PAH Induction upon Pyrolysis of Hydroxyl-Terminated Polybutadiene-Based Solid Rocket Fuels

During the manufacture of pharmaceuticals, <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=45&amp;search=1%2C+4-Dioxane">1, 4-Dioxane</a> is used as a cleansing agent. It is also a byproduct of plastic manufacturing. The most likely exposure to 1, 4-Dioxane is at an industrial site. However, if any 1, 4-Dioxane is released into the environment during manufacturing there is a potential for it to migrate into ground water. The fact that 1, 4-Dioxane is so miscible in water makes degradation of the chemical challenging. Ethanol, on the other hand, has been a popular gasoline additive. Since it burns more quickly and completely than gasoline, emissions from car exhaust are decreased. The downside of this is underground storage tank leakage and fuel spills cause ground water and drinking water to be contaminated with both the fuel and the ethanol additive. Since ethanol is also very miscible in water, the detection of ethanol contamination in water can be difficult.&nbsp;There have been several innovations that help overcome the obstacles of detecting 1, 4-Dioxane and Ethanol. The first one is the SIM mode of the mass spectrometer. This mode allows better detection of hard to extract compounds. Furthermore, mass spectrometers are now equipped to run SIM/Scan, this not only helps detect more difficult compounds, but also enables the detection of an extensive list of <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=45&amp;search=USEPA+Method+8260">USEPA Method 8260</a> compounds without having to run the samples twice. Advancements in purge and trap sampling have also facilitated better detection of these compounds. Most effective in this has been the ability to heat the samples. However, there are drawbacks to better detection. The most problematic of these is the tendency of 1, 4-Dioxane and Ethanol to “stick” to the glass ware. This susceptibility has caused many headaches in environmental labs.&nbsp;This application note will investigate seven variations of <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=45&amp;search=purge+and+trap">purge and trap</a> sampling. The data will then be evaluated in order to recommend the optimum purge and trap sampling parameters for your lab.<h4>Experimental:&nbsp;</h4>The sampling system used for this study was the <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/products/2160">EST Analytical Evolution concentrator</a> affixed with a Vocarb 3000 trap. The <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/products/2159">Centurion WS autosampler</a> equipped with the syringe option was employed as the autosampler. The separation and analysis were performed by an <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=10&amp;search=7890A+Gas+Chromatograph">Agilent 7890A Gas Chromatograph (GC)</a> and <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=10&amp;search=5975C+Mass+Spectrometer">5975C inert XL Mass Spectrometer (MS).</a> The GC was configured with a <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=7&amp;search=Rxi-624+Sil+MS">Restek Rxi-624 Sil MS</a> 30m x 0.25mm x 1.4µm column. The purge and trap and GC/MS parameters used for this study are listed below.<h5>Purge and Trap Parameters</h5><ul><li>Concentrator: EST Encon Evolution</li><li>Trap type: Vocarb 3000</li><li>Valve oven temperature: 150 °C</li><li>Transfer line temperature: 150 °C</li><li>Trap temperature: 35 °C</li><li>Moisture Reduction Trap (MoRT) temperature: 39 °C</li><li>Purge time: 11 min</li><li>Purge flow: 40 mL/min</li><li>Dry purge: Ambient temperature, 40 mL/min, 1.0 min</li><li>Desorb pressure: 5 psi (with control ON)</li><li>Desorb time: 0.5 min</li><li>Desorb preheat delay: 10 sec</li><li>Desorb temperature: 250 °C</li><li>MoRT bake temperature: 210 °C</li><li>Bake temperature: 260 °C</li><li>Sparge vessel bake temperature: 40 °C for 3 min, ramp to 100–110 °C, hold</li><li>Bake time: 6 min</li><li>Bake flow: 85 mL/min</li></ul><h5>Auto-Sampler (EST Centurion WS):</h5><ul><li>Sample type: Water</li><li>Sample volume: 5 or 10 mL</li><li>Internal standard volume: 5 µL</li></ul><h5>GC/MS Parameters</h5><ul><li>System: Agilent 7890A GC / 5975C inert XL MS</li><li>Inlet: Split mode, 220 °C, 40:1 split ratio, 12.153 psi head pressure</li><li>Column: Restek Rxi-624Sil MS, 30 m × 0.25 mm × 1.4 µm</li><li>Oven program: 45 °C (1 min) → ramp 15 °C/min → 220 °C, hold 1.33 min (total run ~14 min)</li><li>Column flow rate: 1 mL/min helium</li><li>Total flow: 44 mL/min</li><li>Source temperature: 230 °C</li><li>Quadrupole temperature: 150 °C</li><li>Transfer line temperature: 180 °C</li><li>Scan range: m/z 35–300, 5.2 scans/sec</li><li>SIM ions:<ul><li>45, 46 (0.7–3.49 min)</li><li>58, 88 (3.5–14 min)</li></ul></li><li>Solvent delay: 0.7 min</li></ul>For each parameter iteration, see the text below, a calibration curve was established with a linear range of 0.5 to 200ppb using standards from Restek. After each of the prescribed curves was determined; Method Detection Limits (MDLs), precision and accuracy and carryover studies were performed. A series of seven low level standards were run in order to establish MDLs per 40CFR Part 136, Appendix B. Next, seven replicate samples of the 50ppb standard were run in order to establish the precision and the accuracy of the experimental parameters. Finally, a series of four 50ppb standards were run with each standard followed by three blanks. The amount of carryover was then analyzed in the first blank. The data from each parameter variation was compiled and compared in order to determine the optimum conditions for this analysis. An average of the results for each analysis condition is listed in Table 1.<h5>Purge and Trap Sampling Test Parameters</h5><ul><li>Baseline: 5 mL traditional sparger, room temp purge, 110 °C sparge bake</li><li>Iteration A: 5 mL traditional sparger, 40 °C purge, 110 °C sparge bake</li><li>Iteration B: 5 mL traditional sparger, 60 °C purge, 110 °C sparge bake</li><li>Iteration C: 5 mL traditional sparger, 40 °C purge, no sparge bake</li><li>Iteration D: 40 mL vial, 10 mL purge volume, 40 °C purge, no sparge bake</li><li>Iteration E: 5 mL fritless bulbless sparger, 40 °C purge, 110 °C sparge bake</li><li>Iteration F: 5 mL fritless bulbless sparger, 40 °C purge, no sparge bake (Iteration E used the patented Water/Soil prep mode)</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_4_Averaged_Results_Summary_306dcbfde6.jpg" alt="EST Analytical: Table 1 Averaged Results Summary" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_4_Averaged_Results_Summary_306dcbfde6.jpg 245w," sizes="100vw" width="1493" height="351">The primary compounds of interest for the study were Ethanol and 1, 4-Dioxane. For this reason, the data for these compounds was compiled separately in order to better distinguish the benefits or detriment of each purge and trap parameter set. The experimental results of the precision and percent recovery studies are displayed in Tables 2 and 3.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_5_Ethanol_and_1_4_Dioxane_Precision_at_50ppb_3a195e1acb.jpg" alt="EST Analytical: Table 2 Ethanol and 1, 4-Dioxane Precision at 50ppb" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_5_Ethanol_and_1_4_Dioxane_Precision_at_50ppb_3a195e1acb.jpg 245w," sizes="100vw" width="1316" height="236"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_6_Ethanol_and_1_4_Dioxane_Percent_Recovery_at_50ppb_cb12616f47.jpg" alt="EST Analytical: Table 3 Ethanol and 1, 4-Dioxane Percent Recovery at 50ppb" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_6_Ethanol_and_1_4_Dioxane_Percent_Recovery_at_50ppb_cb12616f47.jpg 245w," sizes="100vw" width="1318" height="234">For the carryover studies, Ethanol and 1, 4-Dioxane were examined along with the carryover of 1, 2, 4- Trichlorobenzene, Naphthalene and 1, 2, 3-Trichlorobenzene. The reason the heavier compounds were included in this study was a concern that changing the sampling parameters may help the Ethanol and 1, 4-Dioxane carryover, but harm the carryover of the heavier compounds of interest. Table 4 shows a listing of the carryover results, in parts per billion, while Figure 1 displays the percent carryover of the different purge and trap experimental parameters for just the Ethanol and 1, 4-Dioxane.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_7_Carryover_in_First_Blank_after_a_50ppb_Standard_7d2bc81626.jpg" alt="EST Analytical: Table 4 Carryover in First Blank after a 50ppb Standard" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_7_Carryover_in_First_Blank_after_a_50ppb_Standard_7d2bc81626.jpg 245w," sizes="100vw" width="1332" height="426"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Figure_1_Ethanol_and_1_4_Dioxane_Percent_Carryover_after_a_50ppb_Standard_Graphic_f57c981913.jpg" alt="EST Analytical: Figure 1 Ethanol and 1, 4-Dioxane Percent Carryover after a 50ppb Standard Graphic" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Figure_1_Ethanol_and_1_4_Dioxane_Percent_Carryover_after_a_50ppb_Standard_Graphic_f57c981913.jpg 245w," sizes="100vw" width="1358" height="787">After all the studies were completed, two purge and trap parameter variations showed the best precision, percent recovery, and carryover while meeting the USEPA Method 8260 linearity and response factor requirements. An abbreviated listing of the results for these two iterations are shown in Table 5.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_8_Results_of_the_Water_Extraction_and_the_Fritless_Bulbless_Sparge_Vessel_With_Sparge_Bake_Studies_9b71ec4951.jpg" alt="EST Analytical: Table 5 Results of the Water Extraction and the Fritless - Bulbless Sparge Vessel With Sparge Bake Studies" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_8_Results_of_the_Water_Extraction_and_the_Fritless_Bulbless_Sparge_Vessel_With_Sparge_Bake_Studies_9b71ec4951.jpg 161w," sizes="100vw" width="1256" height="1221"><h4>Conclusions:&nbsp;</h4>All seven purge and trap parameter iterations passed the USEPA Method 8260 requirements for linearity and method detection limits. The problem with some of the experimental parameters was found in the carryover and precision and accuracy studies. The carryover using the traditional sparge vessel showed a large amount of carryover for the Ethanol and 1, 4-Dioxane. Since the carryover was so high, the precision and accuracy data suffered. The Fritless/Bulbless sparge vessel, on the other hand, displayed much lower carryover for the Ethanol and 1, 4-Dioxane especially when the patented sparge bake was not used. However, the 1, 2, 4-Trichlorobenzene, Naphthalene and 1, 2, 3-Trichlorobenzene carryover after the 50ppb standard was above the lower limit of the curve.&nbsp;Thus, the sparge bake would be recommended in order to limit the carryover of the heavier compounds. The optimum purge and trap parameters proved to be the patented water extraction technique. This technique provided linearity and method detection limits that met the USEPA Method 8260 requirements, while providing excellent precision and accuracy data. During water extraction, the sample is transferred to an empty 40ml vial and then purged in the soil station of the Centurion. The “fresh” vial provides a clean sparge vessel for every sample thus limiting carryover for both the Ethanol and 1, 4-Dioxane and for the heavy compounds. This lack of carryover aided in providing optimum precision and accuracy and carryover results and would be the recommended method for examining these troublesome compounds.

Optimization of 1,4-Dioxane and Ethanol Detection Using USEPA Method 8260

<a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=45&amp;search=USEPA+Method+524.2">USEPA Method 524.2</a> calls for purge and trap sampling coupled with a Gas Chromatograph (GC) and Mass Spectrometer (MS) for separation and analysis. It has an extensive list of compounds and requires lower detection limits due to its use in drinking water testing. A 20% relative standard deviation for compound response factors is required across the calibration curve while the calibration check standard analytes have to be within 30% of the expected concentration. Currently, this method calls for a 5mL or 25mL purge volume and a four minute desorb time. These method requirements can pose a challenge for the analyst due to the amount of moisture that is created.&nbsp;The negative effects of the increased water vapor include instability of the chromatography, band eluting and poor peak shape to name a few. A side effect of this instability is sample re-runs and lost laboratory productivity. In addition, a common practice for mitigating moisture is increasing the GC inlet split rate. This poses yet another difficulty as the increased split rate can result in reduced sensitivity. EST Analytical’s eight port valve in the Evolution purge and trap concentrator aids in limiting the water exposure because the water management of the system is not part of the desorb pathway. This feature also enables laboratories to use a smaller split ratio at the GC inlet thus increasing sensitivity.<h4>Experimental:&nbsp;</h4>The sampling system used for this study was the <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/products/2160">EST Analytical Evolution purge and trap concentrator</a> and the <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/products/2159">Centurion WS autosampler</a>. The concentrator was affixed with a Vocarb 3000 trap and connected to an <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=10&amp;search=7890A">Agilent 7890A GC</a> and <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=10&amp;search=5975C">5975C inert XL MS</a>. The GC was configured with a <a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/library?mainauthorItems=7&amp;search=Restek+Rxi-624+Sil+MS">Restek Rxi-624 Sil MS</a> 30m x 0.25mm x 1.4µm column. The purge and trap and GC/MS parameters used for this study are listed below.<h5>Purge and Trap Parameters</h5><ul><li>Concentrator: EST Evolution</li><li>Trap type: Vocarb 3000</li><li>Valve oven temperature: 130 °C</li><li>Transfer line temperature: 130 °C</li><li>Trap temperature: 35 °C</li><li>Moisture Reduction Trap (MoRT) temperature: 39 °C</li><li>Purge time: 11 min</li><li>Purge flow: 40 mL/min</li><li>Dry purge Temp.: Ambient</li><li>Dry Purge Flow: 40mL/min</li><li>Dry Purge Time: 1.0 min &nbsp;</li><li>Desorb pressure Control: ON</li><li>Desorb Pressure: 5psi</li><li>Desorb time: 4 min</li><li>Desorb preheat delay: 15 sec</li><li>Desorb temperature: 250 °C</li><li>MoRT bake temperature: 210 °C</li><li>Bake temperature: 260 °C</li><li>Sparge vessel bake temperature: 110 °C</li><li>Bake time: 6 min</li><li>Bake flow: 70 mL/min</li></ul><h5>Auto-Sampler (EST Centurion WS):</h5><ul><li>Sample type: Water</li><li>Water volume: 25 mL</li><li>Internal standard volume: 5 µL</li></ul><h5>GC/MS Parameters</h5><ul><li>System: Agilent 7890A GC / 5975C inert XL MS</li><li>Inlet: Split mode, 220 °C, 40:1 split ratio, 12.153 psi head pressure</li><li>Column: Restek Rxi-624Sil MS, 30 m × 0.25 mm × 1.4 µm</li><li>Oven program: 45 °C (1 min) → ramp 15 °C/min → 220 °C, hold 1.33 min (total run ~14 min)</li><li>Column flow rate: 1 mL/min helium</li><li>Total flow: 44 mL/min</li><li>Source temperature: 230 °C</li><li>Quadrupole temperature: 150 °C</li><li>Transfer line temperature: 180 °C</li><li>Scan range: m/z 35–300, 5.2 scans/sec</li><li>Solvent delay: 0.7 min</li></ul>A calibration curve was established with a linear range of 0.25 to 40µg/L using the USEPA Method 524.2 standards from Restek. After the curve was determined, method detection limits were ascertained by running a series of seven replicate 0.25 µg/L standards and calculated using the procedure outlined in 40 CFR Part 136 Appendix B. Finally, seven 20 µg/L standards were examined in order to verify the precision and accuracy of the analysis. The results of this study are displayed in Tables 1 and 2 while Figure 1 presents a 20 µg/L standard GC/MS chromatogram.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_3_Compound_Linearity_and_Response_Factor_Table_f63b77844f.jpg" alt="EST Analytical: Table 1 - Compound Linearity and Response Factor Table" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_3_Compound_Linearity_and_Response_Factor_Table_f63b77844f.jpg 153w," sizes="100vw" width="1104" height="1126"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Table_4_MDL_and_Precision_and_Percent_Recovery_Table_27572600f0.jpg" alt="EST Analytical: Table 2 - MDL and Precision and Percent Recovery Table" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Table_4_MDL_and_Precision_and_Percent_Recovery_Table_27572600f0.jpg 186w," sizes="100vw" width="1358" height="1143"><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/EST_Analytical_Figure_1_20mg_L_Standard_Chromatogram_7ff795984b.jpg" alt="EST Analytical: Figure 1 - 20 µg/L Standard Chromatogram" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_EST_Analytical_Figure_1_20mg_L_Standard_Chromatogram_7ff795984b.jpg 245w," sizes="100vw" width="1431" height="789"><h4>Conclusions:&nbsp;</h4>This study demonstrated the effectiveness of the Evolution/Centurion purge and trap sampling system. The results passed all of the USEPA Method 524.2 criteria for both linearity and detection limits. Since the Evolution bypasses the water management trap during the four minute desorb process, the amount of water effecting the experiments was limited. Furthermore, the forty to one split ratio at the GC inlet provided excellent detection limits as the system was more sensitive to the low level standard requirements of the method. The lower split rate has an added benefit of reducing laboratory helium consumption when setting it against other system’s higher split ratios. Finally, the precision and percent recovery results showed the reliability of the system in producing accurate experimental findings.

USEPA 524.2 Method Validation Using the Evolution Purge and Trap Concentrator and the Centurion WS Autosampler

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