Some standard content:
Standard of the Ministry of Machinery and Electronics Industry of the People's Republic of China Electronic-grade Gas Chromatographic Analysis Method General Provisions 1 Subject Content and Scope of Application 1.1 Subject Content This standard specifies the general provisions for the gas chromatography analysis method of electronic-grade gases. 1.2 Scope of Application This standard applies to the gas chromatography analysis method of trace impurities in electronic-grade gases. 2 Environmental Conditions 2.1 Instrument Room SJ323989 2.1.1 There should be no fire source, earthquake source, strong magnetic field and electric field, as well as flammable, explosive and corrosive substances in the instrument room and its surroundings to avoid interference with analysis or accidents. 2.1.2 The indoor temperature is generally between 10 and 35°C, and the relative humidity is below 80% to ensure the normal operation of each device. The instrument room is required to be clean and spacious, and should be equipped with air conditioning, drying and exhaust devices. 3.1.3 The instrument is placed on a workbench with a rubber sheet, and a certain amount of space should be left around it for easy operation and maintenance. 2.1.4 Fireworks are strictly prohibited indoors, and safety measures such as fire prevention, explosion prevention and fire extinguishing should be set up. 2.2 Power supply and ground wire
2.1.1 The power supply used should be consistent with the strict requirements of the instrument manual, and it must not be shared with other high-power electrical equipment.
2.2.2 To reduce interference, the instrument should have a dedicated ground wire. 3 Overview of gas chromatography analysis
3.1 Gas chromatography refers to the qualitative and quantitative analysis of gases and solids and liquids that can be vaporized under certain conditions.
3.2 The gas chromatograph is mainly composed of a gas path system, a sample injection system, a chromatographic column, a detector, a temperature measurement and control system, an amplifier, and a recording and data processing system: The general gas chromatography analysis process is shown in Figure 1. Approved by the Ministry of Machinery and Electronics Industry of the People's Republic of China on March 20, 1989 and implemented on March 25, 1989
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Temperature measurement and control system
Alarm and venting
Gas sample
Bridge glass effect amplifier
Auxiliary gas
Figure 1 Gas chromatography harmonic analysis process flow chart
3.2.1 The gas path system is a carrier gas continuous flow pipeline sealing system. 3.2.2 In the injection system, the analyzed sample gas can be quickly and quantitatively introduced into the chromatographic column, and the data
3.2.3 The chromatographic column is used to separate the various components of the analyzed sample. The separation efficiency is mainly related to factors such as the properties of the stationary phase, the preparation technology of the column filler, the column tube material, shape and size, and the operating conditions. 3.2.4 The detector converts the concentration changes of each component into electrical signals that are easy to measure, that is, voltage and current. 3.2.5 The temperature measurement and control system controls and tests the temperature of the vaporization chamber, chromatographic column and detector respectively to ensure that the temperature of the above parts is at the specified value. 3.2.6 In the recording and data processing system, the electrical signal generated by the detector is first recorded truthfully and then the data is processed.
4 Carrier gas
4.1 Carrier gas selection
The selection of carrier gas should mainly consider the adaptability of the detector and the requirements for the analysis object. Thermal conductivity detectors often use hydrogen and nitrogen as carrier gases. When analyzing impurities such as nitrogen, oxygen and argon, using hydrogen as a carrier gas can improve the sensitivity of the analysis. Hydrogen flame detectors and flame photometers often use nitrogen, argon and hydrogen as carrier gases; gas sensitive detectors use air, nitrogen and oxygen as carrier gases; electron capture detectors use nitrogen as carrier gas; nitrogen ionization detectors use nitrogen as carrier gas; argon ionization detectors use argon as carrier gas, etc. 4.2 Carrier gas purity
When analyzing electronic-grade gases, the carrier gas must be strictly purified. Generally, catalysts are used to remove oxygen, molecular sieves are used to dehydrate and carbon dioxide, and inert gases such as nitrogen and argon are purified by getters (zirconium aluminum-16); hydrogen is used as a carrier gas and purified by low-temperature molecular sieve adsorption, palladium diffusion purifiers and hydrogen storage bottles. When analyzing electronic-grade gases, the carrier gas purity must be more than one order of magnitude lower than the impurity content in the gas sample being analyzed. 4.3 Carrier gas flow rate
The carrier gas flow rate affects the column efficiency. The column efficiency is relatively high at the optimal flow rate. Under the premise of meeting the specified separation requirements, a larger carrier gas flow rate should be used. For a packed column with an inner diameter of 3~4mm, the commonly used flow rate is 20~-2
80ml/min.
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The carrier gas flow rate should be controlled by a constant pressure to keep the inlet pressure of the chromatographic column constant to maintain a stable flow rate. The method for measuring the flow rate is usually a soap film flow meter, and the unit is ml/min. 4.4 Carrier gas pressure
In order to make the carrier gas move in the chromatographic column, a certain pressure difference is required between the column inlet and outlet. Under the premise of a given carrier gas flow rate, the inlet pressure is related to factors such as the operating temperature and column conditions. For a chromatographic column with a length of less than 4m, when other conditions are fixed, there should be a linear relationship between the carrier gas inlet pressure and the flow rate. The column length is less than 4m and the diameter is 3-4mm. The carrier gas pressure before the column can be controlled below 6Kgf/Cm2, and the column outlet pressure should be greater than atmospheric pressure.
5 Chromatographic column
5.1 Overview
The separation of sample components is completed in the chromatographic column. The selected chromatographic column should be able to meet the requirements of separation and rapid qualitative and quantitative analysis. Packing columns are commonly used in gas analysis. The stationary phase in the chromatographic column is the key to chromatographic analysis.
5.2 Working conditions of chromatographic columns
5.2.1 Column temperature
The distribution coefficient is closely related to the column temperature. Therefore, the column temperature should be selected by weighing the pros and cons of various aspects. 5.2.2 The capacity of the chromatographic column and the injection volume shall not exceed the capacity of the chromatographic column. 5.2.3 The chromatographic column should be avoided from being contaminated as much as possible. The chromatographic column needs to be activated and regenerated regularly. 5.3 Stationary phase of chromatographic column
5.3.1 Overview
The immobile substance used to separate the mixture in the chromatographic column is called the stationary phase. The stationary phase in gas analysis uses solid adsorbents. The adsorbents include molecular sieves, polymer porous microspheres, carbon molecular sieves, silica gel, etc. Solid adsorbents should have a large surface area, strong adsorption, good selectivity and thermal stability, and a large adsorption heat difference for different gaseous components. They are suitable for gaseous sample analysis. 5.3.2 Molecular sieves
Molecular sieves are the most widely used adsorbents in the impurity analysis of electronic grade gases. The surface area of molecular sieve is very large, generally with an internal surface area of 700 to 800 m/g. The performance of molecular sieve mainly depends on the size of the pore size and surface characteristics.
5.3.3 Polymer porous microspheres
Polymer microspheres are an adsorbent with excellent performance, suitable for high-sensitivity detectors, and can be used as a stationary phase for analyzing corrosive substances. They have a large column capacity and the operating temperature generally should not exceed 250C. Before use, they are generally treated with ventilation and activation at below 200℃ for 8 hours. When filling the column, use an appropriate solvent (acetone) to wipe the wall of the column or cool the column to 0℃ to ensure that the chromatographic column is filled evenly and tightly. 5.3.4 Column efficiency is usually expressed in terms of the number of theoretical plates (n) or the height equal to the plate (HETP). According to the peak of the gas chromatogram, it can be calculated according to formula (1) or formula (2).
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Wherein: ts—-retention time of the component corresponding to the peak; peak base width of the chromatographic peak;
HETP1/n
Wherein: 1. Length of the chromatographic column, m;
—number of theoretical plates, pieces;
The separation of the two peaks is expressed by the separation degree R. R=2tR1-tR2
Where: tri is the retention time of component 1;
is the retention time of component 2;
time (R>tR2);
y, peak 1 base width;
+（3）
y2--peak 2 base width;
When the peak shape is symmetrical and satisfies Gaussian distribution, the separation degree reaches 98%: when R=1.5, the separation degree reaches 99.7%, that is, the two adjacent peaks are completely separated; when R<1, there is a significant overlap between the two peaks. It is generally believed that when R>1.5, the two components can be completely separated.
5.3.5 Column material, column diameter, column length
5.3.5.1 Filling chromatographic column
Use stainless steel, glass or polytetrafluoroethylene tube. The material of the chromatographic column is determined according to the column humidity and column pressure, sample properties, etc. The inner diameter of the filling column is 2-4mm, and the column shape includes straight, U-shaped, spiral and other shapes. The column length mainly depends on the separation needs. The column length generally used is 1-2m. 5.3.5.2 Capillary chromatographic column
Use stainless steel or glass. The inner diameter of the capillary column is generally 0.2-0.5mm, and the length is 30-100m. 5.3.6 Chromatographic column filling
The quality of the stationary phase filling directly affects the column efficiency. A column of suitable length and diameter should be selected, the inner wall should be cleaned and dried, one end should be plugged with glass wool and connected to a vacuum pump, and the other end should be equipped with a funnel. When sucking, slowly add the dry filler into the column, and tap the wall of the tube until it is full, and then plug it with glass wool. The main requirements for filling are even hooking and tightness. After aging, it is loaded into the instrument.
5.4 Column switching technology
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Column cutting technology can change the flow direction of carrier gas and sample gas in each column, so that the sample gas can selectively enter different detectors or vent. It is specifically applied to the following five aspects: a. Solvent cutting can solve the difficulty of quantitative analysis caused by the sample being ejected on the tail of the solvent during single-column gas chromatography analysis.
b. Heart cutting Heart cutting is mainly used to solve the separation of difficult-to-separate components. Backflush is to blow the heavy components out from the column inlet without entering the detector, c.
d. It is used to concentrate trace components.
Analyze complex and ultrapure samples.
6 Detectors
6.1 Detector types
6.1.1 Concentration detectors include thermal conductivity, electron capture and other detectors. The response value of this detector is proportional to the concentration of the component in the carrier gas. When the injection volume is constant, the peak height is independent of the flow rate (within a certain flow rate range), but the peak area is inversely proportional to the flow rate.
6.1.2 Mass detectors include hydrogen flame, oxygen ionization and nitrogen ionization detectors. The response value of this detector is determined by the mass of the component entering the detector per unit time. When the injection volume is constant, the peak height is proportional to the carrier gas flow rate, but the peak area is independent of the flow rate.
6.2 Detector performance indicators
6.2.1 Detector sensitivity
6.2.1.1 The sensitivity (S.) of the concentration detector is: S.
Where: △R is the increment of the corresponding change of the response value, mV; AR
△C is the increment of the concentration of the component in the detector in the carrier gas, mg/ml. The sensitivity of the thermal conductivity detector is about 10°mV·m1/mg (when hydrogen or nitrogen is used as the carrier gas) 6.2.1.2 The sensitivity S of the mass detector is: Sm
Where: △R is the increment of the response value, mV; AR
-mV.S/mg..
△m/△t is the amount of sample entering the detector per unit time, g/s. 6.2.2 Detector linear range
(4)
.·(4)
The linear range of the detector refers to the range in which its response signal is linearly related to the concentration of the component being measured. Definition: The ratio of its maximum or minimum injection volume when the detector is linear. The linear range of the hydrogen flame ionization detector is 106~10%, and the linear range of other 5
detectors is generally 10~10″
6.2.3 Detection limit of the detector
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The detection limit refers to the mass or concentration of the substance represented by the signal when the signal is twice the noise. The detection limit of the thermal conductivity detector is generally 10-mg/ml, and the detection limit of the hydrogen flame detector is on the order of 10~12g/S. 6.2.4 Detector selectivity
Some detectors are universal, that is, they respond to any component, such as the thermal conductivity cell detector. Other detectors only respond to specific compounds. The electron capture detector has a greater response to electronegative compounds such as halogen compounds, and the flame photometer has a greater response to electronegative compounds such as halogen compounds. Phosphorus and sulfur-containing compounds have a greater response. 6.3 Thermal conductivity detector
6.3.1 Basic principle
The thermal conductivity detector (TCD) is based on the different thermal conductivity coefficients of various substances and carrier gases. When the gas composition and concentration passing through the thermal conductivity cell change, different amounts of heat will be taken away from the thermistor, causing a change in resistance. The change in resistance can be measured using a bridge.
6.3.2 Design requirements and selection of operating conditions for the detector 6.3.2.1 The factors that affect sensitivity mainly include bridge current, carrier gas, thermistor resistance and resistance temperature coefficient, geometric factors, and cell body temperature.
a. Bridge current Increasing the bridge current can improve sensitivity, but if the bridge current is too high, the noise will increase, the baseline will be unstable, and the hot wire will be easily oxidized. When nitrogen is used as the carrier gas, it is generally controllable. It is controlled below 120mA. When hydrogen is used as the carrier gas, it is generally controlled below 250mA. When tungsten wire is used as the thermistor, the bridge current can be controlled to 300mA. The specific requirements shall be subject to the instrument manual.
b. Generally, hydrogen or nitrogen with large thermal conductivity coefficient is selected as the carrier gas to obtain a larger response. In electronic grade gas analysis, the carrier gas must be of high purity, and the flow rate per minute must be greater than 20 times the cell volume. c. The resistance value and resistance temperature coefficient of the thermistor. Metals with large resistance temperature coefficient should be selected to obtain high sensitivity.
d. Geometric factor. The sensitivity of the thermal conductivity detector depends to a large extent on the geometric shape of the element and the cell cavity. The design should be as close as possible to the thermal element with a large radius, a long length, and a small cell cavity. e. The cell body temperature. The thermal conductivity cell detector is very sensitive to temperature changes. Sensitive, as the temperature of the detector increases, the sensitivity decreases. High-performance thermal conductivity detectors require that the column temperature change is within ±0.5°C, and the temperature of the rain detection chamber should be controlled within ±0.1°C. Generally, the detector temperature should be selected to be slightly higher than the column temperature to prevent the sample from condensing in the detector. 6.3.2.2 Factors affecting noise and drift
The noise of the thermal conductivity detector should be less than 5μV. The factors that cause noise and drift are as follows: a. The hot wire is contaminated by the decomposition products of organic matter; b. A leak occurs somewhere in the system;
c. The hot wire is oxidized;
d. Chromatographic column loss;
e. Fluctuation of detector temperature;
f Electrical noise,
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Therefore, the presence of the above factors should be avoided. 6.4 Flame detector
6.4.1 Basic principle
The hydrogen flame detector uses the flame generated by the combustion of hydrogen and air as energy. When organic matter enters the flame, many ion pairs are generated due to the ionization reaction. If a pair of electrodes are placed at the upper and lower parts of the flame and a certain voltage is applied, the generated ion flow can be detected, thereby quantifying the organic matter entering the flame. When using, pay attention to the high impedance circuit to prevent leakage. The detector should be heated to above 100℃ to prevent water accumulation inside the detector at low temperatures. 6.4.2 Detector design requirements and operating condition selection 6.4.2.1 Detector design requirements
a. The flame nozzle is replaceable for easy cleaning and maintenance. b. The air should be evenly distributed around the nozzle and have a high linear speed so that a large amount of sample can be introduced without extinguishing the fire. c. The polarization electrode is separated and insulated from the collector. d The collector should have a large enough surface area to improve the collection efficiency. e. The diameter of the flame nozzle is about 0.5mm, and it is equipped with a suitable air flow to achieve fast response and reduce tailing and memory effects.
f. The shape and size of the electrodes and the distance between the electrodes have a significant impact on the response value and collection efficiency. Generally, simple electrodes or trumpet-shaped electrodes are used. The distance between the electrodes and the inner diameter of the collector are also controlled. The distance between the polarizing electrode and the collector is preferably 5mm, and the inner diameter of the collector is preferably 10mm. 6.4.2.2 requires that the generated ion pairs with opposite charges separate as quickly as possible to avoid recombination. The electrode voltage should be selected between 50 and 300V.
6.4.3 The influence of the detector operating conditions on the response value 6.4.3.1 The influence of hydrogen flow rate on the response value When the carrier gas flow rate is fixed, as the hydrogen flow rate increases, the response value will gradually increase to the maximum value, and then gradually decrease. The maximum response value can be determined by experiment. 6.4.3.2 Effect of carrier gas and flow rate on response value Hydrogen flame ionization detector is insensitive to nitrogen, argon, ammonia, hydrogen and carbon dioxide, and can be used as carrier gas. Nitrogen can obtain the best response value when used as carrier gas. There are two situations in which nitrogen flow rate affects the response value: one is that when the response value is expressed as peak height, the peak height is proportional to the flow rate; the other is that when the response value is expressed as peak area, the peak area is independent of the flow rate. 6.4.3.3 Effect of air flow rate on response value Air is used as a combustion-supporting gas for hydrogen flame combustion. If a small amount of air is supplied to the hydrogen flame, the response value will increase with the increase of air flow rate. After reaching a certain value (250-400ml/min), the response value will remain stable. The generally selected value is hydrogen: air = 1:10. 6.4.3.4 Effect of detector temperature on response value As the detector temperature increases, the sensitivity and noise of the detector increase, but not significantly. Generally, the temperature of the detector is controlled to be 20°C higher than the temperature of the chromatographic column. In order to prevent water accumulation in the detector, the detector temperature must be higher than 100℃. 6.4.3.5 Effect of premixed hydrogen flame on response value Premixed hydrogen flame refers to the combustion of the gas and the combustion-supporting gas after mixing. The premixed hydrogen flame supplies appropriate 7
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oxygen or air from the inside of the flame to improve the ionization efficiency, thereby greatly improving the response value. 6.5 Gas-sensitive semiconductor detector
6.5.1 Basic principle
Gas-sensitive semiconductor, also known as gas-sensitive resistor, is a component made of a semiconductor material that is particularly sensitive to gas. This type of material is generally divided into two types: N-type and P-type.When reducing gas is adsorbed by N-type semiconductor and oxidizing gas is adsorbed by P-type semiconductor, the carrier concentration on the surface of gas sensor will increase and the resistance will decrease. On the contrary, the carrier concentration will decrease and the resistance will increase. This change will only change accordingly with the concentration of the gas being measured. The concentration of the measured gas is displayed in the form of an electrical signal, and the resistance change can be recorded by a simple circuit, so as to achieve quantitative analysis of the content of different gases.
6.5.2 Detector selection and application
Gas-sensitive semiconductor detector is a highly selective detector. N-type gas-sensitive semiconductor detector is particularly sensitive to combustible gases such as hydrogen, carbon monoxide, and methane, but has low sensitivity to rare gases and permanent gases such as nitrogen, oxygen, nitrogen and argon, with a signal ratio of 1:10-. P-type gas-sensitive semiconductor detector is particularly sensitive to oxidizing gases such as oxygen, nitrous oxide and chlorine, but is not sensitive to reducing gases and permanent gases. Gas-sensitive semiconductor detector has been widely used in the analysis of trace impurities in rare gases and permanent gases. The minimum detection limit can reach PPb level. 6.6 Electron Capture Detector
6.6.1 Basic Principles
Electron Capture Detector measures the reduction of signal current, not the actual current generated. When nitrogen flows through the detector, the Ni radioactive source ionizes the nitrogen molecules and then generates slow electrons. The slow electrons migrate to the anode under the action of a fixed "chamber voltage". The collected slow electrons are amplified by the electrometer to produce a stable current. If the sample crystal molecules containing electrophiles enter the detector and capture some electrons, the current will decrease. The reduction in current is a measure of the total amount of electrophilic compounds. Electron capture detectors only have signals for substances with electronegativity, such as halogens, sulfur, phosphorus and nitrogen.
6.6.2 Selection of detector operating conditions
6.2.2.1 High-purity nitrogen is required as the carrier gas. The response value decreases with the increase of the carrier gas flow rate. At the same time, when the gas flow rate is low, the detector base flow increases with the increase of the gas flow rate and tends to a saturation value. Under a given sample volume, the maximum values of the peak height and peak area correspond to the optimal flow rate required by the detector, which is generally between 40100ml/min. 6.6.2.2 Under a given polarization voltage, within a relatively low temperature range, the detector response increases with the increase of temperature. The temperature fluctuation should be controlled within 0.1℃. 6.6.2.3 The method to determine the best polarization voltage is to draw a curve of polarization voltage and base flow under given temperature, flow rate and other conditions, and select the polarization voltage when the base flow is equal to 85% of the saturated base flow as the best polarization voltage, which is generally 2~100V.
6.6.2.4 The best pulse period is generally 50~100μS, and the pulse width is 0.5~5uS. It can be appropriately selected according to the measured component and its concentration to obtain good linearity and sensitivity. 6.6.2.5 The injection volume of the measured component should not be too large, generally between 10-9~10~1g, which can be determined according to the base flow. 6.7 Nitrogen ion detector
6.7.1 Basic principle
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The nitrogen ion detector is an ionization detector that uses pure nitrogen as a carrier gas. It uses the fact that the metastable state of nitrogen has a higher energy (i.e., 19.8 eV) than other gases to ionize the analyzed components. Except for hydrogen, the generated current is amplified and converted into a detectable electrical signal. Almost all inorganic gases and organic matter can be ionized. 6.7.2 Selection and application of detectors
The nitrogen ion detector is a universal type that responds to all compounds. However, due to its high sensitivity, it cannot use a stationary phase with loss. It is effective for the analysis of compounds separated by chromatographic columns using polymer microspheres and active solids. The nitrogen ion detector has been used in the analysis of trace impurities in high-purity permanent gases, such as impurities oxygen, hydrogen, nitrogen, carbon monoxide, carbon dioxide and water. 6.8 Argon Ion Detector
6.8.1 Basic Principle
When high-purity carrier gas argon passes through an ionization chamber with a radioactive fluorine source, the irradiation of the beta particles radiated by the fluorine source causes the argon to ionize and produce electrons. Under the action of a strong electric field, the electrons have very high energy and collide with the argon gas, causing the argon atoms to be excited from the ground state to a metastable state with an energy of only 11.6 eV. When a constant concentration of "organic vapor" with an ionization potential lower than the excitation energy of argon is added to the carrier gas, these organics will be ionized by inelastic collisions with metastable argon atoms, and a weak power source (base current) will be generated under the action of the electric field. When the impurities to be measured enter the detector, they collide and recombine with metastable hydrogen ions, so the amount of organic vapor ionization is small, resulting in a decrease in base current, and the decrease in base current is proportional to the impurity content. 6.8.2 Detector Selection and Application
The argon ion detector is a universal type. It responds to all compounds. It is used in the detection of permanent gases and can replace the nitrogen ion detector, which has certain practical significance. 6.9 In addition to the five detectors listed above, there are also thermal ionization detectors, flame photometry detectors, photoionization detectors, mass spectrometers, etc., which are all suitable for the analysis of trace impurities in electronic grade gases. 7 Recording and data processing system
The electrical signals of various parameters generated by the detector are converted into voltage form and recorded by an automatic balanced potentiometer (recorder). Integrators and microprocessors can be used to measure peak height and peak area. 7.1 Recorder The performance of the recorder has a significant impact on chromatographic analysis, so it is required to select a recorder. To the following points:
7.1.1 Full scale range requires 1~5mV for thermal conductivity detectors, and 1~10mV for various ionization detectors. 7.1.2 Full time Generally, a packed column requires a 1S or 2S recorder, and a capillary column requires a 1S or less recorder.
7.1.3 Impedance matching Generally, a recorder with high impedance is selected. 7.1.4 Recorder sensitivity When performing quantitative analysis, generally change the attenuation or control the sample plate to make the peak at 30~80% of the full scale to reduce measurement errors. 7.1.5 Paper speed Chromatographic analysis requires the recorder to have a uniform paper speed, which directly affects the measurement of the half-peak width and retention time of the spectrum, thereby affecting the accuracy of qualitative and quantitative data. The speed of the paper mainly depends on the width of the chromatographic peak. Generally, the half-peak width is preferably 1~5s.
7.1.6 Interference recorder is an instrument that directly records DC signals from microvolt to millivolt. To prevent interference signals, 9
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7.2 Integrators and processors should be operated according to the regulations in the instruction manual. 8 Qualitative analysis
Compare the retention value of unknown components and the retention value of known substances under the same conditions for qualitative analysis. However, a peak obtained under a certain condition does not necessarily correspond to only one substance. It should be used in conjunction with the determination method of changing the stationary phase or the temperature of the chromatographic column, or in conjunction with other methods. The retention value should include retention time, retention volume, etc. The retention time should be measured three times and the average value should be taken. Generally, the peak retention time is measured in 5~30min, and the error of repeated measurement must be less than ±3%. 9 Quantitative analysis
Quantitative analysis is carried out based on the repeatability of gas chromatography measured by the specified method, as well as the relationship between the sample component amount and the peak area and peak height. In this case, to obtain correct quantitative results, the gas chromatographic peaks should be symmetrically and completely separated. 9.1 Whether the measurement of peak area or peak height should be carried out should be determined according to relevant standards or agreements between the supply and demand parties.
9.1.1 Measurement of peak height Draw a vertical line from the coordinate axis of the recording paper from the apex of the peak, and the distance from the apex to the intersection of it and the baseline is the height of the peak.
9.1.2 Measurement of peak area is carried out according to the following method: 9.1.2.1 Half peak width method
a Symmetrical peaks are shown in Figure 2. Draw a straight line parallel to the baseline from the midpoint of the peak height (h), and the length of the line segment tangent to the peak is the half-peak width (W), and the product of the half-peak width and the peak height is the peak height area (A) Aauxh
Figure 2 The area of the peak measured by the half-peak width (symmetrical peak) is shown in Figure 3. The measurement method of the symmetrical peak of a is also applicable to the case of leading waves. b. Leading peak
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Figure 3 The half-peak width method is used to measure the area of the peak (leading peak) Distorted peaks For peaks with significant distortion, the half-peak width method should not be used c.
d. When there are more than two peaks close to and overlapping in the re-entry peak, the above method can be used appropriately according to the degree, but it is not applicable when the peak overlap is significant.
9.1.2.2 Integrator method This method is measured based on the recorded or indicated value represented by the integrator, but it shall not be used when the peaks overlap significantly.
9.2 Normalization method bzxZ.net
The normalization method is based on the concentration of a component (C), which is equal to the ratio of the peak area (A) of the component to the sum of the total area of all peaks (A). The calculation formula is as follows:
Ci%=Ai
Since the detector responds differently to different substances, the relative correction factor is multiplied by the area of the peak, that is, the above normalization equation can be rewritten as follows:
C,% =K(f,A,)/ Z (f,A) × 100-Where: K concentration conversion factor:
f is the relative correction factor of the component i to be measured
Note: When the analyzed sample contains high-boiling point components, the error is large when determining trace impurities, and the normalization method should not be used. 9.3 Internal standard method
·(7)
In internal standard analysis, the amount of the relevant component (C) is related to the amount of the internal standard component, and its correction factor is used to compensate for the different responses of the detector to the relevant component and the internal standard. The calculation formula is as follows: C,=K((A,/FA))ms/m
wherein C is the concentration of component i to be tested;
K is the concentration conversion factor;
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f is the relative correction factor of group i to be tested; A,—-the peak area (peak height) of component i to be tested, mm; f is the relative correction factor of internal standard;
A is the peak area (peak height) of internal standard, mm2;
m, is the mass of internal standard, g,
is the mass of sample g
When using the internal standard method, the sample amount must be accurate, with at least three significant figures. 9.4 External standard method
In external standard analysis, the content of the component in the analyzed sample is obtained by comparing with the concentration of the known component in the calibration sample. The absolute correction factor is calculated using an external standard sample with a known maximum content. The calculation formula is as follows: f=C/A,
Where: C is the content of component i in the external standard sample, %; A,—the area (peak height) of component i in the external standard sample, mm; f is the absolute correction factor.
Under the same operating conditions, take the same volume of analytical sample for chromatographic analysis, and the concentration of its components can be calculated by the following formula:
c,=f,·A,
Wherein: C, the content of the analytical component in the sample, %; A, the area (peak height) of the analytical component in the sample, mm2; (10)
Note: The operating conditions of various instruments are unstable, which has a great influence on the results. Therefore, they must be calibrated in time with standard samples. This method is only suitable for sample analysis whose standard curve passes through the origin. 9.5 Deviation
9.5.1 Absolute deviation (d) The difference between the measured value (X) and the average value (X) of a series of measured values. d=X,x
wherein: x is the arithmetic mean;
is the number of measurements,
·(11)
（12)
9.5.2 Standard deviation The sum of squared deviations divided by the square root of the number of measurements. For a limited number of measurements (n<20), the standard deviation (S) is calculated as follows:
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.