Thermal Desorption Technical Support Note 86a: US EPA Method TO-17 for Monitoring Air Toxics in Ambient Air Using Sorbent Tubes and Automated, Cryogen-free Thermal Desorption Application Note Environmental, Tube, TO-17, Air Monitoring Introduction Volatile (vapor-phase) organic air toxics or Hazardous Air Pollutants (HAPs) are monitored in many industrial and urban environments as a measure of air quality. They range in volatility from methyl chloride to hexachlorobutadiene and trichlorobenzenes, and include polar as well as nonpolar compounds. Several national and international standard methods have been developed for air toxics and related applications including US EPA Method TO-17 (Determination of volatile organic compounds in ambient air using active sampling onto sorbent tubes). In response to increasing demand for ambient air toxics measurement, cryogen free thermal desorber (TD) technologies have been developed, presenting an automated, method compliant analytical platform for both tubes and canisters (for US EPA Method TO-1, see TDTS 81). The latest systems typically feature innovations such as repeat analysis for tubes, together with internal standard addition options for both canister and tube operation. Description of the TD-GC/MS Analytical System The analytical system used for this study comprised a Markes International Series ULTRA-UNITY TD (Figure 1) coupled to a GC/MS. Using this TO-17 compliant system, the sorbent tubes were heated in a flow of carrier gas transferring the analytes to an electrically cooled, sorbent-packed focusing trap inside the UNITY. Figure 1. ULTRA-UNITY. Extensive evaluation work was carried out to determine the best combination of sorbents and trapping temperatures for the focusing trap. A combination of Tenax, Carbopack X and Carboxen sorbents held at a trapping temperature of C, was ultimately found to work best, offering both quantitative recovery of target compounds and selective elimination of water.
N.B. Quantitative recovery of compounds as volatile as propylene from purge volumes up to L has also been demonstrated using this trap under these focusing conditions. Once the process of transferring vapors from the sample/sorbent tube to the focusing trap was complete (primary desorption), the trap was purged with dry carrier gas in the sampling direction to remove residual water. Then, the flow of carrier gas was reversed, and the trap heated rapidly. The retained organics were desorbed into the carrier gas stream and transferred/injected into the GC analytical column. Desorption of a UNITY focusing trap is so efficient, that splitless analysis is possible without significant peak broadening; that is, all of the retained organics can be transferred to the analytical column in a narrow band of vapor, ensuring optimum sensitivity. Air sampling tubes Air Toxic Analyzer (ATA) tubes, packed with a combination of Carbograph 1TD and Carboxen, were used for most of this study. This sorbent combination has demonstrated quantitative retention of air toxics, including the most volatile target compounds, from over L* of air at C. Pumped air sampling flow rates were maintained at ml/min. Universal tubes packed with Tenax TA, Carbograph 1TD, and Carboxen were used for some experiments. Universal tubes limit retention volumes to 1 L for the most volatile air toxics, but facilitate analysis of labile monoterpenes such as D-limonene. *Note: Breakthrough volumes can be compromised by high humidity or elevated ambient temperatures. Analytical Conditions This project was carried out using an Agilent J&W DB 6 column and a mixed air toxic standard containing over 6 analytes, ranging in polarity and volatility. Sample preparation A 6 component 1 ppm gas standard in nitrogen, available from Markes International (p/n CGS1-1PPM), in combination with an air actuated 6-port Valco valve was used to inject 1 ml aliquots of standard gas, carried in pure nitrogen, into the sorbent tubes (Figure ). Parameter UNITY parameters Cold trap: Tubes: Value Cold trap low temperature: C Tube desorption temperature: C Tube desorption time: Trap purge time: Cold trap high temperature: Split ratio: Trap heating rate: Markes Air Toxic Analyser/Soil Gas trap (p/n U-T1ATA-S) Markes Air Toxic Analyser tubes (p/n C AXXX-7) Markes Universal stainless steel tubes (p/n C-AXXX-66) packed with a combination of Tenax, Carbograph 1TD and Carboxen minutes. minutes C for minutes splitless or :1 outlet split C/s TD flow path: C GC parameters Carrier gas: He Column: Agilent DB-6, 6 m. mm, 1.8 µm Constant pressure mode: Temperature program: MS conditions psi MS source temperature: C MS quadrupole temperature: C MSD transfer line temperature: C Full scan mode mass range: C ( minutes), C/min to C ( minutes) - amu 1 ml Standard loop 1 ml Standard loop Needle valve Needle valve Standard out Standard out Standard in Flow meter Carrier in Sample tube Stage 1: 1 ml loop filled with standard Standard in Flow meter Carrier in Sample tube Stage : Carrier flushes standard into the tube Figure. Apparatus for loading 1 ml aliquots of standard gas onto sorbent tubes in a stream of pure nitrogen.
Results and Discussion Figure A shows the chromatogram obtained for a sample equivalent to 1 L of 1 ppb standard analyzed splitless. Figure B shows the chromatogram obtained for a sample equivalent to 1 L of 1 ppb standard analyzed with a :1 outlet split. The peak at. minutes was due to SO released from the carbon molecular sieve sorbent used at the back of the sampling tubes. 8 6 8 6 18 16 1 1 8 6 1 SO 6 7 8 9 1,1 11 1,16 1 18,19 17, 6,7 1 8 9 1 8 6 7 9 1 6 Figure A. Sample equivalent to 1 L of a 1 ppb standard analyzed splitless using ATA tubes and an Agilent J&W DB-6 column. 8,9 7,1 6 8 7 1 9 6 61 6 6 8 8 61 6 6 8 SO 1 1,16 8,9 16 1 8 1 6 7 11 8 9 1,1 18,19 17 1,6,7 1 8 9 6 7 9 7 6 1,1 6 7 8 1 Figure B. Sample equivalent to 1 L of a 1 ppb standard analyzed with a :1 split using ATA tubes and an Agilent J&W DB-6 column. 9 6
Table 1. Elution order for the air toxics standard run on an Agilent J&W DB-6 column. 1. Propylene. Dichlorodifluoromethane. 1,-Dichlorotetrafluoroethane. Methyl chloride. Chloroethane 6. 1,-Butadiene 7. Vinyl chloride 8. Methyl bromide (bromomethane) 9. 1,-Dichloroethane. Trichlorotrifluoroethane (Freon 11) 11. Ethanol 1. 1,1-Dichloroethylene 1. 1,1,-Trichlorotrifluoroethane 1. Acetone 1. Carbon disulfide 16. Isopropyl alcohol 17. Methylene chloride 18. tert-butyl methyl ether 19. cis-1,-dichloroethylene. n-hexane 1. 1,1-Dichloroethane. Vinyl acetate. trans-1,-dichloroethylene. Methyl ethyl ketone. Ethyl acetate 6. Tetrahydrofuran 7. Chloroform 8. 1,1,1-Trichloroethane 9. Cyclohexane. Carbon tetrachloride 1. Benzene. n-heptane. Trichloroethylene. 1,-Dichloropropane. 1,-Dioxane 6. Bromodichloromethane 7. cis-1,-dichloropropene 8. Methyl isobutyl ketone 9. Toluene. trans-1,-dichloropropene 1. 1,1,-Trichloroethane. Tetrachloroethylene. Methyl n-butyl ketone. Dibromochloromethane. 1,-Dibromoethane 6. Chlorobenzene 7-) o-, m-, p-xylene + ethylbenzene 1 Styrene Tribromomethane 1,1,,-Tetrachloroethane. Trimethylbenzene. Trimethylbenzene 6. 1-Ethyl--methyl benzene 7. Dichlorobenzene 8. Dichlorobenzene 9. Chloromethylbenzene (alpha) 6. Dichlorobenzene 61. 1,,-Trichlorobenzene 6. Hexachloro-1,-butadiene 6 Original data 1 1 Figure. 1 L of a 1 ppb air toxics standard, as shown in Figure B. Note the minor baseline anomaly due to residual water early in the run and increasing column bleed and noise as the GC oven reaches its top temperature.
ClearView reprocessed data Note clean selected ion spectrum of Freon 11 (peak ) Original data S/N=1:1 S/N = :1 Minimum detection limits were found to be below.1 ppb for all 6 components tested under both :1 split and splitless conditions, assuming a minimum 1 L air/gas sample volume and full scan mode. Measurement at lower concentrations could readily be achieved using the MS in Selected Ion monitoring (SIM) mode. Linearity Figure 7 illustrates system linearity under splitless conditions with R values of.99 for trichlorotrifluoroethane (Freon 11), dichlorodifluoromethane, chloroform, bromodichloromethane, and hexachloro-1,-butadiene. Note higher interferences in original data Figure. Expanded portions of the air toxics standard analyzed split (Figures B and ). Trap desorption efficiency leads to good peak shape and optimum sensitivity. Trap performance in this case is best illustrated by a close-up of the results for the challenging polar compound isopropyl alcohol (IPA) (Figure 6). Peak area 7 8 7 6 1 Freon 11 Dichlorodifluoromethane Chloroform Bromodichloromethane 6 8 1 1 L ppb equivalents Figure 7. Linearity plots from 1 to ppb standards collected using ATA tubes, and analyzed splitless. 9. 9. 9. Figure 6. Peak shape for IPA at 1 ppb analyzed splitless using ATA tubes and extracted mass ion.
Carryover for 1 L of ppb standard analyzed splitless was less than.% (Figure 8). SecureTD-Q Quantitative recollection of split flow facilitates repeat analysis and validation of TO-17 method/data. The repeat analysis of a sample equivalent to 1 L of 1 ppb air toxics standard, split :1 (Figure 9), demonstrates quantitative recovery across the analyte volatility range. Six repeat analyses were carried out on samples equivalent to a 1 L volume of 1 ppb standard under splitless conditions. Table shows example % relative standard deviation (RSD) for eight compounds, covering the volatility and polarity range of the standard. Typical RSDs were less than 6%. 8 6 8 16 1 8 CO SO 1 Figure 8. Carryover (blue) <.% from 1 L 1 ppb standard (black) analyzed splitless using ATA tubes. CO SO Artifact Recollected (Secure TD) sample - - - - - Original sample 1 Figure 9. Recollection and repeat analysis results from a 1 ppb standard analyzed using ATA tubes and a :1 outlet split. 6
Table. System reproducibility demonstrated using eight compounds, covering a typical range of air toxic volatilities and polarities (n = 6). Conditions: ATA tubes, splitless. Compound Dichlorodifluoromethane.8 1,-Butadiene. Methylene chloride. Freon 11 1.8 Chloroform 1.8 Benzene 6. Toluene 1.7 Hexachloro-1,-butadiene.8 % RSD Real air samples Real air samples were collected onto Universal sorbent tubes. A FLEC pump was used to sample at a flow rate of ml/min for minutes giving a total volume of 1 L in each case. Three different ambient locations were sampled: office, laboratory, and semirural outside air. Each sample tube was analyzed splitless using a full scan MS method from - amu. The data were processed using ClearView and overlaid (Figure ). 1 6 7 8 9 1,11 1 11 16 17 18 19,1 Office air 6 Abundance 1 Laboratory air Semirural outside air 1 Figure. Chromatograms from three 1 L real air samples collected using Universal sorbent tubes and desorbed splitless. Table. Selected compounds detected from three real air samples, run splitless. 1. Methanol. -Methyl butane. Ethanol. Acetone. Isopropyl alcohol 6. -Methyl pentane 7. -Methyl pentane 8. Hexane 9. Ethyl acetate. -Methyl hexane 11. Cyclohexane 1. -Methyl hexane 1. Heptane 1. Acetic acid 1. 1-Methy--propanol 16. Toluene 17. Hexanal 18. Xylene 19. Xylene. alpha-pinene 1. Cyclohexanone. alpha-myrcene. D-Limonene. Phenol. Menthol 6. -Phenoxy ethanol 7
Conclusions These results clearly demonstrate the fundamental sensitivity of the series ULTRA-UNITY Air Toxics Analyzer configuration run with GC/MS. Quantitative detection of TO-17 air toxics ranging from methyl chloride to hexachloro-1,-butadiene has been demonstrated down to.1 ppb on sorbent tubes, and even lower levels would be possible using the MS in SIM mode or sampling larger air volumes. Applications were performed under the stated analytical conditions. Operation under different conditions, or with incompatible sample matrices, may impact the performance shown. Reference 1. E. Hunter Daughtrey, K. D. Oliver, J. R. Adams, K. G. Kronmiller, W. A. Lonneman, W. A. McClenny. A comparison of sampling and analysis methods for low ppbc levels of volatile organic compounds in ambient air. J. Environ. Monit. 1,, 166-17. For More Information These data represent typical results. For more information on our products and services, visit our Web site at www.agilent.com/chem. www.agilent.com/chem Agilent shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. Information, descriptions, and specifications in this publication are subject to change without notice. Agilent Technologies, Inc., 17 Printed in the USA July 6, 17 991-88EN