Topic: conductivity detection

Conductivity detection is by far the most common measurement principle in ion chromatography, and it is sometimes also used in HPLC and other modes of liquid chromatography. This detector measures the change in electrolytical conductivity from the ions passing through. Since all ions increase electrical conductivity of a solution, the conductivity detector is suitable for a wide range of ions, including inorganic ions, and organic ions formed by ionisation of organic acids, bases, and amphoteric compounds. When combined with eluent suppression in ion chromatography, conductivity detection delivers very stable and reliable signals, enabling quantification of trace levels of ions in a variety of samples.

How does a conductivity detector work?

In a conductivity detector the eluent passes through a flow cell with two (in a few designs four) electrodes, between which an alternating current potential is applied. When the sample ions enter the cell, the capability of the solution to conduct electrons increases. The increase in current is proportional to the increase in conductivity, which is in turn a linear function of the ion concentration (unless the ion concentration is too high, or the dissociation is incomplete).

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To learn more, browse the application examples below, return to the knowledge overview, or contact Diduco to discuss your specific analysis.

Applications

ion chromatography

Published case study of analytical quality by design method development and validation

Diduco has published a scientific peer-reviewed case study on how modern analytical method development can be performed in the pharmaceutical industry. The work was performed according to analytical quality by design (AQbD) principles to establish the design space and robust setpoint of the ion chromatography assay, and then validated according to the guidelines established by the International Council for Harmonization (ICH).

ion chromatography

Preserving eluent quality with dedicated storage protected from ambient carbon dioxide

To ensure that liquid chromatography analysis methods meet regulatory demands of retention repeatability as dictated by pharmacopoeia and the ICH guidelines, it is important to protect weakly buffered eluents from ambient carbon dioxide. The formation of carbonate species will otherwise change the pH and strength of the eluent, thus shifting retention.

ion chromatography

Screening of contaminants and forced degradation products in lithium ion battery electrolyte

Electrolytes in rechargeable batteries for cars, mobile phones, and other portable electric devices typically contain negatively charged counterions that together with lithium and a non-aqueous solvent form an ionic liquid. The bis(fluorosulfonyl)imide anion is a rather new ionic liquid constituent which thus need new quality control procedures.

ion chromatography

Analysis of dietary supplement capsules with carnitine using a generic method for counterions

Oral L-carnitine is a dietary supplement that has been shown to reduce fatigue in elderly people with low muscular endurance, but its effects on athletes during physical activity are not well-supported. Although this endogenous compound is well-known for its involvement in the mitochondrial oxidation of long-chain fatty acids, no scientific evidence has been found that carnitine in isolation enhances fat-burning.

ion chromatography

Determination of sulfamate and sulfate in topiramate tablets according to USP monograph

Official quality control method for the second-generation antiepileptic drug topiramate which also have shown effect against migranes. This analysis was performed according to the United States Pharmacopeia monograph and determines the degradation products sulfamate and sulfate which can be formed during storage in humid environments or at elevated temperatures.

ion chromatography

Comparing suppressed and non-suppressed ion chromatography

Suppressed ion chromatography with conductivity detection is a powerful and sensitive technique to analyse charged ionic species, especially anions of strong acids. The chemically regenerated membrane suppressor Xenoic® XAMS can enable analysis of such anions down to levels of a few microgram per litre (part per billion, ppb).

ion-exclusion chromatography

Separation of organic acids by ion-exclusion chromatography

Separation of organic acids can be a challenging task due to their hydrophilic nature and structural diversity. One of the more traditional approaches to this analysis is ion exclusion chromatography, which offer complementary selectivity to other separation techniques, especially for the monovalent acids which tend to be more strongly retained in this mode.

ion chromatography

Modernized assay for foscarnet following ICH guidelines

New preliminary assay for the antiviral medication foscarnet which is a DNA polymerase inhibitor that is used to combat herpes viruses, including drug-resistant cytomegalovirus, and to treat patients with HIV as part of salvage therapy. This method was developed by Diduco to meet the requirements in the ICH guidelines, as a contribution to the United States Pharmacopoeia initiative for modernized monograph methods.

ion chromatography

Quantification of common anions in bottled drinking water according to EPA method 300.1A

Official procedure for quality control of drinking water according to the United States Environmental Protection Agency. This procedure allows quantification of the seven common inorganic anions fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate in the ranges recommended by WHO and national authorities.

ion chromatography

Analysis of clodronate related substances according to European Pharmacopoeia monograph

Official quality control method for the first-generation bisphosphonate clodronate, which inhibits bone resorption and is used to treat bone weakness or pain caused by cancer that has spread to the skeleton. This analysis was performed according to the European Pharmacopoeia monograph method which is used to determine related substances that could be present as impurities in the active ingredient.

ion chromatography

Generic method for isocratic separation of fifteen common pharmaceutical counterions

Many medicines and dietary supplements are bases that carry a positive charge, and consequently these small molecules are accompanied by negatively charged counterions. Such anionic excipients may influence the properties of the pharmaceutical formulation and can also influence the effect of the active ingredient since different ion pairs can have different dissolution rates or abilities to penetrate cell walls.

ion chromatography

Analysis of dietary supplement capsules with glucosamine using a generic method for counterions

Oral glucosamine is a dietary supplement that is marketed to support the structure and function of joints and claimed to provide pain relief for people with arthritis and osteoarthritis, although there is no clear evidence that its benefit is significantly above placebo.

ion chromatography

Column screening using hydroxide gradients for ion chromatography method development

Hydroxide gradient elution is an effective approach in ion chromatography analysis due to its ability to separate organic acids and anions with a wide range of characteristics. During method development of such protocols, scouting gradients is a quick way to rapidly screen different columns and assess their potential for a certain analysis situation and sample composition.

ion chromatography

Alternative method for determination of voriconazole impurity E

Voriconazole is an antifungal medication that is included on the WHO Model list of Essential Medicines. During synthesis of the active ingredient a resolving agent for chiral amines is often used, and it is thus necessary that the quality control prove that this substance is not present at harmful levels in the final product.

ion chromatography

Isocratic separation of four small monovalent organic acids using a weak hydroxide eluent

Singly charged anions of small organic acids can be challenging to separate due to their low retention on many ion chromatography columns. During method development for their analysis several different columns often need to be compared to find a separation selectivity that is suitable for the set of compounds in question.

ion chromatography

Hydroxide gradient elution of organic acids and inorganic anions

Gradient elution is a powerful tool when aiming to separate many compounds having a wide range of different chemical characteristics. Hydroxide gradients are the most common approach in ion chromatography since they can be converted into pure water with nearly zero conductivity.

ion chromatography

Generic method for isocratic separation of ten common pharmaceutical counterions

ion chromatography

Quantification of common anions in drinking water according to EPA method 300.0A

Older version of the official procedure for quality control of drinking water according to the United States Environmental Protection Agency.

ion chromatography

Partial separation of structurally similar organic acids at isocratic conditions

Small organic acids are an important group of chemical compounds that needs to be analysed and quantified in many different industries. This application shows ion chromatography of a variety of organic acids using a non-optimized isocratic carbonate-based eluent.

ion chromatography