Highly sensitive two-dimensional ion chromatography mass spectrometry method for nitrite determination in hydroxypropyl methylcellulose.

Due to their potential adverse health effects, some N-nitrosamines in drug products are strictly regulated with very low maximum daily intake limits. Nitrosamines can be formed from the reaction of nitrite and secondary or tertiary amines when both species co-exist in the drug synthesis or formulation process. One key strategy to mitigate nitrosamine risk in drugs is to select low-nitrite containing pharma excipients for formulation. It is necessary to develop a sensitive method for trace nitrite determination in pharma excipients as it enables drug producers to study nitrosamine formation kinetics and select excipient suppliers. This study details the development and validation of a two-dimensional ion chromatography mass spectrometry (2D-IC/MS) method for trace nitrite determination in hydroxypropyl methylcellulose (HPMC), one of the most important pharmaceutical excipients used in many drug formulations. The 2D-IC system was operated in heart-cutting mode with a concentrator column coupling the two dimensions. A standard bore anion-exchange column was used in the first dimension (1D) to enable a large volume injection for increased sensitivity and provide improved resolution between nitrite and the interfering chloride peak. A high efficiency microbore anion-exchange column with different selectivity was used in the second dimension (2D) to resolve nitrite from other interfering species. The use of 2D-IC resulted in significantly improved resolution, solving the sensitivity loss issue due to ion suppression from an otherwise 1D separation. MS detection with selective ion monitoring and isotope labeled nitrite internal standard further improve the method specificity, accuracy, and ruggedness, as compared with conductivity detection. For trace determination, it is also extremely important to have a clean blank. For this purpose, a novel cleaning procedure using a strong anion wash was developed to remove nitrite contamination from labware. The optimized method was validated with linearity of nitrite in the concentration range of 18.5-5005.8 ng/g having a regression coefficient of >0.9999, precision with RSD at 3.5-10.1 % and recovery of 90.5-102.4 %. The limit of detection and limit of quantitation were 8.9 and 29.6 ng/g relative to the HPMC sample, or equivalent to 89 and 296 pg/g in the sample solution, respectively.

Maximizing two-dimensional liquid chromatography peak capacity for the separation of complex industrial samples.

We report on a study on the use of 2D-LC in industry wherein we maximized the peak capacity by serially coupling up to six 15 cm long columns in the 1st dimension. For the considered aromatic amine oligomer sample, the combination of reverse phase pentafluorophenyl column providing selectivity based on π-π interaction in the 1st and a more retaining reverse phase polymeric C18 column in the 2nd dimension proved to give the highest orthogonality, calculated to be 0.82. Whereas a 1D run on a single column revealed around 120 compounds, the optimized 2D-LC system revealed around 940 compounds. To achieve this, flow splitting to improve the peak capacity in the 1st dimension and shifting gradients in the 2nd dimension were used. The overall peak capacity of the system was calculated to be 11,000 with correction for orthogonality and undersampling. The total analysis time with the 6-column system was around 20 h.