To extract a wide range of polar and non-polar compounds, such as antibiotics, from large aqueous samples (e.g., 500 mL), the most suitable solid-phase extraction (SPE) cartridge is one that offers both high capacity and versatility across different compound polarities. Based on recent studies, the hydrophilic-lipophilic balance (HLB) SPE cartridge is highly effective for this purpose.

Cartridge Selection

The Oasis HLB cartridge is one of the best choices for handling large-volume extractions of both polar and non-polar compounds. This cartridge contains a polymeric sorbent that integrates both hydrophilic and lipophilic components, providing the flexibility to retain analytes with a wide range of polarities. This balance is crucial when dealing with mixed compound classes like antibiotics, which may have varying polarities depending on their chemical structures.

The versatility of HLB cartridges has been demonstrated in multiple studies. For example, Yi et al. (2015) showed that optimizing the pH of the sample can significantly improve the extraction efficiency of antibiotics with low and high pKa values when using HLB cartridges (Yi et al., 2015). Their study highlighted how HLB materials can capture a broad spectrum of antibiotic compounds from environmental water samples, making them an ideal choice for mixed polarity analytes. Additionally, Köke et al. (2018) demonstrated that HLB cartridges outperform traditional methods for both polar and non-polar analytes in aqueous environments, ensuring higher recovery rates (Köke et al., 2018).

Protocol for Large-Volume Extraction (500 mL)

1. Preconditioning the Cartridge:

Start by conditioning the Oasis HLB cartridge with 5 mL of methanol to activate the sorbent material. Follow this by rinsing with 5 mL of ultrapure water to equilibrate the cartridge for sample introduction. This step is necessary to remove any contaminants and prepare the sorbent for efficient binding of both polar and non-polar analytes.

2. Sample Loading:

The pH of the sample should be adjusted depending on the pKa values of the target antibiotics. Antibiotics with lower pKa values (7) require neutral conditions. Studies, including those by Yi et al. (2015), have shown that adjusting the pH can lead to significantly improved extraction efficiencies, especially for polar compounds (Yi et al., 2015).

Pass the 500 mL aqueous sample through the cartridge at a controlled flow rate (10-20 mL/min). This ensures that both polar and non-polar compounds have sufficient time to interact with the sorbent, optimizing retention.

3. Washing:

After sample loading, wash the cartridge with 5-10 mL of water or a weak solvent (such as 5% methanol in water). This step removes any residual matrix interferences while ensuring that the target analytes remain bound to the sorbent.

The study by Wang et al. (2023) emphasized the importance of using sequential extraction methods to reduce competition between analytes and to prevent matrix effects that could displace polar compounds during extraction (Wang et al., 2023).

4. Elution:

For the elution of polar compounds, use 5-10 mL of methanol. This solvent has been shown to effectively elute hydrophilic analytes, while maintaining the integrity of the extraction. For non-polar compounds, a stronger solvent, such as acetonitrile or a methanol-acetonitrile (1:1) mixture, should be used. This ensures maximum recovery of both polar and non-polar compounds, as noted in the work of Sajid & Basheer (2016) on SPE methods (Sajid & Basheer, 2016).

Ensure complete elution by passing the solvent slowly and thoroughly through the cartridge.

5. Post-Elution Concentration:

The eluted fractions should be evaporated to dryness using a gentle stream of nitrogen or a vacuum concentrator. This step concentrates the analytes, preparing them for further analysis, such as liquid chromatography-mass spectrometry (LC-MS).

Reconstitute the dried extract in a small volume (1-2 mL) of methanol or a similar solvent before analysis.

pH Optimization for Efficient Extraction

As mentioned earlier, optimizing the sample pH is critical for maximizing the recovery of both polar and non-polar compounds. Antibiotics with different pKa values respond differently to extraction conditions. Yi et al. (2015) demonstrated that adjusting pH for polar compounds significantly enhances recovery rates. Polar antibiotics, particularly those with lower pKa values, are best extracted at acidic pH, while non-polar compounds are better captured at neutral to slightly alkaline pH (Yi et al., 2015).

Conclusion

For extracting a wide variety of polar and non-polar antibiotics from large aqueous samples, the Oasis HLB cartridge is highly recommended due to its hydrophilic-lipophilic balance, which ensures broad-spectrum retention of analytes. By using the outlined protocol, including steps such as pH optimization, precise washing, and tailored elution, you can maximize the efficiency of your extractions. The results from Yi et al. (2015) and Köke et al. (2018) provide robust evidence for the effectiveness of this approach in handling both polar and non-polar compounds across diverse matrices (Yi et al., 2015), (Köke et al., 2018).

Here are the references:

1. Köke, N., Zahn, D., Knepper, T., & Frömel, T. (2018). Multi-layer solid-phase extraction and evaporation—enrichment methods for polar organic chemicals from aqueous matrices. Analytical and Bioanalytical Chemistry, 410(10), 2403-2411. https://doi.org/10.1007/s00216-018-0921-1

2. Sajid, M., & Basheer, C. (2016). Stir-bar supported micro-solid-phase extraction for the determination of polychlorinated biphenyl congeners in serum samples. Journal of Chromatography A, 1455, 37-44. https://doi.org/10.1016/j.chroma.2016.05.084

3. Wang, Y., Zhou, W., & Pawliszyn, J. (2023). Sequential solid-phase microextraction with biocompatible coating materials to address displacement effects in the quantitative analysis. Analytical Chemistry. https://doi.org/10.1021/acs.analchem.3c00508

4. Yi, X., Bayen, S., Kelly, B., Li, X., & Zhou, Z. (2015). Improved detection of multiple environmental antibiotics through an optimized sample extraction strategy in liquid chromatography-mass spectrometry analysis. Analytical and Bioanalytical Chemistry, 407(30), 9071-9083. https://doi.org/10.1007/s00216-015-9074-7

I hope that helps you if you have another question just ask.

For extracting both polar and non-polar antibiotics from large (500 mL) aqueous samples, use solid-phase extraction cartridges, which offer high capacity and versatility. A recommended protocol includes conditioning the cartridge, loading the sample, washing, eluting with a suitable solvent, and concentrating the extract for analysis.

Dear Phil Käding and Abdelhak Maghchiche

Thanks for your time,

I have a few doubts regarding large-volume (500 mL) sample extraction using SPE:

For reference, we are using a positive pressure SPE assembly (48-position): Agilent Positive Pressure Manifold 48 Processor.