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How to Calculate Ethylene Oxide Residual Levels

Medical devices and laboratory equipment undergo sterilization using ethylene oxide. Analysis of ethylene oxide residues on the equipment must be conducted, and residual levels must be within the allowable limits in regard to ISO standards from the Occupational Health and Safety Administration (OSHA), before the equipment can be used. Several laboratory procedures can be conducted to obtain residual numbers, such as gas chromatography, exhaustive extraction, or water extractions for exhaustive analysis. A calibration curve is created from the laboratory methods, and a calculation is used to find the amount of ethylene oxide per sample.

Things You'll Need

Laboratory procedure for Ethylene Oxide Residual Analysis

Instructions

Calculate Ethylene Oxide Residuals
- 1
  Perform the ethylene oxide residual procedure in your laboratory, whether using a gas chromatography method or extraction method. Follow all procedures as needed and consult laboratory manual if necessary.
- 2
  Create a calibration curve to obtain the amount of analyte of ethylene oxide per sample. The calibration curve should have the mass per sample, in micrograms, on the x-axis and the area counts, in microliters per second, on the y-axis. Record all necessary measurements for weight of sample, volume of air sampled and extraction efficiency.
- 3
  Calculate the concentration of ethylene oxide by weight in the sample. Write the equation, CM = M/VEE. CM represents the concentration by weight in milligrams per meters cubed (mg/m3) . M represents micrograms per sample. V is the amount of liters of air sampled and EE is the extraction efficiency in decimal form. Enter numbers as needed and calculate the concentration.
- 4
  Calculate the concentration of ethylene oxide by volume in the sample. Write the equation, CV = (VM)(CM)/Mr. CM represents the concentration by volume in parts per million (ppm). VM is 24.46, which is the molar volume at NTP. CM is concentration by weight in milligrams per meters cubed (mg/m3). Mr is the molecular weight of ethylene oxide, which is equal to 44.05. Enter numbers as needed and calculate the concentration.

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