideal. For decades, the two most practical advances have been to replace the 3H source with a 63Ni source and to replace other power supply methods with a fixed base current pulsed voltage supply. The main advantage of using 63Ni source is that the detector can work at 350 ~ 400 , which reduces the pollution problem during operation and improves the

1. ECD came out in 1961, it is

ECD concise mechanism

ECD is a type of radioactive ionization detector. It uses radioactive isotopes to emit -particles with a certain energy during the decay process as an ionization source. When only pure carrier gas molecules pass through the ion source, the Under bombardment, ionized into

There are many classification methods for ECD. If you are familiar with these classification methods, you can better understand their operating characteristics, so that they can be used reasonably when different analysis needs.

1. Classified by source used

There are two types of ionization sources used in ECD, radioactive isotopes and non-radioactive sources. Although non-radioactive ECD is available and has the advantages of no radioactivity, high-purity He and some rare gases are used as carrier gas during operation. The ECD structure and electronic equipment are also more complicated, and the operating characteristics are There are some shortcomings, so it is currently in the stage of perfect promotion and use.

2. Classified by the type of radioactive source: it can be divided into 63Ni and 3H.

ECD requirements for radioactive sources

Use safety

Radioisotopes may produce three kinds of rays: , and during the decay process. is a high-speed helium core with a positive charge;

Beta rays are high-speed electrons that are negatively charged; gamma rays are electromagnetic waves with extremely short wavelengths. These three kinds of rays have certain energy, which can ionize gas and other substances. Among them, alpha rays have the strongest ionization ability. Alpha rays can produce 105 ion pairs per centimeter stroke, and beta rays can produce 102 ~ 103 ion pairs per centimeter. is weak, producing only one pair of ions per centimeter. Although alpha ray ionization is efficient, it is too noisy. -rays require sufficient ion current, and large doses of radioactive materials must be selected. -rays have a strong ability to penetrate, which is a great harm to the human body. The beta source has moderate ionization and penetration strength, so it is the most suitable source for ionizing radiation;

The radiant energy of the source should be large enough to provide the necessary ion current;

The range of the ray must be short enough, which is conducive to structural design and safety, although this is inconsistent with the requirements for radiant energy, so we must take into account each other in use;

The half-life should be long enough;

The use temperature should be high;

There are two types of radioactive sources, 63Ni and 3H, which are ideal for ECD. The performance comparison is given in the table below.