For optimal results in HPLC analysis, it is recommended to measure absorbance at a wavelength that matches the absorption maximum of the compound(s) being analyzed. The UV spectrum shown can assist in selecting an appropriate wavelength for your analysis. Please note that certain mobile phases and buffers may block wavelengths below 230 nm, rendering absorbance measurement at these wavelengths ineffective. If detection below 230 nm is required, it is recommended to use acetonitrile and water as low UV-transparent mobile phases, with phosphoric acid and its salts, sulfuric acid, and TFA as buffers.
For some compounds, the UV-Vis Spectrum is affected by the pH of the mobile phase. The spectra presented here are measured with an acidic mobile phase that has a pH of 3 or lower.

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Carbocysteine is a medication that reduces the viscosity of mucus making it easier to cough up. Methylparaben and propylparaben are used as preservatives in cosmetics, pharmaceuticals and food. They can be separated in HPLC on a Primesep 100 mixed-mode column by both hydrophobic and ionic properties present on the stationary phase. The analytical method uses acetonitrile (ACN) gradient and water with sulfuric acid (H2SO4) as buffer and UV detected at 200nm.

Propyl 4-hydroxybenzoate or propylparaben is a very useful compound in cosmetics and often used as a preservative in lotions and creams. The reverse-phase column Legacy L1 was used to retain propyl 4-hydroxybenzoate. Comparisons to Phenomenex columns are available upon request.

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Dextromethorphan is one of the common cough suppressants used in many drug composition. It is in tablets and syrups as an antitussive drug. Composition often has preservatives like parabens. Dextromethorphan is a hydrophobic, basic drug which is used as a bromide salt in drug compositions. Dextromethorphan and two parabens (methyl paraben and propyl paraben) were separated on Primesep C reversed-phase cation-exchange column. Several impurities were observed and are well separated from the main components of the drug composition. Method can be used for various formulations in QC and production environment.

Codeine and two parabens are separated by mixed-mode chromatography. Codeine is retained by reversed-phase and cation-exchange mechanisms and parabens are retained by reversed-phase mechanism. The retention time of codeine can be adjusted by changing the amount of acetonitrile, buffer concentration, and buffer pH. The mobile phase for this column and its separation are fully compatible with UV, ELSD, LC/MS and prep chromatography, various organic and inorganic acids, and corresponding buffers can be used.

Codeine is a hydrophobic basic drug which is used in many drug compositions as an analgetic, antitussive, anxiolytic, and sedative agent. Codeine is widely used as a moderate pain and cough reliever. It is usually part of complex composition and comes in the form of a tablet or syrup. Several preservatives are used in most of the drug composition and include parabens and benzoates. The mixture of codeine, methyl and propyl parabens was separated on Primesep C mixed-mode reversed-phase cation-exchange column. Codeine is retained by reversed-phase and cation-exchange mechanisms and parabens are retained by reversed-phase mechanism. No ion-pairing reagent is required since Primesep C mixed-mode stationary phase has an ion-pairing reagent attached to the surface.

Parabens are common preservatives in pharmaceutical and cosmetic industries. They are esters of p-hydroxybenzoic acid. Method for separation of methyl paraben, propyl paraben, benzonitrile and toluene was developed on a Obelisc R column. All four compounds are neutral and are retained by reverse-phase mechanism. In case of reversed-phase stationary phase, no effect of pH is observed. Retention time for all four compounds changes on an Obelisc R column when pH is changed. pH of the mobile phase affects ionization state of stationary phase. Obelisc R column has C12 carbon chain and carboxylic acid with pKa of 4. At lower pH (pH 2, TFA), carboxylic acid of stationary phase is not ionized and thus adds hydrophobicity to stationary phase. Obelisc R column can be used for analysis of basic, acidic and neutral compounds with suitable detection techniques – UV, ELSD, CAD, LC/MS.

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Parabens possess antibacterial and antifungal properties and are therefore widely used in pharmaceutical and cosmetic industries as preservatives in products. Parabens and benzoic acid can be baseline separated in a short time frame using Primesep B2 reverse-phase HPLC column with a simple mobile phase of water, acetonitrile (ACN, MeCN) and phosphoric acid of 0.1% as buffer. UV detection at 210nm.