SPE in EPA method 625.1: The performance of smaller samples

Application note scope

The purpose of this application note is to outline an automated extraction method utilizing the Atlantic® 8270 OnePass SPE Disk and the Biotage automated and manual SPE solutions for the extraction of acids, bases, and neutrals in wastewater. 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^TM Disk for this application.

Environmental methods for water analysis often specify sampling 1 L of water to provide the sensitivity needed for determination of contaminants at low concentrations for health monitoring. In the past decade sensitivity of the analytical technique (GC/MS) has improved and with split/ splitless introduction and large volume injection options a wide range of concentrations can be effectively measured. Coupled with reduced concern about sample homogeneity and flexibility in sample size for automated samplers, the possibility of smaller samples bears investigation. Other benefits of smaller samples include reduced shipping costs and they are easier to handle and store than large bottles. Less solvent is needed for extraction and therefore less will be evaporated when the sample extract is reduced. If solid phase extraction is used, rather than liquid-liquid extraction, the solvent used may be further reduced.

The US EPA is becoming more flexible about this option. Methods for volatiles in water often require collection of only 5–25 mL of water for analysis. If sampling is done with a continuous sampler, 250-mL sample size is the normal sample size collected. Method 625.1 suggests that 1 L is the normal sample size, but smaller samples are allowed if the data quality objectives can be met.

This application note outlines the procedure for a dramatically reduced sample size of 100 mL. Several different matrices can be extracted, including reagent water, synthetic wastewater, and an acetic acid mixture used in the toxicity characteristic leaching procedure.

Experimental

This protocol is for the extraction of 100-mL wastewater samples for acids and base/neutrals using solid phase extraction (SPE) disk technology using the Biotage® Horizon® 5000. The solid phase extraction (SPE) disk used in this protocol is the Biotage Atlantic® 8270 One-Pass disk that allows the water to be passed through the disk only once because the sorbents included use hydrophobic, hydrophilic and ion exchange mechanisms to fully retain both acid and base/neutral analytes.

The water sample can also be passed through a carbon cartridge after the disk to retain light end and more polar analytes that may pass through the One Pass disk. The carbon cartridge was used in this work.

Outline of the SPE procedure

The sample is acidified to pH 2 with hydrochloric acid (HCl) and placed on the Biotage® Horizon® 5000 automated extractor that has been set up with an Atlantic® One Pass disk and a Max Detect Carbon Cartridge.

Acid & neutral (A&N) disk extract:

The A&N method is started on the Biotage® Horizon® 5000 where the disk is preconditioned with solvents, the sample is passed through the disk and carbon cartridge and the disk (only) is eluted with acetone and methylene chloride for
acidic and neutral semi-volatile organics (SVO). The collected extract is removed and covered until needed for the carbon cartridge extraction.

Ion-exchange disk extract:

A new collection flask is placed on the Biotage® Horizon® 5000 and the ion-exchange method is started. Here the remaining organic bases are eluted off the disk with acetone, 1% ammonium hydroxide, and methylene chloride. The collected extract is removed and covered until the DryDisk® drying step is performed.

Table 1. Acid and neutral extraction method.

*The DryVap™ system has been discontinued. We recommend using the TurboVap® evaporation systems for achieving equivalent results.

Carbon cartridge extract:

The A&N extract or a clean container is placed back on the Biotage® Horizon® 5000, the disk holder is removed and the Carbon Cartridge is attached in its place with a reservoir adapter. The carbon method is started and the light-end SVOs are eluted with acetone and methylene chloride. The combined A&N plus light-end SVO extract is removed and is now ready for extract drying.

DryDisk® drying:

The A&N plus light-end SVO extract is poured into the DryDisk® apparatus and pulled through the membrane with vacuum. The remaining water on top of the membrane is rinsed with methylene chloride and the solvent collected. The DryDisk® apparatus is rinsed with methylene chloride and the water is discarded. The DryDisk® reservoir was rinsed with acetone followed by methylene chloride and discarded before pouring in the ion-exchange extract. The ion-exchange extract is pulled through and rinsed with solvent leaving the remaining water at the top of the DryDisk®. The combined extracts are directly transferred into the DryVap™* evaporation tube for concentration.

DryVap™ concentration:

The extract is concentrated down to 0.9 mL. The tube is rinsed with methylene chloride to bring the volume to 1.0 mL and transferred to a GC vial for analysis. The conditions for the extraction step are shown in Tables 1, 2 and 3. The DryVap™ Conditions are shown in Table 4.

Table 2. Ion Exchange Extraction Method.

Table 3. Carbon extraction method.

Table 4. DryVap™ conditions.

Biotage® VacMaster™ Disk method summary

1. Repeat the following steps for each active Biotage® VacMaster^TM Disk station.
2. Setup the VacMaster Disks 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® 8270 OnePass 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. Detach the water waste one-pass lines from each other. Attach the carbon cartridge cap to the Carbon Cartridge Max Detect, put the carbon cartridge in-line with the water waste line using the one-pass kit lines, and place the cartridge upright to prevent channelling in the carbon media. (Please note: the sample will flow from the bottom of the cartridge to the top of the cartridge and to waste).
5. If using the multifunnel, place onto the disk holder assembly. If not using the multifunnel, omit those directions throughout the method.
6. Condition the SPE Disk:
   
   
   1. Guide for each conditioning step in table 5:
      1. Measure appropriate VOLUME of SOLVENT into a graduated cylinder and pour into the disk holder assembly.
      2. 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).
      3. SATURATE the disk for the time shown (IN SECONDS). (Saturate means: quickly turn the knob to the proper waste destination and back to the “OFF” position. This brings the solvent into the disk media bed).
      4. SOAK the disk for the time shown (IN SECONDS).
      5. DRAIN to proper waste destination for the time shown (IN SECONDS). Switch to the “OFF” position.
         
         Table 5. Disk Conditioning.
         

         Solvent	Volume (mL)	Saturate (sec.)	Soak (sec.)	Waste Destination	Elute (sec.)
         Acetone	8	1	180	Organic	40
         Methylene Chloride	8	1	180	Organic	40
         Methylene Chloride	8	1	60	Organic	40
         Methylene Chloride	8	1	60	Organic	40
         Methylene Chloride	8	1	60	Organic	120

7. Load the Sample:
   1. a. For multifunnel: quickly and efficiently angle the bottle to rest on the multifunnel upside-down.
   2. For no multifunnel: pour a portion of the sample into the disk holder.
   3. 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.
      
      
8. Air Dry the SPE Disk:
   1. 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.
   2. Remove the sample bottle from the multifunnel if it was used.
9. Elute the SPE Disk: (Please note: the elution solvents will go into the collection flask inside the chamber, not to waste containers)
   1. Place a clean 125 mL 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.
   2. Guide for each elution step in table 6:
      
      
      1. Measure 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.
      2. 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).
      3. SATURATE the disk for the time shown (IN SECONDS) to “ORGANIC”.
      4. SOAK the disk for the time shown (IN SECONDS).
      5. DRAIN to “ORGANIC” for the time shown (IN SECONDS). Switch to the “OFF” position.
      6. Remove the chamber lid to release the vacuum from inside the chamber.

Table 6. Disk elution (acid)

Remove the acid flask, label it, and cap it. Set aside. Continue with the base elution (table 7) following the guidelines above.

Table 7. Disk elution (base).

Remove the base flask, label it, and cap it. Set aside. Using the syringe, plunge the cartridge with air through the cap adapter to reseat the carbon bed. Remove the cap adapter and replace it with the cartridge adapter funnel. Reconnect the water waste one-pass lines back together. Remove the chamber and put the cartridge directly on the VacMaster Disk manifold and continue to the next step.

10. Air Dry the SPE Cartridge:

1. Air dry the cartridge to “AQUEOUS” waste for an additional 120 SECONDS. Switch to the “OFF” position.

11. Complete the cartridge elution (table 8) following the guidelines from step 10 for the cartridge and cartridge adapter funnel.

Table 8. Cartridge elution

Literature number: AN121-HOR