Review: Recovery of Oxygenated Ignitable Liquids by Zeolites

Emily C. Lennert, Candice Bridge, Ph.D.

Category: Fire Debris

Keywords: fire debris, ignitable liquid, extraction, oxygenate, zeolite, activated carbon, activated charcoal, alcohol, ethanol, methanol, isopropanol, 1-propanol,1-butanol, acetone, gasoline, diesel, fuel

Articles to be reviewed:

1. Pierre, K. A.; Desiderio, V. J.; Hall, A. B. “Recovery of oxygenated ignitable liquids by zeolites, Part I: Novel extraction methodology in fire debris analysis.” Forensic Science International. 2014, 240, 137–143.
2. Rodgers, C. L.; St. Pierre, K. A.; Hall, A. B. “Recovery of oxygenated ignitable liquids by zeolites, Part II: Dual-mode heated passive headspace extraction.” Forensic Science International. 2014, 240, 144–150.

Additional references:

1. American Society for Testing and Materials Method E 1618-14. “Standard Test Method for Ignitable Liquid Residues in Extracts from Fire Debris Samples by Gas Chromatography-Mass Spectrometry.” ASTM International, West Conshohocken, PA, 2014.
2. American Society for Testing and Materials Method E1412-16. “Standard Practice for Separation of Ignitable Liquid Residues from Fire Debris Samples by Passive Headspace Concentration With Activated Charcoal.” ASTM International, West Conshohocken, PA, 2016.

Disclaimer: The opinions expressed in this review are an interpretation of the research presented in the articles. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.

Summary: The review articles will be evaluated and presented together. ^{1, 2} Zeolites were evaluated for extraction of oxygenated ignitable liquids (ILs.) Alcohols, some lacquer thinners, some industrial solvents, and fuel additives, like ethanol, are examples of oxygenated ILs.

The classification of an IL as an oxygenate is defined in the American Society for Testing and Materials (ASTM) standard E1618.³ Oxygenated ILs are compounds containing oxygen and of low molecular weight. Activated carbon strips are a current standard method for extraction defined in ASTM E1412.⁴ Zeolites were compared to activated carbon strips, and both methods were tested by gas chromatography with mass spectrometry (GC-MS) according to ASTM E1618³ guidelines. Zeolites are highly stable, crystalline mineral structures with molecule sized pores, leading to large surface area for IL collection, similar to activated carbon. Compared to extraction by activated carbon strips, zeolites provided more complete extraction of individual oxygenated ILs. When tested in a 1:1 mixture of water and IL, the presence of water in the samples did not interfere with IL recovery. This is important to note; a fire doused with water will still have debris that can be analyzed for oxygenates with zeolites. A zeolite method was established using zeolite 13X: initial optimal extraction parameters were defined as a 4 hour extraction at 80°C.¹

Heavier hydrocarbon compounds, such as gasoline or diesel fuel, can prevent oxygenate recovery by activated carbon strips.^{2, 4} Oxygenates also evaporate quickly, so early recovery of fire debris and proper packaging are extremely important in oxygenate recovery. The following extractions were faster than the initial zeolite method, performed at 85-90˚C for 2 hours. Single-mode extractions, with either activated carbon strips or zeolites to extract various IL mixtures of oxygenates with gasoline or diesel fuel, were tested: activated carbon strips mostly recovered gasoline and diesel components, and zeolites mostly recovered oxygenates. Dual-mode extractions, where both activated carbon strips and zeolite packets were used simultaneously with IL mixtures of oxygenates and gasoline or diesel fuel, were tested: most recovery of diesel or gasoline components was achieved by activated carbon strips, while zeolites simultaneously recovered greater amounts of oxygenates. The results indicate that dual-mode extraction may be useful in targeted, simultaneous recovery of two distinct types of ILs, oxygenates and hydrocarbon based ILs. It is important to note that all dual-mode sample tests were performed on neat, unburned IL mixtures. Dual-mode data has not yet been presented for recovery of IL residues from burned samples.

Scientific Highlights:

• Zeolites successfully extracted more oxygenates than activated carbon strips alone.
• The zeolite method was created to complement the activated carbon strip method defined in ASTM E1412.⁴
• Zeolite 13X was chosen due to pore size; oxygenates targeted for extraction were less than 10 Å in size.¹
• Due to elution of zeolites by methanol, the method is not suitable for methanol detection.
• The first series of extractions were performed at 80˚C for 4 hours.¹ In the second series, extractions of oxygenates and diesel fuel or gasoline were performed at 85-90˚C for 2 hours.²

Relevance: The research presented in the above articles provides a complementary technique for current methods in IL recovery which will improve recovery of oxygenated ILs in samples of mixed composition and will mitigate the risk of incorrectly concluding that oxygenated compounds are not present in an unknown sample.

Potential conclusions:

• Zeolites provide more complete extraction of oxygenated ILs than activated carbon strips.
• Extraction of multiple classes of ILs by activated carbon strips alone may lead an investigator to incorrectly conclude that no oxygenates were present if heavier ILs were extracted and displaced the oxygenates.
• A dual-mode extraction, which uses activated carbon strips, mirroring ASTM E1412⁴ guidelines, and uses zeolites to complement the activated carbon strips, will lead to better recovery if a several classifications of ILs are present, and may eliminate the risks of displacing oxygenated ILs during extraction.