Open vs. Enclosed Batch Nitrogen Evaporation Systems

Open systems like the Organomation MULTIVAP feature an exposed nitrogen manifold and dry block or water bath heating platform that must be operated within a certified chemical fume hood. The samples remain visible throughout the evaporation process, and solvent vapors are captured and exhausted by the fume hood ventilation system.

Enclosed systems like the RapidVap Vertex incorporate a glass lid that seals the evaporation chamber, creating a contained environment with an integrated exhaust fan and optional nitrogen control valves. These systems can be operated either within a fume hood or connected to external ventilation via an exhaust port.

One of the most significant differences between these two approaches centers on how solvent vapors are managed during the evaporation process.

Fume Hood Requirements for Open Systems

Open nitrogen evaporators require operation within a properly functioning chemical fume hood to provide adequate protection from solvent vapor exposure. The fume hood must maintain face velocities typically between 80-120 feet per minute (fpm) to effectively capture and contain chemical vapors. This requirement ensures compliance with OSHA standards for laboratory chemical hygiene and protects operators from inhalation hazards.

For laboratories with established fume hood infrastructure, this presents minimal difficulty. However, several practical considerations emerge. Fume hoods represent valuable and often limited laboratory real estate. A 48-position MULTIVAP occupies approximately 16" x 14" of hood space, and laboratories must balance evaporator placement with other equipment requiring fume hood operation. Additionally, users must verify proper hood function before each use, checking airflow indicators and ensuring sash positions remain within safe operating limits.

Integrated Containment in Enclosed Systems

The RapidVap Vertex addresses vapor containment through a sealed glass lid and built-in exhaust system. The epoxy-coated chamber and glass lid provide visibility of samples while containing solvent vapors, which are drawn through an integrated exhaust fan and directed through 2-inch diameter polyethylene tubing to either a fume hood exhaust or external ventilation system.

This design offers notable flexibility. While the RapidVap Vertex can certainly be operated within a fume hood, its enclosed design and dedicated exhaust port enable placement on standard laboratory benchtops when connected to appropriate ventilation. This capability is particularly valuable for laboratories with limited fume hood access or where multiple evaporation operations must run simultaneously.

The enclosed design also provides a secondary layer of protection in the event of glassware failure or unexpected solvent reactions. The sealed chamber helps contain splashing or bumping, reducing operator exposure risk compared to fully open systems.

The ability to visually monitor samples during evaporation represents an important operational consideration that differentiates these two approaches.

Superior Visibility with Open Systems

Open nitrogen evaporators like the MULTIVAP provide unobstructed visibility of all samples throughout the entire evaporation process. Operators can directly observe solvent levels, identify when samples approach the desired endpoint, and detect any irregularities such as bumping, foaming, or cross-contamination between adjacent samples. This direct visual access allows for real-time adjustments to nitrogen flow rates or heating parameters based on what is observed.

The rotating sample holder design on the Organomation N-EVAP models further enhances accessibility, allowing operators to easily view and access samples from the front of the instrument without disrupting the evaporation process. This feature proves particularly valuable in academic or multi-user laboratories where different operators may be monitoring diverse sample types with varying evaporation requirements.

Contained Visibility in Enclosed Systems

The RapidVap Vertex provides sample visibility through its glass lid, though this view is necessarily more restricted than fully open systems. The slanted lid design was specifically engineered to improve visibility and allow condensate to drain away from the viewing area. However, the enclosed nature means operators cannot directly access samples during a run without opening the chamber and interrupting the process.

For applications where continuous visual monitoring is less critical—such as standardized protocols with well-established endpoint times—this limitation may be negligible. The system compensates through programmable temperature and time parameters that allow for reproducible, unattended operation. Up to 10 different programs can be stored in the microprocessor, enabling protocol consistency across multiple runs.

The practical aspects of daily operation reveal additional distinctions between open and enclosed batch evaporation systems.

Simplicity and Accessibility of Open Systems

Open nitrogen evaporators like the MULTIVAP are characterized by straightforward operation. Temperature control is managed through a simple digital controller, gas flow is adjusted via a rotameter and manual needle valves, and the dual-band spring hoist assembly allows effortless raising and lowering of the nitrogen manifold. This mechanical simplicity translates to minimal setup time—operators can begin evaporating samples almost immediately after turning on the heating system and adjusting nitrogen flow.

The open design also facilitates mid-run adjustments. If an operator observes that certain samples are evaporating too quickly or too slowly, individual needle valves can be adjusted on-the-fly without interrupting other samples. Row-based shut-off valves allow nitrogen to be conserved when processing partial batches (e.g., only 24 of 48 positions). Samples can be added or removed at any time, providing maximum flexibility for laboratories with variable workflows.

Programmable Automation in Enclosed Systems

The RapidVap Vertex offers more sophisticated control through its touchscreen LCD interface and microprocessor-controlled parameters. Operators can program specific temperature setpoints (30°C to 100°C in 1°C increments), timed endpoints (1 to 999 minutes), and nitrogen flow settings, then store these as reusable methods. This programmability ensures excellent reproducibility between runs and enables true walk-away operation.

The system includes both time-based and temperature-differential endpoint detection. An audible alarm signals run completion, allowing samples to be processed unattended while operators perform other tasks. For high-throughput laboratories running standardized protocols, this automation can significantly improve workflow efficiency.

However, this added sophistication comes with trade-offs. Once a run begins, samples are enclosed until completion or until the operator manually stops the program. The sealed chamber must be opened to make adjustments, which releases accumulated vapors and disrupts the controlled environment. For laboratories requiring frequent intervention or working with highly variable sample types, this reduced flexibility may be limiting.

Sample capacity represents another key decision factor, particularly for high-throughput laboratories.

High-Capacity Open Systems

The MULTIVAP line offers some of the highest batch capacities available in nitrogen evaporation systems. Water bath models accommodate 64 or 100 sample positions, while dry block models handle 30, 48, or 80 positions depending on configuration. This large capacity makes MULTIVAP systems particularly well-suited for laboratories processing numerous samples in parallel, such as environmental testing facilities, forensic laboratories, or pharmaceutical QC operations.

Notably, these high-capacity systems maintain relatively compact footprints. The 100-position MULTIVAP measures approximately 17" x 19", only marginally larger than systems with half the capacity. This space efficiency is particularly valuable given the premium on fume hood real estate.

Moderate-Capacity Enclosed Systems

The RapidVap Vertex accommodates up to 50 sample positions arranged in five horizontal rows of 10 nitrogen-dispensing nozzles. While this represents substantial parallel processing capability, it falls short of the highest-capacity MULTIVAP configurations. For laboratories where sample volume consistently exceeds 50 samples per batch, multiple enclosed systems or a higher-capacity open system may prove more practical.

The RapidVap Vertex does offer advantages in sample versatility through interchangeable aluminum dry blocks that accommodate various tube sizes and configurations. Blocks are available for tubes ranging from small microcentrifuge tubes to larger 60 mL volumes. This flexibility reduces the need for multiple dedicated sample racks, though custom inserts must be purchased for each tube size.

Both approaches utilize dry block or water bath heating to accelerate solvent evaporation, but with notable differences in implementation and performance.

Temperature Range and Control in Open Systems

The MULTIVAP family offers different heating options depending on model selection. Water bath models provide temperature ranges from 30°C to 100°C, controlled via mechanical or digital thermostats. Dry block models extend the upper temperature limit to 120°C, enabling more aggressive evaporation of higher-boiling-point solvents. The aluminum dry blocks provide excellent thermal uniformity and direct heat transfer to samples.

Temperature control on standard MULTIVAP models is straightforward but less sophisticated than microprocessor-controlled systems. Digital temperature controllers provide accuracy of ±2°C, which is adequate for most evaporation applications. The systems include high-temperature limit switches and safety control cover plates to prevent overheating.

Precision Temperature Programming in Enclosed Systems

The RapidVap Vertex features a 900-watt microprocessor-controlled dry block heating system that can be programmed from 30°C to 100°C in 1°C increments. The touchscreen LCD displays both setpoint and actual temperatures for both the heating system and the sample block, providing excellent process visibility. A temperature sensor probe enables monitoring of either block or sample temperature for maximum control.

This precision temperature control facilitates development of optimized methods for specific solvents and sample types. The ability to program exact temperature ramps and hold times supports reproducible results across multiple operators and runs. The dry block heating approach used in both systems eliminates maintenance requirements associated with water baths (no water changes, no biocide additives, no corrosion concerns) and removes potential contamination sources.

Nitrogen gas represents a significant ongoing operational cost for blowdown evaporation systems, and consumption rates differ substantially between these approaches.

Exceptional Gas Economy in MULTIVAP Systems

The MULTIVAP demonstrates remarkably low nitrogen consumption compared to competitive systems. The 48-position MULTIVAP requires only 16 L/min of nitrogen flow, while the 100-position model (with double the capacity) requires just 33 L/min. This translates to approximately 0.33 L/min per sample position—extraordinarily efficient compared to many alternative designs.

For comparison, competitive enclosed systems like the Biotage TurboVap require 160 L/min for 48 positions (3.3 L/min per position)—nearly 10 times higher consumption per sample. This difference has substantial cost implications, whether laboratories use compressed nitrogen cylinders or generate nitrogen in-house via membrane or pressure-swing adsorption (PSA) generators.

The individual row shutoff valves on MULTIVAP systems enable further gas conservation when processing partial batches. If only 24 of 48 positions are in use, rows without samples can be shut off completely, reducing gas consumption proportionally.

Moderate Gas Consumption in Enclosed Systems

The RapidVap Vertex requires a nitrogen source capable of delivering at least 6.5 CFM (approximately 185 L/min) to supply its 50 nitrogen-dispensing nozzles. Five independent nitrogen control valves with on/off switches allow selective activation of horizontal rows, conserving gas during partial runs. A front-mounted pressure regulator with analog display (0 to 45 psi in 2 psi increments) provides pressure control.

While the per-position gas consumption is higher than MULTIVAP systems, the enclosed design may offer offsetting advantages. The sealed chamber potentially reduces the total volume of nitrogen required by maintaining a nitrogen-rich atmosphere rather than continuously displacing ambient air. However, quantitative comparisons of actual consumption in typical laboratory use would require side-by-side testing under identical conditions.

Sample purity is paramount in analytical chemistry, making cross-contamination prevention a critical consideration.

Physical Separation in Open Systems

Open nitrogen evaporators provide inherent cross-contamination protection through physical separation of samples. Each sample vial or tube is isolated in its own position within the sample rack, and nitrogen is delivered independently to each sample via dedicated needles or pipettes. The manifold design directs gas flow downward onto sample surfaces, and the fume hood exhaust continuously removes vapors away from the sample array.

The key risk factor in open systems involves sample bumping or splashing, which can potentially transfer material between adjacent positions if samples boil violently. This risk is mitigated through proper operating technique—maintaining appropriate needle-to-sample distances (typically 0.5 inches above the liquid surface), using moderate nitrogen flow rates, and applying gentle heat. Keeping nitrogen delivery needles clean and free from sample residue is also essential.

Contained Cross-Contamination Risks in Enclosed Systems

Enclosed evaporation systems face a different cross-contamination challenge. When samples are concentrated in a sealed chamber with circulating nitrogen and exhaust flow, there is theoretical potential for volatile analytes to be carried with solvent vapors and deposited in adjacent sample positions. This phenomenon, known as "evaporation crosstalk," is most likely when analyte concentrations vary dramatically between adjacent samples.

Modern enclosed systems like the RapidVap Vertex address this through several design features. The slanted lid and inclined configuration promote directional vapor flow toward the exhaust outlet rather than lateral circulation. The system's exhaust fan actively draws vapors away from the sample area. Additionally, the dry block heater eliminates water bath condensation that could drip onto samples, removing a potential contamination vector.

Research on centrifugal evaporators has demonstrated that cross-contamination can be effectively prevented through proprietary control algorithms and careful pressure/temperature ramping. While the RapidVap Vertex uses nitrogen blowdown rather than vacuum/centrifugation, similar attention to operating parameters (starting with low nitrogen flow, maintaining proper gas-to-liquid distances) helps minimize crosstalk risk.

Long-term maintenance demands significantly impact the total cost of ownership and day-to-day laboratory operations.

Minimal Maintenance for Open Systems

Open nitrogen evaporators are designed for minimal maintenance requirements. Dry block heating elements require no routine servicing beyond keeping surfaces clean and ensuring proper temperature calibration (recommended every 1-2 years). Water bath models require periodic water changes and cleaning to prevent mineral buildup, but mechanical thermostats are known for exceptional longevity and reliability.

The simple mechanical design—spring hoists, manual valves, basic temperature controllers—means fewer electronic components that could fail. Nitrogen delivery needles occasionally require cleaning or replacement if they become clogged, but this is straightforward and inexpensive. Sample racks and holders are durable and rarely need replacement. Many laboratories report MULTIVAP and N-EVAP systems providing reliable daily service for many years with minimal intervention.

Standard Maintenance for Enclosed Systems

The RapidVap Vertex requires routine maintenance typical of microprocessor-controlled laboratory equipment. The sealed chamber and lid gaskets should be inspected regularly and the phenol-free gasket replaced if seal integrity is compromised. The exhaust fan and blower require periodic inspection to ensure proper function. The PTFE-coated aluminum chamber and sample blocks should be cleaned regularly to maintain chemical resistance and prevent sample contamination.

The dry block heating system requires no water or additives, eliminating a major maintenance burden compared to water bath designs. However, the touchscreen interface, microprocessor controls, and electronic motor components represent potential failure points that may require professional service if issues arise. Extended warranty options are available to manage these risks.

Initial acquisition costs and ongoing operational expenses are practical realities that influence equipment selection.

Economical Open Systems

The MULTIVAP line offers notably lower initial investment compared to enclosed automated systems. Water bath MULTIVAP models range from approximately $7,000 to $9,000, while dry block configurations span $4,000 to $9,000 depending on capacity and features. Even the highest-capacity 100-position MULTIVAP with acid-resistant coating remains less expensive than base-model enclosed evaporators.

This cost advantage makes open nitrogen evaporators particularly attractive for academic laboratories operating under grant funding constraints, startup companies with limited capital budgets, or facilities requiring multiple evaporators for parallel operations. The superior nitrogen economy (33 L/min for 100 positions vs. 185 L/min for 50 positions) further reduces ongoing operational costs, whether using cylinder gas or in-house generators.

Premium Enclosed Systems

The RapidVap Vertex represents a higher initial investment, with pricing typically ranging from approximately $11,000 to $15,000 depending on configuration and accessories. This premium reflects the more sophisticated touchscreen programming interface, microprocessor-controlled functions, sealed chamber construction, and integrated exhaust system.

For laboratories where automation, programmability, and walk-away operation provide substantial value—such as high-throughput pharmaceutical QC labs or clinical testing facilities—this additional investment may be justified by improved workflow efficiency and labor savings. The ability to operate outside fume hoods (when properly vented) may also offset costs in laboratories where fume hood space carries a premium.

Certain applications favor one approach over the other based on specific workflow requirements.

When Open Systems Excel

Open nitrogen evaporators like the MULTIVAP are the preferred choice for:

- High-throughput laboratories processing large sample batches (>50 samples) where maximum capacity is essential

- Multi-user or academic laboratories where diverse sample types and protocols require maximum operational flexibility and real-time adjustments

- Budget-constrained facilities where initial investment and ongoing nitrogen costs are primary considerations

- Applications requiring constant visual monitoring to detect endpoint or prevent over drying of samples

- Laboratories with adequate fume hood space and established ventilation infrastructure

- Operations involving highly corrosive solvents where acid-resistant models can withstand up to 3M HCl

When Enclosed Systems Excel

Enclosed systems like the RapidVap Vertex are ideal for:

- Standardized, high-reproducibility protocols where programmable methods ensure consistency across operators and runs

- Laboratories with limited fume hood access where benchtop operation with external ventilation provides flexibility

- Applications requiring unattended operation where walk-away capability and automatic endpoint detection improve workflow

- Facilities prioritizing complete vapor containment where an additional layer of protection beyond fume hood ventilation is desired

- Operations processing moderate sample numbers (up to 50 samples) with well-characterized evaporation parameters

- Laboratories valuing automation features such as programmable temperature ramps, stored methods, and endpoint alarms

Both open nitrogen evaporators like the Organomation MULTIVAP and enclosed systems like the RapidVap Vertex represent excellent solutions for batch solvent evaporation, each excelling in different operational contexts. Your optimal choice depends on carefully weighing your laboratory's specific priorities.

Choose an open system if you value maximum sample capacity, exceptional nitrogen economy, superior sample visibility, operational flexibility, and lower initial investment—and your laboratory has adequate fume hood space to accommodate the equipment.

Choose an enclosed system if your priorities include programmable automation, walk-away operation, complete vapor containment with integrated exhaust, benchtop flexibility (when properly vented), and standardized reproducible protocols—and the premium investment aligns with your operational value proposition.

Regardless of which approach you select, both systems deliver reliable, efficient batch evaporation that will serve your laboratory's sample preparation needs for years to come. The fundamental nitrogen blowdown technology is proven and effective in both configurations; the decision ultimately comes down to matching the system architecture to your specific workflow requirements, laboratory infrastructure, and budgetary constraints. Given the strength of both product families, you can confidently move forward knowing either choice represents a sound investment in your laboratory's analytical capabilities.