FAQs – MISP techniques (Metrohm Inline Sample Preparation)

MIDT can be used to automatically dilute the sample according to a preset dilution factor.

A Dosino is used for handling the liquids. In addition to automatic calibration using one standard solution, logical dilutions can also be carried out. This means that MagIC Net checks whether all the results lie within the calibration range. If this requirement is not met, dilution is triggered once again, followed by injection with an adjusted dilution factor.

Automatic preparation of eluents for continuous IC analyses over several weeks. The 941 Eluent Production Module is used to produce eluents "as required".

MISP method for filtration of sample solutions prior to injection.

The sample is fed past the filtration membrane. A pump is used to filter a small fraction of the sample stream through the membrane (partial vacuum) for subsequent analysis. The remainder of the sample stream flows into the waste container and simultaneously rinses the filtration membrane. This minimizes formation of a filter cake and thus a possible blockage of the membrane pores. Inline Dialysis can be used as an alternative if the samples are too heavily contaminated.

Typical applications: all samples that have to be filtered, e.g., natural waters (surface water, groundwater, wastewater, etc.).

MISP method for automatic sample extraction, e.g., extraction of ions from (bio)diesel.

MISP method for inline removal of particles, large molecules, oil droplets of emulsions, etc. from the sample solution prior to injection.

The "Stopped Flow" dialysis method, patented by Metrohm, is based on the diffusion of analyte ions from the sample stream into a stationary acceptor solution. The sample continues to flow through the cell during the dialysis period. Consequently, the sample concentrations in the dialysis cell always remain constant. Equilibrium between the sample and the acceptor solution is attained for practical purposes within a few minutes.

This means that the concentrations of sample ions are almost identical in both solutions. Since there is no pressure difference during dialysis, the driving force is purely diffusion. Thus the risk of blocking the membrane pores is even lower than for Inline Ultrafiltration.

Typical applications: heavily contaminated waste waters, dairy products, fruit juices, emulsions.

Method using injection of different sample volumes using partial filling of the sample loop by a Dosino.

A multipoint calibration can be carried out with one standard solution. The injection volume can be adjusted for the sample. MiPT can be used for concentration ranges between µg/L and mg/L. Sample volumes between 2 and 200 µL can be reproducibly injected using a 250 µL sample loop.

MISP method to add a known quantity of ions to a sample during preconcentration.

Typical application: check of recovery rates in a preconcentration system.

MISP method to remove the unwanted cationic matrix from the sample.

The sample is injected into a stream of transfer solution (generally ultrapure water). In the sample preparation module, the cations are removed from the sample and replaced by H+, Na+, or other non-critical cations (same reaction as in suppression). The analyte ions are retained by the preconcentration column and then injected for analysis.

Typical applications: Removal of heavy metals from galvanic samples.

MISP method for sample neutralization.

The sample is injected into a stream of transfer solution (generally ultrapure water). The sample is neutralized in the sample preparation module (same reaction as for suppression). The analyte ions are retained by the preconcentration column and then injected for analysis.

Typical applications: trace analysis of anions in NaOH solutions.

The pick-up technique enables sample input from small volumes.

Between 1 and 60 µL can be injected. Only little more than the volume to be injected is required. Automatic multipoint calibration using one standard solution is possible.

MISP method to remove the matrix (unwanted substances in the sample) from the analyte.

The sample is injected into a stream of transfer solution (generally ultrapure water). The analytes are retained on the preconcentration column, and the matrix is then removed using an additional transfer solution. The analytes are injected after this cleaning.

Calibration method for very small concentration ranges (ng/L to µg/L) using a standard solution with a higher concentration that is easier to manage. This requires an additional injector and a preconcentration column.

Inline preconcentration is a method in which the analyte is retained on a short column (the preconcentration column).

This preconcentration column is installed on the injector instead of the sample loop. When the injector is switched over, the preconcentrated analytes are sent to the separation column. Preconcentration is mainly used for very low concentrations (ng/L to µg/L range). It enables preconcentration of analytes from large sample volumes. A Dosino (e.g., with a 5 mL dosing unit) can be used in MiPCT setup for preconcentration of 44,000 µL of the sample solution, an automatic multipoint calibration using one standard solution, or a logical adjustment of the sample volume. This covers a concentration range of the samples of 1:1,000,000 (ng/L to mg/L).