An overview of sample preparation procedures for determination of elemental impurities in medicines

A new ultrasound-assisted microextraction for elemental impurities determination in tablets by ICP-MS according to USP chapters 232 and 233

Along with the United States Pharmacopeia (USP) chapters 232 and 233 regarding elemental impurities in pharmaceutical products, new challenges have been imposed in terms of sample preparation procedures prior to inductively coupled plasma mass spectrometry analysis, considering the matrix complexities. As so, a new microextraction procedure assisted by ultrasound using a cup-horn sonoreactor, minimal reactants, and sample was proposed and validated according to USP. The procedure was optimized with samples of milled tablets and 3 different acid mixtures (HNO3, 3HNO3:1HCl, and 9HNO3:1HF) and it was compared with microwave-assisted acid digestion. In the validation step, recoveries ranging from 85 to 120 % and RSD below 10 % were obtained for 22 analytes (except Ag and Pt) with satisfactory linearity and good sensitivity. The method was then applied for 37 samples of antidepressants, which presented trace levels of As, Ba, Cd, Co, Cr, Cu, Ni, Pb, Pd, Sn, and V.

Greening microwave-assisted digestion method using hydrogen peroxide for determination of elemental impurities by ICP-OES in antihypertensive active pharmaceutical ingredients

Microwave-assisted wet digestion (MAWD) using only H2O2 was proposed for oxidizing active pharmaceutical ingredients (APIs) for hypertension treatment and subsequent determination by inductively coupled plasma optical emission spectrometry (ICP-OES). Diltiazem hydrochloride (DIL) presented the most refractory characteristic for oxidation using MAWD-H2O2. This proposed MAWD-H2O2 method was validated for specificity, accuracy, and precision according to United States Pharmacopeia (USP) Chapter 233 guidelines. Regarding specificity, the most sensitive emission lines were utilized to analyze all elemental impurities in the digests, and no significant spectral interferences were observed. Sample masses of 500 mg for all APIs and a digestion temperature of 250 °C provided digests with residual carbon (RC) below 2400 mg L-1 of C. Additionally, the residual acidity of the MAWD-H2O2 digests was lower than the acidity presented by the HNO3 digests. The highest and lowest residual carbon content (RCC) for digests were observed for DIL and captopril (CAP), respectively, using MAWD-H2O2. When comparing the RCC for MAWD-H2O2 and MAWD-HNO3 digests for APIs containing aromatic rings, it was evident that H2O2 offered equivalent conditions for digesting these compounds. Accuracy tests showed recovery values of 91-110% for all elemental impurities, as recommended by USP chapter 233. Validation experiments for precision presented relative standard deviation (RSD) values below 6.4% and 10% under repeatability and intermediate precision conditions, respectively. The limits of quantification (LOQs) provided by MAWD-H2O2 are at most half of those recommended by of USP and International Council for Harmonisation of Technical Requirements (ICH). In conclusion, MAWD-H2O2 can be considered an alternative method for API digestion, aligning with green analytical chemistry principles, as it does not employ toxic reagents, minimizes waste, and the main products of H2O2 oxidation are water and oxygen. Considering the analytical Eco-Scale, the MAWD-H2O2 method scored 81, classifying it as an excellent green analysis.

Elemental impurities determination in bromhexine hydrochloride injections

Elemental impurities in drug products have no therapeutic effect and may pose toxicological concerns, therefore it is urgent to assess the safety of elements especially in parenteral exposure drug. In the present work, a high throughput inductively coupled plasma mass spectrometry (ICP-MS) method was developed for the quantitative determination of 31 elemental impurities in bromhexine hydrochloride injections from 9 manufactures. The method was successfully validated for linearity, accuracy, precision, stability, the LOD and the LOQ according to the United States Pharmacopeia (USP) < 233 > . All the elemental impurities determined were below the permitted daily exposure (PDE) limits proposed by the International Council for Harmonisation (ICH). However, significant differences were found between different manufactures' products for some elements, particularly for Al, As, B, Ba and Zn. Besides, discussions considering potential risks of elemental contamination were also presented.