ASTM D5623 standard test method for sulfur compounds in light petroleum liquids by gas chromatography and sulfur selective detection
7. Sampling
7.1 Appropriate sampling procedures are to be followed. This test method is not suitable for liquefied petroleum gases. Volatile liquids to be analyzed by this test method shall be sampled using the procedures outlined in Practice D4057. A sufficient quantity of sample should be taken for multiple analyses to be performed (at least 10 to 20 g for quantitation by internal standardization). Store all samples and standard blends at a temperature of 7 to 15°C (45 to 60°F). Do not open the sample or standard container at temperatures above 15°C (60°F).
8. Preparation of Apparatus
8.1 Chromatograph - Place in service in accordance with the manufacturer's instructions. Typical chromatograph and detector operating conditions are shown in 5.2.1.
8.2 Detector - Place in service in accordance with the manufacturer's instructions. After sufficient equilibration time (for example, 5 to 10 min), adjust the detector output signal or integrator input signal to approximately zero. Monitor the signal for several minutes to verify compliance with the specified signal noise and drift.
8.3 System Performance Specification - The inlet system should be evaluated for compatibility with trace quantities of reactive sulfur compounds. Inject and analyze a suitable amount (for example, 0.1 to 2.0-µL) of the system test mixture (6.1.8). All sulfur compounds should give essentially equimolar response and should exhibit symmetrical peak shapes. Relative response factors should be calculated for each sulfur compound in the test mixture (relative to a referenced component) in accordance with Practice D4626 or Eq 1:
where:
Rrn = relative response factor for a given sulfur compound,
Cn = concentration of the sulfur compound as sulfur,
An = peak area of the sulfur compound,
Cr = concentration of referenced sulfur standard as sulfur, and
Ar = peak area of the referenced sulfur standard.
The relative response factor (Rrn) for each sulfur compound should not deviate from unity by more than more or less 10 %. Deviation of response by more than more or less 10 % or severe peak asymmetry indicates a chromatography or detector problem that must be corrected to ensure proper selectivity, sensitivity, linearity, and integrity of the system. If necessary, optimize the system according to instructions from the manufacturers.