LCGC The Peak - July 2007 - (Page 18) 18 THE PEAK JULY 2007 Table II: GC conditions used in this study Gas Chromatograph: Headspace Connection Type: Analytical Column: Injector Temperature: Oven Program: Temperature 30 °C 100 °C 155 °C 240 °C Mass Spectrometer: GC Inlet Temperature: Ion Source Temperature: Function Type: Scan Range: Scan Time: Interscan Delay: Hold Time 0 min 0 min 0 min 2.06 min 250 °C 250 °C Full Scan m/z 35–300 0.2 s 0.1 s PerkinElmer Clarus 600 GC Direct Connection Elite 624 (20 m 0.18 mm 210 °C Rate 20 °C/min 30 °C/min 55 °C/min End 1.0 m) PerkinElmer Clarus 600 T MS allowing for even and consistent heating. The formula for determining the partition coefficient has the concentration of the liquid phase as the numerator and the concentration of the gas as the denominator; thus, the lower the partition coefficient, the less affinity the analytes have to the liquid phase (3). Most compounds in the Method 8260B list have very low partition coefficients, resulting in high gas-phase concentrations and great analytical results. Where purge-and-trap systems are constrained on compounds with poor purging efficiencies, headspace analysis can have an advantage. Two supplemental techniques assist in the analysis of difficult compounds heating and salting. A common example best demonstrates this: bromoform is a compound that has a poor purging efficiency. Many times, analysis with purge-and-trap will result in an initial calibration with a percent RSD close to 15%, while bromoform analysis by headspace trap with heated equilibration typically has a percent RSD of less than 5%, resulting from its low partition coefficient at elevated temperatures. Polar analytes often pose significant problems for volatile analysis; headspace trap allows the laboratory to employ the technique of salting to improve the partition of polar compounds. The user would add a small amount (1–2 g) of salt to each standard and sample. Salting increases the ionic potential of the sample, reducing the partition coefficient of polar analytes and forcing a greater concentration into the vapor phase. If salting is employed, it is necessary to salt both standards and samples so the change to the partition and the resulting detector response is consistent. Table of Contents for the Digital Edition of LCGC The Peak - July 2007 Contents ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 Industry News Events Education LCGC The Peak - July 2007 LCGC The Peak - July 2007 - (Page BB1) LCGC The Peak - July 2007 - (Page BB2) LCGC The Peak - July 2007 - (Page BB3) LCGC The Peak - July 2007 - (Page BB4) LCGC The Peak - July 2007 - (Page 1) LCGC The Peak - July 2007 - (Page 2) LCGC The Peak - July 2007 - (Page 3) LCGC The Peak - July 2007 - Contents (Page 4) LCGC The Peak - July 2007 - Contents (Page 5) LCGC The Peak - July 2007 - Contents (Page 6) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 7) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 8) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 9) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 10) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 11) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 12) LCGC The Peak - July 2007 - ESI-TOF Mass Spectrometry–Based Multitarget Compound Analysis for Comprehensive Quantitative Screening of Pesticides (Page 13) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 14) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 15) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 16) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 17) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 18) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 19) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 20) LCGC The Peak - July 2007 - Applying Novel Sample Introduction and Rapid GC Oven Cooling and Equilibration to Increase Throughput in Method 8260 (Page 21) LCGC The Peak - July 2007 - Industry News (Page 22) LCGC The Peak - July 2007 - Events (Page 23) LCGC The Peak - July 2007 - Events (Page 24) LCGC The Peak - July 2007 - Education (Page 25) LCGC The Peak - July 2007 - Education (Page 26) LCGC The Peak - July 2007 - Education (Page 27) http://www.nxtbookMEDIA.com
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