Anion exchange polymeric sorbent coupled to high-performance liquid chromatography with UV diode array detection for the determination of ten N-nitrosamines in meat products: a validated approach

Among mechanisms and molecules presumably involved in the carcinogenicity induced by meat consumption, the N-nitrosamines (N-NAs) are a class of compounds characteristic of processed meats. In this work, an analytical method for the determination of ten N-nitrosamines (N-nitrosomorpholine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, N-nitrosodiethylamine, N-nitrosopiperidine, N-nitrosodipropylamine, N-nitrosodimethylaniline, N-nitrosodibutylamine, N-nitrosodiphenylamine and N-nitrosodibenzylamine) in fresh meats and meat products was developed, optimised and validated. The method is based on optimised sample purification by solid-phase extraction (anion exchange polymeric sorbent) and separation/detection by high-performance liquid chromatography coupled to UV diode array detection. The validation procedure allowed to ascertaining good analytical performances in terms of sensitivity, selectivity towards interfering compounds, accuracy and robustness. The values obtained for precision (range: 4.3–14.4%) and recovery percentages (range: 80.8–95.1%) were compared to reference values indicated in the Decision No. 657/2002/EC, resulting as compliant. The measurement uncertainty (lower than 14.6%) was satisfactory for each N-NA as well.     

Literature compilation of volatile N-nitrosamines in processed meat and poultry products - an update

ABSTRACT

A compilation of volatile N-nitrosamine levels in processed (e.g., cured, canned, smoked) meat and poultry products is presented. Over 1800 samples of processed meat products including bacon, ham, salami, sausage, and various other processed meat and poultry products have been examined for the presence of eight volatile N-nitrosamines. The database compiled from the literature is based on 25 references published for the period of 1985 to 2018 from 14 countries. N-nitrosodimethylamine (NDMA), N-nitrosopiperidine (NPIP), and N-nitrosopyrrolidine (NPYR), are the most frequently identified volatile N-nitrosamines occurring in processed meat and poultry products. N-nitrosodiethylamine (NDEA), and N-nitrosodibutylamine (NDBA) are also frequently observed to a lesser extent. The processed meat and poultry products with the highest levels of volatile N-nitrosamines were pork (fried, fat only eaten), poultry (fried), poultry (spiced, grilled), and bacon (fried).     

A method for the determination of volatile N-nitrosamines in food by HS-SPME-GC-TEA

A method for the determination of volatile nitrosamines in sausages was developed using headspace sampling by solid-phase microextraction and gas chromatography with thermal energy analyzer detection (HS-SPME-GC-TEA). Two fused silica fibers, one coated with polydimethylsiloxane-divinylbenzene (PDMS-DVB) and another with poliacrylate (PA) were evaluated. A factorial fractional design was employed in order to evaluate the influence of the equilibrium time, ionic strength, extraction time and temperature for the extraction of N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosopiperidine and N-nitrosopyrrolidine in sausages. The method was validated and applied for the determination of nitrosamines in sausages. The described method is simple, rapid, with adequate accuracy, selectivity, sensitivity and precision.     

Bioavailability of iron and zinc from multiple micronutrient fortified beverage premixes in Caco-2 cell model

Abstract: Iron and zinc deficiencies are the most prevalent nutrient deficiencies worldwide. They often coexist as the dietary factors, especially phytate, which impairs iron absorption also affects zinc absorption. Therefore, suitable strategies are required to control multiple micronutrient deficiencies in populations that subsist on high‐phytate foods such as the whole wheat flour based Indian bread (chapatti). The objective of the study, therefore, was to test the bioavailability of iron and zinc in 2 multiple micronutrient beverage premixes in the absence and presence of chapatti. The premix‐1 contained iron, zinc, and vitamin A while premix‐2 contained all micronutrients in premix‐1, plus folic acid and ascorbic acid. Ferritin induction and ⁶⁵Zn uptake were assessed using coupled in vitro digestion/Caco‐2 cell line model as the surrogate markers of iron and zinc bioavailability, respectively. The results show that iron bioavailability from premixes‐1 and 2 was similar in the absence of chapatti. However, premix‐2 showed significantly higher iron bioavailability compared to premix‐1 in the presence of chapatti. In contrast, the zinc uptake was similar from both premixes‐1 and 2 in the absence or presence of chapatti. These results suggest that both the premixes provide bioavailable minerals, but premix‐2 appears to be promising in the presence of foods that have high phytate.     

Volatile N-Nitrosamines in various fish products

N-Nitrosamines (NAs) are a group of carcinogens which have been detected in various fish products. In this study the level of five NAs (N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosodibutylamine, N-nitrosopiperidine, and N-nitrosopyrrolidine) was determined in 294 various samples of fish, and in 77 samples of oil during 2001–2005. For the sample cleaning the two-step solid-phase extraction with Extrelut and Florisil sorbents was used. NAs were separated by gas chromatography and detected by positive-ion chemical ionization using ammonia as reagent gas. The HP 6890 Plus GC/HP 5973 MSD was used in the selected ion monitoring mode with pulsed splitless injection. In this work, the limit of detection and the limit of quantitation of NA were approximately 0.10 and 0.35 μg/kg, respectively with about 85%. The sum of the average of five NAs content in cold-smoked fish was found to be 1.92 μg/kg, in hot-smoked fish – 4.36 μg/kg, in fried fish – 8.29 μg/kg, in pickled fish – 5.37 μg/kg, in salted fish – 3.16 μg/kg, in salted/dried fish – 3.81 μg/kg, and in the fresh fish it was not detected.     

Evaluation of N-Nitrosopiperidine Formation from Biogenic Amines During the Production of Dry Fermented Sausages

The aim of this study was to determine the role of the precursors cadaverine (CAD) and piperidine in N-nitrosopiperidine (NPIP) formation during the production of dry fermented sausages. The influences of pH (4.9 and 5.3), sodium nitrite (0 and 150 mg/kg), and ascorbate (0 and 500 mg/kg) were investigated by the use of a dry fermented sausage model. The biogenic amines and volatile N-nitrosamines were analyzed by HPLC-UV and GC-TEA. The major biogenic amines were tyramine, putrescine, and CAD, but their accumulation could be inhibited by NaNO₂. When no amine precursors were artificially added, no meaningful N-nitrosamine contamination was observed. The artificial addition of 500 mg/kg cadaverine dihydrochloride (CAD·2HCl) could not provoke increased N-nitrosamine formation. In contrast, the addition of PIP (10 and 100 mg/kg) resulted in higher NPIP concentrations. No influence of pH was observed, but the NPIP formation was more pronounced when NaNO₂ was added and sodium ascorbate was excluded from the formulation. The role of ascorbate as N-nitrosamine scavenger was only detectable during the early stage of production. In the end products, NPIP was degraded and the levels were no longer influenced by the initial addition of NaNO₂ or ascorbate.     

Determination of Seven <Emphasis Type="Italic">N</Emphasis>-nitrosamines in Agricultural Food Matrices Using GC-PCI-MS/MS

The quantitative analytical methods for seven N-nitrosamines including N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), and N-nitrosomorpholine (NMOR) were established for agricultural food matrices. Four food matrices were used for the method development: rice soup as a fatless solid matrix, apple juice as a fatless liquid matrix, corn oil as a fat-rich liquid matrix, and 20 % alcohol as an alcohol matrix. A combination of solid-supported liquid-liquid extraction (SLLE) using Extrelut NT and a solid phase extraction (SPE) using Florisil was employed for fatless matrices. For an alcohol matrix, only SLLE was used without SPE, and liquid-liquid extraction (LLE) was established for a fat-rich matrix. The extract was analyzed by gas chromatography-positive chemical ionization-tandem mass spectrometry (GC-PCI-MS/MS) using ammonia gas as an ion source. Linearity, recovery, repeatability, inter-day precision, reproducibility, and uncertainty were evaluated for method validation using four matrices. Method detection limits for all of the investigated N-nitrosamines were ranged from 0.10 to 0.18 μg/kg for the rice soup, from 0.10 to 0.19 μg/kg for the apple juice, 0.10 μg/kg for the corn oil, and from 0.10 to 0.25 μg/kg for 20 % alcohol, depending on N-nitrosamines. Established methods were applied to determine seven N-nitrosamines in some agricultural food products.     

N-nitrosamines and residual nitrite in cured meats from the Dutch market

Summary A total of 140 samples of 16 kinds of cured meats were analyzed for contents of residual nitrite andN-nitrosamines. Nitrite was determined by reaction with sulfanilamide/naphthylethylenediamine and colorimetric measurement.N-nitrosamines were isolated from the samples by vacuum distillation and determined by gas-chromatography with chemiluminescence detection (GC-TEA). In six samples no nitrite was detectable (< 1 mg NaNO₂/kg), the remaining samples contained 1–140 mg NaNO₂/kg, median value 6.8 mg/kg. In 46 samples (33%) noN-nitrosamines were detected, i.e. less than 0.1–0.5 g/kg of the individual nitrosamines, depending upon their structure.N-nitrosodimethylamine (NDMA) was the nitrosamine present most frequently, in 75 samples, contents were 0.1–0.9 g/kg, mean 0.3 g/kg. OtherN-nitrosamines found were:N-nitrosopiperidine (NPIP), 10 times, 0.3-25 g/kg;N-nitrosodiethylamine (NDEA), three times, 0.2–0.9 g/kg;N-nitrosopyrrolidine (NPYR), three times, 1.3–4.2 g/kg;N-nitrosomorpholine, once, 0.7 g/kg andN-nitrosothiazolidine (NTHZ), 36 times, 0.5–91 g/kg, mean 5.7 g/kg. NTHZ was found most often and with the highest contents in smoked products. Frying of bacon and cured, smoked pork bellies led to substantially increased levels of NPYR in both products, and for the pork bellies also of NTHZ. In five samples of cured, smoked pork bellies after frying NTHZ-contents of 3.6–490 g/kg (mean 179) were found. No correlation between residual nitrite levels andN-nitrosamine contents could be established. Investigations during the nineteen seventies gave much higher levels for NDMA, NDEA, NPIP and NPYR in Dutch cured meats than now found; at that time NTHZ was not measured.

---

N-Nitrosamine und Restnitrit in holländischen Fleischerzeugnissen

Zusammenfassung Insgesamt wurden 140 Proben von 16 verschiedenen Fleischerzeugnissen auf ihren Gehalt an Restnitrit und flüchtigenN-Nitrosamine geprüft Nitrit wurde nach Reaktion mit Sulfanilamid/Naphthylethylendiamin colorimetrisch bestimmt.N-Nitrosamine wurden mittels Vakuumdestillation aus den Proben isoliert und mit Gaschromatographie-Chemiluminescenzdetektion (GC-TEA) gemessen. In 6 Proben war kein Nitrit nachweisbar (< 1 mg NaN0₂/kg), die Nitritgehalte der übrigen Proben lagen zwischen 1 und 140 mg NaNO₂/kg, Medianwert 6,8 mg/kg. In 46 Proben (33%) waren keineN-Nitrosamine nachweisbar d.h. weniger als 0,1–0,5 g/kg.N-Nitrosodimethylamin (NDMA) kam am häufigsten vor, in 75 Proben mit Gehalten von 0,1–0,9 g/kg, Mittelwert 0,3 g/kg. Von den sonstigen Nitrosaminen waren nachweisbar:N-Nitrosopiperidin (NPIP), 0,3–25 g/kg (zehnmal);N-Nitrosodiethylamin (NDEA), 0,2–91 g/kg (dreimal),N-Nitrosopyrrolidin (NPYR), 1,3–4,2 g/kg (dreimal),N-Nitrosomorpholin (NMOR), 0,7 g/kg (einmal) undN-Nitrosothiazolidin (NTHZ), 0,5–91 g/kg (36mal), Mittelwert 5,7 g/kg. NTHZ wurde am häufigsten und mit den höchsten Mengen in geräucherten Produkten gefunden. Braten von Bacon und Frühstückspeck erhöhte die Gehalte an NPYR erheblich in beiden Produkten und bei Frühstückspeck auch den Gehalt an NTHZ. In 5 Proben Frühstückspeck wurden nach dem Braten NTHZ-Gehalte von 3,6–490 g/kg (Mittelwert 179) gemessen. Es konnte keine Beziehung zwischen den Gehalten an Restnitrit undN-Nitrosaminen festgestellt werden. Untersuchungen in den siebziger Jahren ergaben viel höhere Gehalte an NDMA, NDEA, NPIP und NPYR in holländischen Fleischwaren als die jetzt gefundenen; auf NTHZ wurde damals nicht analysiert.

     

HPLC-UV determination of total vitamin C in a wide range of fortified food products

A HPLC method for the quantification of total ascorbic acid (AA) and isoacorbic acid (isoAA) in fortified food products, premixes and duomixes has been developed. The method is based on the acidic extraction of AA in the presence of reducing agent Tris [2-carboxyethyl] phosphine (TCEP), which maintained AA in its reduced form. The separation was performed on a C₁₈ column with a sodium acetate eluent (pH = 5.4) containing TCEP and decylamine as ion pairing agent. The limit of detection was estimated at 0.1 mg/100 g and the recoveries were between 93% to 105% when spiking various food products with different amounts of AA. The intra-assay coefficient of variation value was 4.6% (n = 8) for infant formula and 0.8% (n = 9) for the premixes. The relative standard deviation reproducibility values obtained by 9 different laboratories ranged between 2.0% and 8.0% (n = 10). Application of the method to the analysis of 25 fortified food products, different premixes and duomixes revealed similar results to those found by the AOAC official titrimetry method.     

Determination of iodide in high-dose dairy ingredient premixes by high performance liquid chromatography

Anhydrous premixes for inclusion in infant formulations and other nutritional products were analysed for iodide content using high performance liquid chromatography with UV detection at 230 nm. Separation was achieved on a 3 μm Phenomenex C18 column with hexadecyl-trimethylammonium chloride ion-pair in a 50:50 (v/v) acetonitrile:buffer (pH 5.5) mixture. Optimisation of the method has shown quantitative recovery from a variety of matrices, with acceptable repeatability in the 3–4% range. The contribution of sample heterogeneity and sample size to precision is discussed with the conclusion that large subsamples (25–50 g) are required to facilitate a reliable quality-control method. The method is applicable to premixes with iodide content of 20–2000 μg g⁻¹.     

Selenium in feedstuffs and rations for dairy cows including a view of the food chain up to the consumer

Selenium (Se) is essential and the recommendation for dairy cows amounts to 0.2 mg Se/kg feed dry matter (DM). Se at high intake is toxic and in the EU a maximum content of 0.5 mg Se/kg complete feed (grain DM equivalent basis of 880 g DM per kg) should not be exceeded. The present study focused on the Se content in important feedstuffs (1), supplementation mainly via mineral vitamin premixes (2) and the analysis of total mixed rations (TMR) (3) for validation of a total Se intake. 201 concentrate feedstuffs and 32 silage samples from grass and green maize, a total of 22 mineral premixes and compound feeds and 413 TMR were analysed for Se by hydride atomic absorption spectrophotometry. Twenty-one mineral premixes (>40 % ash) were evaluated for Se content and for the expected daily intake according to the labelled recommendation, manufacturers and brands were anonymised. A very low native Se content with a mean of 20–46 μg Se/kg DM was analysed particularly in grain, grain legumes and silage confirming the necessity for Se supplements. There is an immense range in the Se content of premixes and also in the recommended amounts for daily provision. Increasing the recommended daily intake the premix content of Se has to be decreased significantly. However, the increase of the allowance was stronger than the decrease in Se concentration resulting in an overproportionally higher Se intake at high allowance. The mean Se intake of 8 mg per cow and day via mineral premixes results in 0.4 mg Se per kg DM assuming a total daily feed intake of 20 kg DM per cow. Considering a background Se content in native feedstuffs of about 0.04 mg Se/kg DM, a mean content of 0.44 mg Se per kg total diet DM already covers 75 % of the maximum content of 0.57 mg Se/kg complete feedstuffs DM. Investigations of TMR in Saxon and Thuringian cow herds point to a high intake of Se. According to the present study in dairy cows the Se intake via mineral vitamin premixes may reach or exceed the maximum content of complete feedstuffs according to EU legislation. Too high Se feed contents, particularly via selenised yeasts, will be risky for the consumer (adults; toddlers) who ingests high amounts of Se via Se-enriched milk, meat and eggs which may exceed the upper limit. The ration calculations should be improved according to the recommendations of GfE (Empfehlungen zur Energie- und Nährstoffversorgung der Milchkühe und Aufzuchtrinder, DLG-Verlags GmbH, Frankfurt/Main, 2001).     

ning reactions during storage of low-moisture Australian sultanas: Effects of vine nitrogen nutrition on subsequent arginine-mediated Maillard reactions during storage of dried fruit

Ten‐year old Vitis Vinifera L. cv. Sultana (Thompson Seedless) grape vines were transferred into large cement pots in low nitrate soil and supplemented with four levels of nitrogen application in the form of ammonium nitrate as follows: 0 g ( N₀ ), 8.5 g ( N₁ ), 17.0 g ( N₂ ) and 25.0 g ( N₃ ). Grapes were harvested from each nitrogen treatment, dipped and dried to low moisture (?11.4%) and subsequently stored for 10 months at 10^oC and at 30^oC in either the presence or absence of oxygen. The pre‐storage concentration of free arginine, free‐proline and total protein in the dried sultanas increased with soil nitrogen application. Skin‐polyphenoloxidase (PPO) activity was higher in sultanas with added soil nitrogen ( N₁, N₂, N₃ ), however pre‐storage differences in total phenolics, and the PPO substrate, trans‐caftaric acid, were not significantly different. After 10 months storage at 30^oC significant browning was observed in both the presence and absence of oxygen. Greater browning corresponded to higher soil‐nitrogen application rates. The concentration of skin trans‐caftaric acid did not decrease in N₀, N₁ or N₂ after 10 months at 30^oC, in either the presence or absence of oxygen, although some decreases were measured in the highest nitrogen sultanas ( N₃ ). While PPO oxidation of the phenolic substrate trans‐caftaric acid was not the primary route to browning, a number of Maillard reaction products (MRP) were present in both sultanas and arginine‐glucose model systems. Those products were separated via reverse phase HPLC and partially characterised by UV‐diode array spectroscopy. The lack of oxidation of trans‐caftaric acid observed in the nitrogen storage trial was confirmed in an accelerated browning experiment in low‐moisture sultanas, where despite browning at 50^oC after 12 days, no decreases in this primary substrate for PPO‐mediated oxidation were measured.     

The transnitrosation of secondary amines S-nitrosocysteine in relation to N-nitrosamine formation in cured meats.

The reactions at 37°C of S-nitrosocysteine hydrochloride with three secondary amines, N-methylaniline, morpholine and pyrrolidine, have been studied at pH 2.65, 5.5 and 9.75. The reactions result in the formation of the N-nitroso derivatives of the three amines at all three pH values studied. The rates of N-nitrosation and final yields of products in these reactions were compared with those in reactions in which the N-nitrosation of the secondary amines was effected by nitrite. The comparative rates varied considerably according to the amine being studied and the reaction pH. The relevance of these findings to nitrosamine formation in cured meat and in vivo are discussed. Reaction of S-nitrosocysteine hydrochloride with all three amines at pH 9.75 and with N-methylaniline at pH 5.5 resulted in some N-nitrosamine formation in the headspace above the reaction mixture. The stability of S-nitrosocysteine hydrochloride was studied as a function of pH. The compound was fairly stable at pH 2.65, but decomposed rapidly at pH 5.5 and 9.75. The decomposition reaction at pH 5.5 followed three-halves order kinetics, but that at pH 9.75 did not conform to simple kinetics.     

Effect of Zataria multiflora Boiss. essential oil and nisin on Salmonella typhimurium and Staphylococcus aureus in a food model system and on the bacterial cell membranes

The effects of different concentrations of Zataria multiflora Boiss. essential oil (EO: 0, 5, 15 and 30 μl 100 ml⁻¹) and nisin (N: 0, 0.25 and 0.5 μg ml⁻¹), temperatures (T: 25 and 8 °C), and storage times (up to 21 days) on growth of Salmonella typhimurium and Staphylococcus aureus in a commercial barley soup were evaluated in a factorial design study. The growth of S. typhimurium was significantly (P < 0.05) decreased by EO concentrations and their combinations with N concentrations at 8 °C. For S. aureus, the viable count was significantly (P < 0.05) inhibited by EO and N concentrations and their combinations, incubated at both storage temperatures. The mechanism of the antimicrobial action of EO, N, and their combinations against cell membranes of the tested organisms were also studied by measurement of the release of cell constituents and by the electronic microscopy observations of the cells. The significant increase of the cell constituents’ release of both organisms was observed as a result of treatments with EO and EO in combination with N. Electronic microscopy observations revealed that the cell membranes of S. typhimurium treated by EO and EO in combination with N were significantly damaged, while cells treated with only N looked similar to untreated cells. The electron micrographs of treated cells of S. aureus with EO, N, and their combination also showed important morphological damages and disrupted membranes.     

The effects of ascorbic acid and sorbic acid on N-nitrosamine formation in a heterogeneous model system

The effects of competitive nitrosation by ascorbic acid and sorbic acid on N-nitrosamine formation were studied in a heterogeneous protein-based model system containing a 20% non-aqueous phase. The reactions were examined at 37°C with an aqueous phase pH of 5.25. Under certain conditions ascorbic acid enhanced the nitrosation of secondary amines. The overall extent to which ascorbic acid affected N-nitrosation was found to depend on the time-scale of the reaction and also the phase in which N-nitrosamine formation occurred. Sorbic acid reduced N-nitrosation in both phases of the heterogeneous system.     

Influence of refrigeration and carbon dioxide addition to raw milk on microbial levels, free monosaccharides and myo-inositol content of raw and pasteurized milk

The influence of CO₂ treatment on free monosaccharides and myo-inositol in raw and pasteurized milk during cold storage was studied. Pasteurization did not cause significant changes in the monosaccharide fraction. No variations in the level of galactose and myo-inositol in untreated and CO₂-treated samples were observed during cold storage. The content of glucose decreased considerably during cold storage due to bacterial growth in pasteurized milk. During cold storage of pasteurized milk no changes in N-acetylgalactosamine were observed, whereas N-acetylglucosamine decreased considerably after 15 days. No differences between untreated and CO₂-treated milks were found. A substantial decrease in N-acetylglucosamine and a gradual increase in N-acetylgalactosamine were observed in raw milk during cold storage. The former was attributed to consumption of this hexosamine by microorganisms and the latter was probably due to microbial glycosidic enzymes. The addition of CO₂ to raw milk proved to be a useful treatment for milk preservation without modifying the free monosaccharide fraction. Received: 4 October 1999     

Comparison of the antipathogenic effect toward Staphylococcus aureus of N-linked and free oligosaccharides derived from human,bovine, and goat milk

N-linked oligosaccharides (N-glycans) derived from milk were recently found to be antipathogenic. This study compares the antimicrobial activity of N-linked glycans and free oligosaccharides from human, bovine, and goat milk against Staphylococcus aureus. Milk N-glycans showed a bactericidal/bacteriostatic effect on the pathogen when compared to free milk oligosaccharides, evidenced by the clear zone from the halo assay, with the order of human milk >goat milk >bovine milk. None of the free milk oligosaccharide samples were bactericidal/bacteriostatic, despite its positive results in growth curve and minimum inhibitory concentration (MIC) assays which are believed to be related to hyperosmosis. Both N-glycans and free milk oligosaccharides can reduce the adhesion of Staphylococcus aureus to Caco-2 cells, however, N-glycans worked significantly more effective than free milk oligosaccharides. Structural analysis of all free oligosaccharide and N-glycan samples showed the obvious interspecies differences, and the structure/function relationship of the respected N-glycans is of interest for future study. The significant bactericidal/bacteriostatic activity possessed by human, bovine, and goat milk N-linked glycans holds great potential as a novel substitute for antibiotics.     

Oleoylation of sugarcane bagasse hemicelluloses using N‐bromosuccinimide as a catalyst

Conditions for the preparation of esters of sugarcane bagasse hemicelluloses with oleoyl chloride using N‐bromosuccinimide (NBS) as a catalyst in the N,N‐dimethylformamide/lithium chloride system under mild conditions were studied comparatively. The oleoylation was followed in terms of yield and degree of substitution (DS). The parameters optimised included oleoyl chloride concentration as the molar ratio of oleoyl chloride/anhydroxylose units in native hemicelluloses (1:1–8:1), NBS concentration (0.5–3.0%), reaction time (20–100 min) and reaction temperature (30–100 °C). Results were also compared with those for other catalysts such as H₂SO₄ and four tertiary amine catalysts, pyridine, 4‐dimethylaminopyridine, N‐methyl pyrrolidine and N‐methyl pyrrolidinone. An oleoyl chloride/hemicellulose molar ratio of 3:1 was found to be necessary for the reaction to proceed smoothly and to yield a product with a low DS. The new materials were characterised by FT‐IR and ¹H and ¹³C NMR spectroscopies as well as thermal analysis. The thermal stability of the oleoylated hemicelluloses decreased slightly upon chemical modification, but no significant further decrease in thermal stability was observed for DS ≥ 0.29. Copyright © 2004 Society of Chemical Industry     

Analysis of six synthetic adulterants in herbal weight-reducing dietary supplements by LC electrospray ionization-MS

A liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method was developed for the simultaneous determination of six synthetic adulterants, namely fenfluramine, phenolphthalein, N-di-desmethyl sibutramine, N-mono-desmethyl sibutramine, sibutramine, and orlistat. The method was applied to the analysis of herbal weight-reducing dietary supplements. Chromatographic separation of the analytes on a C₈ reversed-phase column was achieved using a gradient elution of solvent A: acetonitrile and solvent B: aqueous 20 mM ammonium formate solution. Sildenafil was utilized as an internal standard for quantification. The MS detector was operated in positive electrospray ionization mode. Selected-ion monitoring (SIM) was carried out for m/z 232, 319, 252, 266, 280, 496, and 475 for fenfluramine, phenolphthalein, N-di-desmethyl sibutramine, N-mono-desmethyl sibutramine, sibutramine, orlistat, and sildenafil, respectively. The method was validated for accuracy, precision, linearity, and selectivity. The limits of detection for the six synthetic adulterants ranged from 0.0018 to 0.73 µg g^?1. The proposed method was used for a small survey of 22 dietary supplements of which eleven samples were adulterated with phenolphthalein, N-mono-desmethyl sibutramine, and sibutramine at levels from 0.212 to 96.2 mg g^?1.