计量科学与技术

Linear Fitting in Gas Measurement

WANG Defa, LI Qi, YE Jing, ZHOU Fengran, ZENG Wu

2022, 66(10): 3-9. doi: 10.12338/j.issn.2096-9015.2022.0100

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Abstract:
Various calibration methods such as single-point, double-point, and linear can be used in gas composition measurements, and linear calibration can be divided into various subdivision methods such as ordinary linear least squares and weighted bivariate least squares linear fitting. In this paper, the above two methods introduced in different literatures are compared and analyzed, and the matters that should be noted in the weighted bivariate least squares linear fitting are introduced. When the uncertainty of the measured signal is already close to or even lower than the uncertainty level of the gas standard, it is more reasonable to use the weighted bivariate least squares linear fitting method to process the measurement results. When using the weighted bivariate least squares linear fit, the weights are the reciprocal of the squared standard uncertainty, and the values of the intercept and slope can be calculated using the two-step iterative method; the standard uncertainty of the intercept and slope is calculated using the numerical differentiation method. Both analytical and calibration functions can be used for weighted bivariate least squares linear fitting. For the calculation of the measured sample concentration and its uncertainty, the results obtained by using these two functions are the same, but it is easier to use the analytical function when calculating the uncertainty.

Establishment of Metrological Traceability System for Mass Concentration of Ambient Air Particle

ZHANG Wenge, LIU Wei, LIU Junjie, ZOU Yaxiong, XU Xiao

2022, 66(10): 10-15. doi: 10.12338/j.issn.2096-9015.2022.0166

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In view of the difficulties of uncertainty and traceability in the measurement of ambient air particle concentration, and in close combination with the requirements of national standards and Metrological Development Plans for measurement and traceability of aerosol particle mass concentration, the key technologies such as particle sampling, particle size separation and particle mass concentration measurement are focused on, and the metrological traceability system for ambient air particles has been established through scientific and technological research, which is carried out systematically on national reference materials, measurement standard devices, international equivalence of technologies and national standards. The project research ensures the accuracy and reliability of the monitoring data of ambient air particles, the consistency with international monitoring data and the traceability standard’s establishment in the field in China.

Domestic Status Quo and Quantity Value Verification of Certified Reference Materials for Electrolytic Conductivity

WANG Hai, WANG Meiling, REN Danhua, WANG Xiangnan, SHU Hui, ZHANG Airui, SONG Xiaoping

2022, 66(10): 16-19, 64. doi: 10.12338/j.issn.2096-9015.2022.0162

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The certified reference materials (CRMs) for electrolytic conductivity are crucial to ensuring accurate and consistent conductivity measurement results. In this paper, the current situation of existing conductivity CRMs in China is reviewed in terms of their characterization methods and scope of application, and the characteristics of existing CRMs and their shortcomings are analyzed in depth. In view of the current situation that more than 50% of the existing conductivity CRMs in China are characterized by comparative measurement methods, the primary standard for the conductivity of electrolyte solutions was used to verify the values of these CRMs. The results of the verification show that: the accuracy and quality of the comparative measurement method for the characterization of the CRMs are poor (overall pass rate of 58%, the rate of CRMs with lower characterization values is 20%), and there is an urgent need to strengthen the market regulation in the process of replication of the reference materials. When the comparative measurement method for the characterization of the CRMs is being applied, several important technical aspects deserve attention, namely, the accuracy level of the conductivity meter used, the accurate determination of the conductivity of type II water in the laboratory, the correction of the air buoyancy when weighing the mass, the accurate fixing of the solution volume, and the scientific and reasonable assessment of the uncertainty of the characterization of the CRMs.

Application of Fourier Transform Near-Infrared Spectrometer in Gasoline and Diesel Analysis

LI Qi, DU Biao, ZHANG Zhengdong, CHEN Xiaoxiang, LI Ke, FANG Xu, LI Qingwu, SHU Hui

2022, 66(10): 20-27. doi: 10.12338/j.issn.2096-9015.2022.0171

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Gasoline and diesel are important energy sources for China. The quality of gasoline and diesel has an important impact on environmental governance, public health and personal safety. Therefore, China has made detailed regulations on the scope of various indicators in gasoline and diesel, including octane number, aromatic hydrocarbons, olefins, benzene, distillation range and other 30 indicators. The traditional method for the determination of gasoline and diesel parameters requires the use of cetane number analyzers, gas chromatographs and other instruments, which take a long time and have low efficiency. At present, the Fourier transform near-infrared spectroscopy (FT-NIRS) method can quantitatively analyze the above parameters at the same time, and has the advantages of many measurement parameters, fast speed and high measurement accuracy, and has been rapidly popularized and applied in the petroleum industry. This paper expounds the research progress of FT-NIRS, introduces the basic principle of FT-NIRS, the main structure and key technology of the device, and the method of FT-NIRS to analyze the composition of gasoline and diesel , and the future research and application prospects are prospected.

Development of Reference Materials for Nitrogen Content of Petroleum Products

WANG Haifeng, LI Jia, SUN Guohua

2022, 66(10): 28-33. doi: 10.12338/j.issn.2096-9015.2022.0125

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The chemiluminescence nitrogen meter needs to be calibrated with the standard material of nitrogen content in petroleum to realize the traceability of the quantity value. In the present study, the development of six Certified Reference Materials (CRMs) for petroleum with nitrogen content ranging from low to middle were described. This series of CRMs were prepared and certified by the internationally recognized gravimetric method, and the certified value, nitrogen content, was traceable to SI unit of mass and volume, as well as to the pure organic substance CRM for elemental content. The homogeneity and stability of CRMs were technically qualified. The certified nitrogen concentrations of this series of CRMs were 2.04 mg/L, 5.03 mg/L, 9.91 mg/L, 19.6 mg/L, 50.3 mg/L, and 100.7 mg/L, with corresponding uncertainty U (k=2) of 0.08 mg/L, 0.10 mg/L, 0.16 mg/L, 0.5 mg/L, 0.9 mg/L, and 1.2 mg/L, respectively. The development process of this series of reference materials conforms to relative standards, and the uncertainty has reached the same level as that of similar reference materials in China. It is suitable for the verification and calibration of chemiluminescence nitrogen meters and is conducive to ensuring the accuracy and reliability of the nitrogen content of petroleum products.

Research Progress on Gasoline Standards and Gasoline Octane Number Reference Materials

LI Shuo, DU Biao, LU Xiaoxin, LIU Zhe, LI Qingwu, ZHANG Zhengdong

2022, 66(10): 34-40. doi: 10.12338/j.issn.2096-9015.2022.0131

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Gasoline motor vehicles are still the main component of civil motor vehicles, and the pollution of motor vehicle exhaust emissions caused by gasoline quality problems has caused widespread concern. The development of the gasoline octane number certified reference materials (CRMs) plays an essential role in strengthening the quality supervision of gasoline, promoting the prevention and control of atmospheric pollution, and ensuring people's health. With the renewal of the National Standard of Gasoline for Motor Vehicles, the existing gasoline octane number CRMs have been developed to meet people's demand for an improvement of gasoline quality. Based on a comprehensive summary of gasoline grades and knock resistance technical standards, the components, additives and other ingredients that affect the octane number of gasoline and their environmental impact are described, aiming at analyzing the status quo, trend and future direction of the certified reference materials.

Development of Reference Materials for Phosphorus Element in Light Oil Products

REN Danhua, ZHANG Airui, WANG Meiling, WANG Xiangnan, WANG Hai

2022, 66(10): 41-45, 9. doi: 10.12338/j.issn.2096-9015.2022.0161

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In this paper, a certified reference material (CRM) for phosphorus in isooctane (GBW11211) was developed to meet the national standard for measuring the content of phosphorus in light oil. The CRM was prepared with isooctane and phosphorus element standard hydrocarbon oil as raw materials, and inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used as the characterization methods for the CRM, which were jointly characterized by several laboratories, and the homogeneity and stability of the CRM for elemental phosphorus in isooctane were evaluated. The results show that the certified value of the CRM of the phosphorus component in isooctane is 0.44 mg·kg⁻¹, with an extended uncertainty of 0.05 mg·kg⁻¹ (k =2), and the validity period is 36 months. The CRM can be used for quality control and method verification of related oil products.

Development of Accurate Measurement Method for Coefficient of Thermal Expansion and Related Certified Reference Materials

LI Jia, WANG Haifeng, SUN Guohua

2022, 66(10): 46-51. doi: 10.12338/j.issn.2096-9015.2022.0182

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The coefficient of thermal expansion is an essential index for evaluating the thermal stability of materials. Its accurate measurement directly affects the processing and application of materials. In this paper, the precise measurement method of the coefficient of thermal expansion was studied, the traceability of the quantity value and the influence of thermal history were explored, and the optimal experimental conditions of static force value and heating rate were selected. To establish an accurate measurement method of coefficient of thermal expansion, two kinds of certified reference materials (CRM) for the coefficient of thermal expansion, GBW (E) 130779 of aluminum and GBW (E) 130780 of polyetheretherketone (PEEK), have been developed. 6 Institutions, including research institutes, universities, and instrument manufacturers, characterized the CRMs, and the average value of the characterization results was the certified value of the CRMs. The certified values of aluminum and PEEK coefficient of thermal expansion were 24.7×10⁻⁶ K⁻¹ and 53.9×10⁻⁶ K⁻¹, with relative extended uncertainty of 2% and 3% (k=2).

Research Progress of Gas Spectroscopy Technology

GUO Ruimin

2022, 66(10): 52-56. doi: 10.12338/j.issn.2096-9015.2022.0145

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The use of spectroscopic technology for gas measurement is to trace the gas value to the line intensity of the gaseous molecule. This paper introduces the latest research progress of gas spectroscopy measurement technology by the National Institute of Metrology, China. The cavity length stabilization, Pound-Drever-Hall frequency locking, temperature controlling technique. and optical frequency combs are used in the experimental setup of the cavity ring-down spectrometer. The temperature change does not exceed 5 mK in 3 hours, and the vacuum leakage does not exceed 0.013 Pa in 1 hour. The absorption line of CO₂ molecule was measured by the developed experimental device, and the source of uncertainty of the transition line intensity was analyzed and given. The relative standard uncertainty of the evaluation was about 0.08%.

Research Progress of Sample Pre-Treatment Methods for TXRF Analysis and its Application in Environmental Monitoring Field

ZHANG Airui, WANG Hai, REN Danhua, WANG Meiling, WANG Xiangnan

2022, 66(10): 57-64. doi: 10.12338/j.issn.2096-9015.2022.0128

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Total reflection X-ray fluorescence (TXRF) spectroscopy is an X-ray analytical technique different from conventional X-ray fluorescence spectroscopy (XRF), mainly used for chemical analysis of trace samples and trace elements, and has been widely used in the field of environmental science. Sample pretreatment is an essential step in the analysis and measurement process. It is necessary to select an appropriate pretreatment method according to the nature of the sample to be tested. The quality of the sample pretreatment process plays a decisive role in the measurement results. In this paper, the development history of TXRF analysis technology is reviewed, its principles and characteristics are briefly introduced, and the sample pretreatment methods of TXRF analysis technology and their applications in environmental science are summarized in focus.

Determination of Gaseous Elemental Mercury by Microwave Digestion and Inductively Coupled Plasma Mass Spectrometry Analysis

ZHOU Fengran, WANG Defa, ZHANG Tiqiang, YE Jing, FENG Heping

2022, 66(10): 65-70, 33. doi: 10.12338/j.issn.2096-9015.2022.0158

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The improvement of gaseous mercury concentration measurement technology is conducive to the accurate monitoring of atmospheric mercury, which can further provide technical support to the implementation of the “Minamata Convention on Mercury” and promote the prevention and control of mercury pollution in China. In this paper, a microwave digestion and inductively coupled plasma mass spectrometry (ICP-MS) was developed to measure the concentration of gaseous mercury. Specifically, the factors affecting the experimental results were evaluated, including (1) the factors of activated carbon particle size and gas flow to mercury adsorption in sample preparation, and (2) the factors of digestion temperature, volume ratio of HNO₃∶HCl and digestion time to the digestion efficiency in sample pretreatment. The external standard method for the quantitative determination of mercury based on ICP-MS was also established. The results showed that 50 mesh activated carbon and lower gas flow were more favorable for the adsorption of gaseous mercury, and the best efficient digestion was obtained when the digestion temperature was 190℃, the volume ratio of HNO₃∶HCl was 5∶3, and the digestion time was 50 min. In this method, the linear correlation coefficient R² is 0.9999 and the detection limit is 0.0509 ng·g⁻¹, which shows good linearity and a lower detection limit for the measurement of gaseous elemental mercury. The samples were determined by the external standard method based on the certified reference material of single elemental mercury. The differences between the results calculated by the external standard method and the theoretical data are less than 2.5%, which proves the high accuracy of this method and further verifies the accuracy of the quantity of mercury gas standard prepared by the dynamical generation method.

Development of an Intelligent Metrological Platform for Particulate Matter Mass Concentration

XU Xiao, CHI Shunxin, LI Xiang

2022, 66(10): 71-76. doi: 10.12338/j.issn.2096-9015.2022.0178

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The dust, smoke, fugitive dust and particulate matter in the ambient air generated by factories and mines are the focus of attention in the fields of labor protection, industrial emission control and ambient air pollution monitoring in my country, which also puts forward higher requirements for the verification and calibration of particulate matter concentration monitoring instruments. An intelligent metrological platform for mass concentration of particulate matters is developed based on the feedback control of dust generation, digital image processing and optical character recognition, in order to provide the universal hardware and software infrastructure for the verification and calibration of dust measuring instruments, PM_2.5/PM₁₀ mass concentration monitors and particulate matter sensors. By implementing the feedback control of dust generation, the standard deviation of the mass concentrations during 20 min is reduced from 3.6%～6.4% down to 0.3%～0.7%, and the range of the mass concentrations during 4 h is reduced from 1.9%～12% down to 0.6%～1.9%. By applying automated calibration procedure control and data acquisition, 88% of manual repetitive operations in the calibration of PM_2.5/PM₁₀ monitors, as well as all the manual processes in the verification and calibration of dust monitors, can be eliminated, with improved efficiency and data quality.

2022 Vol. 66, No. 10

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