Optimizing the Analysis of Volatile Organic Compounds

More documents

Recommendations

Info

26 www.restekcorp.com FID Maintenance and Troubleshooting: Contamination and a clogged jet are common problems associated with using an FID in analyses of volatile compounds, such as gasoline range organics (GRO) analyses that involve samples containing diesel fuel or oils. Flameouts at the beginning of a VOCs analysis usually are the combined result of incorrect gas flows and excessive water from the purge trap. When performing maintenance on an FID always check the gas flows before calibrating the instrument. Water management is discussed on page 13. ELCD (Hall ® detector) Operation In typical applications, an electrolytic conductivity detector, ELCD (Figure 21), is a chemical detector that catalytically reduces halogenated materials to haloacids, HCl and HBr, by mixing them with high-temperature hydrogen in a heated nickel reaction tube. In other words, this detector pyrolyzes these analytes in the presence of a catalyst and a reaction gas (hydrogen): H2 + CH3(CH2)nCH2R (heat and catalyst) –> CH3(CH2)nCH3 + RH where R=halogen (Br or Cl) Example: H2 + CH3Cl –> CH4+HCl The haloacid molecules flow into the electrolytic conductivity cell via a PTFE transfer line, and are dissolved in a stream of n-propanol. The conductivity of the alcohol is monitored because the concentration of hydrogen halide is directly proportional to the current. The signals thus produced characteristically have tailing peaks. Although the ELCD is most commonly used for halogenated compounds and, in the halogen mode, it is selective only for these species (Figure 21), it can be configured to detect sulfur, nitrogen, and nitrosamine compounds. Figures 22-25 and Figure 27 show various important parts of the ELCD system. Figure 21. ELCD configured for detecting halogens. TFE Transfer Line Reactor Reaction Tube Reaction Gas Vent Solvent Exit Silicone “O” Ring PTFE Seal Signal Out Cell Excitation Voltage Solvent In Conductivity Cell Outer Electrode Inner Electrode Tube Nut Gas Effluent from Reactor Outer Electrode Cell Body Insulator Inner Electrode Cell Cap Wave Spring Courtesy of Thermo Finnigan
Figure 22. Cross-section of the Thermo Finnigan PID/ELCD Solvent In He Vent Make-Up Gas Figure 23. Electrolytic conductivity detector: top view Drain Line PID Propanol Reactor H2 Conductivity Cell PTFE Transfer Line Reactor Capillary Column Reaction Tube Lamp Conductivity Cell Outer Electrode Inner Electrode Solvent Exit Courtesy of Thermo Finnigan Figure 24. Side view of the tandem detectors. Reactor ~900°C Propanol Vapors Out CH4, HCl, Hxr, He, H2 Resin Cleaned Propanol Stringently cleaned with HCl. Convenient precut pieces. Fit Tracor, Tremetics, O.I., many other ELCDs. 27 PTFE Transfer Lines for ELCDs Description cat.# PTFE Transfer Lines for ELCDs (five 6.5-inch lines), 5-pk. 20121 Chromatographic Detectors: Design, Function, and Operation Comprehensively covers the design, construction, and operation of gas chromatography, liquid chromatography and thin-layer chromatography detectors—all in one convenient, up-to-date source. R.P.W. Scott, Marcell Dekker, Inc., 1996, 514pp., ISBN 0-8247-9779-5 cat.# 21090 www.restekcorp.com
Page 1 and 2: Optimizing the Analysis of Volatile
Page 3 and 4: EPA Method Definitions Many EPA met
Page 5 and 6: Table I. State gasoline methods inc
Page 7 and 8: Purge and Trap Theory Concentration
Page 9 and 10: Step 5. Desorb Once the desorb preh
Page 11 and 12: Adsorbent Materials Tenax ® Adsorb
Page 13 and 14: Table II. Compositions and characte
Page 15 and 16: Troubleshooting Common Problems Ass
Page 17 and 18: Broad Peaks: Peak broadening is ano
Page 19 and 20: Figure 14. Configuring your GC is s
Page 21 and 22: Narrow-bore Systems (0.18mm ID - 0.
Page 23 and 24: Detection Systems VOCs can be analy
Page 25: FID Operation The flame ionization
Page 29 and 30: Similarly, the PTFE transfer line b
Page 31 and 32: Figure 29. Electromagnetic fields f
Page 33 and 34: Abundance 320000 280000 240000 2000
Page 35 and 36: Connect the capillary column, 0.25m
Page 37 and 38: Applications Using GC Detection Sys
Page 39 and 40: Figure 39B. An Rtx ® -VGC primary
Page 41 and 42: Rtx ® -502.2 75m, 0.45mm ID, 2.55
Page 43 and 44: Figure 41B. Analytes listed in EPA
Page 45 and 46: Figure 42B. An Rtx ® -VGC / Rtx ®
Page 47 and 48: Purge and Trap Applications Using P
Page 49 and 50: Gasoline Analysis with Oxygenates a
Page 51 and 52: Figure 47. Volatile organics by US
Page 53 and 54: 1. dichlorodifluoromethane 2. chlor
Page 55 and 56: 1. chloromethane 2. vinyl chloride
Page 57 and 58: Table IX Volatile organic compounds
Page 59 and 60: Table XI. Choosing a Volatiles GC C
Page 61 and 62: Ordering Information | Rtx ® Rtx -
Page 63 and 64: Siltek -Deactivated Guard Columns/
Page 65 and 66: Leak Detective II Leak Detector Af
Page 67 and 68: Method 8260 8260 Internal Standard
Page 69 and 70: 8021/502.2 Surrogate Mix #1 1-bromo
Page 71 and 72: 04.2 & 04.1 SOW CLP 04.1 VOA CAL200

Optimizing the Analysis of Volatile Organic Compounds

Create successful ePaper yourself

Delete template?

Save as template?