The Aberdeen Chemical Agent Neutralization Facility (ACANF) was designed to neutralize the chemical warfare agent HD (mustard) which is stockpiled in bulk quantities at the Aberdeen Proving Ground (APG), Maryland. The facility was constructed at the Aberdeen Proving Ground (APG) located adjacent to the Town of Edgewood in Hartford Harford County, Maryland approximately 21 miles northeast of Baltimore on the Gunpowder Peninsula. The selected process is the hydrolysis of HD in water at low temperature (<200oF) and low pressure (<20 psig) to produce reaction products which are biodegradable, and can be readily made to meet all applicable regulatory requirements. This process eliminates almost all airborne emissions and produces biomass which can be disposed of with minimal risk to public safety.
HD is a purified mustard agent, Bis(2-chloroethyl) sulfide (ClCH2CH2)2S, which is classified as a persistent blister agent. Mustard has been identified as a carcinogen. Blister agents (also called vesicants) are systemic poisons, attacking the eyes and lungs and blistering the skin with either liquid or vapor contact. Most blister agents cause little or no pain on contact. Symptoms of exposure do not usually appear for several hours. HD is an amber to dark brown liquid with a garlic-like odor. Hazards from mustard are through vapor contact with eyes or the respiratory tract and liquid contact on skin. Mustard vapor may be absorbed through the respiratory tract and eyes or may be ingested through the gastrointestinal tract.
Air emission limits for both worker safety and for discharge have been set by the U.S. Department of Health and Human Services (DHHS). Workplace exposure time-weighted average (TWA) limits are based on an 8-hour day, 40-hour work week, and are established as 0.003 mg/m3 for HD. Although the Surgeon General has set these limits with certainty that exposure will not result in adverse health effects, the limits are based on the best available technology for monitoring, given the carcinogenic properties of HD. A 72-hour General Population Level (GPL) is defined as 0.0001 mg/m3 for HD. At this level, unprotected, continuous exposure will not result in adverse health effects over a 70-year lifetime.
The HD monitoring system largely relies upon DAAMS analysis to provide a record of agent vapor level in plant areas and at the facility perimeter. The DAAMS analysis involves the collection of an air sample on sorbent (Tenax) tubes for a predetermined sampling time and rate. At the conclusion of the sampling, the tubes are removed and taken to the laboratory for analysis by GC/FPD and/or GC/MSD.
GC/FPD and GC/MS analysis requires calibration of analytical instrumentation using known and verified standard solutions of HD, followed by analysis of sorbent tube samples. Reported results are obtained through the development of a calibration curve from analysis of the known standards, followed by correlating the instrument response to plant samples with the curve generated to determine quantitative results.
On a recent site visit to Aberdeen, CDC representatives reviewed the air monitoring systems and obtained the following calibration data from a GC/MS analysis calibration:
Calibration Amount Injected
Instrument Response (Ion count at 158 mass to charge ratio)
Questions:
1. Draw the structure for the HD ion with a 158 mass to charge ratio (remember the isotopes of Cl) and clearly support your answer.
2. Use the above calibration data to conduct a linear regression of calibration data and to generate a plot clearly showing the calibration points and the regression line. Also clearly shown the calibration equation for these data.
3. A quality control sample was spiked with a known amount of HD; the resulting GC/MS response (ion count at 158) was 188,470 ion counts. Calculate the amount of HD in ng that the Aberdeen laboratory should have reported for this analysis. Also calculate the uncertainty in your answer using propagation of error techniques that account for uncertainties in slopes, intercepts, and y values.
4. If the known quality control sample amount was 6.0 ng, calculate the percent error associated with the analysis.
5. Calculate the ng of HD collected on the sorbent tube that would correspond to the DHHS established air monitoring TWA concentration of 0.003 mg/m3 and that would correspond to the GPL concentration of 0.0001 mg/m3 for HD; assume that for both TWA and GPL samples, sorbent tubes sample plant or outside air for 8 hours at a time at flow rates of 60 mL / min.
6. Based upon your two answers in the above question, comment
on the appropriateness of the above calibration curve to analyze sorbent
tubes that monitor TWA concentrations and comment on the appropriateness
of the curve to analyze sorbent tubes that monitor GPL concentrations.