The control of pharmaceutical impurities is currently a critical and challenging issue to the pharmaceutical industry. Impurities in pharmaceuticals are the unwanted chemicals that remain with the active pharmaceutical ingredients (APIs), or develop during formulation, or upon aging of both API and formulated APIs to medicines. The presence of these unwanted chemicals or impurities can have unwanted pharmacological or toxicological effects even in small amounts, and may influence the efficacy and safety of the pharmaceutical products.

There is an ever increasing interest in impurities present in APIs recently, as not just the purity profile but also the impurity profile has become essential as per various regulatory requirements.

Impurity profile describes the identified and unidentified impurities present in a new drug substance. Impurity profiling is the common name of a group of analytical activities, the aim of which is the detection, identification/structure elucidation and quantitative determination of organic and inorganic impurities as well as residual solvents in bulk drugs and pharmaceutical formulations.

The impurities present in formulation are usually by-products, degradation products, interaction products, intermediates, penultimate intermediates, related products, transformation products. They can be produced by chemical syntheses which are organic impurities (process and drug related), inorganic impurities, and residual solvents. There are various sources of impurity like heavy metals, ligands, catalysts other materials like degraded end products obtained during or after manufacturing of bulk drug or products.

In the current scenario of API and pharma market, it is important to identify the impurities for safety and efficacy of drug as per the stringent guideline of regulatory authorities. Impurity synthesis is now an upcoming market, which will play a vital role in the pharma industry.

Impurity synthesis helps synthesize the molecules which are unpredicted or by-products which are very tough to eliminate. In impurity profiling identification plays crucial role and the methods for impurity detection are Isolation and characterization, Column chromatography, Gas chromatography, Flash chromatography, TLC, GC, HPLC, HPTLC, Capillary electrophoresis (CE).

Following are important methods of impurity profiling:

Nuclear magnetic resonance (NMR)

Detection of impurity is challenging while looking at complex or multi-component mixture analysis of API.

NMR plays an important role in structural detection of impurities which provides information about specific bonding between peak area and number of nuclei responsible for peak. NMR spectroscopy is used for identification and structure elucidation of the impurity present in API.

Mass spectroscopy (MS)

Mass spectroscopy is the most accurate method for determining the molecular mass of the compound and its elemental composition of impurities. It is used to prove identity of structure, give exact molecular mass, give molecular formula and most importantly, for structure elucidation of new compound.

Nowadays mass spectroscopy connected with various hyphenated techniques like GC-MS, LC-MS, LCMS-MS HPLC-DAD-MS, HPLCDAD-NMR-MS, Tandem Mass spectroscopy and capillary electrophoresis-Mass spectroscopy deliver very high sensitivity up to picogram level with high separation efficiency.

GC-MS

To identify different substances within a test sample, gas chromatography-mass spectrometry (GC-MS) method is used, that combines the features of gas-liquid chromatography and mass spectroscopy. In this method gas chromatography separate volatile and semi-volatile compounds with great resolution.

Mass spectrometer can provide detailed structural information on most compounds such that they can be exactly identified, but it cannot readily separate them. Sample vaporized by injection into a heated system, eluted through a column by inert gaseous mobile phase and detected. The sample is transported through the column by the flow of an inert, gaseous mobile phase, the carrier gas. Flow is regulated by the pressure regulators and gas metering valves. GC operates at atmospheric pressure and the MS ion source at 10-5 Torr.108 fold pressure difference. The carrier gas must be removed and GC peak components transferred to the MS ion source.

LC-MS

LC/MS is a hyphenated technique, combining the separation power of HPLC/UPLC, with the detection power of mass spectrometry.

LC/MS became really popular with the introduction of the thermo spray interface and the particle beam interface. This is same as GC-MS but removal of liquid carrier from an HPLC eluent before samples are passed in to the MS source. To handle normal eluent flow rate 0.5-2.0 ml/min which is not handled by MS pumping system, moving belt inlet systems, jet separators and vacuum nebulizers are used.