Shortly after Minnesota mandated that all diesel fuel sold in the state contain 2 percent biodiesel blended with petroleum diesel, the weather turned cold and truckers and bus drivers began complaining that the biodiesel blend was clogging fuel filters. This resulted in the mandate being lifted for a total of 51 days. The Agricultural Utilization Research Institute (AURI) researched the problem and found that while biodiesel was not the only contributor to the clogging problem, it was indeed one of the contributors. Unfortunately for proponents of biodiesel, it appeared that it was the 2 percent biodiesel blended into the fuel mixture that received most of the blame for the problem.

This example and others similar to it bring to light the importance of measuring free and total glycerin in biodiesel that is to be used as a motor fuel. ASTM D 6584 and EN 14105 methods both prescribe gas chromatography (GC) as the method for this analysis. For someone who has spent years working with GC, configuring a system to perform such an analysis may not seem like a daunting task. For novices at this technique, the array of letters such as PPC (programmable pressure control), POC (programmable on column) and FID (flame ionization detector) can be more than just mildly bewildering. Some of the latest technologies feature out-of-the-box preconfigured systems for performing a specific analysis like free and total glycerin in biodiesel. These systems provide a supply of consumables to analyze samples and often special training courses are available for the inexperienced chromatographer.

Having a GC system come preconfigured is most helpful, but let's not forget that standards and samples also must be prepared for introduction into the GC. Fortunately, this operation is quite straightforward and can be performed by an operator with basic laboratory skills.

For preparation of the standards, it is recommended to use a biodiesel calibration standards kit that contains reference solutions that meet the specifications called for in ASTM D 6584 and EN 14105. A set of calibration standards containing external and internal standards can be created using the kit, a pipette and the solvent heptane. The external samples will be used to build a calibration curve on the GC and the internal standards will be added to the sample itself. All external standards can be made up in autosampler vials. Sample preparation is stated in ASTM D 6584 and requires only a few steps. In a 10 milliliter (ml) septa vial, add 100 milligrams of biodiesel, 100 microliters (µl) of the internal standard, 100 µl of the derivitizing solution, shake and allow to react for 20 minutes. Dilute with eight ml of heptane and shake to mix. This solution is now ready for analysis and can be transferred to an autosampler vial. The five external standards and the samples to be analyzed can be loaded into the autosampler tray and the analysis begun.


Figure 1. A chromatogram of B100 shows the peaks for free and bound glycerin.

The biodiesel sample will provide a chromatogram that will appear much like the one shown in Figure 1. Peak identification algorithms built into the system's software show that the free glycerin is a single peak that elutes in about 4.5 minutes. The bound glycerides elute later and appear as three separate families of peaks. It is a good idea to compare the chromatogram from your sample to that generated from the external standards to be sure that the peaks of interest are eluding at the proper time.

At this point the software provided with the turnkey biodiesel GC system can become very helpful to identify the peak or peaks for each of these values and then calculate the concentration of each component based upon the intensity of the peak.

Free glycerin is quite easy to calculate since the GC is actually measuring glycerin itself, and the value determined by the GC can be directly reported as the free glycerin. The peaks used for bound glycerin determinations are actually peaks for various glycerides (monoglyceride, diglyceride and triglyceride), which are glycerin with additional hydrocarbon chains attached. ASTM D 6584 provides the factors needed to convert the values for glycerides in the accepted values for glycerin. The software contains these factors and automatically performs the calculation. The software then takes one more step as it adds the free glycerin value to those values calculated for the bound glycerin and determines a total glycerin value. Figure 2 is an example of a report of the values for free and bound glycerin.


Figure 2. A report generated from PerkinElmer's trademarked TotalChrom software shows the values for free glycerin (glycerin) and bound glycerin (total mono, total diglycerides and total triglycerides).

Laboratories interested in archiving their analyses or generating certificates of analysis will find that there are several new laboratory information management system products that serve this purpose very well. These biofuels-specific data handling packages can collect data from all instruments in the laboratory-either directly or indirectly-and can use those data to provide high-quality reports. As can be seen from the example of a report shown in Figure 3, complete data including the property, ASTM method (EN methods can also be entered), units, limit set by the method, and the standard range of the method can all be built into a report. The appropriate data from your laboratory can then be added alongside this information so that the reviewer will know at a glance how the sample results compare to the criteria set by the method.

Conclusion
Analyzing biodiesel for free and total glycerin in compliance with ASTM 6584 and EN 14105 methods is not a trivial undertaking. This task can be made much easier through the use of a turnkey GC biodiesel system that is preconfigured with all of the hardware and software needed to perform this analysis almost immediately upon installation. Ready-made standards can be commercially obtained which further reduces the complexity of the analysis. Once the analysis is performed, data from the GC, as well as data from other tests instruments, can be entered into the data handling software for data reporting and archiving.

For more information on preconfigured turnkey systems and laboratory information management system solutions tailored for the biofuels industry, visit www.perkinelmer.com/biofuels.

Dave Armstrong has global leadership responsibilities for the strategic marketing, planning and execution for the Hydrocarbon Processing, Biofuels and Semiconductor businesses for PerkinElmer Life and Analytical Sciences. Reach him at david.armstrong@perkinelmer.com. Tim Ruppel is the GC application specialist for PerkimElmer Life and Analytical Sciences.

The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of Biodiesel Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).