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In the second part of our series behind the development of high quality ion chromatography instrumentation at Metrohm, I will cover the mid 1990's until the mid 2000's. During this time, Metrohm focused on modular IC, lowering background suppression, as well as bringing further robust detection methods on to the market.
2nd generation: The modular IC system – 1996
While the Labograph was soon replaced by integrators (initially with integrators and later on by PC-based integration tools), the conductivity detector stood unbeaten for a long period. Improvements to the system setup, as well as additional liquid handling tools and automation capabilities, yielded the second generation of Metrohm IC: the modular system.
At the same time, the initial patents on chemical suppression were about to expire, allowing the possibility to begin the development of the Metrohm Suppressor Module.
Metrohm Suppressor Module (MSM)
The idea for the MSM is based on the suppression column as described in the paper by Small, Stevens, and Baumann [1]. Its main purpose is to remove the eluent conductivity after the separation and prior to the conductivity detection. Thus, the eluent needs to be convertible to water by ion exchange.
In the case of anion chromatography, sodium hydroxide is an example of such a candidate. By replacing sodium by a proton through ion exchange, the eluent is converted to water alone. The authors applied a suppressor column of opposite charge (compared to the analytical column) after the analytical column [1].
As with all things, suppressor columns do have a couple of disadvantages. They have to be externally regenerated on occasion. Depending on the amount of cations already bound to the suppressor column, its separation and ion-exclusion behavior is modified. This leads to changes in retention times of the ions, especially regarding the carbonate peak, which shifts quite strongly and interferes with other peaks of interest. On the other hand, one of the most positive points of suppressor columns is their ruggedness.
When HPLC fails: unleashing the potential of ion chromatography
Metrohm was looking for solutions to the disadvantages without compromising the ruggedness of this column-based approach.
To overcome the shifting retention time over the usage of suppressor columns, the dimensions of the column were reduced dramatically. This yielded in a small cartridge-like compartment. The exchanger capacity needed to stay high enough for running, minimally, one single chromatogram. Under the precondition that only one chromatogram is suppressed with a single suppressor compartment, in this way all determinations have exactly the same conditions and no retention time shifts can occur.
Now it was required to regenerate the suppressor compartment prior to the next sample injection. Here, the idea of a rotating unit with three compartments was born.
All three compartments are connected to a liquid stream: unit 1 suppresses the eluent conductivity in the analytical stream, unit 2 gets regenerated with acid, and unit 3 is rinsed (acid-free) with ultrapure water or with the detector effluent (now known as STREAM). Prior to each injection, the MSM rotor is switched by one position. In this way, each injection uses its own freshly regenerated and rinsed suppressor unit.
Robust IC: The Metrohm Suppressor Module (MSM) explained
The final suppression setup was launched as the 753 Suppressor Module in 1996 together with the modular system consisting of the 732 Conductivity Detector, 709 IC Pump, 733 IC Separation Center, and the 766 IC Sample Processor plus further liquid handling modules. Together with IC Net, the PC-based data acquisition and handling software, full automation of the ion chromatographic system was available.
While modular IC was extremely flexible and opened up possibilities for a high grade of automation opportunities, it also was quite complex for straightforward, everyday applications.
This routine IC required for general users was introduced in 1999 as the first all-in-one ion chromatograph – the 761 Compact IC. It was the ideal instrument to run standard applications on directly due to the integration of all basic components required for IC analysis. These included: IC pump, injector, Metrohm Suppressor Module with peristaltic pump for regeneration (when required) and rinsing and the conductivity detector. The 761 Compact IC was the first instrument available in only a metal-free version.
IC with built-in amperometric detection
The initial 641 VA Detector and its successor the 791 Amperometric Detector were electronic high-performance instruments requiring a quite high level of knowledge in electrochemistry. Handling and maintenance were not easy tasks, however, analysts which were familiar with these products were extremely happy.
By then, setting voltages manually, as well as compensating the background with potentiometers was outdated. Therefore, Metrohm introduced the 817 Bioscan in 2001.
It was based on the concept of Compact IC. The 817 Bioscan consisted of the amperometric detector used mainly for Pulsed Amperometric Detection (PAD) applications, a built-in column oven, the 812 Valve Unit (injector), and the 709 IC pump. This was Metrohm’s entry to the analysis of sugars.
Amperometric Detection
The 791 Amperometric Detector (introduced in 1998 as the successor of the of the 641 VA Detector), was still dedicated for use as the ideal detector for applications applying DC amperometric detection.
3rd generation: Advanced Modular IC – 2003
In 2003, Metrohm introduced the «Advanced Modular IC» system, featuring the same modularity and remote control concept as the previous «Modular IC», but with improved capabilities added to the individual modules. Both the data acquisition and remote control were still managed by the IC Net software.
Around the same time period, the 811 Online IC was developed, as a more suitable instrument for the harsh environmental conditions of industrial production processes. Weighing in at approximately 450 kg, this heavyweight was built with a top-of-the-line Metrohm modular IC system and was controlled by IC Net software, coming in two versions: single channel as well as a dual channel version to measure both anions and cations. This process analyzer was combined with a modular wet part setup, which allowed the use of various modules (e.g., 10-way sampling valve or tubing pump), so the IC could be fully customized to meet customer requirements for any application.
Due to the success of the 811 Online IC, in 2002 a smaller version was introduced: the 821 Compact Online IC. It was commonly referred to as the «little brother» due to its lighter weight and reduced size.
In 2005, the 861 Advanced Compact IC was introduced to the laboratory world, and in the same year the 844 UV/VIS Compact IC was placed on the market. This was both the first Metrohm UV/VIS IC as well as the first all-in-one UV/VIS ion chromatograph. It was dedicated to direct as well as post-column reaction applications with photometric detection. The 844 UV/VIS Compact IC was complementary to the Bischoff Lambda 1010, used in modular systems as an optional optical detector.
What’s next?
In Part 3, we continue into the later 2000's and beyond, covering the evolution of sequential suppression (the combination of chemical suppression and CO2 suppression) in addition to the 4th and 5th generations of Metrohm ion chromatography.
Your knowledge take-aways
"When HPLC fails: IC in food, water, and pharmaceutical analysis"
This White Paper presents the possibilities of ion chromatography for analyses where HPLC fails.
Reference
[1] Small, H.; Stevens, T.S.; W.C. Baumann. Novel ion exchange chromatographic method using conductimetric detection. Anal. Chem. 1975, 47 (11), 1801–1809. https://doi.org/10.1021/ac60361a017
