The determination of dispersed oil in water using automated SPE in compliance with OSPAR and ISO 9377-2 methods in Norway

Scope

This application note will outline the appropriate methods for the extraction of dispersed oil in water in compliance with OSPAR and ISO9377-2 methods, using Biotage automated or manual SPE solutions. 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 vacuum manifold for this application.

Introduction

Accurate measurement of dispersed oil-in-water (OIW) has become increasingly more important as international regulations are implemented, including the 2000/2001 Oslo/ Paris Convention (OSPAR) and ISO 9377-2, the UK Dispersed Oil in Produced Water Trading Scheme, and the Norwegian State Pollution Control Authority (SFT). Each of these regulations now requires offshore oil platforms to monitor their discharge into the sea. OSPAR also recommends that no individual offshore installation should exceed a set performance standard for dispersed oil of 30 mg/L for produced water discharged into the sea. Oil refineries in the designated regions are also beginning to comply to both the OSPAR method and ISO 9377-2.

With the implementation of these regulations, it is imperative that offshore platforms and refineries demonstrate to regulators and government bodies that effective and accurate OIW monitoring is taking place, as non-conformance to these regulations can result in financial penalties. In addition to the benefits to the environment and opportunities to participate in emission trading schemes, reduced OIW concentrations also reduce the clogging of disposal wells, lines, pumps, and valves thereby reducing the total cost of maintenance.

OSPAR now recommends using gas chromatography and flame ionization detection (GC-FID), as described in the modified ISO 9377-2 GC-FID. Although the legal requirement to use this analysis method has not yet been mandated, and because chlorinated solvents can no longer be used, Norway has chosen to adopt this method. The implementation of these new methods has many oil refineries researching the impact of bringing both sample preparation and testing on-site, as outsourcing can be expensive.

The use of solid phase extraction (SPE) eliminates many of the problems that can occur during the extraction step. SPE involves passing the liquid sample through a solid phase disk. This eliminates emulsions totally and therefore the use of chemicals that would be required to break these emulsions.

The use of an automated SPE system decreases solvent usage, the amount of operator time involved and improves the accuracy and consistency of results. This can save a laboratory a substantial amount of money in the long run as compared to conventional extraction techniques.

Instrumentation

• Biotage Instruments
  »  Biotage® Horizon 5000 Automated Extraction System
  » Atlantic® DVB SPE Disk
• 125 mL separatory collection vessel
• Gas Chromatograph w/ Flame ionization detector
• Absolute Standards: BAM K0009 reference oil (PN: 95200)
  
  

Method summary

1. 1000 mL water samples are used and weighed to calculate actual volume. Adjust to a pH of 2.0.

2. Spike any control samples with 4.0015 mg of the reference oil.

3. Place the sample bottle on the Biotage® Horizon 5000 Extraction System and place the Atlantic® DVB disk in the standard 47mm disk holder.

4. Place the separatory funnel on the extractor with 1 mL of DI water in it (to help draw out any trace water from the pentane phase).

5. Start the method shown in table 1 below and collect the final elution.

6. Decant the lower methanol/water layer to waste.

7. Measure the amount of pentane in the final collection volume.

8. Spike the volume with C10 and C40 to allow the limits of integration to be easily identified.

9. Analyze by GC/FID.

Acknowledgements

Biotage would like to extend our thanks to Merat Behzadzadeh of StatoilHydro, Mongstad, Norway and Terje Aasoldsen, Managing Director, Samsi Analytical Applications Services, Nustadveien, Norway.

Application modifications

Biotage® VacMaster™ Disk method summary

1. Repeat the following steps for each active Biotage® 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 (47mm): ensure the support screen is flat in the centre of the disk holder. Place the Atlantic® DVB 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 manifold 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 2 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 appropriate 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 125mL 24/40 tapered Erlenmeyer flask into the VacMaster™ Disk collection chamber. Place the cover on the chamber. Remove the disk holder assembly and place the disk holder assembly into the luer fitting on top of the collection chamber. Attach the luer fitting of the collection chamber assembly onto the manifold.
b. Guide for each elution step in table 3 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 the time
indicated (in SECONDS). Switch to the “OFF” position.
VI. Remove the chamber lid to release the vacuum from inside the chamber.

Literature number: AN037