36 Buyers’ Guide 2021
Hybrid Structures for Complex Analytical Instruments
Christian Ruf, R&D Manager, Agilent Technologies (
christian.ruf@
agilent.com), Armin Steinke, R&D Manager, Agilent Technologies (
armin.steinke@
agilent.com)
The use of microfluidic metal structures in complex integrated analytical systems that are mostly composed of conventional elements, brought with it a vast number of interfaces. This introduced challenges regarding reproducibility, dwell volumes, variances, method compatibility and standardisations. Hybrid structures drastically reduce the number of interfaces while increasing the proximity between the electronic and fluidic realm, thus providing a solution to complex integrated assemblies, requiring fewer external interfaces, and offering new possibilities regarding integration depth, allowing for entirely new arrangements of parts impossible by means of conventional technologies such as capillaries, machined parts, and separate electronic components.
Introduction
This article outlines the basics of hybrid structures (HS) in their current state along with the implementations as well as the implications. Hybrid structures are based on the fundamental building blocks of multi-layer circuit boards (MLCB) and metal microfluidic (MMF) structures. MMF structures are the counterpart to multi- layer circuit boards in the fluidic realm. While circuit boards allow for the precise manipulation of electrons, MMF devices make it possible to precisely manipulate solvents, or the molecules solvents are composed of. MMF devices and the related technology are already in use in applications that require high temperatures and high pressures, or both, such are aerospace equipment, high power propulsion systems and high precision analytical equipment such as chromatographs. The integration of MMF devices and circuit boards into one integrated assembly does however introduce new possibilities, such as combining multiple components into one compact, complex precise device, that have not been utilised before. This is in part due to the unique setting that an ultrahigh-performance liquid chromatograph ((U)HPLC) system provides for those technologies, e.g. the low flow rates (between 0 and 10 ml/min), the high pressure (up to 1500 bar), and the absence of temperatures above 150ºC.
Some modern (U)HPLC systems already use MMF devices for different applications such as heat exchangers, mixers, and manifolds.
Figure 1. Example of a current application for MMF devices. Conventional pump head that is equipped with an MMF heat exchanger.
Those devices are generally surrounded by conventional capillary tubing, machined parts such as pump heads, valves, and circuit boards [1, 2]. Figure 1 shows a conventional pump head that is equipped with an MMF heat exchanger. The heat exchanger is used to connect the primary and the secondary pump head via a heat transfer element to reduce the impact of thermal contraction in the secondary head, which can impact the flow rate accuracy. While the devices themselves already bring value to the current configurations by serving the use case they are designed for with minimal overhead, maximum reliability, and a high performance, they do remain islands in a
‘sea of capillaries and interfaces’. They are much like the first integrated components that were introduced into phones, radios, TVs, and other electronic equipment as more complex integrated components in a ‘sea of wires and plugs’ [3]. To fully leverage the advantages of MMF, a migration of capillaries and interfaces is required. Radios and phones only started to shrink in size and grow in performance when the functional blocks were combined into fewer main circuit boards. To improve the performance and reliability, it is necessary to reduce the failure modes and performance limiters in the system. Failure modes in (U)HPLC systems are often caused by interfaces and
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