Analytical Method Development Using Quantum Laser Cascade Spectroscopy with Diffuse and Attenuated Total Reflectance for Determining Low Concentrations of Active Pharmaceutical Ingredients

Research Article

Austin J Anal Pharm Chem. 2023; 10(1):1157.

Analytical Method Development Using Quantum Laser Cascade Spectroscopy with Diffuse and Attenuated Total Reflectance for Determining Low Concentrations of Active Pharmaceutical Ingredients

Plata-Enríquez JL1-2; Puche-Mercado JF1; Palmer-Velázquez S1; Carrión-Roca W1,3; Francheska M Colón-González1; Hernández-Rivera SP1*

¹Center for Chemical Sensors (CC) / Chemical Imaging and Surface Analysis Center (CISAC), Department of Chemistry, University of Puerto Rico-Mayagüez, Mayagüez, PR 00681, USA

²Department of Polymer Engineering, University ECCI, Bogota, Colombia

³AbbVie Biotechnology Ltd., Barceloneta, PR, 00617, USA

*Corresponding author: Hernández-Rivera SP Center for Chemical Sensors, Department of Chemistry, University of Puerto Rico-Mayagüez, PO Box 9019, Mayaguez, PR 00681, USA. Tel: +1 787-342-1729 Email: [email protected]

Received: July 13, 2023 Accepted: August 24, 2023 Published: August 31, 2023


Quantum Cascade Laser Spectroscopy (QCLS) will quantify acetaminophen as an active pharmaceutical ingredient in different low concentrations formulations in tablet presentation. Tablets contain acetaminophen in nine blends ranging from 0.0% to 3.0% w/w, with mannitol, croscarmellose, cellulose, and magnesium stearate, as excipients. The tablets were analyzed in non-contact mode by mid-infrared attenuated total reflectance and diffuse reflectance backscattering. Measurements were conducted covering the spectral range 770–1890 cm-1. Calibrations were generated by applying multivariate analysis using principal component analysis. The high power of the quantum cascade laser-based spectroscopic system attached to attenuated total reflectance and diffuse reflectance backscattering resulted in the design of discrimination methodologies for pharmaceutical applications with acetaminophen as an active pharmaceutical ingredient in the formulation. The main conclusion is that attenuated total reflectance is better for other analyses. For tablet analysis using mid-infrared quantum cascade lasers, diffuse reflectance backscattering is more accurate for predicting the API content. QCLS is gaining even more acceptance as a valuable tool in Process Analytical Technology.

Keywords: Quantum cascade lasers; Content uniformity; Active pharmaceutical ingredients; Diffuse reflectance backscattering; Principal component analysis; Process analytical technology

Abbreviations: CU: Content Uniformity; APIs: Active Pharmaceutical Ingredients; PAT: Process Analytical Technology; HPLC: High-Performance Liquid Chromatography; NIR: Near-Infrared; MIR: Mid-Infrared; T-RS: Transmission Raman Spectroscopy; QCL: Quantum Cascade Laser; QCLS: Quantum Cascade Laser Spectroscopy; MVA: Multivariate Analysis; DRBS: Diffuse Reflectance Backscattering; ATR: Attenuated Total Reflectance; PCA: Principal Components Analysis; SNV: Standard Normal Variate; FD: First Derivative; SD: Second Derivative


Active Pharmaceutical Ingredients (APIs) commercialization requirements are related to the product's efficacy and Content Uniformity (CU). Testing is a crucial task in pharmaceutical manufacturing, as it ensures that each product that reaches a consumer contains a safe dosage of the API. The most extensively used analytical technique for determining API in pharmaceutical products, High-Performance Liquid Chromatography (HPLC), is used offline in a quality control lab to monitor the dosage of finished tablets due to its sensitivity and the ability to obtain a measurement from the entire tablet volume. However, HPLC analysis involves many solvents and consumables and often takes hours. This slow and destructive technique requires trained personnel and can cause delays in the manufacturing process. Analytical methods in Process Analytical Technology (PAT) in pharmaceutical applications to perform CU testing should be fast, noninvasive, and achieved with limited sample preparation. Other commonly used techniques are Near-Infrared Spectroscopy (NIR) [1] and Transmission Raman Spectroscopy (T-RS) [2-6] and have been explored as alternative methods for rapid and non-destructive on- and at-line CU testing with no sample preparation. These two methods have been widely used in the pharmaceutical industry for decades, resulting in extensive databases and calibration models for various APIs and excipients. Mid-Infrared (MIR) laser spectroscopy using Quantum Cascade Lasers (QCLs) might have fewer available databases and models, making it more challenging to establish robust analytical methods for certain applications.

From a different point of view, NIR and RS may have limited sensitivity for low-concentration impurities and APIs. This fact can be attributed to the limited penetration depths in thick or highly scattering tablets. In contrast, Quantum Cascade Lasers Spectroscopy (QCLS) can penetrate the sample deeper, allowing for the analysis of API distribution and potential inhomogeneities within the tablet. QCL spectroscopy can offer higher sensitivity, allowing for the detection and quantification of trace amounts of substances. This advantage is particularly beneficial when dealing with complex pharmaceutical formulations where overlapping spectra can be problematic. QCLS can target specific molecular vibrations, specifically identifying individual compounds more precisely than NIR.

In this regard, MIR-QCLS [7] can contribute to the pharmaceutical environment by serving as a platform for methods development in PAT applications [8]. QCLS is rarely used to determine the low-concentration dosage of APIS. QCLs are semiconductor lasers specifically designed to emit light in the MIR and Far-Infrared (FIR) regions of the electromagnetic spectrum. Unlike traditional lasers that rely on electronic transitions, QCLs operate on electron intersubband transitions in quantum wells. The structure of the QCLs allows for precise control of the energy levels, enabling the emission of a tunable and narrowband infrared beam at specific wavelengths that match molecular vibrational transitions. This tunability allows researchers to target specific molecular vibrations of interest and achieve high selectivity and sensitivity in their measurements.

Because this extremely sensitive MIR technique can be combined with the powerful statistical routines of Multivariate Analysis (MVA) [9] to provide a new and efficient method for determining the low-concentration dosage of APIs. This article linked these two methodologies, demonstrating a proof of concept for the CU analyses of tablet formulations containing acetaminophen, mannitol, croscarmellose, cellulose, and magnesium stearate. Spectral data of the various formulations was collected using QCLS in two different optical configurations: Diffuse Reflectance Backscattering (DRBS) and Attenuated Total Reflectance (ATR).

The ATR optical setup (Figure 1) is a spectroscopic technique used to study the properties of a material by measuring the amount of light reflected by the surface of the sample. This technique is typically used to study the properties of thin films or surfaces, as it allows for the measurement of the optical properties of a material without the need for direct contact with the sample. The technique utilizes optical components (MIR mirrors and optomechanical components) to direct light onto the sample at a specific angle, and the reflected light is then analyzed to determine the material's properties.