Determination of PAH Compounds from Aqueous Samples Using a Non-Halogenated Extraction Solvent and Atlantic C18 Disks

Transcription

1 Determination of PAH Compounds from Aqueous Samples Using a Non-Halogenated Extraction Jim Fenster, Kevin Dinnean,, David Gallagher, Michael Ebitson, Horizon Technology, Inc., Salem, NH Introduction Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants, naturally occurring in coal, crude oil, gasoline, and their byproducts (e.g. coal tar or creosote). In addition, PAHs are formed in the incomplete combustion processes of all organic materials, such as wood or fossil fuels. Consequently, the EU water framework directive (WFD) lists in its annex X the whole group of PAHs as priority hazardous substances [1]. The traditional extraction solvents used for solid phase extraction (SPE) methods involving PAH compounds is dichloromethane (DCM) and acetone. DCM has been used in the past because of its excellent solvating properties and its low boiling point which results in higher yields after extraction, drying, and concentration. DCM however is dangerous to work with as it has been proven to be a carcinogen at very low exposure levels. As such, many laboratories have now mandated that solvent extractions in environmental methods not use any halogenated solvents, in particular DCM. Previous work, done by Frederick Weres [1], has demonstrated good extraction efficiencies using acetone as the eluting solvent. However; acetone creates a problem with residual water in the final extracts due to its miscibility with water. The restriction placed on the types of solvents used has given rise to a need for an extraction method which makes use of a non-halogenated, non-polar solvent for the extraction of PAH compounds. This solvent must achieve excellent recoveries when using traditional SPE methods. This application note was developed to demonstrate the extraction of 16 PAH compounds listed by the US Environmental Protection Agency (EPA) as priority pollutants, including all PAHs listed in the content of the EU WFD, using the Horizon SPE-DEX 4790 automated SPE extraction system. It will show the efficiency of the extraction while demonstrating the excellent recoveries of PAH compounds using hexane and minimal amounts of acetone. Methods were developed and results are shown using 47 mm Atlantic C18 disks. Samples used in this study consisted of aqueous samples containing dissolved PAH compounds with and without particulates. The water samples with particulates were extracted using the Fast Flow Sediment Disk Holder (FFSDH). The FFSDH allows the whole sample to be extracted (including particulates and other debris in the water) without having to separately filter the water samples first. The Horizon Technology SPE-DEX 4790 Automated Extraction System, Envision Platform Controller, and DryVap Automated Drying and Concentrating System. Instrumentation Horizon Technology - SPE-DEX 4790 Automated Extractor System - Envision Platform Controller - DryVap Concentrator System - DryVap Software - 65 mm DryDisks (PN HT) - Solid-Tip Concentration Tube (PN ) ml Concentration Tube (PN ) - Atlantic C18 SPE Disks (PN ) - 47mm Disk Holder (PN ) - Fast Flow Sediment Disk Holder (PN ) - Atlantic Fast Flow Prefilter Fine (PN FFAP-100- HS1) -Atlantic Fast Flow Prefilter Coarse (PN FFAP-100- HS5) -Erlenmeyer Flask, 125 ml (PN ) -Separatory Funnel, 125 ml (PN ) Agilent Gas Chromatograph Mass Selective Detector - Column: Phenomenex Zebron ZB-5MS, 30 m x 0.25 mm ID, 0.25 μm Method Summary 47 mm Disk Holder Method (Non-Particulate Aqueous Samples) 1. Adjust 1 L aqueous sample to ph 2 with HCl, cap the bottle and mix. 2. Spike PAH Standard mix (100 ug/ml in MeOH) into samples. 200 µl for 20 ug spike and 300 µl for 30 µg spikes. Pg. 1 of 6

2 3. Place an EZ-Seal over the opening of the bottle and screw on the bottle cap adaptor. 4. Load the disk holder with the Atlantic C18 47 mm disk. 5. Place a clean VOA vial or equivalent receiver onto the extractor. 6. Load the sample bottle onto the SPE-DEX Start the PAH extraction method in Table 1 and collect extract at high vacuum of -25 in. Hg (15.5 in. Hg at the Solvent To Waste bottle) and 15.5 psi Solvent Bottle Pressure 8. Collect the extract (approximately 30 ml). 9. Cap and label extract as PAH. 10. Dry and Concentrate the extract on the Horizon DryVap Concentration System at the following settings: Dry Volume = 20 ml Heater Power = 5 Heater Timer = Off AutoRinse = Off Table 1: 47 mm and FFSDH Envision Method for PAH Extraction from Clean Aqueous Samples Step Solvent Soak Time Dry Time Prewet 1 Methanol 2:00 min 5 Sec Prewet 2 Reagent Water 1:00 min 5 Sec Prewet 3 Reagent Water 30 Sec 2 Sec Sample Process Air Dry 1:00 min Rinse 1 Acetone 2:00 min 2:00 min Rinse 2 Hexane 2:00 min 2:00 min Rinse 3 Hexane 1:00 min 1:00 min Rinse 4 Hexane 1:00 min 1:00 min FFSDH with 47 mm Disk Method (Aqueous Samples with Particulates) 1. Install the 8 second Elution Magnet over the IR sensor on the SPE-DEX Install the Tefzel Plug into the SPE-DEX 4790 platform adjustment hole. 3. Adjust 1 L aqueous sample to ph 2 with HCl, cap the bottle and mix. 4. Spike PAH Standard mix (100 ug/ml in MeOH) into samples. 200 ul for 20 µg spike and 300 µl for 30 µg spikes. 5. Place an EZ Seal over the opening of the bottle and screw on the bottle cap adaptor. 6. Load the FFSDH with an Atlantic C18 47 mm disk, a Fine Atlantic Prefilter and Coarse Atlantic Prefilter. 7. Place a clean 125 ml Separatory Funnel onto extractor. 8. Load the sample bottle onto the SPE-DEX Start the PAH extraction method in Table 1 and collect extract at high vacuum of -25 in. Hg (15.5 in. Hg at the Solvent To Waste bottle) and 15.5 psi Solvent Bottle Pressure 10. Collect the extract (approximately 80 ml). 11. Cap and label extract as PAH. 12. Dry and Concentrate the extract on the Horizon DryVap Concentration System at the following settings: Dry Volume = 100 ml Heater Power = 5 Heater Timer = Off Auto Rinse = Off Results To demonstrate the loss of analytes due to concentration on the DryVap system, a 30.0 µg mix of PAH analytes was spiked into 30 ml of solvent with an Acetone to Hexane ratio of 20:80 which represents the final analyte volume for 47 mm disk holder extracts. When using the DryVap concentration system, it is important to optimize the heater settings (T13) for the particular solvent mix being used. Horizon ships the DryVap optimized for methylene chloride. Since this extraction procedure uses an acetonehexane mix, it is necessary to adjust the DryVap settings for these solvents so that the heating time is optimal for that solvent mix. Prior to concentrating the solvent spikes to their final volume endpoints, a blank solvent mix of 30 ml of acetone: hexane (80:20) was added to three DryVap concentration tubes and the heater settings were altered using the procedure listed in Horizon s Application Note AN049 - Using the Learn Mode to Optimize Recoveries with the Dry Vap Concentrator System [2]. Also, the DryVap setting value that controls sparge time (T5) was changed using the DryVap Software to a value of 1200 (2 minutes) from the factory setting of (1 hour). This value turns off the Nitrogen Sparge gas after two minutes and allows for the final volume to be reached faster. The extract was then transferred to a 10 ml graduated cylinder and brought to a final volume of 10 ml. The recoveries of these solvent spikes are shown in Table 3 with final end point volumes of 1 ml and 10 ml. Of the 16 compounds, recoveries were excellent and resulted in an average recovery range with a low of 82% to a high of 96% for the 1 ml endpoints and a low of 99% to a high of 102% for the 10 ml endpoints. This data also demonstrates excellent reproducibility s with the RSD s lying between 0.8% and 5% for the 1 ml endpoints and 3% to 10% for the 10 ml endpoints. Ten ml endpoint recoveries were higher than the 1 ml endpoints for the light end (more volatile PAH components). Also, the heavy end components of the PAH mix were equal in recovery due to the lower volatility of these. The difference in recovery in the light end compounds (i.e. napthalene) was due to the amount of time it takes on the DryVap concentrator after heater shutoff to achieve the final endpoint and the loses associated with that additional time. Extractions of aqueous samples were carried out using a 47 mm C18 extraction disks and also on FFSDH equipped with Fine and Coarse prefilters. Results of this series of extractions are shown in Tables 4, and 5. Extraction results in Table 4 showed very good recoveries with a low of 77% and a high of 96% for the 1 ml endpoints and a low of 81% and a high of 94 % for the 10 ml endpoints. The data Pg. 2 of 6

3 also shows very good reproducibility with RSD s between 0.5% to 7% for the 10 ml endpoints and 3% to 7 % for the 1 ml endpoints. In general higher recoveries and more consistent results are achieved using a 10 ml endpoint. The reason for this is two-fold; the 10 ml final volume extracts needed considerably less nitrogen sparge time than the 1 ml final volume endpoint, this resulted in less loss of the lighter end constituents in the PAH mix. Also the 1 ml final volume extracts had five hexane rinse steps and the volumes of these extracts were higher than the 10 ml final volume extracts which were extracted with only 3 hexane rinses. The larger volume fractions required more time in the heat stage on the DryVap concentrator and it is possible that this extra time negatively impacted the recoveries of the PAH constituents in the list. Acknowledgements & References [1] Friedrich Werres, Peter Balsaa, Torsten C. Schmidt, Journal of Chromatography A, 1216 (2009) [2] Robert Johnson Horizon Application Note 049 Using the Learn Mode to Optimize Recoveries With the Dry Vap Concentrator System The data in Table 5 shows very good recoveries using the FFSDH. This setup has been optimized for use with highly particulated samples, and recoveries are consistently high for the PAH analytes from 79% to 92%. The data in Table 5 also shows the negative effect of longer air dry times in the extraction procedure. As can be seen in the data, the light end PAH analytes are affected more than the heavy end components when air dry times are reduced from 2 minutes to 1 minute. The 1 minute air dry times gave a result with a low of 79% for Napthalene and a high of 92% for both Dibenz(ah)Anthracene and Benzo(ghi)peryline ( Ave RSD 4.69%). The 2 minute air dry times gave a recovery range of 73% to 90% (Ave RSD 10.26%). One other phenomenon associated with the use of the DryDisk was observed when using the FFSDH and the acetone: hexane as the rinsing solvents. Hexane being lower in specific gravity than water has a tendency to sit on top of the water layer when going through the DryDisk. Compound recoveries were higher on average by 6% when using a 125 ml sepratory funnel to collect eluted fractions vs. the 125 ml Erlenmeyer flask. The use of the separatory funnel made it possible to easily drain off the bottom acetone/water layer and concentrate only the hexane fractions. This last step was more difficult with the 125 ml Erlenmeyer flask and resulted in partial blockage of the DryDisk and lose of some of the PAH compounds on the drying step resulting in lower recoveries. Conclusions This application note demonstrates an efficient SPE disk extraction scheme for PAH compounds in aqueous samples that are clean or dirty. The method demonstrated excellent recoveries for an extraction scheme which uses acetone and hexane in place of chlorinated solvents. This safe, efficient extraction scheme utilizes Horizon Technology s Atlantic C18 SPE disks and Fast Flow Sediment Disk Holder to extract the whole sample, sediment and liquids, in one step without a separate filtration and extraction of the solids contained in the sample. This combination of products and consumables aids sample flow rates through the disk allowing for faster extraction times while yielding excellent recoveries. Pg. 3 of 6

4 Table 3: Loss of Analytes Due to Concentration on the DryVap Using 25 ml of Hexane and 5 ml of Acetone With 1mL and 10 ml Endpoints Final Volume 1.0 ml 10 ml Compound % Rec % Rec % Rec Ave % Rec % RSD % Rec % Rec % Rec Ave % Rec % RSD Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenz(ah)anthracene Benzo(ghi)perylene Pg. 4 of 6

5 Table 4: Recovery Data from Clean Aqueous Samples Using 47 mm C18 Disks 1mL and 10mL Final Volumes 1.0 ml Final Volume 5 Hexane Rinses 10 ml Final Volume 3 Hexane Rinses Spiking Concentration 20 µg/l 20 µg/l 20 µg/l 30 µg/l 30 µg/l Average 20 µg/l 20 µg/l 20 µg/l Average Compound % Rec % Rec % Rec % Rec % Rec % Rec % RSD % Rec % Rec % Rec % Rec % RSD Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenz(ah)anthracene Benzo(ghi)perylene Pg. 5 of 6

6 Table 5: Recovery Data of 20 µg PAH Spike from Clean Aqueous Extractions Using FFSDH and C18 Disks 2 and 1 Minute Airdry Times Air Dry Time Collection Vessel 2 Minutes 125 ml Erlynmeyer 1 Minute 125 ml Separatory Funnel Compound % Rec % Rec % Rec Average % Rec % RSD % Rec % Rec % Rec Average % Rec % RSD Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenz(ah)anthracene Benzo(ghi)perylene Averages Averages Pg. 6 of 6