Determining PAHs in sea water using automated SPE

Application Note Scope

This application note will outline optimized methods for the extraction of polycyclic aromatic hydrocarbons from sea water using the Atlantic® HLB solid phase extraction disk processed using Biotage automated or manual SPE solutions and DryVap™* Concentrator System. The first section will highlight the use of the Biotage® Horizon 5000 fully automated extraction system and the method used for this application. Additionally, there will be an Application Modification section that will highlight the use of the Biotage® VacMaster™ Disk for this application.
 

Introduction

Although not frequently a problem, recent incidents at sea have led to large amounts of crude oil being released and dispersed throughout the Gulf of Mexico. Originally presumed to be Louisiana Sweet Crude, sample testing later revealed a harsher form of crude containing a high amount of asphaltenes was being released. The differences are substantial, as Louisiana Sweet degrades more readily in nature than crude oil containing asphaltenes. While data is still mixed as to what type of oil is being released, the need for a fast and reliable method of testing still exists within the environmental industry of the Gulf Coast states.

One of the most frequently tested for groups of compounds within petroleum and petroleum distillates are polycyclic aromatic hydrocarbons or PAHs. PAHs are comprised of aromatic rings which are strongly lipophilic. Larger PAH compounds are less water soluble and less volatile than smaller compounds and, therefore, pose more of a risk in nature. PAHs have been found to be carcinogenic, mutagenic, and tetrogenic and can bioaccumulate within the environment. It is estimated that up to 30% (by weight) of crude oil are PAH compounds.

Traditional techniques used for the extraction of PAH samples, such as liquid-liquid extraction (LLE), can be problematic. Emulsions and corrosives may form, requiring the use of costly chemicals such as biocides, emulsion breakers, and corrosion inhibitors. Errors may occur, as the efficient and accurate use of these chemicals is reliant on factors such as the amount of oil in the water and droplet size, which are not always known.

This application note will highlight the use of the Biotage® Horizon 5000 Automated Extraction System to extract PAH analytes from seawater samples which typically contain up to 35 g/L of salt. For the analytes of interest in this study, the Atlantic® HLB SPE disk is used due to the nature of its reverse phase interactions.

Instrumentation

Biotage instruments

» Biotage® Horizon 5000 Automated Extraction System
» Atlantic® HLB-M SPE Disk
» DryVap™ Concentrator System
» DryDisk® Separation Membrane
» Biotage® Solvent Recovery SVOC System

Method summary

1. Add 0.5 mL of a 100 µg/mL PAH Spiking Mix into the appropriate laboratory control and matrix spike samples.
2. Adjust 1 L aqueous samples to pH 2 with HCl, cap the bottle and mix.
3. Place the sample bottle on the Biotage® Horizon 5000 Extraction System and place the Atlantic® HLB-M disk in the standard 47 mm disk holder. Attach collection vessels to the system.
4. Extract the samples using the Biotage® Horizon 5000 and the method shown below in table 1.
5. Dry and concentrate the extracts using the DryVap™ settings shown in table 2 to a final volume of 5 mL and transfer the extracts to GC vials.
6. Add the appropriate amount of internal standard to each extract.
7. Perform the final analysis using a GC-MS.

Application modifications

Biotage® VacMaster™ Disk method summary

1. Repeat the following steps for each active VacMaster® Disk station.
2. Setup the VacMaster™ Disk manifolds ensuring all waste lines and vacuum lines are attached. Set the vacuum pump to -24”Hg.
3. Prepare the disk holder assembly (47 mm): ensure the support screen is flat in the centre of the disk holder. Place the Atlantic® HLB-M Disk on top of the support screen with the ripples of the disk on top and add any prefilters on top of the disk. Place the disk holder assembly on the VacMaster Disk ensuring there is a tight seal with the luer fitting.
4. If using the multifunnel, place onto the disk holder assembly. If not using the multifunnel, omit those directions throughout the method.
5. Condition the SPE Disk:
   a. Guide for each conditioning step in table 3 below:
   
   i. Measure the appropriate VOLUME of SOLVENT into a graduated cylinder and pour into the disk holder assembly.
   ii. Using a Nalgene Wash Bottle (phthalate free), rinse the multifunnel and disk holder in a circle for about 3 seconds using the same SOLVENT (approximately 5 additional mL).
   iii. SATURATE the disk for the time indicated (in SECONDS). (Saturate means: quickly turn the knob to the appro- priate waste destination and back to the “OFF” position. This brings the solvent into the disk media bed).
   iv. SOAK the disk for the time indicated (in SECONDS).
   v. DRAIN to the appropriate waste destination for the time indicated (in SECONDS). Switch to the “OFF” position.
   
   

6. Load the Sample:

a. For multifunnel: quickly and efficiently angle the bottle to rest on the multifunnel upside-down.

b. For no multifunnel: pour a portion of the sample into the disk holder.

c. Adjust the vacuum between -10”Hg and -15”Hg for sample load (please note, if the sample is flowing too slowly, the vacuum can be increased). Drain the sample to “AQUEOUS” waste. Continue to pour the sample into the disk holder ensuring the disk does not go dry or overflow for the duration of sample load.

7.  Air Dry the SPE Disk:

a. Return the vacuum to -24”Hg and continue to air dry the SPE disk to “AQUEOUS” waste for an additional 60 SECONDS. Switch to the “OFF” position.

b. Remove the sample bottle from the multifunnel if it was used.

8. Elute the SPE Disk: (Please note: the elution solvent will go into the collection flask inside the chamber, not to waste containers).

a. Place a clean 125 mL 24/40 tapered Erlenmeyer flask into the Biotage® VacMaster™ Disk collection chamber. Place the cover on the chamber. Remove the disk holder assembly and place the disk holder assembly into the lure fitting on top of the collection chamber. Attach the lure fitting of the collection chamber assembly onto the manifold.
b. Guide for each elution step in table 4 below:

i. Measure the appropriate VOLUME of SOLVENT into a graduated cylinder, pour into the sample bottle, and swirl around. Pour the solvent in the sample bottle into the disk holder assembly.
ii. Using a Nalgene Wash Bottle (phthalate free), rinse the multifunnel and disk holder in a circle for about 3 seconds using the same SOLVENT (approximately 5 additional mL).
iii. SATURATE the disk for the time indicated (in SECONDS) to “ORGANIC”.
iv. SOAK the disk for the time indicated (in SECONDS).
v. DRAIN to “ORGANIC” for time indicated (in SECONDS). Switch to the “OFF” position.
vi. Remove the chamber lid to release the vacuum from inside the chamber.

Literature number: AN065-HOR