Pyrolytic profiling nitrosamine specific chemiluminescence detection combined with multivariate chemometric discrimination for non-targeted detection and classification of nitroso compounds in complex samples

Natural Occurrence of Nitrite-Related Compounds in Malt and Beer

Despite sufficient control of volatile N-nitrosamines in foods and beverages, little attention remained on nonvolatile nitroso compounds, which are mostly unknown and relative to nitrite reactions. In a recent study, new compounds related to reactions of nitrite in beer were pyruvic acid oxime, 4-nitrosophenol, 4-cyanophenol, N-nitrosoproline ethyl ester, nitrosoguaiacol, and 2-methoxy-5-nitrophenol, as well as the already known N-nitrosoproline. The present study is intended to observe their natural occurrence in commercial beers and malts. All 22 nitrite-related products (N-products) were monitored in almost 200 samples of beers and malts. As many as 17 N-products were detected in malts, and all 22 N-products were found in beers. The hierarchical clustering grouped samples based on similarities of detected N-products by frequency of their appearance and level of response. Between N-products and N-nitrosodimethylamine concentrations in malts, only moderate Pearson correlations were found. The same applied to N-product correlations with the apparent total nitroso compound determination in beers.

Characterization of Nitrite-Related Reaction Products in Beer

The effect of nitrites in foods and beverages still raises discussion due to the possible formation of harmful nitroso compounds. However, as most of these compounds in beer were not structurally characterized yet, the research about their toxicological relevance for consumers is limited. This study is focused on identification of the products formed by nitrite (or isotopically labeled nitrite ¹⁵N) reactions in beer using gas chromatography with tandem mass spectrometry. In total, 19 products were identified, and some of them were structurally characterized and confirmed by comparing retention indices and mass spectra of standard/synthesized compounds. Identified compounds were representatives of nitroso, nitro, oxime, and even cyano compounds. For the peaks which were not structurally identified, primary structural characteristics were also listed. Found products were further screened in 16 authentic beer samples which showed the apparent occurrence of found compounds in non-treated beers.

Investigation of the limit of discovery using tile-based Fisher ratio analysis with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) is followed by tile-based Fisher ratio (F-ratio) analysis to investigate the "limit of discovery" for low concentration levels of sulfur-containing compounds in JP8 jet fuel. A mixture of 14 sulfur-containing compounds was spiked at 30 ppm, 15 ppm, 3 ppm and 1.5 ppm into the neat fuel prior to GC×GC-TOFMS analysis with a "reversed" column format (aka polar first dimension (¹D) and non-polar second dimension (²D) column). Prior standard implementation of tile-based F-ratio analysis utilized an average F-ratio requiring a minimum of 3 mass channels (m/z) with the highest F-ratios. Herein, we explore the notion that use of the top F-ratio m/z for hitlist ranking is superior to the standard implementation for analytes near their limit-of-quantitation (LOQ), defined as an analyte concentration that produces a signal equal to ten times the standard deviation of the baseline noise (10σ_n). Hitlist ranking comparisons revealed that using only the top F-ratio m/z resulted in impressive improvements in discoverability for the low concentration comparisons. Specifically, for the 3 ppm versus neat hitlist, 1,4-oxathiane (LOQ = 2.5 ppm) improved from hit 114 via standard F-ratio analysis, to hit 25. For the 1.5 ppm versus neat hitlist, 2-propylthiophene (LOQ = 0.64 ppm) improved from hit 59 to 17, benzo[b]thiophene (LOQ = 1.1 ppm) from hit 98 to 28, and 2,5-dimethylthiophene (LOQ = 1.3 ppm) from hit 262 to 39. Additional hitlist ranking comparisons revealed the importance of proper tile size selection, as analyte discoverability deteriorated upon using either an inappropriately too small or too large of a tile.

Progress in the pretreatment and analysis of N-nitrosamines: an update since 2010

As highly toxic substances, N-nitrosamines (NAs) have been proved to cause carcinogenesis and mutagenesis in humans. Therefore, to carefully monitor safety and preserve human health, the development of rapid, accurate, and high-sensitivity determination methods of NAs is of substantial importance. This review provides a current-status comprehensive summary of the pretreatment and determination methods of NAs in various samples since 2010. Common pretreatment methods that have been used to extract and purify targets include solid-phase extraction, liquid-liquid extraction and various microextraction methods, such as solid-phase microextraction and liquid-phase microextraction, among others. Determination methods include liquid chromatography, gas chromatography, supercritical fluid chromatography and electrochemical methods, among others. In addition, we discuss and compare the advantages and disadvantages of various pretreatment and analytical methods and examine the prospects in this area.