The influence of pH on dissolved organic matter fluorescence in inland waters

• Published in: Analytical Methods
• Main Authors: Groeneveld, M., Catalán, N., Einarsdottir, K., Bravo, A., Kothawala, D.
• Other Authors: Uppsala University, Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Centre d'Investigació i Desenvolupament Barcelona (CID-CSIC), Consejo Superior de Investigaciones Científicas Madrid (CSIC), European Project: 839709,CHROME - EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Arctic
• Online Access: https://hal.science/hal-03625863; https://hal.science/hal-03625863/document; https://hal.science/hal-03625863/file/d1ay01702k.pdf; https://doi.org/10.1039/D1AY01702K

International audience Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolvedorganic matter (DOM). Despite widespread use, there has been some confusion about how robustfluorescence spectroscopy is to differences in solution pH. Here we assess fluorescence characteristicsof three natural water samples and one commercially available standard (Nordic Reservoir) by modifyingthe pH across a range from 3.5 to 9.0 at 0.5 pH increments. We used two statistical approaches toassess if fluorescence intensity shifted significantly across this pH range. We identified that humic-likeand protein-like fluorescence was largely stable within the pH range of 5.5 to 7.5, which represents 80%of Swedish lakes and streams. Likewise, we found that the three commonly used fluorescence indiceswere robust across the full pH range tested with the exception of the humification index, which hada narrower range of stability. The commerical humic substance sample was highly unstable with changesto pH in the regions of protein-like fluorescence being particularly sensitive. One of our conclusions isthat differences in fluorescence intensity in the pH range of 5.5 to 7.5, typical for most inland waters, aregenerally minor. We recommend adjusting the pH when samples fall outside this region and to beespecially careful in interpreting results from commercial humic substances.