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Why do spark optical emission spectrometer need to be equipped with standard samples

Author : Jerry He

Update time : 2020-09-07 14:19:04

In the industry of optical emission spectrometer, customers often ask why optical emission spectrometer need to be equipped with standard samples? Shouldn’t the optical emission spectrometer be very accurate when measuring products directly? Why do we need standard samples for calibration? And other issues. These problems all involve standard materials. In response to these questions, I would like to share the knowledge about standard materials with you.

In the daily production process, experimental research, scientific exploration and other industries, we can actually see people using a variety of instruments and measuring appliances. So how to ensure and measure the reliable and accurate operation of these equipments, there must be a standard reference material for reference and comparison, then this reference material can also be simply defined as a standard material.

Definition of reference material

Reference material (RM) is a material or substance that has one or more sufficiently uniform and well-defined characteristics to calibrate measurement devices, evaluate measurement methods, or assign values to materials.
Note: A standard substance can be a pure or mixed gas, liquid or solid.

Certified reference material (CRM) is a reference material attached with a certification. It is a reference material (RM) with one or more specified characteristics measured by a valid metrological procedure, and a certificate is attached to provide the specified characteristic value and its Statement of certainty and measurement traceability.

The reference material has three notable characteristics:
1. It is used for measurement purposes.
2. It has the accuracy of the measurement value.
3. The accuracy of the measurement value can be traced to the relevant national measurement standards.

The role of reference materials

Used as a calibration substance for instrument calibration. Because chemical analysis instruments are generally designed according to the relative measurement method, it is necessary to use standard materials for calibration or prepare a "standard curve" before or during use.

As a known substance, it is used to evaluate the measurement method. When the measurement is carried out with different methods or different instruments, the known substances can help to judge the reliability of the results measured by the new method and the new instrument.

As a controlled substance, it is analyzed simultaneously with the substance to be tested. When the analytical result obtained by the standard substance is consistent with the value given in the certificate within the specified limits, it proves that the analytical result of the substance to be tested is credible.

Classification of reference materials

Classified by technical characteristics

No.	Category Name	Features and Main Application
1	Chemical composition standard material (Also known as component standard material)	It has a certain chemical composition, and its chemical composition is accurately measured by a technically correct method. It is used for the calibration of component analysis instruments and the evaluation of analysis methods. Such as metal, geological, environmental and other chemical composition standard materials.
2	Physicochemical characteristics standard material	It has some good physical and chemical properties and is accurately measured. It is used for the evaluation of calibration, calibration or measurement methods of physical and chemical properties measuring instruments. Standard materials such as pH, combustible material, polymer molecular weight, etc.
3	Engineering technical characteristic reference material	It has certain good technical characteristics and is accurately measured for the calibration of engineering technical parameters and characteristic measurement instruments, the evaluation of measurement methods, and the comparative measurement of material or product technical parameters. Such as particle size standard material, standard rubber, standard photosensitive fading paper, etc.

Classification according to the accuracy level of the reference material

China	USA	Russia		ISO
Primary standard material (reference material)	Standard Reference Material (SRM)	Reference sample	Reference material with identification certificate (CRM)
		Primary standard sample
	Research substance		Reference material (RM)
standard material	General substance	Secondary standard sample

Classification and code of reference materials

Grade	Grade 1 standard material	Grade 2 standard material
Codename	GBW	GBW(E)
Meaning	Use absolute measurement method or two or more different principles of accurate and reliable method to determine the value, its different certainty has the highest level in China, with good uniformity, stability for more than one year, and a packaging form that meets the technical specifications of standard materials.	The uncertainty and uniformity of the measurement method compared with the first-level reference material or the determination method of the first-level reference material does not reach the level of the first-level reference material, and the stability is more than half a year, which can meet the general measurement If necessary, the packaging form meets the requirements of the standard material technical specification.

Classified by purpose
Curve building standard samples: used to draw the working curve of the spectrometer, so the curve building standard samples are all complete sets.
High and low standard samples: used for standard calibration of the working curve. At least two high and low standard samples should be used simultaneously.
CRM: used to check whether the working curve of the spectrometer is accurate, and at the same time to calibrate the working curve, the purpose is to make the analysis result of the sample to be tested more accurate

The role of CRM and the principle of selection

When analyzing samples with optical emission spectrometer, there will always be differences between the analysis data obtained and the true value (or calibration value). These differences come from curve drift, surface condition, sample smelting and processing technology. By controlling the sample to establish a specific analysis program, the analysis error can be automatically compensated. Principle: The control sample should be a standard sample that is consistent with the metallurgical process and physical state of the analysis sample. The content of each element should be accurate and reliable, uniform in composition, without physical defects such as pores, trachoma, and cracks, and the content of each element should be located Within the calibration curve content range, as close as possible to the content of the analyzed sample. Through experimental comparison, it is found that the analysis accuracy of self-melted calibration samples is better than that of samples purchased on the market. Therefore, it is recommended that powerful manufacturers should re-value their products as control samples after smelting.

The standard material that customers use most when using optical emission spectroscopy is the CRM. Whether to choose a suitable control sample will directly affect the test accuracy of the direct reading spectrometer, so attention must be paid to the use of CRM.

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