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D5453_10 (16e1)

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Based on anticipated sulfur concentration, select one of the suggested curves outlined in Table 2 of the written standard. Narrower ranges than those indicated may be used if desired. However, the test method precision using narrower ranges than those indicated, have not been determined. Ensure the standards used for calibration bracket the concentrations of the samples being analyzed. Carefully prepare a series of calibration standards accordingly. Make other volumetric dilutions of the stock solution to cover the various ranges of operation within these calibration curve guidelines. The number of standards used per curve can vary, if equivalent results are obtained. Flush the microliter syringe several times with the sample prior to analysis. If bubbles are present in the liquid column, flush the syringe and withdraw a new sample. A sample injection size recommended for the curve selected from Table 2 of the written standard shall be quantitatively measured prior to injection into the combustion tube or delivery into the sample boat for analysis (Notes 8 through 10 of the written standard). There are two alternative techniques available. Injection of the constant or similar sample size for all materials analyzed in a selected operating range promotes consistent combustion conditions. Injection of 10 microliter of the 100 nanograms per microliter standard would establish a calibration point equal to 1,000 nanograms or 1.0 micrograms. Other injection sizes can be used when complete sample combustion is not compromised and accuracy and precision are not degraded. The volumetric measurement of the injected material can be obtained by filling the syringe to the selected level. Retract the plunger so that the air is aspirated and the lower liquid meniscus falls on the 10% scale mark and record the volume of liquid in the syringe. After injection, again retract the plunger so that the lower liquid meniscus falls on the 10% scale mark and record the volume of liquid in the syringe. The difference between the two volume readings is the volume of sample injected (Note 11 of the written standard). An automatic sampling and injection device can be used in place of the described manual injection procedure. Fill the syringe as described in 10.3.1 of the written standard. Weigh the device before and after injection to determine the amount of sample injected. This procedure can provide greater accuracy than the volume delivery method, provided a balance with a precision of 0.01 milligram is used. Once the appropriate sample size has been measured into the microliter syringe, promptly and quantitatively deliver the sample into the apparatus. Again, there are two alternative techniques available. For direct injection, carefully insert the syringe into the inlet of the combustion tube and the syringe drive. Allow time for sample residues to be burned from the needle (Needle Blank). Once a stable baseline has re-established, promptly start the analysis. Remove syringe once the apparatus has returned to a stable baseline. For the boat inlet, quantitatively discharge the contents of the syringe into the boat containing quartz wool or suitable equivalent (see 6.8 of the written standard) at a slow rate being careful to displace the last drop from the syringe needle. Remove the syringe and promptly start the analysis. The instrument baseline shall remain stable until the boat approaches the furnace and vaporization of the sample begins. Instrument baseline is to be reestablished before the boat has been completely withdrawn from the furnace (Note 12 of the written standard). Once the boat has reached its fully retracted position, allow at least one minute for cooling before the next sample injection (Note 12 of the written standard). Slowing boat speed or briefly pausing the boat in the furnace can be necessary to ensure complete sample combustion. Direct injection can ease sample handling and improve sample combustion characteristics for materials containing very volatile sulfur compounds. The level of boat cooling required and the onset of sulfur detection following sample injection are directly related to the volatility of the materials analyzed. For volatile materials, effective cooling of the sample boat prior to sample injection is essential. The use of a refrigerated circulator to minimize the vaporization of the sample until the boat begins approaching the furnace or an increased time for boat cooling can be required. Calibrate the instrument using one of the following two techniques. Perform measurements for the calibration standards and blank using one of the procedures described in 10.2 to 10.4 of the written standard. Measure the calibration standards and blank three times. Subtract the average response of the blank injections from each calibration standard response. Then determine the average integrated response of each concentration (See 6.4 of the written standard). Construct a curve plotting of the average integrated detector response (y-axis) versus micrograms of sulfur injected (x-axis) (Note 13 of the written standard). This curve shall be linear and system performance must be checked each day of use. See section 14 of the written standard. Other calibration curve techniques can be used when accuracy and precision are not degraded. If the apparatus features self calibration routine, measure the calibration standards and blank three times using one of the procedures described in 10.2 to 10.4 of the written standard. If blank correction is required and is not an available instrument option (See 6.4 or 10.5.1 of the written standard), calibrate the analyzer in accordance with manufacturer's instructions to yield results expressed as nanograms of sulfur (Note 13 of the written standard). This curve shall be linear and system performance must be checked with each day of use (See section 14 of the written standard). If analyzer calibration is performed using a different calibration curve than listed in Table 2 of the written standard, select an injection size based on the curve closest in concentration to the measured solutions. Construct the calibration curve to yield values that can be used to report sulfur content on a mass for mass basis.

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Posted by: abuckmaster on Aug 23, 2018

D5453_10 (16e1)

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