Gas chromatography—mass spectrometry

Abstract

This report has been reviewed by the staff of the California Air Resources Board and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Air Resources Board, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. SOP No. MLD 120A-PROCEDURE FOR THE ANALYSIS OF C3 TO C12 HYDROCARBONS IN AUTOMOBILE EXHAUST SAMPLES BY GAS CHROMATOGRAPHY/MASS SPECTROMETRY 2 Method Summary 2.1 This procedure uses a GC/MS with a GC equipped with a capillary column system, a single-stage quadrupole mass spectrometer and a cryogenic pre-concentration system. 2.2 All sampling, sample transfer from Tedlar bags, cryogenic pre-concentration, analytical column separation, data acquisition and data processing are either manually controlled or data system (DS) controlled. 2.3 A GC/MS data system is used to acquire, store and process data. Data processing includes peak enhancement, background subtraction and compound identification. Reports are prepared and submitted in hard copy and on the Air Resources Board's data communication system or on an appropriate electronic data storage medium. 2.4 Excessive water or carbon dioxide in the sample (as in the case when a large volume of sample is passed through the trap) may block the helium flow in the cryogenic trap or the GC column at sub-ambient temperature. When this happens, Ascarite may be used to remove water and carbon dioxide in the sample prior to cryogenic pre-concentration. 3 Interferences and Limitations 3.1 Compounds which do not elute from the gas chromatograph capillary column system under the described operating conditions will not be detected. Examples include heavy hydrocarbons, some oxygenates, and compounds with acidic and basic functional groups. 3.2 Compounds with molecular weights less than 35 atomic mass units (amu, including methane and C2 hydrocarbons), the starting mass of mass spectrometer scan range, will not be detected. 3.3 When Ascarite is used prior to cryogenic pre-concentration, compounds which are removed by Ascarite will not be detected. Some of these compounds include water, carbon dioxide and compounds with acidic functional groups. 3.4 Co-eluting compounds and compounds with very close GC retention times may not have peak resolution clean enough for positive identification.

Proximate Composition and Nutritive Value of Some Leafy Vegetables from Faisalabad, Pakistan

“…Carbohydrate content was determined by difference method. All the proximate values are reported in percentage [26,27].…”

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“…Carbohydrate content was determined by difference. All the proximate values are reported in percentage [27,28]. Gross energy content was calculated using Atwater's conversion ratios: 4 kcal/g for protein, 9 kcal/g for fat, and 4 kcal/g for carbohydrates [29].…”