Cation suppression in ion chromatography Straightforward cation analysis at trace levels Suppression in cation analysis – benefits and applications 02 Trace analysis of cations, amines, and transition metals erant. As the cartridges are rotated one step before each is possible with or without suppression. However, some new injection, there is always a freshly regenerated supapplications require particularly high sensitivity of the pressor cartridge ready for the next injection. analysis. This can only be achieved by sequential suppression, as suppression considerably lowers the detection STREAM – the green way of suppression limits for the analytes. Such analyses are common, for ins­ STREAM (Suppressor Treatment Re­using Eluent After tance, in power plant applications or in pharmaceutical Mea surement) adds even more benefits to the suppresapplications. Moreover, there are a number of norms and sion technique described. STREAM refers to a process standards that request cation analysis with suppression. whereby, instead of simply disposing of the suppressed eluent after detection, it is used to rinse the regenerated In short, suppression reduces background conductivity suppressor unit. Moreover, the use of the STREAM techto a minimum and decreases baseline noise. Both effects nique results in considerably lower consumption of re getogether improve the signal­to­noise ratio and increase ne rant. the sensitivity of the measuring system. Thus, whenever the quantification of very low concentrations of cations The advantages of STREAM is re quired, analysis with sequential suppression is the • Less waste method of choice. • Less use of consumables • No additional rinsing solutions required The Metrohm Suppressor Module • Longer system run times due to lower The patented Metrohm Suppressor Module (MSM) is a regenerant consumption very effective and highly robust solution when suppression is needed. The heart of the MSM is a small rotor that STREAM enables users to perform sustainable, «green contains three cartridges, filled with anion exchange chemistry» while saving on operating costs. Moreover, resin. While the first cartridge is being used for suppreslonger system run times frees up more time for the user sion, the second one is regenerated. At the same time, to perform other tasks in the laboratory. the third cartridge is rinsed to remove any residual regen­ Connection to 1st cartridge Connection to 2nd cartridge Connection to 3rd cartridge Determination of cations, amines, and transition metals after sequential suppression Some typical examples are: 03 • Traces and ultratraces of sodium in the presence of manganese and cadmium in various types of water monoethanolamine at high concentrations (typical samples. of sample matrices in nuclear power plants). • Aliphatic and aromatic amines in pharmaceuticals, • Trace and ultratrace concentrations of alkali and e.g., piperazine in cetirizine•HCl, tetrabutylammo­ alkaline earth metals such as lithium, sodium, nium in atorvastatin, dimethylamine in meropenem, ammonium, potassium, magnesium or calcium in dimethylamine in imatinib mesylate, meglumine in ultrapure water. meglumine salts. • Traces of transition metals, e.g., cobalt, nickel, zinc, • etc. Advantages • Ultratrace range can be quantified • Lower detection limits • Higher measurement sensitivity due to improved signal­to­noise ratios • Stable baselines with minimal noise, < 0.1 nS/cm • Rapidly eluting peaks are better evaluated • Option of using gradients • 100% pressure stability • 100% resistance to solvents • Short conditioning time • STREAM – the green way of suppression • Robust analyses a) non-suppressed b) suppressed cation chromatography cation chromatography Lower limits of detection through improved signal-to-noise ratios Differences between non­suppressed (a) and suppressed (b) cation chromatography. Sensitivity is increased by factor of 10 to 20. Determination of 10 μg/L standard cations in ultrapure water; column: Metrosep C Supp 1 ­ 150/4.0; eluent: 5 mmol/L HNO + 50 μg/L Rb+; column temperature: 40 °C; sample volume: 3 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression How does cation suppression work? 04 Chemical Suppression Sequential Suppression The Metrohm Suppressor Module (MSM) is regenerated For sequential suppression, chemical suppression is comusing a carbonate buffer. All counterions are converted bined with subsequent CO suppression. This is accom2 into hydrogen carbonate salts. Dissociated acids (e.g., plished with a Metrohm CO Suppressor (MCS). In the 2 nitric acid) are used as the eluent. In addition, trace MCS, the eluent is passed through a capillary made of amounts of rubidium are added to stabilize the baseline a gas­permeable membrane which is surrounded by a in trace analysis. va cuum. This serves to remove the carbon dioxide that is formed by the decomposition of carbonic acid into car­ Reactions that take place during chemical bon dioxide and water. In this way, the carbonic acid cation suppression equilibrium is constantly shifted in the direction of carbon dioxide and water. This results in the removal of Analyte: nearly all the hydrogen carbonate from the flow path, so Na+ + NO – + TNR +HCO – → Na+ + HCO – + TNR +NO – that what remains in addition to the analyte is mainly 3 3 3 3 3 3 water. T = MSM substrate The sequential suppression configuration described re ­ Eluent: CO + H O duces background conductivity (< 0.2 μS/cm) and in crea2 2 + HCO – ses the detection sensitivity of the analysis. Sup pres sion 3 MSM: H+ + NO – H CO 3 2 3 makes the injection peak very small. This means higher – – NO 3 H+ + HCO – resolution between the injection peak and the early elut3 ing cations, e.g., lithium, which makes the integration + HCO – 3 Rb+ + NO – Rb+ + HCO – and quantification of these peaks easier. 3 3 – – NO3 Reactions that take place in the Metrohm CO2 The eluent counter ions are also replaced with hydrogen Suppressor (MCS) carbonate. The carbonic acid that is produced in this way is unstable and only weakly dissociated, meaning that a CO ( O�H CO �H+ + HCO – � � 2 ↑) + H2 2 3 3 lower background conductivity is measured than would be found with the non­suppressed eluent. Depending on CO ( O CO – � � 2 ↑) + H2 �H2 3�Rb+ + HCO3 the eluent composition, background conductivity values of approximately 0.8–1.2 μS/cm are typical for chemical suppression. The remaining hydrogen carbonate fraction is present as rubidium hydrogen carbonate in the suppressed elu ate. This means that all of the hydrogen carbonate is bound as rubidium hydrogen carbonate. This provides stable background conductivity independent of whether analytes are present. Trace analysis of cations with the new 05 Metrosep C Supp 1 column The Metrosep C Supp 1 column is ideally suited for cation (e.g., piperazine in cetirizine•HCl) and the energy industry chromatography with suppression. The column excels by (e.g., sodium in the cooling water of nuclear power plants). its outstanding separating efficiency, short retention times and high stability. Applications can be found in all Alkali and alkaline earth metals can also be detected with major industries where cations, amines, and transition small injection volumes (20 μL) down to the low μg/L metals have to be determined at trace levels. Examples to concentration range. A linear calibration function can be be mentioned here include the phar maceutical industry applied over a wide concentration range. Determination of 1 μg/L standard cations in ultrapure water Column: Metrosep C Supp 1 ­ 150/4.0; eluent: 5 mmol/L HNO + 50 μg/L Rb+; 3 column temperature: 40 °C; sample volume: 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Linear calibrations in the trace range 1–50 μg/L lithium, sodium, Ammonium, linear calibration of 1–50 μg/L, 3 injections per level ammonium, potassium, magnesium, calcium Column: Metrosep C Supp 1 ­ 150/4.0; eluent: 5 mmol/L HNO + 50 μg/L 3 Column: Metrosep C Supp 1 ­ 150/4.0; eluent: 5 mmol/L HNO + 50 μg/L Rb+; column temperature: 40 °C; sample volume: 20 μL; flow rate: 3 Rb+; column temperature: 40 °C; sample volume: 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression 1.0 mL/min, conductivity detection with sequential suppression Applications 06 The Metrosep C Supp 1 column in combination with the column length ensures that the chromatography can be IC cation suppressor is recommended, for routine analyflexibly adapted to any application require ment. ses as well as for research applications. The free choice of Typical applications • Cations in the ultratrace range • Aliphatic and aromatic amines in pharmaceuticals • Ammonium determination in difficult matrices • Transition metals in aqueous extracts Determination of 1 μg/L alkali, alkaline earth, and transition metals in the cooling water of a nuclear reactor, with fully automatic removal of the matrix Column: Metrosep C Supp 1 ­ 250/4.0; eluent: 4 mmol/L HNO 3 + 50 μg/L Rb+; column temperature: 40 °C; sample volume: 100 μL; sample preparation: Inline Matrix Elimination and Inline Preconcentration with Metrosep C PCC 1 HC/4.0; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Determination of 1 μg/L lithium (1) and sodium (2) in a power plant sample with 4 mg/L monoethanolamine (3) (red). For comparison (black): Standard cations 0.1 μg/L Column: Metrosep C Supp 1 ­ 250/4.0; eluent: 4 mmol/L HNO3 + 50 μg/L Rb+; column temperature: 40 °C; sample volume: 2000 μL; sample preparation: Inline Matrix Elimination and Inline Preconcentration with Metrosep C PCC 1 HC/4.0; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Determination of choline in baby food analogous to standard AOAC 2012.20 07 Calculated for the original sample weight, the chloline content is 82 mg/100 g of milk powder. Column: Metrosep C Supp 1 ­ 250/4.0; eluent: 4 mmol/L HNO + 50 μg/L Rb+; column tempe3 ra ture: 40 °C; sample volume: 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Analysis of zinc in a sports beverage The relative standard deviation (n = 36) makes the precision of the measurement clear: Sodium 0.11%, potassium 1.60%, magnesium 0.31%, zinc 1.16% and calcium 2.01%. Column: Metrosep C Supp 1 ­ 250/4.0; eluent: 5 mmol/L HNO + 3 50 μg/L Rb+; column temperature: 40 °C; sample volume: 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Determination of aliphatic amines (1 mg/L each) Column: Metrosep C Supp 1 ­ 250/4.0; eluent: 2.5 mmol/L HNO + 7.5% (v/v) acetonitrile + 50 μg/L Rb+; column tempe­ 3 rature: 40 °C; sample volume: 20 μL; flow rate: 1.0 mL/min, conductivity detection with sequential suppression Technical information Rotor MSM-HC C Design Micro packed­bed suppressor, robust, chemically resistant Capacity > 50 min* (0.25 meq) Dead volume < 250 μL Regeneration Chemical regeneration with STREAM Maximum flow rate Extremely robust: irreversible damage not possible Backpressure limitations Extremely robust: irreversible damage not possible, no specific backpressure required Solvent stability 100% solvent stability Temperature range No limit Separation column Metrosep C Supp 1 Substrate Polyvinyl alcohol with carboxyl groups Particle size 5 μm Standard eluent 5 mmol/L HNO + 50 μg/L Rb+ 3 Standard flow rate 1.0 mL/min Maximum flow rate 1.5 mL/min Maximum pressure 15 MPa Standard temperature 40 °C Temperature range 20–40 °C Capacity 30 μmol K+ (250 mm column) pH range 1–12 Organic modifier (in eluent) 0–30% (no methanol) Organic modifier (in sample) 0–100% acetone, acetonitrile and methanol Storage At 2–4 °C rinsed with ultrapure water *Standard conditions: Metrosep C Supp 1 ­ 250/4.0; eluent: 5 mmol/L HNO + 50 μg/L Rb+, flow rate: 1.0 mL/min 3 Ordering information Suppressor rotor 6.2842.200 MSM­HC C ­9100 Herisau Accessories G, CH 6.2835.010 Connecting piece for MSM­HC and SPM ohm A Dosino Regeneration 2.800.0010 800 Dosino witzerland by Metr 6.5330.190 IC equipment: Dosino Regeneration , printed in S Separation Columns www.metrohm.com SW 6.1052.410 Metrosep C Supp 1 ­ 100/4.0 ­10 6.1052.420 Metrosep C Supp 1 ­ 150/4.0 6.1052.430 Metrosep C Supp 1 ­ 250/4.0 6.1052.500 Metrosep C Supp 1 Guard/4.0 Subject to modifications Layout by Ecknauer+Schoch A 8.000.5163EN – 2015 6.1052.510 Metrosep C Supp 1 S­Guard/4.0