The ASTM D1319 standard test method, commonly known as the “FIA Dyed Gel” method, is a legacy method used for several years for the determination of saturates, olefins, and aromatic group types in petroleum fractions. The test is used for the characterization of petroleum fractions as blending components for motor and aviation fuels and for the determination of fuel quality as specified in Specification D16551.
The FIA Dyed Gel method is a relatively inexpensive and straightforward test method that separates the saturate, aromatic, and olefinic group types as discrete bands (over the concentration ranges from 5-99 vol% aromatics, 0.3-55 vol% olefins, and 1-95 vol% saturates in petroleum distillates below 315 °C) using a column chromatography approach. A dyed gel material is used to identify the target group types with the assistance of the human eye as a detector.
The “FIA Dyed Gel” Situation
The dyed gel material used in the D1319 test method has been manufactured by a sole-source supplier. In the past couple of years, the proprietary formula was modified by the supplier and no was no longer suitable for the test method. The modified production dyed gel lots were identified as non-useable by ASTM and the Federal Aviation Administration (FAA). The sole source supplier has developed a molecularly equivalent replacement dye gel to address this concern. This replacement dyed gel is currently being reviewed by the industry for suitability.
With the limitation of commercially available useable dyed gel and with the dwindling supply of legacy dyed gel, laboratories have scrambled to find suitable alternatives. Several alternative approaches are available as solutions. This article will argue the merits of one of these alternatives: ASTM D6379—a High-Performance Liquid Chromatography (HPLC) approach.
What’s Old is New Again
ASTM D6379, “Determination Of Aromatic Hydrocarbon Types In Aviation Fuels And Petroleum Distillates—High Performance Liquid Chromatography Method With Refractive Index Detection”, is not a new test standard but it has gained some attention in recent years—especially with the current dyed gel situation. The D6379 method is harmonized with the European Standard (EN) IP-436 and is a fully vetted method. The data has been correlated to D1319. The method utilizes a high-performance pump, autosampler, and refractive index detector for an automated and sophisticated approach. Advancements in HPLC instrumentation and column technology have offered reliable, reproducible, and user-friendly methods in characterizing petroleum fractions..
Simple, Reliable, Cost Effective
HPLC systems may be used for a variety of applications using complex instrument configurations—incorporating gradient elution programming, multiple detectors, and column switching. The D6379 method, used for aviation fuel applications, uses a single channel elution (isocratic separation) and a single detector (refractive index detector). The method, a 10-15 minute run, separates the saturates and aromatics with little operator experience needed. It can almost be considered a “beginner system”. Many of the laboratories that have incorporated D6379 are pleasantly surprised at the ease-of-use and the benefit of automated sampling. With some basic understanding of HPLC operation and functionality, a system may run for many years with minimal maintenance!
An HPLC system capable of producing saturate and aromatic group type separation is competitively priced and robust. Modern HPLC instrumentation has shown to be far more reliable than SFC systems and far less expensive than the VUV methodology (currently under review).
Samples with limited volatility (lubebase stocks and heavy distillate fractions) that cannot be characterized by gas chromatography (GC) may be analyzed using HPLC. HPLC technology, once established in the laboratory, may be used as a powerful tool for a variety of ASTM/EN applications. The following ASTM HPLC methods are currently supported by Envantage:
- ASTM: D1319-19