Application of chromatographic techniques in the analysis of total nitrosamines in water

Validation of the identification reliability of known and assumed UDMH transformation products using gas chromatographic retention indices and machine learning

Thirty two commercially available standards were used to determine chromatographic retention indices for three different stationary phases (non-polar, polar and mid-polar) commonly used in gas chromatography. The selected compounds were nitrogen-containing heterocycles and amides, which are referred to in the literature as unsymmetrical dimethylhydrazine (UDMH) transformation products or its assumed transformation products. UDMH is a highly toxic compound widely used in the space industry. It is a reactive substance that forms a large number of different compounds in the environment. Well-known transformation products may exceed UDMH itself in their toxicity, but most of the products are poorly investigated, while posing a huge environmental threat. Experimental retention indices for the three stationary phases, retention indices from the NIST database, and predicted retention indices are presented in this paper. It is shown that there are virtually no retention indices for UDMH transformation products in the NIST database. In addition, even among those compounds for which retention indices were known, inconsistencies were identified. Adding retention indices to the database and eliminating erroneous data would allow for more reliable identification when standards are not available. The discrepancies identified between experimental retention index values and predicted values will allow for adjustments to the machine learning models that are used for prediction. Previously proposed compounds as possible transformation products without the use of standards and NMR method were confirmed.

Dispersant-First Dispersive Liquid-Liquid Microextraction (DF-DLLME), a Novel Sample Preparation Procedure for NDMA Determination in Metformin Products

Since December 2019, global batch recalls of metformin pharmaceutical products have highlighted an urgent need to control N-nitrosodimethylamine (NDMA) contamination to demonstrate patient safety and maintain supply of this essential medicine. Due to their formulation, the metformin extended-release products present difficult analytical challenges for conventional sample preparation procedures, such as artefactual (in-situ) NDMA formation, gelling, and precipitation. To overcome these challenges, a new version of dispersive liquid-liquid microextraction (DLLME) termed dispersant-first DLLME (DF-DLLME) was developed and optimized for the analysis of NDMA in metformin extended-release products using a detailed Design of Experiments (DoE) to optimize sample preparation. Gas chromatography-high resolution accurate mass-mass spectrometry (GC-HRAM-MS) combined with automated DF-DLLME were successfully applied to monitor the NDMA levels of two different metformin extended-release AstraZeneca products to ultra-trace levels (parts per billion). The additional benefits associated with DF-DLLME, which include automation, time/costs saving, and greener sample preparation, make this novel technique easier to transfer from a development to Quality Control (QC) environment. In addition, this also offers an attractive candidate for the wider platform analysis of N-nitrosamines in pharmaceutical drug products.

Method for trace determination of N-nitrosamines impurities in metronidazole benzoate using high-performance liquid chromatography coupled with atmospheric-pressure chemical ionization tandem mass spectrometry

Genotoxic impurity control has been a great concern in the pharmaceutical industry since the recall of the large round of sartans worldwide in 2018. In these sartans, N-nitrosamines were the main contaminants in active pharmaceutical ingredients and formulations. Numerous analytical methods have been developed to detect N-nitrosamines in food, drugs, and environmental samples. In this study, a sensitive method is developed for the trace determination of N-nitrosamine impurities in metronidazole benzoate pharmaceuticals using high-performance liquid chromatography/atmospheric-pressure chemical ionization tandem mass spectrometry in the multiple reaction monitoring mode. The method was validated regarding system suitability, selectivity, linearity, accuracy, precision, sensitivity, solution stability, and robustness. The method showed good linearity with R² ≥ 0.999 and F_Mandel  < F_tab(95%) ranging from 0.33 to 8.00 ng/ml. The low limits of detection of N-nitrosamines were in the range of 0.22-0.80 ng/ml (0.0014-0.0050 ppm). The low limits of quantification were in the range of 0.33-1.20 ng/ml (0.0021-0.0075 ppm), which were lower than the acceptable limits in metronidazole benzoate pharmaceuticals and indicated the high sensitivity of the method. The recoveries of N-nitrosamines ranged from 84% to 97%. Thus, this method exhibits good selectivity, sensitivity, and accuracy. Moreover, it is a simple, convenient, and scientific strategy for detecting N-nitrosamine impurities in pharmaceuticals to support the development of the pharmaceutical industry.

Fluorescent paper-based sensor integrated with headspace thin-film microextraction for the detection of acyclic N-nitrosamines following in situ photocatalytic decomposition

BACKGROUND

In this work, a novel analytical approach based on the photocatalytic decomposition of N-nitrosamines combined with headspace thin-film microextraction of the generated nitrogen oxides such as NO has been developed for the determination of the acyclic N-nitrosamine fraction in drinking water samples. A hydrophilic cellulose substrate modified with fluorescent silver nanoclusters (Ag NCs) was used both as extractant and sensing platform. A quenching effect of Ag NCs fluorescence occurs as the concentration of N-nitrosamines increases. Front-face fluorescence spectroscopy with a solid sample holder was employed for directly measuring the fluorescence quenching onto the cellulose substrate.

RESULTS

In order to achieve an optimal analytical response, different parameters involved in the photocatalytic reaction as well as those concerning the microextraction step were fully investigated. It is demonstrated that the photodegradation rate of cyclic N-nitrosamines at acidic pH is much lower than that of acyclic ones, which can be the basis for the determination of the later fraction in waters. Under optimal conditions, a detection limit for the acyclic N-nitrosamine fraction around 0.08 μg L^-1 using N-nitrosodimethylamine (NDMA) as model compound for calibration was obtained. Several drinking waters were spiked with acyclic N-nitrosamines showing recoveries in the range of 98-102% with a relative standard deviation of 3-4% (N = 3).

SIGNIFICANCE AND NOVELTY

N-nitrosamines generated as by-products during disinfection processes applied to water cause multiple adverse effects on human health being classified as potential human carcinogens. This study highlights the suitability of a fluorescent paper-based sensor for the rapid analysis of the acyclic N-nitrosamine fraction (i.e. the most abundant fraction) as a total index in drinking water, being useful as screening tool before exhaustive chromatographic analysis, which saves costs, time and reduces waste generation.

Simultaneous Determination for Nine Kinds of N-Nitrosamines Compounds in Groundwater by Ultra-High-Performance Liquid Chromatography Coupled with Triple Quadrupole Mass Spectrometry

The ability to effectively detect N-nitrosamine compounds by liquid chromatography-tandem mass spectrometry presents a challenge due to the problems of high detection limits and difficulty in simultaneous N-nitrosamine compound detection. In order to overcome these limitations, this study reduced the detection limit of N-nitrosamine compounds by applying n-hexane pre-treatment to remove non-polar impurities before the conventional process of column extraction. In addition, ammonium acetate was used as the mobile phase to enhance the retention of nitrosamine target substances on the chromatographic column, with formic acid added to the mobile phase to improve the ionization level of N-nitrosodiphenylamine, to achieve the simultaneous detection of multiple N-nitrosamine compounds. Applying these modifications to the established detection method allowed the rapid and accurate detection of N-nitrosamine in water within 12 min. The linear relationship, detection limit, quantification limit and sample spiked recovery rate of nine types of nitrosamine compound were investigated, showing that the correlation coefficient ranged from 0.9985-0.9999, while the detection limits of the instrument and the method were 0.280-0.928 µg·L^-1 and 1.12-3.71 ng·L^-1, respectively. The spiked sample recovery rate ranged from 64.2-83.0%, with a standard deviation of 2.07-8.52%, meeting the requirements for trace analysis. The method was applied to the detection of N-nitrosamine compounds in nine groundwater samples in Wuhan, China, and showed that the concentrations of N-nitrosodimethylamine and NDEA were relatively high, highlighting the need to monitor water bodies with very low levels of pollutants and identify those requiring treatment.

Comparison of EI-GC-MS/MS, APCI-LC-MS/MS, and ESI-LC-MS/MS for the Simultaneous Analysis of Nine Nitrosamines Eluted from Synthetic Resins into Artificial Saliva and Health Risk Assessment

Nitrosamines can be produced during the manufacture of rubber-type products such as pacifiers or the nipples of baby bottles. Humans can be exposed to the nitrosamines in these products when they are eluted into saliva. In this study, we compared the efficiency of electron impact ionization (EI), atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI) methods for the analysis of nine nitrosamines eluted into artificial saliva. In addition, nine nitrosamines eluted from 54 rubber-type products (rubber, thermoplastic elastomer, thermoplastic polyurethane, and polyurethane) marketed in Korea were monitored. Finally, non-carcinogenic and carcinogenic risk assessments of oral exposure to nine nitrosamines were performed based on the monitoring results. EI-GC-MS/MS performed the best for the simultaneous analysis of these nine nitrosamines with respect to overall linearity, trace analysis limit of detection (less than 1 μg), recovery (average 108.66 ± 9.32%), and precision (less than 6%), compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS) (APCI and ESI) methods. Using the EI-GC-MS/MS method, these nine nitrosamines eluted into artificial saliva from 54 rubber-type products were monitored. Based on the monitoring data, risk assessment was performed by calculating the margin of exposure (MOE) for the respective nitrosamines detected. As a result, these nitrosamines were confirmed to be safe with regard to both non-carcinogenic and carcinogenic risks.

Drinking water nitrosamines in a large metropolitan region in Brazil

Nitrosamines are a concerning group of carcinogens, which have gained increasing attention over the last years, frequently found in drinking and recycled water systems. In this work, an analytical method was developed for the detection and quantification of seven nitrosamines (NDMA, NMEA, NPYR, NDEA, NPIP, NDPA, and NDBA) in drinking water. The method is based on gas chromatography coupled with a single quadrupole mass spectrometer (GC-MS) with electron ionization (EI) mode. Sample enrichment and matrix cleanup by solid-phase extraction (SPE) were performed using the US EPA Method 521 cartridge packed with coconut-based charcoal. The simple method allowed reliable identification and quantification of nitrosamines in the water at nanogram per liter levels. The optimized method was validated at three concentration levels (20, 100, and 200 ng L-1) in ultrapure and drinking water samples. Average recoveries were 63-87% for ultrapure water and 38-79% for drinking water with relative standard deviations (RSD) below 10% for both matrices. Method detection limits were 1.23-3.14 ng L-1. The described method was applied to eighteen drinking water samples collected from 13 cities of the Metropolitan Region of Campinas (São Paulo, Brazil). NDMA was the most frequent nitrosamine detected (89% of samples) and had the highest concentration level found (67 ng L-1). The levels of nitrosamines found in drinking water samples are of considerable relevance since the selected area is a major urban center that has amply expanded industrial and agricultural activities over the last few decades. To the best of our knowledge, this is the first evaluation of nitrosamines in drinking water conducted in Brazil to date.