Many of the most commonly used solvents in analytical workflows aren’t considered “green” – often volatile, toxic, and derived from non-renewable petrochemical resources. Analysts have, therefore, sought out greener alternatives, relying on environmental, health, and safety data to make an informed choice. However, Elia Psillakis, from the School of Chemical and Environmental Engineering at Technical University of Crete, Greece, believes that, while important, this lens is too narrow.
“Relying solely on these data can create an illusion of greenness, where risks are relocated to another stage of the solvent’s life cycle,” says Psillakis. “A solvent favored by this limited view might be ruthlessly energy-intensive to produce, or pose major challenges in waste treatment.”
To fill this void, Psillakis and colleagues created GreenSOL, a comprehensive solvent selection guide which reveals the full life story of solvents from production to disposal. “The aim was to help analysts understand hidden costs, risks, and trade-offs from a life-cycle perspective,” she says.
GreenSOL is also the first guide tailored specifically to solvents used for analytical chemistry. “The needs of analytical chemistry are distinct,” says Psillakis. “A key innovation that highlights this analytical focus is the inclusion of deuterated solvents, essential for techniques like NMR but previously overlooked in green solvent guides.”
We caught up with Psillakis to find out more about the GreenSOL, whether there were any surprises when solvents are ranked according to their full lifecycle impact, and what practical tips analysts can take away to improve the greenness of their methods.
Pharmaceutical companies have developed several solvent guides over the years. Why do you think similar tools haven’t emerged for analytical chemistry?
The solvent selection tools developed by major pharmaceutical companies are essentially the same as those used by the broader fine chemical batch chemical operations. The pharmaceutical industry has led in this area for two key reasons: the enormous scale of solvent use in drug manufacturing – accounting for 80–90 percent of the total mass used – and the strong regulatory pressures to minimize impacts.
In contrast, analytical laboratories have historically operated under less regulatory pressure. So, progress toward greener solvents – and to be fair, toward Green Analytical Chemistry as a whole – has been more gradual and fragmented. The delay in proposing a solvent guide was also rooted in a persistent perception gap: the small solvent volume per analysis led to an underestimation of its cumulative impact.
However, unlike industrial processes, solvent use in analysis is highly diffuse – spread across countless laboratories worldwide, rather than concentrated in a finite number of large facilities. While each laboratory may be a minor point source, the sector collectively functions as a significant, diffuse source of solvent waste. Therefore, our core challenge is not managing a single industrial batch reactor, but influencing millions of small, daily decisions at analytical labs. The most effective path forward in our field lies in a combination of top-down regulation, education, cultural change, and providing tools like GreenSOL to empower millions of analysts.
How did you approach selecting which solvents to include, given the diversity of applications across analytical chemistry?
Our objective was to ensure broad coverage across the chemical classes and physicochemical properties essential for the diverse applications of solvents in analytical chemistry. The selection began with a foundational list of solvents commonly used in, e.g., sample preparation, separation, and spectroscopy. This list was then cross-referenced with major chemical supplier catalogs to identify solvents that we might have missed and finally expanded through a comprehensive review of analytical applications to capture important niche solvents. The final selection includes 58 solvents: 49 common and less-common organic solvents, plus 9 deuterated solvents.
A significant challenge in building our solvent list was data availability. Our initial candidate list was larger, but Life Cycle Inventory (LCI) data – essential for calculating the production phase score – was missing for certain solvents. In such cases, we tried to identify proxy processes based on chemical structure and production pathways, and if this was not possible, the solvent was excluded from the final assessment. We also encountered data discrepancies and gaps for key parameters of some solvents, such as vapor pressure or autoignition temperature. These issues are not new in the literature, and our methodology transparently details the approaches we adopted to address them.
What criteria form the backbone of the GreenSOL scoring system?
GreenSOL is based on a three-phase life-cycle evaluation: production, laboratory use and waste. Each phase is broken down into key sub-categories and depends on many attributes. The guide provides both composite phase scores and individual sub-category scores that range from 1 (least favorable) to 10 (most recommended), enabling transparent identification of high-impact stages across a solvent’s entire life.
The three phases evaluated are:
● Production Phase: Quantifies the upstream environmental burden using a cradle-to-gate Life Cycle Assessment (LCA). The key sub-categories are Cumulative Energy Demand and environmental impact during production.
● Use Phase: Assesses immediate laboratory risks by considering physical and health hazards.
● Waste Phase score: Evaluates the downstream fate of the solvent through two lenses:
○ Environmental Impact: The impact to aquatic species and air resulting from an uncontrolled solvent release into the environment.
○ Treatment Potential: The effectiveness of controlled disposal via the three most common methods: biotreatment, recycling, and incineration.
A key design principle was to avoid redundant penalization for a particular property. We ensured that a single solvent characteristic (e.g., high volatility) is accounted for appropriately within each phase, preventing unfair multiple penalties for the same characteristic.
Did any of the scores or life-cycle findings surprise you?
I was struck by the excellent production scores of some conventional solvents – notably alkanes, like hexane and heptane, and simple alcohols, like methanol and ethanol. These perfect scores reflect their highly optimized industrial production, characterized by low emissions and high energy efficiency. However, this finding raised a provocative question: if these fossil-derived solvents are such high performers in production, are their bio-based counterparts truly greener? This is especially relevant for biosolvents like first-generation bioethanol, whose crop-based production competes directly with food supply and land use.
In many ways, GreenSOL is full of surprises, precisely because it exposes an uncomfortable reality: solvent greenness is a complex, multi-layered compromise, and not a simple label. Our results powerfully reinforce the need to evaluate the entire lifecycle. For instance, we were not surprised to see hexane score poorly in the lab use phase. However, its proposed “greener” replacements reveal their own trade-offs. Pentane reduces laboratory risks but has a substantial environmental impact upon uncontrolled release, and heptane lowers health risks but retains high physical hazards and poses a greater risk to aquatic species.
What do your results suggest about current solvent choices in analytical labs?
The field is certainly moving in a greener direction, driven by growing awareness among analysts. However, many analytical labs don’t have the operational “freedom” to choose their solvents and remain “locked in” to using options with surprisingly high lifecycle impacts. This barrier is particularly significant for labs that follow official standard protocols, which often discourage or prohibit solvent substitution.
The scale of this effect was quantified in our recent IUPAC study, which assessed 174 official standard methods and their 332 procedural variations. Using the AGREEprep metric, we found that 67 percent of these methods scored below 0.2, where 1 represents the maximum possible greenness score. This poor performance stems from a combination of poor solvent choices, use of toxic reagents, and reliance on energy-intensive, outdated techniques. So, while awareness is growing, this institutional inertia shows that the transition to greener practices is still in its early stages. Tools like GreenSOL are designed to accelerate this shift by providing the data needed to question, and eventually update, these entrenched standards.
For analysts looking to improve the greenness of their workflows, are there any practical “quick wins”?
There are no such things as “quick wins” in greenness. Meaningful progress requires deep changes, patience, and solving root problems rather than just symptoms. While easy shortcuts do not exist, GreenSOL’s free web app supported by Shimadzu Europa and TUCrete, provides actionable steps by transforming the guide from an academic exercise into a decision-support system for routine lab work, method development, and educational training.
Here are actionable steps:
Use the GreenSOL web app to inform every solvent choice. Analysts can interactively visualize the data and filter solvents by chemical class or the physicochemical properties their method requires. The app will instantly reveal viable alternatives within that subset.
Set and enforce green procurement and safety standards using GreenSOL’s scores. Exclude any solvent with a critically poor score in a non-negotiable category, such as a health hazard. For the rest, use sub-category scores to select the option with the least overall burden, making informed trade-offs between, for example, production energy demand and waste treatment viability.
Optimize your waste stream using the waste phase data to build your waste treatment strategy. For solvents with high recycling scores, implementing even simple on-site recovery can turn a costly lab into a circular asset.
And don’t forget that the color-coded tables and interactive web tool can be used as training material to foster a “green” culture among students and staff.
In developing the guide, were there overarching lessons or principles that emerged about how to think about solvent choice more holistically?
One thing that GreenSOL teaches us is that greenness is about navigating inevitable trade-offs with greater responsibility and insight. Transparency is key to avoiding burden shifting. A solvent guide must reveal – not conceal – trade-offs. If we only look at toxicity, we might miss a high energy burden. If we only look at production, we might create a waste problem. The holistic approach forces us to ask: "Are we solving one problem by creating another elsewhere in the solvent's life?" This life cycle thinking is the overarching lesson.
There’s ongoing debate about whether a solvent can ever truly be considered “green.” From your perspective, how useful is the concept of a “green solvent,” and is reducing or eliminating solvent use ultimately the more realistic goal?
The search for a perfectly green solvent is like chasing a myth. No single solvent satisfies all criteria across its entire life cycle. Consider water, which typically ranks highest in green solvent guides. In GreenSOL, water achieved perfect scores for its production and laboratory use phases. However, its score for waste treatment was moderate – and only the biotreatment option received a perfect score. One point to think about is that all solvent guides evaluate the treatment of pure water, whereas aqueous waste from analytical labs is typically contaminated with various chemicals, the removal of which in a wastewater treatment plant can be a challenge.
In reality, a green solvent is the one you do not use. Our practical goal is not to pursue a mythical "green" solvent, but to make informed choices that minimize overall impact. Indeed, the biggest gains from our considerable efforts in reducing solvent impacts are directly related to decreases in solvent use and method optimization. So rather than debating about green solvents, it is probably better to shift the conversation toward minimizing solvent use and understanding their life-cycle impact.
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