Spectroscopy Top 10 Articles of the Month (June 2026)

Each article has been selected based on the number of successful DOI page views by readers as reported by [email protected]. The articles showcase key developments and insights in spectroscopy and chromatography. Spectroscopy covers the main topics of electronic spectroscopy, vibrational spectroscopy, magnetic resonance, imaging techniques, atomic spectroscopy, and data analysis and integration. LCGC covers most aspects of liquid and gas chromatography, mass spectrometry, and related technical aspects of separation science.

This month we highlight articles from the ever-popular Spectroscopy and LCGC International columns and feature articles.

1. Infrared Spectroscopy of Polymers VIII: Polyesters and the Rule of Three

Author: Brian C. Smith

This article introduces the infrared spectroscopy of ester-containing polymers and presents the author’s “Rule of Three” approach for interpreting polyester spectra. Important industrial polymers, including polyethylene terephthalate (PET), are examined in detail. The article reviews ester-group spectroscopy and demonstrates how characteristic carbonyl and C–O stretching bands facilitate the identification and analysis of polyester materials.

2. Tackling PFAS Complexity with HRMS and Bioanalytical Techniques

Authors: Carrie McDonough and Wesley Scott

Per- and polyfluoroalkyl substances (PFAS) continue to present major analytical challenges because of their structural diversity and environmental persistence. This article discusses how high-resolution mass spectrometry (HRMS) and emerging bioanalytical methods can be combined to improve PFAS detection, identification, and risk assessment. The authors highlight current analytical workflows and discuss future directions for comprehensive PFAS characterization.

3. Enhancing Extractions by Salting Out

Author: Douglas E. Raynie

Addition of a salt during the course of an extraction, known as “salting out,” often quantitatively enhances the extraction yield and provides the basis for techniques such as QuEChERS. This article examines the fundamental mechanism behind the salting out effect, including the role of ionic strength and the Hofmeister series in selecting an appropriate salt. Practical guidance is offered for applying salting out principles to enhance analytical extractions and reduce emulsion formation.

4. The Infrared Spectra of Polymers II: Polyethylene

Author: Brian C. Smith

Polyethylene remains one of the most important commercial polymers and serves as an excellent model system for learning polymer infrared spectroscopy. This article continues the discussion of polyethylene spectral interpretation, showing how synthesis methods affect polymer morphology and spectroscopic behavior. Particular attention is given to crystalline splitting and methylene rocking vibrations, illustrating how subtle spectral changes reveal structural differences in polyethylene materials.

5. Infrared Spectroscopy of Polymers X: Polyacrylates

Author: Brian C. Smith

Acrylic polymers represent a large and commercially important family of materials. This article focuses on polyacrylates, especially polymethyl methacrylate (PMMA), commonly known as Plexiglas. The discussion demonstrates how infrared spectroscopy can distinguish PMMA, copolymers, and polymer blends through characteristic ester and methyl-group vibrations. Applications in materials identification and quality control are emphasized.

6. Interpretation of Raman Spectrum of Proteins

Author: Fran Adar

Proteins present complex Raman spectra that contain information about molecular structure, conformation, and biological function. This article provides a practical guide to interpreting protein Raman spectra, including assignments of amide bands, side-chain vibrations, and structural markers. The discussion demonstrates how Raman spectroscopy can be used to investigate protein folding, aggregation, and biochemical interactions.

7. Pharmaceutical Regulations: An Overview for the Analytical Chemist

Authors: Leon Doneski and Michael W. Dong

The pharmaceutical industry is regulated by government authorities to ensure the safety, efficacy, and quality of drug products before they reach patients. This article provides a high-level overview of pharmaceutical regulations, including Good Manufacturing Practice (GMP), Good Laboratory Practice (GLP), and Good Clinical Practice (GCP), along with the roles of health authorities and public quality standards. The discussion is aimed at helping analytical chemists understand how their work within a GMP environment contributes to product quality and patient benefit.

8. Understanding the Limits of the Bouguer-Beer-Lambert Law

Authors: Thomas G. Mayerhöfer, Susanne Pahlow, and Juergen Popp

The Bouguer-Beer-Lambert law is frequently applied in spectroscopy, but it is often assumed to accurately describe light-matter interactions when, in many cases, this is not true. This article examines the fundamental limits of the law, including the effects of reflection, interference, and sample inhomogeneity that can compromise its accuracy. The authors offer practical guidance on recognizing when the approximation breaks down and how to interpret spectra accordingly.

9. Applications of Raman Spectroscopy in Solvent Distillation and Exchange During Early-Phase Chemical Synthesis

Authors: Ravikumar Ramachandran, Karthik Jayaraman, Mallikarjun Narayanam, and co-workers

Raman spectroscopy is applied as a process analytical technology (PAT) tool for monitoring solvent content during distillation and solvent exchange in early-phase active pharmaceutical ingredient (API) synthesis. Two case studies demonstrate how inline Raman analysis can estimate solvent levels in real time, reducing reliance on time-consuming offline gas chromatography (GC) measurements. The results show strong agreement with GC and highlight significant potential reactor-time savings.

10. Hydrophilic Interaction Liquid Chromatography for Oligonucleotide Therapeutics: Method Considerations

Authors: Szabolcs Fekete, Makda Araya, Balasubrahmanyam Addepalli, and Matthew Lauber

Hydrophilic interaction liquid chromatography (HILIC) is presented as a promising alternative to traditional ion-pair reversed-phase methods for separating oligonucleotide therapeutics. This work investigates the effects of ionic strength, temperature, mobile phase composition, and gradient optimization on the separation of oligonucleotide sequence and length variants, duplexes, and single-stranded components. A sequential (bracketed) injection procedure is also proposed to eliminate breakthrough effects and peak splitting, along with considerations for generic platform methods.

References

1. Smith, B. C. Infrared Spectroscopy of Polymers VIII: Polyesters and the Rule of Three. Spectroscopy 2022, 37 (10), 25–28. https://doi.org/10.56530/spectroscopy.ta9383e3.

2. McDonough, C.; Scott, W. Tackling PFAS Complexity with HRMS and Bioanalytical Techniques. LCGC Supplements 2023, 41 (s9), 12–16. https://doi.org/10.56530/lcgc.na.nr4267c9.

3. Raynie, D. E. Enhancing Extractions by Salting Out. LCGC North America 2023, 41 (7), 262–265. https://doi.org/10.56530/lcgc.na.ax9490j4.

4. Smith, B. The Infrared Spectra of Polymers II: Polyethylene. Spectroscopy 2021, 36 (9), 24. https://doi.org/10.56530/SPECTROSCOPY.XP7081P7.

5. Smith, B. C. Infrared Spectroscopy of Polymers X: Polyacrylates. Spectroscopy 2023, 38 (1), 10–14. https://doi.org/10.56530/spectroscopy.mi9381w4.

6. Adar, F. Interpretation of Raman Spectrum of Proteins. Spectroscopy 2022, 37 (2), 9–13, 25. https://doi.org/10.56530/spectroscopy.lo2270l5.

7. Doneski, L.; Dong, M. W. Pharmaceutical Regulations: An Overview for the Analytical Chemist. LCGC North America 2023, 41 (6), 211–215. https://doi.org/10.56530/lcgc.na.ua3181v7.

8. Mayerhöfer, T. G.; Pahlow, S.; Popp, J. Understanding the Limits of the Bouguer-Beer-Lambert Law. Spectroscopy 2023, 38 (8), 29–30, 58. https://doi.org/10.56530/spectroscopy.iq2368r9.

9. Ramachandran, R.; Jayaraman, K.; Narayanam, M.; et al. Applications of Raman Spectroscopy in Solvent Distillation and Exchange During Early-Phase Chemical Synthesis. Spectroscopy 2022, 37 (5), 28–39. https://doi.org/10.56530/spectroscopy.cd1689c2.

10. Fekete, S.; Araya, M.; Addepalli, B.; Lauber, M. Hydrophilic Interaction Liquid Chromatography for Oligonucleotide Therapeutics: Method Considerations. LCGC International 2025, 2 (2), 20–26. https://doi.org/10.56530/lcgc.int.et8776w7.