ASTM Method D2887 is a widely used test procedure for simulated distillation (SimDist) analysis. This method is applicable to petroleum fractions with a final boiling point between 55 \u00b0C and 538 \u00b0C at atmospheric pressure and with vapor pressures that allow sampling at ambient temperatures. ASTM D2887 is used to evaluate process stream samples in order to provide accurate data for optimizing refinery operations, and it can also be used for product specification testing as allowed by contractual agreements. Most often, the method is run using a wide-bore (0.53 mm ID) column with a 0.88 to 2.65 \u00b5m polydimethylsiloxane (PDMS) layer. Thick-film columns offer more sample loading capacity and are preferred over traditional packed columns because of their comparatively low-bleed characteristic and reduced analysis times.<\/p>\n\n\n\n
Method D2887 includes an accelerated option (procedure B) for use when faster analyses are desired. Recently, the method also included an allowance for alternate carrier gases so that the standard helium carrier gas can be replaced with either hydrogen or nitrogen. Using these alternate carrier gases allows companies to take advantage of significant cost savings and to employ reliable and more easily available carrier gases. The easiest way to switch carrier gases is to use method translation, which is well known to preserve elution order and compound separation. An interesting derivative of method translation can be used to preserve retention times. Here, our approach was to translate the original method to alternative carrier gases so that the original retention times would be maintained. We show that with an MXT-1HT SimDist column and Restek\u2019s EZ<\/em>GC online method translator, existing methods based on helium carrier gas can be easily converted to either hydrogen or nitrogen carrier gas without sacrificing the accuracy of the method. Because retention times are preserved with proper method translation, there are minimal changes to peak identification tables and method validation is a much simpler task.<\/p>\n\n\n\n Helium carrier gas is traditionally used for ASTM D2887 because it is nonflammable and gives good resolution at an acceptably fast flow rate. However, helium is expensive and it can fluctuate in availability. Using methodology based on the accelerated parameters (procedure B) for helium carrier gas, along with an MXT-1HT SimDist column, provided very good chromatographic results (Figure 1). Requirements for resolution and skewness were met. In addition, excellent linearity was obtained for the C10-C44 calibration curve of retention time versus boiling point. Note that to extend the linearity of the curve down to C5, the initial column temperature can be lowered to subambient temperatures, or a thicker film column (2.65 \u00b5m) can be used.<\/p>\n\n\nHow to Match Your Helium Method<\/h2>\n\n\n\n