Making HPLC More Sustainable

There is a lot we can do to optimize our methods.

Often, we are only aware of a fraction of the possibilities, as technical options are usually available only to those who have worked for several years with a specific instrument.

However, there are several actions we can take that are simple in nature and will greatly benefit not only the environmental impact but also the time, money, and sample required.

I want to give you an (almost) exhaustive list of opportunities I am aware of for optimizing your HPLC workflows.

I created this list because there are plenty of opportunities, but you should be able to review it quickly to identify where you might find unused potential in your lab:

I compiled the following:

I’ll start with Technical Components & Set-up, because I think these are low-hanging fruit: the practices are straightforward, and add-ons can be quickly purchased and installed—even by non-experts.

Before we start, big shout out to Michael Meyer who significantly helped with collecting these ideas!

Technical Components & Setup for a More Sustainable HPLC

Let us start with some technical tips and gadgets that will greatly benefit your work, health and the environment:

SCAT filter units for eluent and waste bottles are an effective way to improve both safety and sustainability in the lab.

Why it matters: Reduced solvent evaporation lowers VOC emissions and solvent waste, and using the right size filter minimizes unnecessary material use.

Protecting the Column and Reducing Waste

Inline filter frits for the eluent system protect the column from particles and contamination, extending its lifetime and reducing the need for costly replacements.

Why it matters: Column replacements are expensive and resource-intensive to manufacture. Protecting them saves money and reduces environmental impact.

Minimizing Dead Volume with Smart Capillaries

Dead-volume-free capillary connections (e.g., Thermo Viper / nanoViper) significantly improve efficiency and sustainability.

Why it matters: Lower dead volume and reproducible fittings improve separation quality, save solvent, and reduce the number of re-runs caused by leaks or poor connections.

Preparing the System Before Runs

Proper preparation reduces errors, prevents re-runs, and extends the lifetime of expensive components — saving time, money, energy, and solvents.

System Care After Sequences

Post-run maintenance protects both the column and the instrument, reducing the frequency of repairs and replacements.

Adapting Methods to Your Column Dimensions

When using a column with different dimensions from the one specified in a method (e.g., from a paper), adjustments are essential to maintain performance.

Modern Column Selection and Method Adaptation

Why Column Choice Matters for Sustainability

Liquid chromatography consumes significant amounts of solvents, particularly methanol and acetonitrile — globally estimated at over 150,000 tons per year. Producing and disposing of these solvents has a considerable carbon footprint. Even small efficiency improvements can significantly reduce waste when multiplied across thousands of runs.

One of the most direct ways to reduce HPLC’s environmental impact is by reducing column internal diameter (i.d.) and optimizing method parameters accordingly. This cuts mobile phase use, lowers waste, and can even improve sensitivity.

Narrow-Bore Columns: Small Changes, Big Savings

Advantages:

Considerations:

Translating Methods to Smaller Columns

When switching to a smaller i.d., you must scale flow rates and injection volumes to maintain performance:

Practical tip: Use free online method translation tools (e.g., Agilent Method Translator, Restek Pro EZLC) to calculate correct flow rates, gradient times, and injection volumes for your new column size.

Reducing column length (L) while maintaining particle size lowers analyte retention time and shortens the run. Halving the column length can cut mobile phase consumption by ~50%. If the particle size (dP) is also halved (keeping L/dP constant), the same separation efficiency can be maintained — meaning you save time and solvent without losing performance.

Benefits include:

Translating Legacy Methods to Modern Formats

Many older methods still use 250–150 mm, 4.6 mm i.d. columns packed with >5 μm particles. These can often be translated to shorter columns with smaller particles while keeping the same stationary phase chemistry to preserve selectivity and peak spacing.

Example solvent savings:

Energy savings:

Very Short Format Columns

For some applications, excess separation efficiency can be traded for speed and solvent savings.

Example: Translating a 150 × 4.6 mm, 5 μm C18 method to a 30 × 2.1 mm, 1.7 μm C18-PFP column gave better resolution than the original method while greatly reducing solvent use.

Ultra-Short Cartridges for Targeted Analysis

With LC–MS, full separation isn’t always needed — as long as analytes are retained long enough to separate from interferences.

Practical Tips for Implementing Shorter Columns

Choosing the Right Column for the Job

The right column choice can dramatically improve both efficiency and sustainability. Still:

Tip: Always know the minimum column specifications required for your analytes. Consult:

Some suppliers provide online column search tools based on analytes; in the past, mobile app solutions were discussed, though availability should be verified before relying on them.

Solid Core Particles

Solid core (superficially porous) particles improve kinetic performance compared to fully porous silica.

Key benefits:

Practical tip: The extra efficiency can be traded for sustainability by using shorter solid core columns (50–75 mm), further reducing run time, solvent use, and energy consumption without sacrificing resolution.

UHPLC and Particle Size Advantages

Modern UHPLC systems (>1,500 bar) support smaller sub-2 μm fully porous particles or superficially porous particles in narrow-bore columns. These allow:

Note: While UHPLC hardware is optimized for low dispersion, the principles of narrow-bore column scaling also apply to conventional HPLC.

Shorter and Smarter Gradients

Most HPLC users stick with the gradient they first developed — or copied from a paper — without questioning if it’s the most efficient. But gradients are one of the biggest levers for sustainability: shorten them, optimize them, and you save solvent, energy, and time every single run.

Why gradients matter

A gradient isn’t just a ramp of mobile phase composition. It determines:

Unoptimized gradients often mean unnecessary “flat” baseline time, overlong separation windows, or excessive re-equilibration — all of which waste solvents and hours.

What shorter gradients can achieve

Scientific studies show that halving run times by adjusting gradient slopes can save 40–60% mobile phase per injection without losing separation quality. For example:

In practice, this means one lab running 50 injections a week could save multiple liters of acetonitrile per month — simply by trimming dead time.

2 Tips to optimize gradients

  1. Remove unnecessary plateaus
    Look at your chromatogram: are there long stretches where nothing elutes? Those are prime candidates for trimming.
  2. Steepen the slope strategically
    Instead of a slow, linear gradient, use segmented ramps: shallow slopes where resolution is critical, steeper slopes where analytes elute cleanly apart.

A note on regulations vs. flexibility

If you’re working under pharmacopeial methods (e.g., in pharma QC), gradient changes aren’t always allowed — regulatory frameworks often require methods to be followed exactly, even if they’re almost obsolete and wasteful. In academic or research settings, however, you usually have much more freedom. Don’t be afraid to question inherited methods: trimming gradients or re-optimizing equilibration can save solvents and time without breaking any rules.

UHPLC can make a difference Modern UHPLC systems (ultra-high pressure LC) allow the use of smaller particles and shorter columns while maintaining separation efficiency. This means gradients that once took 30–40 minutes on a 5 µm, 250 mm column can often be completed in 10–15 minutes on a 50–100 mm, sub-2 µm column — with equivalent or even better resolution, and a fraction of the solvent use.

Flow Rate Optimization

UV Detection and Flow Rate: Practical Implications

Sustainability takeaway:
Reducing flow rates without increasing total rune time decreases solvent use and can increase sensitivity for certain analyses, potentially allowing you to inject smaller sample volumes and shorten gradients.

Greener Alternatives to Conventional HPLC Eluents

Switching solvents is one of the most direct ways to make HPLC more sustainable – but it’s also one of the most complex. The choice of organic modifier in a mobile phase affects everything: separation efficiency, system back pressure, detector compatibility, method robustness, and even instrument wear.

For decades, acetonitrile (ACN) has been the default choice but greener alternatives do exist — from bio-based alcohols like ethanol to emerging solvents like ethyl lactate and Cyrene. While every substitution has to be well considered, if established they are much greener and in several cases even improved process and data quality. Moreover, incidents like the “Acetonitrile Crisis” showed how a bottleneck in ACN supply can limit research processes and drive prices significantly higher.

Therefore, the sections below outline realistic solvent alternatives, their pros and cons, and practical tips for implementation – so you can make informed changes without sacrificing chromatographic performance.

Why Focus on Acetonitrile (ACN) Reduction or Replacement?

Acetonitrile (ACN) is one of the most widely used organic solvents in reverse-phase HPLC due to its:

However, ACN has drawbacks:

Reducing or replacing ACN can therefore lower environmental impact, improve laboratory resilience, and sometimes reduce costs. Below are realistic, technically tested alternatives.

Ethanol (EtOH)

Pros:

Cons & considerations:

Practical tips:

Propylene Carbonate (PC)

Pros:

Cons & considerations:

Ethyl Lactate

Pros:

Cons & considerations:

Example:
A mobile phase of 87% water, 10% ethyl lactate, 3% acetic acid achieved baseline separation of three pharmaceuticals on a C18 column at 60 °C in under 3 minutes.

100% Aqueous Mobile Phases

Pros:

Cons & considerations:

Cyrene

Pros:

Cons & considerations:

Example:
In RP-HPLC, ternary mixtures of Cyrene + ethanol + buffer allowed separation of metronidazole and moxifloxacin at 50 °C on a monolithic column with acceptable back pressure (~130 bar).

Practical Strategies for Using Alternative Eluents

  1. Start with partial replacement (e.g., replacing 20–30% ACN with EtOH) to evaluate performance.
  2. Adjust temperature to manage viscosity-related back pressure.
  3. Use compatible columns — superficially porous or monolithic formats often handle viscous solvents better.
  4. Validate sensitivity impact — higher UV cut-off solvents may require detection at higher wavelengths or MS-based detection.
  5. Test method robustness — alternatives may affect retention time stability under small variations in pH, temperature, or composition.

Smarter Method Development

Optimizing Sample Preparation

When people think about making HPLC greener, they usually start with the instrument — smaller columns, alternative solvents, clever fittings. But sample preparation is often the hidden giant in both time consumption and environmental footprint. It’s easy to overlook because it feels like “the routine bit before the actual analysis.” Yet, if you optimise your prep, you can save hours of work each week and cut waste dramatically.

Why optimising it matters:

Practical changes that deliver:

Using Combination Method

If you plan to use an HPLC–MS (LC–MS) approach, there are often opportunities for savings that go beyond just getting great data. LC–MS setups are already among the most sensitive analytical systems available — often 10–1000× more sensitive than UV detection — which means you don’t always need the long columns, high flow rates, or large sample volumes that standard HPLC methods rely on.

Why This Matters for Sustainability

Capillary HPLC for LC–MS

Capillary HPLC reduces column internal diameter to 100–500 μm, running at 0.4–100 μL/min instead of the 1–2 mL/min of a typical analytical column.

In practice, this means:

Solvent Recycling: Turning Waste Back into Usable Mobile Phase

In isocratic HPLC, the mobile phase composition stays constant throughout the run. This means that the solvent exiting the detector is identical in composition to the one entering the column — apart from minor changes due to analyte and impurity carryover.

This makes it straightforward to collect the “clean” post-detector solvent and feed it back into the mobile phase reservoir after appropriate filtration and (if necessary) degassing.

In gradient elution, however, the mobile phase composition changes over time, so the effluent is constantly varying in proportion of organic and aqueous components. Recycling would require real-time composition matching — impractical in most lab setups and potentially risky for method reproducibility.

Solvent Recycling Systems

Basic principle of solvent recycling can summarized as: divert the post-detector solvent to a collection system.

There are two main approaches:

A. Manual Recycling (No Computer Support)

Pros:

Cons:

Automated Recycling (Computer-Controlled)

Pros:

Cons:

Practical Considerations for Safe Recycling