LC-MS/MS and Ultrapure Water - an Essential Partnership for Environmental Research

As discussed in a previous blog, the great variety of applications involving analysis by liquid chromatography - tandem mass spectrometry (LC-MS/MS) have at least one thing in common - they all use ultrapure water (UPW).

Modern LC-MS would not be half as powerful a technique if UltraPure Water was not used to minimise impurities in the preparation of samples, standards and blanks and for the mobile phases. This blog aims to remind the reader of the range of these LC-MS/UPW applications to study the roles and levels of contaminants in the environment taking some examples of research using UPW from PURELAB Chorus 1 units.

Contamination of ground waters is usually thought of as originating from human activity but there is a range of naturally occurring toxins which can contaminate natural waters. Two such substances are the carcinogen ptaquiloside and its degradation product pterosin B. In 2016 Clauson-Kaas and colleagues1 have increased the speed and reliability of a method for their determination in natural waters using solid phase extraction and UPLC-MS/MS. Loganin was used as an internal standard and total run cycle could be reduced to only 5 min. Detection limits  were 8 and 4 ng/L respectively. Buffering samples to pH 5.5 with ammonium acetate before transport significantly improved recoveries.

In a wide-ranging study of pesticides in drinking water sources in the Netherlands Rosa Sjerps et al.2 developed a LC-MS/MS method for 24 recently authorized pesticides, selected based on their mobility and persistence. 15 of these pesticides were detected, including seven in concentrations above the water quality standard from the Water Framework Directive. Two neonicotinoids were found in the highest concentrations: acetamiprid (1.1 mg/L) and thiamethoxam (0.4 mg/L). Overall, the study showed that pesticides are of major concern in drinking water sources across the Netherlands. In one third of the abstraction areas pesticide and/or metabolites concentration exceeded water quality standards. The occurrence of recently authorized pesticides in drinking water sources demonstrated the importance to keep routine monitoring methods up to date. 

Benzisothiazolinone is used in cosmetic products (e.g. hand wash, sun-block, air freshener) as a preservative and on an industrial scale as a biocide on buildings (to kill fungus on roofs and buildings) as well as a preservative in paints and cleaning products. Its widespread use inevitably results in its presence in the environment. Varga³ has investigated its photodegradation in water which was found to produce fourteen products and elucidated their structures using GC-MS, FT-ICR-MS and LC-MS/MS. Oral rat LD50 data was used to assess toxicity. The photoproducts with a phenolic or a sulfino group were more toxic than benzisothiazolinone.

Reference: 

1. UPLC-MS/MS determination of ptaquiloside and pterosin B in preserved natural water Frederik Clauson-Kaas, Hans Christian Bruun Hansen & Bjarne W. Strobel Analytical and Bioanalytical Chemistry volume 408, pages7981–7990(2016)
2. Occurrence of pesticides in Dutch drinking water sources Rosa M A Sjerps, Pascal J F Kooij, Arnaut van Loon, Annemarie P Van Wezel Chemosphere 2019 Nov. 235:510-518. doi: 10.1016/j.chemosphere.2019.06.207. 
3. Photodegradation of benzisothiazolinone: Identification and biological activity of degradation products Zsuzsanna Varga, Edith Nicol, Stéphane Bouchonnet Chemosphere Volume 240, February 2020, 124862

Dr Paul Whitehead 

After a BA in Chemistry at Oxford University, Paul focused his career on industrial applications of chemistry. He was awarded a PhD at Imperial College, London for developing a microwave-induced-plasma detector for gas chromatography. He spent the first half of his career managing the analytical support team at the Johnson Matthey Research/Technology Centre,specialising in the determination of precious metals and characterising applications such as car-exhaust catalysts and fuel cells. Subsequently, as Laboratory Manager in R&D for ELGA LabWater, he has been involved in introducing and developing the latest water purification technologies. He now acts as a consultant for ELGA.