Accurate environmental testing for petroleum hydrocarbons is essential, particularly when utilizing EPH (Extractable Petroleum Hydrocarbons) Fractionation. This analytical technique divides petroleum hydrocarbons into distinct fractions, aliphatic and aromatic, for use in risk assessments and to meet regulatory standards. However, like any highly sensitive analytical method, EPH fractionation is vulnerable to contamination, which can distort results, trigger false positives, cause compliance challenges, or require costly reanalysis. Managing EPH contamination presents real challenges, but there are proven steps to minimize the risk. In this blog, we’ll break down the most common sources of contamination during EPH fractionation and share effective ways to prevent them from appearing in your data.
Before diving into contamination sources, let’s clarify how contamination is introduced during EPH testing. Contamination is anything that causes reported hydrocarbon levels to not accurately reflect what’s truly present in the sample. In other words, EPH contamination is the introduction of unwanted hydrocarbons from external sources. Those hydrocarbons can come from various points in the workflow, with the most common sources being sampling, storage, and preparation/laboratory analysis. Let’s break each of these down individually and discuss ways to prevent cross-contamination with your EPH samples.
Controlling EPH contamination begins at the very first step. Proper sample collection and management are crucial to deliver a contaminant-free sample to the lab for analysis. Never handle samples with bare hands, as the natural oils and lotions can inadvertently introduce hydrocarbons. Make sure your nitrile gloves are powder-free, clean, and are free from any oils or residual petroleum products before handling samples. Any visibly soiled gloves should be immediately replaced and discarded.
Pre-cleaned amber glass containers should be used to collect all samples. Samples should never be collected in plastic containers unless they are certified to be contaminant free. Standard plastic containers can leach hydrocarbons into your sample, potentially trigger false positives or further enhance results. To assist in collection, use only tools made of Teflon, glass, or stainless steel, and ensure that the tools are cleaned thoroughly between uses using solvents like methanol or hexane followed by rinsing with DI water. After collecting, ensure samples are properly sealed to prevent aerosol contamination from vapors. Once samples arrive at the laboratory, they should be analyzed as soon as possible and kept refrigerated to slow down any chemical reactions that may occur.
When analyzing EPH samples, it’s important to use high purity solvents such as GC or pesticide-grade, and confirm the cleanliness of each new lot by running them as blanks. It is good practice to clean and bake all glassware used in the extraction process at a minimum of 400°C to remove any contaminants from manufacturing or handling. When possible, conduct all extractions and fractionations in a fume hood or an area with minimal potential for aerosol contamination. As with sampling, laboratory personnel should avoid hand creams, lotions, or petroleum-based perfumes and wear powder-free nitrile gloves when processing samples.
Considering all these variables, the best sample preparation methods minimize human interaction and variables. That’s where automation is beneficial. When it comes to EPH Fractionation the Biotage® Extrahera™ Classic is an effective, high-throughput platform capable of processing up to 48 samples in less than 2 hours. The automated pipetting reduces human interaction with the samples and robotic pipetting ensures consistent delivery of correct sample and solvent volume. Although the pipetting tips are plastic, an added feature on the Biotage® Extrahera™ is the use of tip rinsing with solvent prior to sample loading. Tip rinsing removes leachable hydrocarbon contaminants from the plastic sample and solvent tips. With this innovative approach, the Biotage® Extrahera™ system can meet method blank criteria even for reduced sample volume applications.
Table 1 below shows the aliphatic results of hexane solvent blanks that were run on the Biotage® Extrahera™ compared to LC Fractionation Systems. The Fractionation system featured Teflon tubing to give Non-Detect (N.D.) values. Tip rinsing allowed the blanks to have values that were all less than 0.08 ppm, even when the sample volumes were reduced, which further enhances background levels.
Table 1: Comparison of four system blanks using the Biotage® Extrahera™ (SPE-SB#1-4) against Teflon plumbed LC fractionators. Data shows that tip rinsing brings background contamination levels down to acceptable levels. Values in (mg/L, ppm).
For the analysis by Gas Chromatography - Flame Ionization Detection (GC-FID), proper maintenance should be conducted to help prevent carryover between samples. Check injection syringes regularly, and clean or replace them when necessary. Always use the highest purity of solvents that are minimally HPLC grade or higher. Injection of solvent blanks is a common way to monitor background levels of the GC-FID.
Any noticeable signs of septa bleed should be addressed promptly. Septa bleed can originate from either the inlet septum or the vial cap septum and can be readily identified in the GC chromatograms as it shows up as a series of sharp, repetitive peaks, often seen at higher temperatures. Figure 1 below demonstrates a typical septa bleed pattern. The bleed in this chromatogram can impact your background contamination and cause false positives in your results.
Figure 1: Sharp, repetitive peaks in a GC chromatogram indicating the presence of septa bleed.1
EPH contamination isn’t always noticeable until it’s too late, but there are steps that can be taken to minimize the risks. Understanding where contamination can be introduced (during sampling, storage, preparation, and analysis) is important. Knowing the potential hazards and how to approach them can make the difference between routine laboratory analysis and a time-consuming scavenger hunt.
To learn more about SPE automation for EPH fractionation read our application note here!
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