Rethinking Food Testing with Dried Spot Microsampling

Q. How does the automated DBS extraction system work and what are its advantages over manual methods?

A: Automated extraction of the wine dried spots (Wine-DS) is implemented using a DBS autosampler, which combines robotic handling of DBS cards and automated spot extraction by flow-through desorption.¹ After a small volume of wine (10 μL) is deposited and dried on a paper card, the cards are placed into the card rack and then a robotic arm transfers each card to the extraction module, where digital images are automatically acquired before and after extraction. The extraction module comprises an extraction head, where the card is clamped and desorption takes place, with different clamp diameter options available. The extraction solvent is passed through the clamped area of the card at apredetermined volume and flow rate, generating an extract ready for liquid chromatography–mass spectrometry (LC–MS) analysis. After each extraction, the system performs an automated cleaning cycle to prevent carryover.

The manual preparation of the dried spots is usually tedious, involving punching of the discs followed by extraction in a tube or a multi-well device and/or additional sample pretreatment. These steps can becircumvented with the use of a robotic DBS extraction system, which only requires manual insertion of a batch of cards into the card rack at the start of the analytical run. The automated extraction systemoperates with minimal operator attendance and risk of errors, while achieving high-throughput analysis and improved reproducibility. Importantly, the sample remains physically linked to the original card throughout the process, preserving traceability and minimizing the risk of sample misidentification. Furthermore, the use of such systems reduces organic solvents consumption compared to manual preparation, hence making the approach environmentally friendly and well suited for routine, high-capacity analytical workflows.

Q. How were the extraction parameters optimized for the analysis of wine dried spots?

A: Being a rich source of bioactive constituents, wine is an aqueous matrix presenting a complex chemical profile. Several extraction parameters were carefully adjusted to enhance sensitivity and cover the entire spectrum of metabolites. This is of critical importance for comprehensive characterization of complex food matrices such as red wine, where even minor constituents can influence quality attributes.

Optimization of the automated extraction procedure for Wine-DS included the evaluation of different extraction solvent systems and compositions, both in terms of extraction efficiency and metabolome coverage, using untargeted liquid chromatography–high-resolution tandem mass spectrometry (LC–HRMS/MS) analysis. A mixture of 80:20 (v/v) water–acetonitrile proved to be the most promising system for non-selective extraction, providing comparable results to benchmark sample preparation procedures conventionally used for wine analysis, while ensuring good repeatability andextraction efficiency. Further optimization of extraction solvent volume and flow rate additionally improved method sensitivity. Moreover, during method optimization, whole-spot extraction using an 8-mm clamp head provided improved chromatographic performance and repeatability compared to partial spot extraction.

Importantly, one of the most convincing arguments supporting the applicability of the Wine-DS/Food-DS approach was the direct comparison with classical, already established methods routinely used for wine metabolomic profiling. The highly comparable chemical profiles obtained between conventional sample preparation and the Wine-DS workflow strongly support the reliability and robustnessof the proposed methodology (Figure 1).

Q. What are the potential limitations when applying this method to solid foods versus liquids?

A: Since the proposed workflow was specifically developed for wine and generally liquid products, otherfoodstuffs may require some matrix-specific optimization. While liquid samples are the moststraightforward to apply in the dried spot format, solid food matrices can also be successfully analyzed following a simple preliminary pretreatment step, such as homogenization and extraction, to obtain a solution suitable for deposition onto the paper card.

Given the inherent heterogeneity of many solid foods, careful sampling is important to ensure that the collected aliquot is representative of the overall sample. In addition, depending on the sample composition (for example, lipid, sugar, or protein content), matrix-related effects may influence spot spreading, drying behavior, and spot homogeneity. Nevertheless, these parameters can be optimizedaccording to the characteristics of each food matrix, highlighting the versatility and broader applicability of the dried spot approach. Indeed, we have already preliminarily applied this methodology to hemp extracts and obtained very promising metabolite profiling results, further supporting its potential applicability to diverse matrices.

Q. How does the chemical stability of wine compounds change when dried on paper cards?

A: Wine samples spotted onto paper cards, left to dry at ambient laboratory conditions, and then stored for a short-term period (up to a few days) did not show noticeable differences in chemical profiles, despite the exposure to air during drying, when compared to conventionally treated fresh samples (simple dilution). This suggests that Wine-DS are chemically stable over a timeframe practical for sample transport from the sampling site to the analytical facilities via regular post. This observation is supported by previous findings,^2,3 where the dried spot format has been shown to improve analyte stability in biological matrices compared to liquid samples. Nevertheless, the present results refer to short-term stability under the conditions evaluated. Comprehensive long-term stability studies using diverse wine types are still required to fully validate this new, dried spot approach for wine analysis.

Q. What other food matrices could benefit from this dried spot approach?

A: Dried spot techniques applied to food matrices may offer a promising solution to existing challenges in food quality assessment, significantly streamlining logistics by eliminating cold-chain requirements, reducing transportation complexity, and substantially lowering overall shipping and storage costs, while also minimizing the required sample volume. Various highly commercialized food matrices rich in bioactive constituents that require effective quality monitoring to ensure consumer safety, such as olive oil, edibleoils in general, honey, and spirit beverages, could be characterized using the dried spot microsampling technique following appropriate matrix-specific optimization. Applications such as quantification of authentication markers in olive oil and other edible oils, as well as detection of antibiotic residues in honey, could be facilitated with dried spot microsampling, reducing the need for liquid–liquid extraction. For example, in on-site sampling scenarios, raw milk collected at remote locations could be screened for antibiotic residues or aflatoxins. Moreover, the potential applications of this technique are not limited solely to foodstuffs. Liquid samples generally represent the most straightforward application domain.These include authentication, traceability studies, and regulatory compliance testing of beverages such as coffee, juices, fermented beverages, and spirits.

Q. How does this method address current challenges in food supply chain quality control?

A: The proposed approach provides an attractive solution to existing analytical bottlenecks and logistical constraints across the food quality monitoring chain. First, dried spot microsampling constitutes an easy and rapid microsampling technique requiring only a minute sample volume (typically 10–30 μL), while thelightweight card format enables convenient sample transportation via regular postal services, practically allowing worldwide sample transfer. As a result, the dried spot format greatly reduces the need for cold-chain requirements (dry ice, temperature-controlled packaging, overnight courier services) for degradation-prone matrices and facilitates remote sampling even by non-specialized personnel(producers in the field), who can collect, dry, and mail samples directly to analytical laboratories using only a paper card and a desiccant pouch.

Unlike conventional methods that require freezers and specialized laboratory equipment, the dried spot format can be conveniently employed in low-resource and decentralized environments. Moreover, theminimal sample quantity and the non-liquid nature of dried spot samples may help overcome legal and logistical restrictions associated with the international transport of food products and biological materials, including limitations frequently encountered during cross-border shipment of products such as honey and other food commodities. This significantly simplifies international sample exchange for collaborative studies and routine monitoring purposes.

In addition, dried spot microsampling offers a substantially lower-cost alternative to traditional sampling approaches that rely on expensive cold-chain logistics, thereby rendering regular quality monitoring affordable for small-scale producers. With respect to long-term storage, the minimal physical footprint of paper cards substantially reduces space requirements compared to conventional liquid vials or bottles, enabling high-density food specimen archives analogous to clinical biobanks. This supports space-efficient long-term sample preservation for retrospective and other analytical applications.

It is worth noting that the Wine-DS or Food-DS workflow can be easily integrated with a wide range of analytical platforms and detection systems, such as high performance liquid chromatography (HPLC)–UV, thereby further extending its applicability depending on the analytical objective. Overall, the proposed workflow is highly suitable for large-scale metabolomic studies, both targeted and untargeted, as itsubstantially reduces analytical time, operational effort, and cost, while simultaneously enhancing the robustness, reproducibility, and overall reliability of the analytical pipeline.

References

1. Deli, I.; Tzimas, P. S.; Beteinakis, S.; Halabalaki, M. Introducing Dried Spot Techniques in Food Characterization: The Case of Red Wine. J Chrom A 2025, 1757, 466113. DOI: 10.1016/j.chroma.2025.466112
2. Jacques, A. L. B.; Santos, M. K.; Gorziza, R. P.; Limberger, R. P. Dried Matrix Spots: An Evolving Trend inthe Toxicological Field. Forensic Science, Medicine and Pathology 2022, 18 (1), 86–102. DOI: 10.1007/s12024-021-00434-5
3. Palmer, E. A.; Cooper, H. J.; Dunn, W. B. Investigation of the 12-Month Stability of Dried Blood and Urine Spots Applying Untargeted UHPLC-MS Metabolomic Assays. Anal Chem 2019, 91 (22),14306–13. DOI: 10.1021/acs.analchem.9b02577