Development and validation of a method for direct, underivatized analysis of free amino acids in rice using liquid chromatography-tandem mass spectrometry.

Inspired by the apparent relationship of free amino acids (FAAs) which are present in minute quantities with the organoleptic characteristics of food, there is an increased demand for analytical methods sensitive in trace level detection. This study presents the validation results of a simple and rapid method developed for direct, underivatized analysis of FAAs in rice using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI). The method demonstrated satisfactory selectivity for twenty FAAs with minimum matrix effect. The recoveries obtained for samples fortified at three concentration levels: low mid and high, covering the working range of the method were in the range 80%-110%. The precision measured in terms of repeatability and reproducibility of the method expressed as percentage relative standard deviation (% RSD) were below 10% for the amino acids analyzed. The detection limits (LODs) and quantification limits (LOQs) of the method were in the range 0.4-1.0 mg/kg and 0.6-1.2 mg/kg respectively. Method had a wide linear range between 1.25-100 mg/kg with regression coefficients greater than 0.999 obtained over seven calibration levels. The method was also found robust over other cereals including corn, wheat and finger millet with satisfactory recoveries and precision values. The percentage expanded uncertainties calculated with the coverage factor of 2 (k = 2), were below 14% for the analyzed amino acids. The developed, simple and rapid LC-MS/MS method is accurate and reproducible, allowing determination of underivatized FAAs in rice and comply with the international method validation guideline requirements.

Validation of a reversed-phase high-performance liquid chromatographic method for the determination of free amino acids in rice using l-theanine as the internal standard.

The study presents the validation results of the method carried out for analysis of free amino acids (FAAs) in rice using l-theanine as the internal standard (IS) with o-phthalaldehyde (OPA) reagent using high-performance liquid chromatography-fluorescence detection. The detection and quantification limits of the method were in the range 2-16µmol/kg and 3-19µmol/kg respectively. The method had a wide working range from 25 to 600µmol/kg for each individual amino acid, and good linearity with regression coefficients greater than 0.999. Precision measured in terms of repeatability and reproducibility, expressed as percentage relative standard deviation (% RSD) was below 9% for all the amino acids analyzed. The recoveries obtained after fortification at three concentration levels were in the range 75-105%. In comparison to l-norvaline, findings revealed that l-theanine is suitable as an IS and the validated method can be used for FAA determination in rice.

Contribution of dissolved sulfates and sulfites in hydrogen sulfide emission from stagnant water bodies in Sri Lanka.

Accumulation of sulfur-containing compounds and their bacterial mediated reductions have led to the emission of pungent odors from stagnant water bodies. This study is focused on the contribution of inorganic sulfur compounds in the emission of hydrogen sulfide. The measured dissolved oxygen levels have demonstrated good negative correlations with the dissolved sulfide levels implying the oxygen deficiency is the key for the reduction of sulfate ion and sulfite ion to sulfide ion. Particularly, the dissolved molar fractions of sulfide from the total dissolved sulfur compounds (sulfates, sulfites and sulfides) have a very good correlation with the dissolved oxygen for the stagnant water bodies except the artificially aerated prawn farms. For the stagnant water bodies with significant correlations, linear regressions are reported for them to be utilized in estimating one component of the regression from the measurement of the other. The measured data were further utilized to estimate the levels of hydrogen sulfide gas. The pH of the water bodies has confined much of the dissolved sulfides in the form of bisulfide ion and they can be easily escaped to the atmosphere upon acidification due to industrial discharges and/or acidic precipitations. The estimated levels of hydrogen sulfide just above the water surface were plotted for the most polluted stagnant water body in Sri Lanka for the pH range of 5-10 and temperature range of 25-35 degrees C.

Cyclohexane oxidation and carbon deposition over metal oxide catalysts.

Catalytic activity of V, Mn, Ni, Cu, Zn, Mo, Zr and Ce oxides over an alpha-alumina support was evaluated for cyclohexane oxidation under oxygen deficient conditions in order to understand the relation between carbon deposition and catalytic activity/selectivity. Carbon formation over the catalysts during the oxidation reaction was measured by means of Fourier transformed infrared spectroscopy (FTIR). Catalysts Mn/Al2O3 and Ce/Al2O3, which are selective for deep oxidation of cyclohexane, possessed relatively carbon free surfaces. The catalysts with relatively high carbon deposition (V, Ni, Cu, Zn, Mo and Zr) produced CO in addition to CO2. Traces of formaldehyde were produced over the catalysts Mo and V.

Toxic volatile organic compounds in simulated environmental tobacco smoke: emission factors for exposure assessment.

Environmental tobacco smoke (ETS) is suspected to be a major source of exposure to many of the compounds identified as toxic air contaminants. However, we lack emission factors for many of the ETS air toxics for the brands of cigarettes which currently dominate the market and therefore cannot adequately estimate contributions of ETS to such exposures. This study provides up-to-date emission factors for selected air toxics and other volatile organic compounds (VOCs) in simulated ETS and uses them in a mass balance model to evaluate the potential contribution of ETS to air toxics in indoor air and, therefore to indoor exposures to air toxics. Emission factors (microgram/cigarette) were determined for 21 VOCs (including two aldehydes), nicotine and particulate matter in a room-sized (20-m3) environmental chamber with stainless-steel walls, operated under static conditions, using diluted sidestream smoke (no exhaled mainstream smoke) to simulate ETS. Experiments were conducted for Kentucky Reference cigarette 1R4F and for each of six commercial cigarette brands with major market shares. The variabilities in the ETS emission factors among brands of cigarettes were relatively small, ranging from 16 to 31% (expressed as the coefficient of variation) among the six brands. The concentrations of most of the VOCs did not change over the 4-hour periods of the experiments. However, concentrations of 3-ethenylpyridine, phenol, o-cresol and m,p-cresol showed consistent decreases over time, indicating removal by means other than the very low air infiltration rate (0.03 h-1), e.g., deposition onto the chamber surfaces. Emission factors for these compounds were calculated to take these losses into account and the rate constants for these losses were estimated. To estimate indoor concentrations and inhalation exposures to 16 VOCs, nicotine and PM-2.5, the average emission factors for the six commercial brands were used in a time-dependent mass-balance model for two scenarios: a typical office building and an average residence. In general, the indoor concentrations of the air toxics from ETS, under conditions selected to be "typical" rather than extreme, are comparable in magnitude to average outdoor concentrations, indicating that ETS can be a significant contributor to the total indoor concentration and the inhalation exposure for these species. At higher smoking rates, exposures to VOCs from ETS could be several times higher than those modeled under more "typical" conditions.

Effectiveness of smokeless ashtrays.

Most environmental tobacco smoke (ETS) issues from the tips of smoldering cigarettes between puffs. Smokeless ashtrays are designed to reduce ETS exposure by removing particulate and/or gas-phase contaminants from this plume. This paper describes an experimental investigation of the effectiveness of four smokeless ashtrays: two commercial devices and two prototypes constructed by the authors. In the basic experimental protocol, one or more cigarettes was permitted to smolder in a room. Particulate or gas-phase pollutant concentrations were measured in the room air over time. Device effectiveness was determined by comparing pollutant concentrations with the device in use to those obtained with no control device. A lung deposition model was applied to further interpret device effectiveness for particle removal. The commercial ashtrays were found to be substantially ineffective in removing ETS particles because of the use of low-quality filter media and/or the failure to draw the smoke through the filter. A prototype ashtray using HEPA filter material achieved better than 90% particle removal efficiency. Gas-phase pollutant removal was tested for only one prototype smokeless ashtray, which employed filters containing activated carbon and activated alumina. Removal efficiencies for the 18 gas-phase compounds measured (above the detection limit) were in the range of 70 to 95%.

Determination of vitamin K1 in powdered infant formulas, using supercritical fluid extraction and liquid chromatography with electrochemical detection.

Vitamin K1 (phylloquinone) is extracted from commercial soy protein-based and milk-based powdered infant formulas by using supercritical fluid extraction with CO2 at 8000 psi and 60 degrees C. Quantitative extraction requires only 15 min, and does not suffer from the problems associated with conventional solvent extraction of lipophilic materials from media such as formulas. Vitamin K1 is determined in the extracts by using reverse-phase liquid chromatography (LC) with reductive mode electrochemical detection at a silver electrode polarized at -1.1 V vs SCE. LC run time is 9 min. The minimum detectable quantity is 80 pg, and response is linear over at least 5 orders of magnitude. Recovery of vitamin K1 from a milk-based powdered formula was 95.6% with RSD of 7.4%, and from a soy protein-based product, 94.4% recovery with RSD of 6.5%.