Optimizing the Analysis of Volatile Organic Compounds

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46 www.restekcorp.com Importance of Resolution in GC Analysis Figure 43 shows the effects of resolution on quantification for methylene chloride and Freon ® 113 (1,1,2-trichloro-1,2,2-trifluororoethane) when separated on an Rtx ® -VRX column. The first three replicates are check standards analyzed on a six-point curve. These values are taken from integrating the areas for the two closely eluting peaks. Based on peak height (the methylene chloride peak is about twice the height of the Freon ® 113 peak), the contribution of the first peak, methylene chloride, to the Freon ® 113 peak is more than twice the contribution of Freon ® 113 to the methylene chloride peak. Both compounds are quantified from the ELCD, creating another quantification issue with tailing peaks: the tail of the methylene chloride peak contributes to the area of the Freon ® 113 peak, thereby increasing the quantification error. Next, we analyzed methylene chloride and Freon ® 113 separately, to determine if there would be quantification differences off the six-point curve. With the addition of the peak tail, the peak area for methylene chloride increased slightly, and the peak area for Freon ® 113 decreased. Without the contribution from methlyene chloride, Freon ® 113 exhibited a noticeably lower quantification value of 16ppb. This experiment illustrates the importance of resolution for accurate quantification of analytes in environmental samples taken from the field. Obviously, no column can provide baseline separation of all Method 502.2/8021 compounds. The key to accurate quantification is to recognize which compounds are most commonly present in your samples and choose a column that best resolves these analytes. As shown in the example described above, both the Rtx ® -VRX column and the Rtx ® -VGC column have difficulty resolving methylene chloride from Freon ® 113. Figure 43. Peak shape affects quantification: separation of methylene chloride and Freon ® 113 on a “VRX” column. 4.5 4.57 4.66 Quantification Values Methylene Chloride & Freon ® 113 Replicate 1 19.85 18.48 Replicate 2 19.29 18.48 Replicate 3 19.36 18.52 Methylene Chloride Replicate 1 21.48 Replicate 2 20.79 Replicate 3 20.95 Freon ® 113 Replicate 1 16.3 Replicate 2 16.46 Replicate 3 16.25 Results of resolution tests @ 20ppb. 20ppb each component in 5mL RO water, analyzed according to US EPA Method 5030A/502.2.
Purge and Trap Applications Using PID/FID in Tandem: EPA Method 602 and Others; State Gasoline Methods EPA Methods 602, 8015, 8020, and 8260 describe analyses of gasoline and oxygenates. Most environmental laboratories have relied on one of these methods to report gasoline and oxygenate concentrations in difficult sample matrixes. Success with these methods is based on the ability of the capillary column to resolve close-eluting pairs. An analysis according to Method 8015, for example, involves separating ethylbenzene from m/p-xylene (Figure 44). Figure 44. An Rtx ® -VGC column separates ethylbenzene from m/p-xylene, according to EPA method 8015. 1. benzene 2. toluene 3. ethylbenzene 4. m-xylene 5. p-xylene 6. o-xylene 7. isopropylbenzene 8. ethylmethylbenzene 9. 1,2,3-trimethylbenzene 10. 1,2,4-trimethylbenzene 11. napthalene 12. 2-methylnapthalene 13. 1-methylnapthalene GC_EV00467 Rtx fi -VGC 30m, 0.45mm, 2.55 m (cat.# 19408) 500ppb in 5mL of RO water Oven program: 40 C (hold 2 min.) to 130 C @ 6 C/min. (hold 0 min.) to 230 C @ 30 C/min. (hold 2 min.) Carrier gas: helium @ ~8mL/min. Detector: Thermo Finnigan PID, make-up 7mL min., purge 7mL/min., set @ 0.35mV, base temperature 200 C 47 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 and 26: FID Operation The flame ionization
Page 27 and 28: Figure 22. Cross-section of the The
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: Figure 42B. An Rtx ® -VGC / Rtx ®
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

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