Dead Volume in Tecan Reagent Troughs: Why the Taper Changes Everything

A geometry problem that flat-bottom users don't have

If you've spent time with Hamilton reagent reservoirs and are now working with a Tecan Fluent, the first thing to understand about Tecan troughs is this: the bottom is not flat.

Tecan's standard reagent troughs, including the widely used 100 mL reservoir that fits on Tecan's standard reagent and tip carriers, have a tapered or V-shaped base profile. The trough narrows toward the bottom, concentrating liquid in a channel running along the length of the vessel. This isn't an oversight in the industrial design. It's a deliberate choice, and it has real consequences for dead volume that a flat-bottom calculation won't capture.

Why Tecan tapered troughs exist

The taper serves a practical purpose: it allows liquid to drain toward a single low point, so the robot can aspirate from a concentrated pool rather than a thin film spread across a flat base. At low liquid volumes, this is an advantage. The available liquid is pooled in the channel rather than spread thinly across a wide base.

The taper also means the cross-sectional area of the liquid changes as volume decreases. Near the top of the trough, the cross-section is wide. Near the bottom, it's narrow. This non-linearity has two important consequences.

First, volume-to-height is not linear. Removing 1 mL from a nearly full trough causes a much smaller drop in liquid height than removing 1 mL from a nearly empty trough. This affects LLD tracking, aspiration height calculations, and dead volume estimates.

Second, the dead volume calculation is not a simple multiplication. You can't use base area x minimum height the way you can for a Hamilton flat-bottom reservoir. The real dead volume depends on the shape of the taper, and this must be obtained from the labware specification or measured empirically.

What actually drives dead volume in a tapered trough

There are three contributing factors.

1. The physical channel geometry. The taper concentrates liquid, which is good. But the very bottom of the channel is a finite profile, not a point, and there's a volume of liquid sitting in the base of the taper below which the robot can't reliably aspirate. This volume is the irreducible minimum dead volume and it's smaller than the equivalent flat-bottom dead volume, provided the robot can actually reach the taper.

2. The minimum aspiratable Z-height. As with any vessel, the tip must clear the physical bottom by some margin. For a tapered trough, this means the tip is positioned in the narrow part of the taper. The liquid available in that cross-section at the minimum aspiratable height can be very small, sometimes under 1 mL, which is one of the design advantages.

3. Tip-to-wall clearance in the channel. In a narrow tapered channel, a 1000 µL tip may not be able to physically reach the base of the taper due to the width of the tip shaft. A 300 µL tip, with its narrower body, may reach further into the taper. Tip selection directly affects dead volume in a tapered trough in a way that's less significant in a flat-bottom reservoir.

Calculating dead volume in a tapered trough

You can't derive dead volume from first principles without the exact taper profile. The standard approaches are:

From the labware datasheet. The trough manufacturer, or Tecan's FluentControl labware library, specifies the dead volume for each reservoir format. This is typically expressed as a minimum working volume: the volume below which the trough shouldn't be used. For the standard Tecan 100 mL trough, the specified dead volume is typically in the range of 3 to 5 mL, depending on the tip type and aspiration parameters.

From empirical measurement. Fill the trough with a known volume of water containing a dye. Run your method until the robot generates an LLD error or begins aspirating air. Measure the residual volume by pipette. Do this three times and average the result.

The 10% rule revisited. At 100 mL working volume, a 10% buffer (10 mL) is a substantial overestimate of the real dead volume for a tapered trough. At 20 mL working volume, 10% (2 mL) may be an underestimate. The 10% rule is at its least reliable for tapered troughs because the non-linear geometry means the percentage relationship isn't consistent across volume ranges.

For high-value reagents, use the datasheet figure or the empirical measurement. The rule of thumb is a planning approximation, not a protocol parameter.

The LLD tracking complication

Capacitive LLD (cLLD) on the Tecan Fluent detects the liquid surface as the tip descends. In a tapered trough, the LLD will work correctly as long as there's sufficient liquid to cover the full width of the trough at the detected level. At very low volumes, the liquid may only cover the bottom of the taper. If the LLD tip is positioned toward the side of the trough rather than in the centre of the channel, it may detect the trough wall rather than the liquid surface.

This is why tip positioning within the trough matters more for Tecan tapered designs than for Hamilton flat-bottom reservoirs. In FluentControl, the aspiration position within the trough can be defined. The Y-offset should target the centreline of the trough to ensure the tip descends into the liquid channel rather than toward the sloped wall.

If you're working with small remaining volumes (under 10% of trough capacity), LLD-triggered errors become more likely due to the narrow channel and the reduced liquid surface presented to the sensor. Design your protocol to stop aspirating before reaching the taper dead zone.

Labware definitions for tapered troughs

The FluentControl labware definition for a Tecan trough must accurately capture:

• The well depth (distance from the trough rim to the true bottom of the taper)
• The bottom height (Z-position of the lowest aspiratable point within the taper)
• The well shape, which for tapered troughs is typically defined as a trapezoid or V-profile rather than a rectangle

The critical issue is the ZBottom parameter in the labware definition. This sets the minimum Z-position the robot will send the tip to during aspiration. If ZBottom is set too high (the definition thinks the bottom is further from the tip than it actually is), the robot will stop aspirating before it reaches the taper channel. You'll be leaving liquid in the taper that the robot believes is already dead volume, when it's in fact still accessible.

A correct labware definition for a tapered trough should allow the tip to reach the centreline of the taper channel at minimum safe clearance. This is confirmed during teach/calibration, not taken on trust from a default labware file.

Teaching and calibration for tapered troughs

Teaching a Tecan trough involves confirming that the ZBottom value in the labware definition places the tip at the correct minimum height within the taper. On the Tecan Fluent, this is done via the teaching utility in FluentControl.

Two specific risks with tapered troughs during teaching:

Under-teaching (Z-bottom set too high). The robot stops aspirating several millimetres above the true taper floor. You may be leaving 2 to 5 mL of accessible reagent untouched because the definition thinks the bottom is higher than it is. This is a waste in routine workflows and a real problem when working with limited reagent volumes.

Over-teaching (Z-bottom set too low). The tip contacts the trough wall or base. For a tapered trough, the geometry means that a tip aimed for the centreline can contact the side wall if the Z is set too aggressively. This risks tip damage, positional errors, and well contamination.

The safest teaching practice: start with the manufacturer's recommended Z-bottom, verify with a dye aspiration test at minimum working volume, and adjust upward by 0.5 mm increments if you're seeing aspiration errors, or downward if you're seeing significant residual volume after the method completes.

Tip type and channel count

The interaction between tip geometry and trough taper is more significant for Tecan workflows than for flat-bottom vessels.

• DiTi 1000 µL tips have a wider tip shaft that may not physically centre in a narrow taper channel. The minimum aspiratable height will be higher than for narrower tip types.
• DiTi 200 µL or 50 µL tips can reach further into the taper and will have a lower effective dead volume.
• Multi-channel aspiration (8 or 16 channels from a single trough) presents a particular challenge in tapered troughs. The 8 channels will be spread across the Y-axis of the trough. The outer channels may be positioned over the sloped wall of the taper rather than directly over the channel floor. At low liquid volumes, outer channels will begin aspirating air before inner channels are exhausted.

For multi-channel workflows with a tapered trough, the practical minimum working volume is higher than the single-channel dead volume figure from the datasheet. Add at least 10 to 15% on top of the datasheet dead volume as a multi-channel buffer.

When the taper helps and when it hurts

The taper benefits you when total reagent volumes are large. The pooling effect extends the minimum reliable aspiration level lower than you'd achieve with a flat-bottom reservoir of the same capacity, and reduces the liquid wasted as a thin unaspirated film.

The taper works against you when working with small total volumes, when using wide tip types, or when running multi-channel aspirations at low fill levels. In these scenarios, the non-linear geometry and the narrow channel create conditions where dead volume can be higher than a flat-bottom design would produce. For a direct side-by-side comparison of the two trough designs, see Hamilton vs Tecan troughs: a dead volume comparison.

Dead volume checklist for Tecan tapered troughs

• Don't use the flat-bottom formula (base area x height); it doesn't apply
• Obtain the dead volume specification from the Tecan trough datasheet or from empirical measurement
• For multi-channel workflows, add 10 to 15% above the single-channel dead volume figure
• Use the labware definition from Tecan's official library and verify the ZBottom value during teaching
• Position aspirate Y-offsets at the trough centreline to remain over the taper channel
• For low-volume, high-value reagents, use a tip type narrow enough to reach the taper channel floor
• Enable LLD tracking and design the protocol to terminate aspiration before reaching the taper dead zone