Analysis of Ethylene Oxide by US EPA Method 327 Using Nutech 8910 Precentration System

Abstract

Ethylene oxide is known to be a toxic and carcinogenic compound present in ambient air. It is also released from certain industrial processes and hospital sterilization facilities. The U.S. EPA developed EPA Method 327 to address the analysis of ethylene oxide in ambient air, including monitoring at fenceline areas and within nearby communities. This article outlines a rapid detection method for ethylene oxide in ambient air, as well as in fenceline areas or unregulated emissions from the mentioned sources. The method employs canister sampling and Nutech 8910 pre-concentration technology combined with GC-MS for analysis. This rapid method can complete the analysis of ethylene oxide samples within 20 minutes. Results demonstrate that, with a 300 ml sample injection, the detection limit for ethylene oxide can reach as low as 10 ppt. The precision of the method ranges from 3.75% to 4.43%, with a calibration linearity between 0.05 ppb and 5 ppb and an RSD of 5.29%. The spiked sample recovery rate ranges from 95.70% to 101.36%, and the method blank is below the MDL. Using the Nutech 8910 with GC-MS for rapid analysis of ethylene oxide meets the requirements of both EPA Method 327 and EPA TO-15A.

Introduction

Ethylene oxide is a synthetic compound produced through the catalytic oxidation of ethylene and cannot occur naturally. It is a broad-spectrum, highly effective gas disinfectant, widely used in medical disinfection and industrial sterilization. While ethylene oxide does not naturally exist in the environment, low levels of it may be detected in industrial areas or near medical facilities that use it as a disinfectant. The International Agency for Research on Cancer (IARC), part of the World Health Organization, has classified ethylene oxide as a carcinogen. Long-term exposure to ethylene oxide can lead to breast cancer, leukemia, and lymphoma.

Historically, the detection of ethylene oxide has focused on residual levels in disinfected items, raw materials, or concentrations in the air at production sites, with less emphasis on detecting ethylene oxide in ambient air. Existing detection methods suffer from low accuracy and insufficient sensitivity, failing to meet regulatory requirements. The U.S. EPA’s TO-15A method introduces pre-concentration technology combined with GC-MS for ethylene oxide detection. However, challenges remain, such as background contamination from canisters, unclean sampling trains, and detection limits that do not meet the necessary standards. EPA Method 327 provides new guidelines for the analysis of ethylene oxide using pre-concentration technology with a GC-MS system, including updated QA/QC controls and testing procedures.

This article presents the development of a rapid method for detecting ethylene oxide using pre-concentration technology with GC-MS, following EPA Method 327. Improvements were made to the sampling train, canisters, pre-concentration techniques, and GC-MS conditions to enhance the results. The study demonstrates that using the Nutech 2703 sampling train and improved silica-coated canisters, followed by analysis with the Nutech 8910 pre-concentration system and GC-MS, enables reliable detection of ethylene oxide according to EPA Method 327. All QA/QC requirements outlined in EPA Method 327 were successfully met.

1. Experiment

1.1 Instrument Configuration (As shown below)

• Pre-concentration System: Nutech 8910/3610 Preconcentrator with Autosampler, Nutech 2208 Static Dilutor, Nutech 2104 Canister Cleaning System, and 6 L Silica-Coated Canisters.
• GC/MS: Thermo Scientific Trace 1300 GC / ISQ7000 MS

1.2 Standard Gases

All standard gases were sourced from Linde, except for ethylene oxide.

1.2.1 VOC Standards

• 65 Compounds TO-15 Standard: Concentration: 1.00 ppm (for separation purposes).
• Ethylene Oxide Standard: Concentration: 1.00 ppm, supplied by Sichuan Zhongce Standard Material Technology Co., Ltd.

1.2.2 Internal Standard/Surrogate Standard

• Internal Standards: Bromochloromethane, 1,4-Difluorobenzene, Chlorobenzene-d5, 4-Bromofluorobenzene

1.3 Preparation of Working Standards

Connect two high-concentration standards and a certified clean 6-liter silica-coated canister to the Nutech 2208. Set up working standards at concentrations of 0.5 ppb and 5 ppb. Follow the same procedure for the internal/surrogate standards but prepare them at a concentration of 1.0 ppb. The canisters were humidified to 20% relative humidity.

1.4 Instrument Parameters

1.4.1 Nutech 8910 Method Settings:

• Trap 1: -10°C
• Trap 2: -50°C
• Transfer from Trap 1 to Trap 2: 10°C
• Trap 2 Desorption Temperature: 235°C
• Focuser: -120°C
• Focuser Injection Time: 20 seconds
• Transfer Line: Room temperature

1.4.2 Thermo Scientific Trace 1300 GC Settings:

• Injection Temperature: 140°C
• Injection Mode: Split/Splitless
• Column: Agilent Technologies DB-624UI, 60 m × 0.25 mm × 1.4 µm
• Temperature Program:
  • Start at -40°C (hold for 5 min)
  • Ramp at 100°C/min to 220°C (hold for 7 min)
• Carrier Gas: Constant flow at 1.0 ml/min

1.4.3 Thermo Scientific ISQ7000 MS Settings:

• Ion Source Temperature: 300°C
• Transfer Line Temperature: 260°C
• Scan Mode: SIM
• SIM Ions (amu): 29, 44, 94, 96, 95, 128, 130

1.5 Initial Calibration Loading Volume

Using the Nutech 8910/3610, load volumes of 30 ml, 60 ml, 150 ml, and 300 ml of the working standard with a concentration of 0.5 nmol/mol, as well as 60 ml, 150 ml, and 300 ml of the working standard with a concentration of 5.0 nmol/mol. The basic volume is set to 300 ml.

The corresponding concentrations will be: 0.05 ppb, 0.1 ppb, 0.25 ppb, 0.5 ppb, 1.0 ppb, 2.5 ppb, and 5.0 ppb. The calibration curve will be plotted as concentration (ppb) versus response (peak area). The internal/surrogate standard is loaded at 30 ml with a concentration of 1.0 ppb.

2. Results

2.1 Ethylene Oxide Mixed with TO-15 Compounds Chromatography

From the four chromatograms obtained, the following observations were made:

a. The total run time is as short as 14 minutes. All high-boiling-point compounds in ambient air are fully eluted by the end of this run time. The last TO-15 compound, hexachlorobutadiene, is eluted at 13.2 minutes, while ethylene oxide is retained at 5.91 minutes.

b. The retention time of acetaldehyde is distinct from that of ethylene oxide. Trans-2-butene and chloroethane are well separated, appearing before and after ethylene oxide, respectively. Bromomethane coelutes with ethylene oxide but can be distinguished due to differing MS ions. Bromomethane has m/z 94 and 96, whereas ethylene oxide has m/z 44 and 29.

c. CO2, present in ambient air, is eluted early in the run and can be effectively managed by adjusting the scan delay.

2.2 Initial Calibration (ICAL)

An initial calibration was performed using ethylene oxide concentrations of 0.05 ppb, 0.1 ppb, 0.25 ppb, 0.5 ppb, 1.0 ppb, 2.5 ppb, and 5.0 ppb, establishing a linear range of 1:100. Bromochloromethane was used as the internal standard (IS). The calibration data for ethylene oxide are shown below:

2.3 Continuing Calibration Verification (CCV)

For the CCV, a 5 ppb working standard was used, with a 60 ml sample resulting in a concentration of 1.0 ppb. The CCV results are shown in the following table:

2.4 Blank Spike Recovery % (Accuracy %)

A blank spike evaluation was conducted by spiking 0.5 ppb of ethylene oxide into a canister. The recovery results are shown below:

2.5 Replicates

Replicate analyses were performed at concentrations of 0.5 ppb and 2.5 ppb across seven data points. The results showed that the RSD% for most compounds was less than 10%.

2.5.1 Replicate Data (0.5 ppb Level)

2.5.2 Replicate Data (2.5 ppb Level)

2.6 Method Detection Limit (MDL) Study

The MDL for ethylene oxide was determined to be 4.0 pptv. Taking into consideration a 10 ppt standard, the signal-to-noise ratio, method blank, and canister blank, the combined MDL was determined to be 10 ppt.

2.7 Blank Analysis

After analyzing a 300 ml sample of 5 ppb standard gas, a 300 ml nitrogen blank was immediately loaded and analyzed. No compounds were detected above the MDL. The blank chromatogram is shown below.

3. Conclusion

The Nutech 8910 pre-concentration system, combined with GC/MS SIM technology, successfully detects ethylene oxide with a run time of 15–20 minutes. The certification of the sampling train (details provided in a separate appendix), initial calibration, continuing calibration verification, method blanks, second-source standard spike verification, MDL, and all other QA/QC data meet the requirements of EPA Method 327.