The principle of organic element analyzer and comparison of several instruments

Principles of Organic Element Analysis

It mainly uses the principle of high temperature combustion method to analyze the content of conventional organic elements in samples. Common elements in organic matter include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), etc. Under high temperature and oxygen conditions, organic matter can burn, and after combustion, the organic elements in it are converted into corresponding stable forms, such as CO2, H2O, N2, SO2, etc.

reaction process

On the premise that the sample mass is known, the content of each element in the sample can be obtained by measuring the amount of gaseous products generated after the sample is completely burned and converting them.

The CHNS/O elemental analyzer uses the classic analytical technique - combustion of the corresponding reagent in a pure oxygen environment or high-temperature cracking in an inert gas to determine C, H, N, S, and O in organic matter.

The instrument has three measurement modes: CHN mode, CHNS mode and oxygen mode.

In the CHNS mode, the sample is burned in pure oxygen and converted into CO2, H2O, N2 and SO2, which are separated by a chromatographic column and then subjected to thermal conductivity detection to measure the contents of C, H, N and S in the sample.

In oxygen mode, the sample is cracked at high temperature in H2/He to obtain CO and other gases. CO is separated and detected by thermal conductivity to measure the oxygen content in the sample.

Detection signal characteristics

The mixing chamber provides a continuous, uniform and basically constant pressure for the sample combustion products, N2, CO2, H2O (SO2, CO2), which enter the chromatographic column for separation. Each gas is separated step by step and stably. The gas separated later always flows through the detector at the same time as the gas separated earlier. Due to the approximate superposition of the TCD detector, the signal is in a step shape. The signal just detected minus the previous signal is the true signal value of the gas being detected.

Calculation method

Blank: The blank of the PE element analyzer is equivalent to the baseline. There are usually two types of blanks: instrument blank and analytical blank. The instrument blank is further divided into carrier gas blank and carrier gas and oxygen blank.

Blank calculation method:

NB=NR－ZR

CB=CR－NR

HB=HR－CR

SB=SR－HR

OB=OR－ZR

K factor: The K factor is the calibration factor of the detector on the PE element analyzer. It runs a sample with a known content and obtains a calibration factor with a physical unit of CNTS/ug through the following calculation method, where CNTS is the digital quantization value of the signal measured by the instrument's TCD detector after amplification and analog-to-digital conversion.

KN=[(NR－ZR)－NB]×100/[SW×N THEORYWt%]

KC = [(CR-ZR)-CB] × 100/[SW × C THEORYWt%]

KH=[(HR－CR)－HB]×100/[SW×H THEORYWt%]

KS=[(SR－HR)－SB]×100/[SW×S THEORYWt%]

KO=[(OR－ZR)－OB] ×100/[SW ×OTHEORY Wt%]

K factor range: KC 13~20; KH 30~70; KN 3~9; KS 3~9; KO 6~12

Sample Preparation

Sample requirements:

1. The sample should not contain solid particles or liquids that absorb moisture uniformly;

2. Volatile samples are sealed and weighed in a low melting point alloy container;

3. Corrosive liquids should be sealed and weighed with low-melting-point glass capillaries, and explosion-proof measures should be taken during oxidation;

4. It is prohibited to analyze strong chemicals such as acids, alkaline solutions, solvents, explosives, etc.;

5. Samples containing fluorine, phosphate or heavy metals may affect the analysis results or the life of instrument parts and should not be analyzed.

Notes on sample preparation:

1. Because the element content measured by the element analyzer contains H, the sample to be tested must be dry and cannot contain water. It is best to vacuum dry it before the measurement (the drying time depends on the sample);

2. The sample purification method has a great influence on the test results. The results of samples obtained by ordinary filtration will have a large deviation from the expected value, while the purity of samples obtained by crystallization is guaranteed and the test results will be better;

3. When packing the sample during weighing, be careful not to break the sample dish. Otherwise, the sample weight will be inaccurate, which will cause the result to be invalid.

4. The oxygen mode does not allow the compounds to be tested to contain phosphorus, fluorine, silicon and metal cations. Mineral samples must be free of these minerals before analysis.

Requirements for reagents and gases

The required reagents are of high purity, analytical purity or prepared by distillation; standard substances include benzoic acid, acetanilide, cyclohexanone-2,4-dinitrophenylhydrazone, p-aminobenzenesulfonic acid, etc.

Operation flow chart

Notes on using the instrument

1. When filling the reaction tube, use a fume hood, protective glass cover, rubber gloves and work clothes. Wash your hands and face thoroughly after contact with reagents.

2. When replacing the combustion tube and reduction tube, be sure to turn off the furnace and wait for it to cool to room temperature.

3. When the reduction tube is at room temperature, measurements must not be carried out unless the oxygen valve is turned off.

4. The fan on the left side of the furnace must be working properly.

5. When starting the machine, you must first supply gas and then turn on the electricity.

6. Please follow the shutdown procedures when shutting down the machine.

7. When opening the gas cylinder, first turn off the low-pressure gauge, open the main valve, and then adjust the low-pressure gauge to an appropriate value to avoid damaging the low-pressure gauge.

8. The desorption tube used for oxygen analysis needs to be sealed after removal.

9. All opened reagents must be placed in a desiccator.

10. When using an automatic balance to add or remove samples, please raise the support to hold the tray.

Application of Organic Element Analyzer

The analysis scope includes chemical and pharmaceutical products, fine chemical products, fertilizers, petrochemical products, rubber, plastics, polymer materials and additives, construction and insulation materials, coal, solid waste, etc.

Organic element analyzer is a common laboratory instrument.

Its most basic application is the identification of compound composition.

Reveal changes in the properties of compounds,

It is an effective means of scientific research.

Comparison of several organic element analyzers

1. The analysis range of the American CE-440 organic carbon, hydrogen, nitrogen, oxygen and sulfur element analyzer (CHN OS) includes chemical and pharmaceutical products, fine chemical products, drugs, fertilizers, petrochemical products, rubber, plastics, polymer materials and additives, construction and insulation materials, coal, solid waste, etc. It is widely used in research and analysis in different fields such as chemistry, chemical industry, pharmaceuticals, agriculture, environmental protection, energy, and materials.

2. PerkinElmer PE 2400II CHNS/O Organic Element Analyzer

Founded in 1937, it is one of the famous suppliers in the field of chemical analysis instruments. As early as 1965, the company developed and launched the 2400 element analyzer, which became a representative of the development of self-integrating thermal conductivity element analyzers at that time. Later, due to the expansion of the company's R&D field and the shift of focus, it was unable to make new breakthroughs in the technology of developing element analyzers. The 2400 Series II CHNS/O element analyzer was launched by the company later. Its design concept has changed a lot, mainly reflected in the change of mixed gas separation technology. It now adopts advanced cutting-edge chromatographic separation technology. However, the current model is relatively old and has not been updated for a long time.

3. Thermo Fisher FLASH 2000 CHNS/O Organic Element Analyzer The organic element analyzer is another masterpiece after the great success of Thermo Flash EA1112 launched after Thermo acquired CarloErba (Carralba, Italy) and Fison Group. It is improved and upgraded with the latest advanced design and is currently the most reliable and accurate element analyzer.

As a pioneer in elemental analyzers, CarloErba began commercializing its elemental analyzers in 1948. In 1968, it first launched a combustion furnace with automatic sampling and vertical loading in the world, the representative model is EA1102; in 1975, it first launched a CHNO concentration range from trace (100ppm) to 100%, the representative model is EA 1106; in 1988, it launched an analyzer that can simultaneously determine CHSN, the representative model is EA1108. Since entering China in the early 1980s, its various models have a wide range of user groups in domestic universities and research elements. Since joining the American Thermo Electron Group in 1996, the elemental analyzers produced have become Thermo Electron's representative products due to their excellent performance. At present, there are more than 3,000 installations worldwide, and they have an excellent reputation among customers. In particular, its combination with isotope ratio mass spectrometers has an absolute dominant position in the market.