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3.
3.
Start the chromatograph and make necessary adjustments to make it work stably under the best operating conditions
3.
Column temperature: about 80℃ or a suitable temperature selected by the user;
Detector temperature: suitable temperature higher than 100℃;
Vaporization chamber temperature: suitable temperature higher than 100℃;
Thermal conductivity bridge current: 200mA or the bridge current value selected by the user that can meet the measurement requirements;
Carrier gas flow rate: Use hydrogen as the carrier gas, with a flow rate of about 60 mL/min or the user can select a carrier gas flow rate that meets the separation requirements
After the chromatograph is stabilized under the above working conditions, a stable baseline will be obtained and the test can be carried out
3.
Before or after each analysis of the sample, use the standard sample for external standard calibration, and the prepared standard sample should be injected more than twice in a row, and the peak area AE or peak height h E of each impurity can be measured , or by the chromatographic data processor Determine the correction factor of each impurity peak as the external standard quantitative calculation
3.
Under the same operating conditions as the analytical standard, use a micro syringe to inject 2uL of the sample from the injection port (the injection volume of the sample and the standard sample is the same), the number of injections is more than two, and the area of each impurity peak is measured A i or peak height h i is used for external standard quantitative calculation.
3.
The impurity content expressed in mass fraction (X 0 , X 1 , X 2 , X 3 ) is calculated according to formula (2), formula (3), formula (4), formula (5) or directly obtained by chromatographic data processor The content of each impurity:
In the formula: X 0 , X 1 , X 2 , X 3 —— the mass fraction of ammonia, monomethylamine , dimethylamine , and trimethylamine impurities in the sample ;
E 0 , E 1 , E 2 , E 3 —— the mass fraction of ammonia, monomethylamine, dimethylamine, and trimethylamine impurities in the standard sample;
A 0 , A 1 , A 2 , A 3 —— peak areas of ammonia, monomethylamine, dimethylamine, and trimethylamine impurities in the sample;
AE 0 , AE 1 , AE 2 , AE 3 —— the average peak area of ammonia, monomethylamine, dimethylamine, and trimethylamine impurities in two or more standard samples during calibration
When the peak height is used for quantification, formulas (2) to (5) replace the peak area with the corresponding peak height
3.
The main amine content in the sample expressed by mass fraction is calculated according to formula (6), formula (7), and formula (8):
Where:
X M ——the mass fraction of the monomethylamine component in the monomethylamine aqueous solution sample;
X D ——The mass fraction of the second amine component in the dimethylamine aqueous solution sample;
X T —mass fraction of trimethylamine component in trimethylamine aqueous solution sample;
X——Total alkalinity calculated according to the mass percentage of the main amine of the sample;
X0, X1, X2, X3——respectively are the mass fractions
of ammonia, monomethylamine, dimethylamine, and trimethylamine impurities ; respectively are the conversion coefficients of ammonia, monomethylamine, dimethylamine, and trimethylamine impurity converted to main amine ;
M main ——The mass of main amine expressed in grams equivalent to 1.
00mL hydrochloric acid standard titration solution [c(HCl)=1.
000mol/L], monomethylamine is 0.
03106, dimethylamine is 0.
04508, and trimethylamine is 0.
05911
.
3.
2.
5 Tolerance
Take the arithmetic average of two or more measurement results as the measurement result
.
The allowable difference of parallel determination results is shown in Table 2
.
Table 2 The allowable difference of the measurement results of industrial methylamine aqueous solution
Related links: Industrial methylamine aqueous solution test method (2)