ASTM D7620 Standard Test Method for Determination of Total Sulfur in Liquid Hydrocarbon Based Fuels by Continuous Injection, Air Oxidation and Ultraviolet Fluorescence Detection
10. Sampling
10.1 Collect the samples in accordance with Practice D4057 or Practice D4177. To preserve volatile components which are in some samples, do not uncover samples any longer than necessary.
11. Preparation of Apparatus
11.1 Place the analyzer in service in accordance with the manufacturer's instructions.
11.2 Typical instrument parameters are listed in Table 1.
11.3 Prepare the sample introduction accessories, if required, according to the manufacturer's instructions.
11.4 Adjust the instrument sensitivity and baseline stability and perform instrument blanking procedure following manufacturer's guidelines.
12. Calibration
12.1 Choose which type of calibration method is required (mass/volume or mass/mass), and prepare a calibration standard from the stock solution (8.5) by volume or mass dilution.
12.2 If a mass/mass analysis is being done with a calibration standard in a different matrix than the sample, the calibration is set for the product derived from the weight/weight concentration estimate (see Eq 1 in 14.1 and Note 4).
NOTE 4 - Apparatus capable of accepting a fixed or variable density input and utilizing an automatic density compensation and result calculation are acceptable if precision and accuracy are not degraded.
12.3 Based on anticipated sulfur concentration carefully prepare a series of calibration standards that bracket the concentrations of the samples being analyzed. Table 2 lists typical calibration curves. The calibration curve shall contain at least three points, otherwise the number of standards used per curve can vary.
12.3.1 Prepare the instrument for calibration and fill the millilitre syringe to approximately the 0.75 mL mark with sample prior to analysis. Eliminate any bubbles that are present in the liquid column and cap the syringe with a septum seal.
12.3.2 Install the millilitre syringe, enter the density of the calibration standard and inject the standard into the analyzer according to the manufacturer's instructions.
12.3.3 Continue instrument calibration (by repeating 12.3.1 through 12.3.2) to construct a calibration curve. The calibration curve shall be linear and system performance shall be checked each day of use. See Section 16.
