New High Capacity Anion Suppressor for 850 Professional IC from Metrohm for Gradient Applications

19 May 2009
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A gradient separation can be employed for the analysis of anions in difficult sample matrices where one employs a concentration gradient going from a weak to a concentrated eluent over the course of the chromatographic run to enable separation of anions that have a hugely differing range of affinities towards the analytical column.

In terms of gradient chemistry then Metrohm has two choices with its flagship 850 Professional IC with high and low pressure versions based upon its robust and proven MSM technology. The 850 Professional IC represents the third generation of Metrohm IC and the first IC in the market where Intelligence comes equipped as standard.

New from Metrohm in 2009 is a High Capacity version of its Metrohm Suppressor Module (MSM) also known as MSM-HC designed for its 850 Professional IC. The MSM-HC is manufactured from the same material as the MSM and possesses the same excellent characteristics that have made the MSM the class leader in suppressor technology. The MSM-HC is completely 100% solvent compatible, is not adversely affected by the presence of transition metals and amines, contributes very little noise to the analysis (as no electrolytic current is generated) and importantly comes with a ten year warranty – only the MSM and MSM-HC can offer this level of guarantee due to their robust design. The inclusion of the MSM-HC is particularly suited to the 850 Professional IC Gradients systems.

Generally speaking for Ion Chromatography (IC) then the correct choice of separation column and mobile phase mean the majority of applications can be solved isocratically and these systems are easier to manage for the individual. Gradient instruments would for example play an important role in a research laboratory where new applications are being developed ahead of being transferred to the main analytical analysis laboratory where the application is then performed isocratically.

In gradient chemistries, anions that are weakly retained by the column elute first and as the mobile phase concentration is increased, the stronger adhering anions can then be eluted with the more powerful eluent. A gradient system offers the user the option to clean up the separation column after injection of heavily loaded samples. A high pressure gradient uses for example two pumps and a mixing chamber to form the concentration gradient whilst a low pressure system uses a single pump with a proportionating valve that switches quickly between the different mobile phases again with a mixing device. It is important to realise that any gradient separation also requires an additional equilibration step at the end of the separation where the mobile phase is returned to its original (weaker) state before the next sample can be analyzed.

Historically the use of gradient systems in IC has been restricted to the use of hydroxide eluents as any change in the carbon dioxide concentration caused a marked rise in the baseline when a carbonate/bicarbonate eluent was used as the mobile phase. The eluting power of hydroxide is weak compared with that of carbonate and meant that high alkali concentrations had to be utilised to achieve the desired separation. The Metrohm CO2 Suppressor (MCS) means that the carbonate and bicarbonate eluents can be employed with no dramatic rise in the background conductivity. The MCS works downstream of the MSM-HC and the two suppressors in tandem give the unique and novel Metrohm sequential suppression with the low baseline helpful for gradient work. The increased suppression capacity of the MSM-HC compared to the standard MSM means it can easily handle concentrated hydroxide or carbonate based eluents.

Typical applications for a gradient system would be for example higher phosphor species (pyrophosphate, tripolyphosphate and trimetaphosphate etc) in cleaning products or citrate, iodide, thiosulfate and tungstate in for example healthcare products.

The Intelligence built into the 850 Professional IC Instruments means that all the intelligent hardware is equipped with a memory chip that stores device specific data that can be accessed at any time using the MagIC Net software. When the method is started the parameters are checked ensuring accurate, reliable results time after time.

The iPump has a chip that stores its working life and can flag when maintenance is required, self optimization contributes to reduced pump noise which in conjunction with other hardware helps lower the achievable detection limits. The Metrohm iDetector has a single range that can accommodate 0-15000µS with no auto-ranging or scale selection; test chromatograms are stored on the detector for training and validation purposes. The iColumn from Metrohm contains the recommended analysis parameters for the column and can be automatically imported into the working method and records the number of determinations per column. Intelligent dosing devices (Dosino) can be used for sample dilution or matrix elimination if working with difficult sample matrices. The build quality of the system ensures low detection limits of less than 1µg l-1 for both anions and cations with direct injection.

The MagIC Net software includes comprehensive control and monitoring functions, the control functions graphically display the data whilst the monitoring limits trigger a pre-defined alarm that can send an email or turn off the IC for example in the event of a method violation. Expiry date and exchange intervals can be set for everything from validity of calibration graph, lifetime of eluents and standards through to a maximum number of injections performed per column.

All the data generated goes into a database from where it can be automatically exported into another application or into a LIMS system.

The flexibility of MagIC Net is one of its outstanding features so whether the IC is operated by the laboratory “expert” or “novice” then the interface can be customized accordingly to suit their requirements. If a Dosino is added to the instrument then it is recognized automatically by the software and the smart wizard templates make writing methods intuitively simple.

Client server functionality enables a centralized data administration allowing all determinations and methods to be stored and accessed by each station (depending upon allowed access privileges).

Metrohm means flexibility so the 850 Professional IC can also be run isocratically if required and the same instrument can also perform cation and organic acid analysis with a simple change of eluent, column and method. Intelligent 850 Professional IC’s have fast equilibration times and robust suppressors that are designed to be turned off when not in use and do not need to recycle reagents to enable fast start up times.

Automation is performed by the 858 Professional Sample Processor, for trace level analysis then an optional external rinsing station located on the edge of the carousel is recommended so that the needle is rinsed (inside and out) with a fresh supply of ultra pure water in between injections. The 858 can accommodate Metrohm Inline Sample Preparation (MISP) so for example a dialysis or ultrafiltration cell can be incorporated to minimize sample handling, improve the sample throughput and protect the separation columns from heavily loaded samples. As the analyst is not manually preparing the samples they are free to perform other duties in the laboratory and so the cost of analysis is reduced.

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