Full fluidic control in processing and no troubles with bubbles® — Biotech Fluidics AB shows you the way
The Silicon Review
“With a sampling speed of up to 13 Hz (78 ms), the Biotech Liquid Flow Meter provides process insight and understanding in an unprecedented way.”
Managing liquid flows in precision applications can be very demanding. Dissolved gasses not only add undesired properties like the corrosiveness of oxygen but also compromise the flow characteristics by off-gassing. It is well-known that such events affect both flow and pressure stability. Biotech Fluidics addresses the challenges with dissolved gasses and liquid flow rate monitoring by relying on its expertise and powerful tools, enabling full control on the millisecond timescale.
Nature presents us with some challenges that we must simply acknowledge and address. The solubility of gases in liquids is one such challenge. At times, we find value in this characteristic, as seen in our sparkling beverages. Yet, even more crucially, life in the ocean is entirely reliant on this phenomenon. In other situations, dissolved gasses may cause us troubles by off-gassing causing the formation of microbubbles and by the reactivity of the gases. Just as oxygen dissolved in water forms the basis of life in the sea, it also makes the water a corrosive environment by the oxidation potential. The ability to dissolve gases is a dynamic process and there is no such thing as a bottle of degassed liquid. The gas solubility is dependent on the type of gas and liquid, but most importantly, on the pressure and temperature of the system. In reality, the solubility of gases in liquids increases as the temperature decreases.
In industry applications, dissolved gasses cause troubles either by bubble formation, compromising the flow stability or by the nature of the gas in question. Bubble formation by off-gassing occurs when the solubility of the gas is exceeded. This is a quick and dynamic process that sometimes makes it difficult to detect as the bubbles formed may re-dissolve when the solubility is better again. The solubility is, first of all, dependent on pressure and temperature with decreased solubility at higher temperatures. Formation of microbubbles is most frequently seen at negative pressure transients, especially in pressurised systems, and at local hot spots. The dependence of temperature and pressure on the solubility of air in water is described in Figure 1. Mixing of solvents can also cause off-gassing as the gas solubility in the mixture frequently is lower than in the separate solvents. One such example is a mixture of methanol and water that are well-known to off-gas on mixing.
Figure 1: Solubility of air in water at different pressures as a function of temperature. The solubility of air decreases with approximately 40% on warming up a refrigerated solution to room temperature. Reduced pressure or negative pressure transients, frequently produced by pumps, reduces the solubility even further resulting in out-gassing and dispensing errors.
Biotech Fluidics both has the tools and the expertise to manage this. With very effective in-line degassers dissolved gasses are effectively reduced continuously. These degassers have been designed to meet the very high requirement of chemical compatibility and monomer leakage essential to chemical analysis such as HPLC. Teflon AF is used in the gas permeable membranes fulfilling these demands with elegance. The unique degasser DEGASi Prep+ effectively degasses flows of up to 100 mL/min/channel while still fully compatible with all common organic solvents, making it a unique device. Still, DEGASi® Prep+ only has a hold-up volume of 22 mL. The chemical compatibility, flow capacity and low hold-up volume very well demonstrate the uniqueness of this product. DEGASi® Prep+ is a ready-to-use standalone degasser available in configurations with 1, 2 or 4 channels. Customers in the semiconductor industry have found this degasser very useful, though they are not willing to declare the exact use.
Figure 2: DEGASi® Prep+ units with two and four chambers
For lower flow rate applications, the DEGASi® Plus and DEGASi® Integration series offer very compact stand-alone degassers optimized flow rates in the range 0-3 and 3-6 mL/min/channel with hold-up volumes in the range 480 to 925 uL.
Figure 3: Schematic of the Systec AF membrane of degassing chambers (left) and degassing membrane (right). The well-controlled vacuum in the degassing chamber (brown) provides the driving force for the dissolved gas to pass the degassing membrane (right).
Frequently users oversee gas permeability in polymeric tubing of fluidic systems. This is important to consider for all tubing after the degassing step. Gas permeable materials like silicone and PTFE must be avoided to eliminate gas re-uptake through the lines. This becomes even more important when system tubing becomes longer. Biotech Fluidics provides FEP, or even more preferably, Tefzel and suitable fittings, minimizing the risk of gas re-uptake and maintaining good system properties. By choosing the proper polymeric material, metal tubing can be avoided making service and assembly very much easier.
In flow process applications, especially with several liquid flows, the actual flow rates are the outermost critical. Even with the best quality pumps, actual flow rates are not as well controlled as many users may think. This happens as pumps are often calibrated under ideal conditions with pure solvents, while processing often involves quite concentrated solutions where viscosity may differ. Pump pulsation can also be very significant contributing to deviations in the fluidic profile and net process outcome. With a sampling speed of up to 13 Hz (78 ms), the Biotech Liquid Flow Meter provides process insight and understanding in an unprecedented way. The continuous read-out can be used as feedback to fine adjustment of the pump settings. This device, much like the degassers, is built to be entirely compatible with the fundamental principles of any chemistry. The opportunity to measure flow rates with a high time resolution is a unique feature that is creating a new understanding of how fluidic systems work. This is in great contrast with the long-established Coriolis technology that cannot at all compete in terms of time resolution.
Figure 4: Biotech Liquid Flow Meters are available in four versions covering flow rates from 10 nL/min to 650 mL/min.
Biotech Fluidics also supplies components for fluidic management, including line filters, pressure sensors, bubble detectors, and circulation valves.
Over the last 15 years, Biotech Fluidics has provided outstanding fluidic solutions to original equipment manufacturer (OEM) customers specializing in analytical chemistry. Initially, Biotech’s key customers were instrument manufacturers within analytical scientific instrumentation. Now the number of customers within processing is constantly growing. This expansion is in accordance with Biotech’s growth strategy, driven by the needs of the customers. The company’s headquarters is situated in Onsala, Sweden, and it enjoys global reach through its subsidiaries in the United States and Japan.