INSTRUMENTS IN. Enhanced Preconcentrator for the Analysis of Vapor Phase Volatile Organic ompounds Application Note 00 Preconcentrator G/MS Analysis Authors Thomas X. Robinson, Daniel B. ardin, Entech Instruments, Inc. 0 Agate ourt Simi Valley, A 90 USA Abstract Analysis of volatile organic compounds (VOs) in ambient air or other vapor phase matrices, such as soil gas, product off gassing, or large volume headspace has been enhanced by improvements in design of a new automated, preconcentration system. Many advancements have been made to previously available technology for the analysis of vapor phase samples to improve productivity and data results. An increased dynamic range of calibration, allowing sample volumes from to 000 milliliters to be concentrated, increases productivity by analyzing samples with varying concentrations without having to perform manual sample dilutions. A new trap design and improved coating technology using Silonite-D creates a very inert sample flow path, allows higher molecular weight compounds to be recovered, and adds the ability to analyze highly reactive species such as formaldehyde and hydrogen sulfide. A three stage trapping design provides a matrix insensitive concentration technique due to the ability to remove water and all major air components including oxygen, nitrogen, carbon dioxide. Data quality has been improved using Accu-Sample technology which measures volume by pressure differential of a fixed volume vacuum reservoir. This feature creates calibration curves with excellent relative standard deviations. Data is presented to show improved linearity of calibration curves and method detection limits for a wide range of VOs. Entech Instruments, Inc.
Introduction The 00 Preconcentrator with Accu-Sample technology (Entech Instruments, Inc., Simi Valley, A), represents the next generation in G and G/MS sample preparation systems for the analysis of vapor phase volatile organic compounds. The 00 features improvements in -stage preconcentration and water management technology and many past limitations seen in rotary valve based devices are resolved by combining digital valve isolation with direct inlet canister autosampling which drops potential carryover and cross-contamination far below what was previously possible. A Silonite-D coating throughout the flow path virtually eliminates unwanted chemical reactions, ensuring complete recovery of volatile and light semi-volatile compounds. The 00 s advanced water and O management technologies provide superior analysis of polar and non-polar organics and an inert, heated flow path recovers hydrocarbons in the range of - (depending upon trapping conditions). the 00 Preconcentrator includes four built in inlets available for direct sample introduction, or as inlets for multi-position autosamplers such as the 00, 0, and 0D (Entech Instruments, Inc., Simi Valley, A). Internal traps feature an optimized geometry that improves trap temperature consistency during analysis. Accu-Sample technology, (patent pending) combines digital valve control with direct volume measurement rather than indirect time integrated flow measurements to allow better small volume accuracy down to 0cc over a wider pressure range and permits both air / non-air matrices to be analyzed accurately. A loop injection valve can also be added to further reduce quantitative sample volume analysis down to as low as cc. System Hygiene: Like the previous generation 00A system, the new 00 Preconcentrator includes the ability to backflush lines out to the sample ports to eliminate any previous sample in each line prior to connecting to the next sample. However, with laboratories now faced with analyzing both ambient air and soil gas samples routinely, system hygiene must go beyond a simple backflush. Isolation to prevent undesired exposure to traps, tubing, and valve rotors during the analytical process has become much more important. The 00 features a shorter sample path than its predecessor, and also includes the ability to prevent any cross-contamination when moving its Stream Select Valve to the next desired port. This is accomplished by isolating the downstream flow path using Entech s new digital rotary valve technology. In addition, new autosampling inlets are available for the 00 that make only a brief contact with a sample, just long enough to withdraw the requested aliquot, rather than for hours or days as with rotary valve based autosamplers. This further reduces the possibility of cross-contamination when analyzing higher concentration soil gas samples. Quality Assurance: The 00 comes equipped with tools for validating system performance, including the ability to perform automated leak checking and matrix spiking. The 00 also records important parameters during each sample preconcentration to verify proper system operation, including trapping flow rates, flow volumes, trap pressure drop, trapping temperatures, water management parameters, desorption temperatures / flows, autosampler position, and sample transfer times. Data is saved into a SQL Database for easy integration into LIMS systems, and an automated summary is generated that provides critical run time parameters in an easily interpretated one page report. Leak hecking: A significant source of errors in many G inlet systems is the presence of leaks that go undetected. The 00 performs automated leak checking using both pressure and vacuum techniques to ensure a secure leak-tight system exists before any samples are analyzed. A report is generated giving the starting and pressure during the monitoring period. Leak checks can be done by either by selecting individual sample ports or by selecting a sequence table (which defines a group of samples on the autosampler). Leak checks for canister samples on autosampling inlets such as the 00 or 0 are not required since all samples remain closed and isolated until accessed for analysis. 00 Preconcentrator G/MS Analysis
Matrix Spiking: G or G/MS calibration is performed using carefully prepared standards in a clean matrix (Nitrogen or Zero Air). It is easy to assume that no interferences exist in actual samples that will change response factors or detection limits, but this may not always be the case. The true detection limit of benzene, for example, may be altered if it co-elutes with a high concentration interferent that was not present in the standard. The only way to determine whether interferences are changing response factors for target compounds in more complicated matices is to spike low levels of the analytical standard right into the sample matrix. For example, by adding ppb of target compounds to the sample being analyzed, all responses should go up by about ppb. The 00 simplifies this process of interference determination by allowing a co-preconcentration of sample and calibration standard. This capability ensures analytical accuracy on the most critical of samples and can help to uncover any matrix interferences if they exist. Experimental The G Analytical data was generated using a 00 Preconcentrator interfaced with a Shimadzu QP00 Ultra G/MS. G oven temperature started at ( min) ramped at /min to 0, then 0 /min to a final temperature of 0 ( min). The MS acquisition was from to 0 amu (it is necessary to start at if you are including Formaldehyde in the analysis, otherwise 0 amu would be used at least for the first minutes for some of the lighter compounds). alibration standards were obtained from Linde Gas and Scott Specialty Gases. Three cylinders at ppmv were blended together using a 00A Dynamic Dilution System (Entech Instruments, Inc., Simi Valley, A), then diluted to 0 ppbv for the calibration curve and ppbv for the Method Detection Limit Study. alibration was performed by picking a nominal volume to be trapped and used for all samples needing quantitation, and the curve was obtained by varying the volume of the 0 ppbv standard. A nominal volume of 0cc, was used. This volume being equal to 0 ppbv volumes of 0cc, cc, 0cc, 00cc, 0cc, 00cc, and 000cc, yields a calibration range from 0. ppbv to 0 ppbv. The MDL was analyzed with seven 00cc replicates of the ppbv standard, this equates to an amount of 0.0 ppbv when the nominal volume is 0cc. The results of these analyses are summarized in table. Sample trapping conditions of the 00 Preconcentrator are shown below in table. 00 Preconcentrator, shown with 00 Autosampler. 00 Preconcentrator Trapping Sweep M M M M Bakeout Module Empty Trap -0-0 0 N/A 0 Module Tenax Trap -0-0 -0 0 0 Module Open Tube N/A N/A N/A -0 Minute Volume (cc) 0cc cc 0cc 0cc N/A Flow Rate (cc per minute) 00 00 0 N/A Table - 00 Preconcentrator trapping conditions for old Trap Dehydration. 00 Preconcentrator G/MS Analysis
00 00 0D System onnections Focusing Module MS G Reservoir Isolation Valve Reservoir Evacuation Valve Flow ontrol Valve Dehydration Module 00 Volume Determination Reservoir Pump He/SP N NO Pump Isolation Valve old Tenax Module Sample al. Standard G arrier Gas Helium In Internal Standard Analyze up to Additional anisters using the 00 s Expansion Ports! 00 Preconcentrator 00 Autosampler 0D Autosampler Figure - G/MS shown with 00 Preconcentrator, 00 Autosampler, and the 0D Autosampler. 00 Preconcentrator Pump He/SP G arrier Gas Sample Sample Sample Helium In Sample al. Standard Internal Standard Volume Determination Reservoir Dehydration Module old Tenax Module N NO Reservoir Evacuation Valve Flow ontrol Valve Reservoir Isolation Valve Focusing Module Pump Isolation Valve Smart Lab A The 00 is controlled by Entech s SmartLab A control network operating under Microsoft Win XP or Windows using the latest high-speed USB interface technology. Figure - 00 Preconcentrator Flow path featuring Silonite-D coated tubing. 00 Preconcentrator G/MS Analysis
EPA TO- Standard 0ml Headspace 0 PPB / omponent, Splitless 000000 00000 000000. Freon. tert-butyl Alcohol +,-Dichloroethene. arbon Disulfide + Freon. Trichloroethene. Tetrachloroethene. m,p-xylene + Bromoform. Bromofluorobenzene.,,-TMB + tert-butylbenzene 9. Napthalene 0. Hexachlorobutadiene Inlet: 00 Sample Size: 0ml Headspace, TO- Standard Split Mode: Splitless olumn: DB, 0m, 0.mm ID, μm film arrier: He,. cc/m constant flow Oven Temp: min, /min to 0, /min to 0, min hold. GMS: Shimadzu G 00 Plus and MS QP 00 Ultra MS Operation: 9-0 amu (first 9 min),-0 amu (remaining time). Amu at scans/sec. 0 00000 000000 9 00000 000000 00000 000000 00000.00.00 0.00.00.00.00.00 0.00.00.00.00.00 Figure - 0mL, 0 PPBV omponent EPA Method TO- Standard. Discussion Extended old Trap Dehydration (ETD) is the concentration technique utilized by the 00 Preconcentrator, as illustrated in Figure and Figure. The sample first flows through an empty Silonite-D coated trap at -0 and then through a second trap at -0 containing Tenax TA. Water is removed by direct conversion from the gas to the solid phase in trap, eliminating the potential loss of highly polar VOs (HPVOs) into any liquid water. This allows recovery of compounds such as formaldehyde and hydrogen sulfide that would not be properly recovered using other water management techniques. Although some of the heavier VOs may also temporarily condense in the first cold trap, a secondary step is used whereby the first trap is heated to +0, this enables another 0 to 0cc of nitrogen to purge any remaining VOs to the cold Tenax trap, with only a minimal transfer of water vapor. ooling the Tenax trap to -0 makes the Tenax 00x stronger than Tenax at 0, and allows quantitative trapping of the lightest EPA Method TO- compounds, while taking advantage of unreactive nature of Tenax to recover all compounds during desorption. Rapid, splitless injection onto the G column requires a final focusing stage accomplished by back desorbing the Tenax trap at 0 into a third trap at -0 that contains an empty / Silonite-D coated transfer line. Rapid heating of the final focusing trap releases the sample almost instantly, providing unparalleled injection rates and light-end resolution. Accu-Sample technology developed by Entech for the 00 Preconcentrator uses a combination of three new technologies to improve system performance and reliable quantitation. First, the 00 isolates all downstream flow volumes before rotating the inlet rotary valve to effectively remove about 9% of the downstream volume. This virtually eliminates the introduction of other...discussion continued on page. 00 Preconcentrator G/MS Analysis
00 Preconcentrator EPA Method TO- Standard Analyte % RSD MDL Formaldehyde.0.9 Propene. 0.0 Dichlorodifluoromethane. 0.00 hloromethane 9.9 0.00 Dichlorotetrafluoroethane 0. 0.0 Acetaldehyde. 0.09 Vinyl hloride.9 0.00,-Butadiene. 0.0 Bromomethane.9 0.00 hloroethane. 0.0 Ethanol 0. 0.00 Bromoethene. 0.00 Trichlorofluoromethane.0 0.00 Acrolein.9 0.0 Acetonitrile.0 0.0 Acetone. 0. Propanal. 0.0,-Dichloroethene.9 0.00 Acrylonitrile. 0.0 Trichlorotrifluoroethane. 0.0 Tert-Butanol 9. 0.0 Allyl hloride. 0.0 Methylene hloride.0 0.0 arbon Disulfide.0 0.0 trans-,-dichloroethene. 0.0 Methyl tert-butyl Ether. 0.0 Vinyl Acetate.9 0.00 -hloroprene. 0.0 -Butanone (MEK).9 0.0,-Dichloroethane Hexane. 0.0 Di-isopropyl Ether. 0.0 cis-,-dichloroethene. 0.00 Ethyl Acetate.9 0.00 Ethyl Tert-Butyl Ether. 0.0 hloroform. 0.0 Tetrahydrofuran. 0.0,,-Trichloroethane.9 0.009,-Dichloroethane.9 0.0 Benzene. 0.0 arbon Tetrachloride. 0.0 yclohexane. 0.0 Tert-Amyl Methyl Ether. 0.00 00 Preconcentrator EPA Method TO- Standard Analyte % RSD MDL,,-Trimethylpentane.0 0.00 Heptane. 0.0 Trichloroethylene. 0.0,-Dichloropropane.9 0.0,-Dioxane.9 0.0 Methyl Methacrylate. 0.0 Bromodichloromethane. 0.00 cis-,-dichloropropene. 0.0 -Methyl--Pentanone (MIBK).09 0.0 trans-,-dichloropropene.0 0.0 Toluene. 0.00,,-Trichloroethane.9 0.0 -Hexanone. 0.0 Dibromochloromethane.9 0.00 Tetrachloroethylene. 0.009,-Dibromoethane (EDB). 0.00 hlorobenzene. 0.00,,,-Tetrachloroethane. 0.0 Ethylbenzene. 0.0 m-xylene.0 0. p-xylene. 0.0 Styrene. 0.009 o-xylene. 0.0 Bromoform 9. 0.0,,,-Tetrachloroethane. 0.0 umene.0 0.009 n-propylbenzene 9. 0.0 o-hlorotoluene 9. 0.00 -Ethyltoluene 0.9 0.0,,-Trimethylbenzene. 0.00 Tert-Butyl Benzene. 0.0,,-Trimethylbenzene 9. 0.00,-Dichlorobenzene. 0.00 Sec-Butyl Benzene.0 0.0 Benzyl hloride 0.00 0.00,-Dichlorobenzene 0.90 0.009 o-ymene 0. 0.00,-Dichlorobenzene 0. 0.00 n-butyl Benzene 0. 0.00,,-Trichlorobenzene.0 0.00 Naphthalene 0. 0.0 Hexachlorobutdiene. 0.009 Table - % Relative Standard Deviation and Method Detection Limit (in PPB). 00 Preconcentrator G/MS Analysis
Discussion (continued from pg. ) gases connected to the inlet rotary valve when selecting the next inlet, avoiding cross-contamination. Secondly, Entech has developed an Electronic Volume ontrol (EV) module which is used in place of mass flow controllers to directly meter in a requested volume, rather than trying to time integrate the flow output of a mass flow controller to determine volume. This technology yields far better accuracy, especially when measuring small volumes in the range of 0 00cc. Finally, the use of Entech s exclusive Silonite-D coatings throughout the instrument results in much less chemical interaction with tubing surfaces, providing a more complete transfer through to the G/MS. Figure shows a typical G/MS chromatogram of a TO- standard, with a much enhanced backend recovery (TB, Naphthalene, HB) relative to other TO- inlet systems on the market. Table shows the type of calibrations possible with the 00 Preconcentrator using Accu-Sample technology. Some compounds, such as Acetone, were elevated due to a slight background in the system, or in the calibration standards. Excellent MDLs are also shown in Table, many of which are down at, or near, 0 part-per-trillion. These values were obtained by analyzing a 0. PPB standard times. For Further Information To learn more about our products and services, visit our web site at www.entechinst.com. onclusion The 00 Preconcentrator represents the next generation in laboratory air preconcentrators. The excellent level of isolation and quantitation offered by the 00 s exclusive Accu-Sample technology provides the ideal platform for today s challenging sample types, including soil gas samples where concentrations could vary from low-ppb to high-ppm from one sample to the next. ombined with Entech s latest robotic autosampler, the 0, the 00 provides the air laboratory with extremes levels of sample isolation which virtually eliminates any chance of cross-contamination. Using the 00 s optional built-in loop for volume measurements down to 0.cc, the 00 also boasts the largest dynamic range of any system on the market, maximizing the number of samples that can be analyzed without prior dilution. www.entechinst.com Entech Instruments, Inc. 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. Entech Instruments, Inc., 0 Printed in the USA April, 0 AM_AN0E Entech Instruments, Inc. SPME / Active SPME Food Analysis