Rethinking Pharmaceutical Drying: How mass spectrometry is transforming visibility, control, and production confidence

Drying is one of the most deceptively critical steps in pharmaceutical manufacturing. It’s a moment that seems quiet on the surface, but beneath it lies a cascade of implications for quality, throughput, and compliance. Whether drying removes water, ethanol, isopropanol, or more complex solvent mixtures, getting this step right is foundational.

Historically, the drying process has been governed by two forces: tradition and safety margin. Batch after batch, timelines are padded to ensure compliance with loss-on-drying (LOD) limits. But this conservative approach comes at a cost—lost time, over-drying, increased risk of polymorphic changes, and reduced responsiveness.

As the pharmaceutical industry faces accelerating demands for speed, traceability, and control, the limitations of outdated drying strategies are being exposed. In response, leading manufacturers are shifting toward continuous monitoring using process mass spectrometry—an approach that captures solvent dynamics in real time and enables control at the molecular level.

Drying delays in a time-sensitive world

In traditional operations, the success of a drying cycle is determined at the end. After hours of processing, a sample is pulled and analyzed. If residual solvent exceeds specifications, the batch is sent back through the process. In vacuum systems, that can mean depressurizing, sampling under risk of exposure, and often, complete restart.

To avoid these failures, manufacturers increase drying times by hours or even days. But this introduces a ripple effect. Longer drying cycles delay the next batch. They may create scheduling conflicts downstream. And in cases of over-drying, the API’s polymorphic form may shift, potentially affecting drug performance or bioavailability.

When the drying process becomes the rate-limiting step, it often leads to expensive workarounds—new dryers, expanded cleanroom footprints, or outsourced capacity. The drying step, once seen as simple, becomes a major driver of cost and complexity.

The urgency of solving this isn’t hypothetical. In a post-COVID landscape, where new modalities, accelerated approvals, and just-in-time supply chains are the norm, manufacturers can’t afford to guess or delay. Precision isn’t optional. It’s operational.

The challenge of measuring in motion

As part of the FDA’s Process Analytical Technology (PAT) framework, drying was quickly identified as a target for improvement. The ability to understand and control drying in real time could unlock faster release, better yields, and tighter control of critical quality attributes.

At first, many teams turned to spectroscopy. Near-infrared (NIR) and other probe-based methods seemed promising. They sampled directly in the bulk API. But their limitations soon became clear. Sampling probes were vulnerable to coating or damage, especially in paddle dryers. More importantly, they offered only spot-level data—hardly representative of bulk solvent content.

For multi-solvent systems, spectroscopy often required extensive chemometric modeling. This introduced added validation complexity and posed challenges when switching between products or formulations. In highly regulated, high-mix facilities, flexibility is key. Complexity is not.

Mass spectrometry offered a better approach. Rather than probing the solid or liquid phase, it analyzes the gas-phase composition above the product or at the dryer outlet. This is where solvent vapor concentration reveals how much drying is truly left to go—and where changes in headspace content can indicate the actual endpoint.

Sampling where it matters: the headspace advantage

By capturing samples from the headspace, process mass spectrometry overcomes the challenge of inhomogeneity within the dryer. It reflects the drying status of the entire batch, not just one location. This is particularly important in large-scale or poorly mixed systems, where residual solvent may remain trapped in localized zones.

The implementation is straightforward. In most systems, a heated sample line and standard filter can draw vapor directly from the outlet or vacuum line. There’s no need to expose the product or open the chamber. Installation is non-invasive and can be tailored to virtually any dryer configuration.

Each solvent in a process has a unique fragmentation pattern—its own fingerprint in the mass spectrometer’s ion source. Whether the process involves isopropanol, n-propanol, ethanol, or a mix of over 30 potential solvents, modern analyzers can detect them with specificity, even in the presence of background gases or overlapping signatures.

This provides real-time, continuous insight into the removal of each solvent component. But getting reliable data across a wide pressure range requires a new level of agility.

The pressure paradox: why stability matters

One of the main reasons real-time solvent drying hasn’t been widely adopted until now is the challenge of pressure control. Pharmaceutical drying often involves transitioning from atmospheric pressure down to deep vacuum—sometimes below 1 mbar. The analyzer must maintain a constant internal pressure despite these swings.

In early systems, pressure control was handled by a single voltage-sensitive orifice (VSO) valve. While sufficient at moderate pressures, this approach failed to offer meaningful control below 5 mbar. As pressure dropped, the valve fully opened, making it impossible to stabilize the mass spectrometer’s internal environment.

When switching between dryers in different stages of drying, this created signal drift, response delays, and inconsistencies. Long switching intervals had to be built in, slowing down the very processes these tools were meant to optimize.

Modern analyzers overcome this by using a dual-valve variable pressure inlet, where two valves work in opposition. As one opens, the other closes, enabling rapid, precise adjustments. This allows the analyzer to hold a stable inlet pressure of 0.1 mbar, even while sample pressures move from 1,000 mbar to 0.3 mbar or lower.

That stability enables more than just data acquisition. It enables reliable process decisions.

Moving from raw signal to actionable insight

In early mass spectrometry systems, users monitored drying progress by observing ion currents—essentially raw signal intensity from a target mass-to-charge ratio. While these patterns revealed general solvent trends, they were limited by drift, overlap, and poor reproducibility.

As drying cycles changed or batches varied in size, ion current alone wasn’t enough. What users needed was quantitative solvent concentration—data they could trust across cycles, runs, and formulations.

Today’s analyzers integrate calibration gas inputs directly into the system. With the right process analysis software, these reference points are used to convert ion currents into actual concentrations. This enables operators to track, in real time:

The rate of solvent removal
The simultaneous drying of multi-solvent mixtures
The precise moment drying reaches end-point
Cross-dryer comparisons and process control logic

These values can be pushed directly to manufacturing control systems, supporting closed loop drying strategies and enabling true PAT alignment. One instrument can support up to 10 dryers with a multipoint inlet, offering facility-wide visibility.

A modern drying curve: precision from start to finish

One example of a two-solvent drying process showed the removal of water and isopropanol over several hours. As the process pressure decreased from atmospheric to 2 mbar, the inlet pressure remained fixed at 0.1 mbar, ensuring stable signal output.

Each solvent followed a distinct curve. Isopropanol levels dropped rapidly in the early stages. Water persisted longer. At each inflection point, operators could see the rate of removal slowing, and eventually, leveling off. These curves provided an unmistakable marker for the true endpoint of drying—no sampling, no guesswork, no added time.

This is how real-time gas analysis turns drying into a transparent, controllable process.

Why now: the urgency for smarter drying

The shift toward advanced drying control isn’t just about science. It’s about meeting the operational and regulatory demands of today’s pharma landscape.

Manufacturers are facing:

Compressed timelines for clinical and commercial delivery
Greater product diversity, including small batch and high-potency APIs
Increased scrutiny from regulators around process understanding and reproducibility
Digital transformation initiatives, requiring scalable, data-driven technologies

Drying, once an afterthought, is now recognized as a critical point of leverage. Getting it right means faster release, higher yield, fewer deviations, and less rework.

Mass spectrometry offers a practical, scalable, and proven method to achieve that. It allows drying to become not just safer or faster—but smarter.

Final thought: from black box to crystal clear

For years, drying has been one of the least visible stages in pharmaceutical production. Hidden behind steel walls and governed by conservative estimates, it was rarely questioned—until now.

Today, teams are realizing that what you can measure, you can manage. And what you can see, you can improve.

Mass spectrometry allows drying to become an informed decision, not an educated guess. It enables science-backed timing, cross-batch repeatability, and process understanding worthy of today’s regulatory and production demands.

This is not just better monitoring. It’s better manufacturing.