Flame Photometric Detector Research Articles

Thin layer chromatography performed in stages to identify the presence of aromatic like fraction in chosen bitumen modifiers

The organic modifiers are used to alter the rheology of the binder in the asphalt concrete at an added cost. For quality control purpose, recognizing if such material is present in the final blend is of an interest. The thin layer chromatography (TLC) using a flame photometric detector (FPD), in addition to the typical flame ionization detector, was demonstrated hereby as a potential analytical tool for this problem, differentiating between tall crude oil based anti-aging agent, polymer, oxidized bitumen and gilsonite. Gilsonite and anti-aging agent consists of the material soluble in solvent used in the development of the fraction referred to as aromatics. Due to the hindered mobility of modifier molecules on the stationary phase, the elution of aromatic fraction stops at position convoluted with polars I and polars II fraction regions, colloquially referred to as resins and asphaltenes. However, for the color of this fraction within gilsonite is different. The presence of gilsonite is thus identifiable visually after the second development bath, but also to an extent with FPD from the final chromatogram. The thin layer chromatography-flame ionization detectors (TLC-FID) procedure is suggested to be supplemented by infrared spectroscopy to discriminate between non-bituminous and bituminous modifiers of similar response during fractionation. • The analysis of thin layer chromatography of bitumen performed in stages. • The procedure to distinguish gilsonite in blends with bitumen is suggested. • The hidden aromaticity of materials such as gilsonite and rejuvenators based on their response to a solvent is demonstrated.

Monitoring of the Organophosphate Pesticide Chlorpyrifos in Vegetable Samples from Local Markets in Northern Thailand by Developed Immunoassay.

Chlorpyrifos is an organophosphate pesticide that is wildly used among farmers for crop protection. However, there are concerns regarding its contamination in the environment and food chain. In the present study, an in-house indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) specific for detecting chlorpyrifos is developed and validated against gas chromatography–flame photometric detection (GC-FPD) as the conventional method. The developed ic-ELISA was used for detecting chlorpyrifos residue in vegetable samples. The developed ic-ELISA showed good sensitivity to chlorpyrifos at an IC50 of 0.80 µg/kg, with low cross-reactivity to other organophosphate pesticides. The 160 samples were collected from local markets located in the Chiang Rai, Chiang Mai, and Nan provinces in northern Thailand. The positive rate of chlorpyrifos residues in the vegetable samples was 33.8%, with the highest levels found in cucumbers, coriander, and morning glory, at 275, 145, and 35.3 µg/kg, respectively. The highest median levels of chlorpyrifos found in the detected samples were Chinese cabbage (332 μg/kg), cucumber (146.3 μg/kg) and Chinese Kale (26.95 μg/kg). The developed ic-ELISA is suitable for the rapid quantitation of chlorpyrifos residues.

Simultaneous determination of organophosphorus residues on curry leaf, decontamination through household techniques and risk assessment

A simple analytical method was developed and validated, as per SANTE 2017 guidelines, for simultaneous determination of 10 organophosphorus residues in curry leaf using gas chromatography with flame photometric detection, and confirmed using gas chromatography-mass spectrometry. Samples were extracted with ethyl acetate and cleaned up with primary secondary amine and graphitized carbon black. Average recoveries were in the range 80–108% with the RSD of less than 8%. The effects of different household cleaning techniques to reduce the concentration of pesticide residues in curry leaf were evaluated and found to remove 2–65% of residues. The method was applied to analyse sample to fresh curry leaf samples, and analysis of potential health risks estimated the residues did not pose a direct hazard. This method could be useful for routine analysis of organophosphorus residue for monitoring purposes.

Pollution status of volatile organic sulfur compounds causing odor in Xi River and factors influencing spatial distribution

Abstract This study investigated the pollution status of volatile organic sulfur compounds (VOSCs) and the factors influencing their spatial distribution in the Xi River in Shenyang, China. A method for simultaneous determination of 14 VOSCs that cause odor in water samples was developed by using purge and trap coupled with gas chromatography and a flame photometric detector. The results indicated that each target compound could be identified from 15 sampling sites, and the total concentration of 14 VOSCs ranged from 2.575 to 52.981 μg L−1. Dimethyl sulfide (DMS) was the most important contaminant with an average concentration of 4.029 μg L−1, a detection rate of 93.33% and a variation coefficient of 0.72. The VOSCs were primarily distributed in suburban and rural sections, and the suburban section was the worst in regard to pollution by VOSCs. Dimethyl trisulfide was primarily distributed in urban and suburban sections of the Xi River due to industrial emissions. Ethanethiol, DMS, and ethyl methyl sulfide, which are typical by-products of microbial anaerobic decomposition from domestic wastewater, were found in abundance in the suburban section. Diethyl sulfide, diethyl disulfide, methyl propyl disulfide, and 1-propyl disulfide representing agricultural nonpoint source pollution were mostly distributed in the rural section.

Identification of the transformation features of heteroatomic compounds in a low rank coal by combining thermal extraction and various analytical approaches

Solvent extraction is an effective approach to analyze the molecular features of coal and to reveal the transformation mechanism of heteroatoms. In order to accurately figure out the transformation and distribution of heteroatoms during extraction, Naomaohu coal (NMHc), Hypercoal (HPC), and Extraction residue (ER) were systematically analyzed with Fourier transform infrared (FTIR) and X-ray photoelectron spectrometer (XPS). The liquid extract was characterized using Atomic Emission Detector for Gas Chromatography (GC-AED) and gas chromatograph with mass spectrometer (GC–MS). In addition, the distribution characteristics of gas products were examined by gas chromatograph (GC). The results suggest that the solvents with high polarity, strong hydrogen donating capacity, and similar solubility to coal could promote the separation of organic compounds from coal. The extraction yield of xylene with coal increased with increasing temperature. Based on the “Similarity-Intermiscibility” principle, the extracts of xylene were mostly aromatic hydrocarbons and alkanes. The heteroatom-containing species were difficult to be extracted by xylene. Sulfur and oxygen were easily transformed into gas products such as H2S, SO2, CO, and CO2. Moreover, nitrogen compounds were hard to be extracted and recombined. Most of the compounds containing O, S, Cl, and other inorganic substances can be almost completely transferred into the residue through the extraction process. After the thermal solvent extraction, the heteroatoms were primarily present as organic matter in the ER and extract, such as thiophene, pyrrole, pyridine, ketone,and their homologues. The molecular structure of coal was reorganized to be of high thermal and chemical stability, especially for the heteroatom-containing species.

Rapid and accurate determination of trace volatile sulfur compounds in human halitosis by an adaptable active sampling system coupling with gas chromatography.

Halitosis with the main components of trace volatile sulfur compounds widely affects the quality of life. In this study, an adaptable active sampling system with two sample-collection modes of direct injection and solid-phase microextraction was developed for the rapid and precise determination of trace volatile sulfur compounds in human halitosis coupled with gas chromatography-flame photometric detection. The active sampling system was well designed and produced for efficiently sampling and precisely determining trace volatile targets in halitosis under the optimized sampling and detection conditions. The analytical method established was successfully applied for the determination of trace targets in halitosis. The limits of detection of H2 S, CH3 SH, and CH3 SCH3 by direct injection were 0.0140-23.0μg/L with good recoveries ranging from 82.2 to 118% and satisfactory relative standard deviations of 0.4-9.5% (n=3), respectively. The limit of detections of CH3 SH and CH3 SCH3 by solid-phase microextraction were 2.03 and 0.186 × 10-3 μg/L with good recoveries ranging from 98.3 to 108% and relative standard deviations of 5.9-9.0% (n=3). Trace volatile targets in positive real samples could be actually found and quantified by combination of direct injection and solid-phase microextraction. This method was reliable and efficient for the determination of trace volatile sulfur compounds in halitosis.

Characterization of important sulfur and nitrogen compounds in Lang baijiu by application of gas chromatography-olfactometry, flame photometric detection, nitrogen phosphorus detector and odor activity value

The volatile compounds in three Lang baijiu (“Honghualangshi, Y1”, “Langjiulangge, Y2”, and “Laolangjiu, Y3”) were identified by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC–MS), flame photometric detection (FPD), and nitrogen phosphorus detector (NPD) with the aid of stir bar sorptive extraction (SBSE). The results showed that a total of 60, 62, and 61 compounds with aroma contribution were present in samples Y1, Y2, and Y3, respectively. Additionally, the odor activity value (OAV) was used to evaluate the important compounds. The results indicated that 2-methyl-3-furanthiol (OAV: 20–30), 3-mercaporhexyl acetate (OAV: 13–20), β-damascenone (OAV: 30–57), (E)-2-nonenal (OAV: 9–22), heptanal (OAV: 4–13), hexanal (OAV: 9–12) and 2-isopropyl-3-methoxypyrazine (OAV: 4–14) contributed to the aroma of Lang baijiu. Finally, six compounds (ethyl hexanoate, 2-methyl-3-furanthiol, (E)-2-decenal, guaiacol, 3-mercaporhexyl acetate, and 2-isopropyl-3-methoxypyrazine) with different OAVs were used to determine the effect on the threshold of aromatic reconstitution (AR). It can be seen that ethyl hexanoate, 2-methyl-3-furanthiol, 3-mercaporhexyl acetate, and 2-isopropyl-3-methoxypyrazine could significantly decrease the threshold of AR. The possible reason was that these four compounds had synergistic effects with the aroma compounds in AR. Compared to ethyl hexanoate and 2-methyl-3-furanthiol, the threshold of AR had a slight difference in the presence of (E)-2-decenal in AR. After the addition of guaiacol, the threshold value of AR was significantly increased, indicating a masking effect between guaiacol and the original aroma compounds in AR.

Solid-phase microextraction for the determination of iron organic compounds in seawaters and soils by gas chromatography coupled to microwave-induced plasma with atomic emission detection spectrometry

A rapid solvent-free method for determining ferrocene and five derivatives (1,1´-dimethylferrocene, ferrocenecarboxaldehyde, acetylferrocene, ferroceneacetonitrile and benzoylferrocene) in seawaters and soils using direct immersion solid-phase microextraction (DI-SPME) and gas chromatography coupled to microwave-induced plasma with atomic emission detection (GC-MIP-AED) is developed. The bonded divinylbenzene/Carboxen/polydimethylsiloxane commercial fiber provided good extraction efficiency in the DI mode for all the compounds, applying a fiber time exposure of 15 min at ambient temperature. The analytes were previously isolated from the soil matrices (0.2 g) by ultrasound-assisted extraction using 7 mL of 0.1 M acetate/acetic buffer solution. The absence of a matrix effect was confirmed in the case of seawaters, which permitted calibration against aqueous standards. However, the standard additions method was required for soil analysis. Detection limits (DLs) were in the 3–110 pg mL−1 and 0.9–4 ng g − 1 for seawater and soils, respectively. Analysis of the different samples using the proposed DI-SPME-GC-AED method only provided an analytical signal for ferrocene in one seawater sample at a concentration near its DL (3 pg mL−1).

Laser-induced breakdown spectroscopy of BaF2-Tm3+

Our recent study was focused on the emission from Laser Induced Plasma (LIP) at the delay times of tenths of microseconds after the laser pulse. At these long delays, the spectrum is dominated by the broadband molecular emission and plasma induced luminescence (PIL) produced by a luminescent matrix; only solitary atomic emission lines can be seen. Barium fluoride BaF2 activated by thulium (Tm) is a famous scintillator that presents the promising object for LIP in terms of both the potential for BaF molecular emission and Tm3+ PIL. The detection of molecular and PIL bands presents a new opportunity for analysis of halogens and rare-earth elements, which are the difficult objects for LIBS. In this paper, we show that the UV, Green, Extreme Red, and Infrared molecular bands from BaF and blue luminescence from Tm3+ are present in the LIP emission spectra while the detection of atomic emission from F I and Tm I was impossible with the same experimental setup. Thus, the detection of molecular emission and PIL can be more sensitive than the traditional detection of emission from atoms and ions.

Methanethiol, an Off-Flavor Produced from the Thermal Treatment of Mandarin Juices: A Study of Citrus Sulfur Volatiles.

The off-flavor produced after thermal stabilization of mandarin (Citrus reticulata, Blanco) juices has limited the production of commercial juices. Methanethiol, a putrid-smelling sulfur volatile, has been identified for the first time in heated mandarin juices. Identification was achieved using a combination of capillary gas chromatography with two dissimilar columns and a dual sulfur-specific pulsed flame photometric detector and selected ion mass spectrometry detection. Static headspace solid-phase microextraction quantitation found that average odor activity values (OAVs) in heated juices were 25.5 for methanethiol compared to 10.8 for dimethyl sulfide. OAVs for methanethiol and dimethyl sulfide in fresh juices were ND (not detected) and 5.5, respectively. Hydrogen sulfide, carbonyl sulfide, carbon disulfide, and dimethyl disulfide were also identified and quantitated. Thermal decomposition studies of nonvolatile sulfur-containing potential precursors indicated that methionine was the major source of methanethiol. Additional heating studies with model juices demonstrated that ascorbic acid greatly accelerated the formation of methanethiol and methional, as well as dimethyl di and tri sulfides.

Fast and Easy Method of 55 Pesticide Residues Determination in Commonly Fruits and Vegetables Collected from Egyptian Local Markets

The highest concerns of consumers who need food safety are pesticide residues in fruits and vegetables. In this study, a total fifty-five pesticide residues from different chemical groups including insecticides, fungicides, herbicides, acaricides and others compounds were detected in different kinds of fruits (apple, grapes, and guava) and vegetables (squash, cucumber, tomatoes, pepper and cantaloupe) collected from local markets in Cairo Governorate. The method is based on a modified QuEChERS procedure (quick, easy, cheap, effective, rugged & safe) using acetonitrile for extraction and partition.. Analytical determinations of the 55 pesticides were carried out with gas chromatography using micro electron capture detector (µECD) and flame photometric detector (FPD).. The data obtained indicated that, the mean recoveries of the pesticides were between 81.20 and 98.70 %. The detection limits (LOD) and quantification limits (LOQ) of pesticide residues for the method were ranged (0.002 - 0.009 µg/g) and between 0.01 - 0.05 (µg/g), respectively. Of the 55 pesticides analyzed,32 (58.2%), 31(56.4), and 34(61.8) of pesticide residues were detected in the apple, grapes and guava respectively, while 30(54.5%), 31(56.4%), 30(54.5%) 24(43.6) and 27(49.1) of pesticide residues were detected in the squash, cucumber, tomatoes, pepper and cantaloupe respectively. The percentages of pesticide residues that exceeded the MRLs in both fruits and vegetables (apple. grape and guava) were12.7%, 16.4% and 16. (squash, cucumber, tomatoes pepper and cantaloupe) were 5.5%, 7.3%, 3.6%, 9.1% % and 3.6% respectively.

Determination of 1,2,4-Trithiolane in Oil and Petroleum Products by Gas Chromatography

A procedure is developed for the quantitative determination of 1,2,4-trithiolane in oils and petroleum products by gas chromatography with flame photometric detection. The analytical range is 2‒100 mg/kg, relative standard deviations are 2‒5%. A possibility of using the developed procedure for establishing the fact of using formaldehyde-containing absorbers of hydrogen sulfide in the preparation of oil is shown.

Arc Atomic Emission Analysis of Rare Earth Metals and Their Oxides with Preliminary Sorption Concentration of Impurities

This work investigates in analytical capacities of arc atomic emission analysis (AAEA) in determination of As, Bi, Sb, Cu, and Te in rare earth metals (REM) and their oxides after preliminary group concentration using S,N-containing heterochain polymer sorbent. The investigations have been carried out using a Grand-Extra high-resolution spectrometer developed by VMK-Optoelektronika (Russia). Sorption kinetics and impurity extraction rate as a function of solution acidity have been studied for a selection of conditions of sorption concentration. Aiming at optimization of arc atomic emission detection of As, Bi, Sb, Cu, and Te, various flowcharts of their sorption concentration and subsequent treatment of obtained concentrated product have been considered with addition of a collector at various sorption stages. Powdered graphite has been used in this work as a collector in analysis of rare earth oxides, which is attributed to the relative simplicity of its emission spectrum and versatility. Analytical conditions and spectrometer parameters affecting the analytical signal (sample weight and composition, shape and size of electrodes, current intensity and operating mode of generator, interelectrode distance, wavelengths of analytical lines) have been selected. The evaporation curves of detected impurities have been analyzed, and the exposure time of As, Bi, Sb, Cu, and Te in the obtained sorption concentrate has been determined. Accuracy of the results has been evaluated using reference samples and by comparisons between methods. The results have been used for development of arc chemical atomic emission analysis of yttrium, gadolinium, neodymium, europium, scandium, and their oxides in the concentration range of n × (10–5–10–2) wt %.

Occurrence of Ehrlich-Derived and Varietal Polyfunctional Thiols in Belgian White Wines Made from Chardonnay and Solaris Grapes.

Although almost disappeared at the end of the 20th century, Belgian wine production reached a million liters in 2017. The aim of the present work was to identify aroma markers for two white cultivars widespread in Belgium: Chardonnay (the most commercially grown cultivar worldwide) and Solaris (an interspecific fungus-resistant variety). Specific p-hydroxymercuribenzoic acid extraction followed by gas chromatography with a pulsed flame photometric detector was applied to single-varietal wine samples from 2015 to 2018 harvests. Among the Ehrlich-derived thiols, all found below their sensory thresholds, 3-sulfanylpropyl acetate usually outranged 3-sulfanylpropan-1-ol, while 2-sulfanylethan-1-ol concentrations always exceeded 2-sulfanylethyl acetate levels. The data confirm the occurrence, in both Chardonnay and Solaris wines, of 3-sulfanylhexan-1-ol and phenylmethanethiol (grapefruit and gunflint aroma, respectively), at concentrations far above their thresholds. This work also revealed, for the first time, the presence of 3-sulfanylheptan-1-ol, the branched alcohols 2-methyl-3-sulfanyl propan-1-ol, 2-methyl-3-sulfanylbutan-1-ol, and 3-sulfanyl-3-methylbutan-1-ol, and the carbonyls 3-sulfanylbutan-2-one (not in sparkling wines) and 3-sulfanylpentanal.

Synthesis of Molecularly Imprinted Polymer on Surface of TiO2 Nanowires and Assessment of Malathion and its Metabolite in Environmental Water

Molecularly imprinted polymer (MIP) for malathion and its major metabolite malaoxon was prepared with sol‒gel polymerization method using malathion as template molecule, (3-aminopropyl)triethoxysilane (APTES) as functional monomer, tetraethyl orthosilicate as crosslinker, TiO2 nanowires as support and methanol as solvent. Interaction of APTES with malathion by hydrogen bond with a ratio of 2 : 1 was evaluated by the molecular recognition mechanism. The properties of MIP were characterized by Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope, X-ray diffractometry, surface area and porosimeter analysis, elemental analysis and thermogravimetric/differential thermal analysis. Molecularly imprinted polymers showed high affinity, recognition specificity and efficient adsorption performance for malathion. The residues of malathion and malaoxon in tap water were cleaned up by MIP-solid-phase extraction cartridge, determined by gas chromatography with flame photometric detector. The quantification limits of malathion and malaoxon were both 0.01 mg/L. The spiked recoveries of malathion and malaoxon in environmental water were 62.1‒76.7% (RSD 4.2‒6.5%) and 82.1‒95.4% (RSD 7.0‒7.7%), respectively. Gas chromatography‒tandem mass spectrometry analysis for confirmation was also performed.

QuEChERS-based gas chromatography-electron capture/flame photometric detection method for multi-pesticide residues analysis in Andrographis paniculata: a popular Indian medicinal herb

ABSTRACT Andrographis paniculata (kalmegh) is a medicinal plant consumed at ton scale worldwide. This herb has a high demand both in traditional ayurvedic formulations and in the pharmaceutical industry. Owing to the continuous global demand for pharmaceutical applications, quality of cultivated kalmegh is very important and the presence of pesticide residues may pose serious restrictions by various national/international regulatory bodies for consumer safety. The European pharmacopoeia, require validated methods to determine the pesticide residues in each specific medicinal plant. In order to achieve such requirements, a modified quick, easy, cheap, efficient, rugged and safe (QuEChERS) method coupled with gas chromatography with electron capture detector or flame photometric detection (GC–ECD/FPD) was developed for the determination of the multiclass pesticide residues of 12 organochlorines (OCs), 8 organophosphates (OPs), 6 synthetic pyrethroids (SPs) insecticides, 5 herbicides, and 3 fungicides in kalmegh. Initially, pesticides were extracted with acetonitrile and then, the extracts were purified by dispersive solid-phase extraction clean-up. The developed method showed good linearity for all pesticides with high values of correlation coefficients (0.973–0.997) coupled with low limits of detection (LOD) and quantification (LOQ) values ranging from 0.001–0.01 µg/mL and 0.01–0.075 µg/g, respectively. Matrix effects were also investigated and matrix-matched calibration curves were used for all studies. Mean recoveries (60.8–111.8%, with RSD 8.1%) were within the international acceptable limits (70–120%) along with uncertainty analysis ranging from 7.69 to 21.15%. The validated established method was effectively employed for determining the pesticide residues in real field samples and can be extended for commercial and regulatory residue analysis.

Effect of Wine Matrix Composition on the Quantification of Volatile Sulfur Compounds by Headspace Solid-Phase Microextraction-Gas Chromatography-Pulsed Flame Photometric Detection.

The analysis of volatile sulfur compounds using headspace solid-phase microextraction (HS-SPME) is heavily influenced by matrix effects. The effects of a wine matrix, both non-volatile and volatile components (other than ethanol) were studied on the analysis of several common sulfur volatiles found in wine, including hydrogen sulfide (H2S), methanethiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), methyl thioacetate (MeSOAc), and ethyl thioacetate (EtSOAc). Varying levels of devolatilized wine and common wine volatiles (acids, esters, alcohols) were added to synthetic wine samples to act as matrices. Sulfur standards were added and analyzed using gas chromatography with pulsed-flame photometric detection (GC-PFPD). Five internal standards were used to find best representatives of each compound despite matrix effects. Sensitivity remained stable with the addition of devolatilized wine, while addition of volatile components decreased sensitivity. DMS was found to be best measured against EMS; DMDS and the thioacetates were best measured against DES; H2S, MeSH, DEDS, and DMTS were best measured against DIDS. The method was used to quantitate the volatile sulfur compounds in 21 wines with various ethanol contents and volatile profiles.

Characterization of the Key Aroma Compounds in Three Truffle Varieties from China by Flavoromics Approach.

The volatile compounds of three different fresh-picked truffle varieties (Tuber sinensis, T1, Tuber sinoalbidum, T2 and Tuber sinoexcavatum, T3) were extracted by headspace solid-phase microextraction (HS-SPME). Separation and identification of volatile components and sulfur compounds were investigated by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC–MS) and gas chromatography with flame photometric detection (GC-FPD). The results showed that 44, 43 and 44 volatile compounds were detected in T1, T2 and T3 samples, respectively. In addition, 9, 10 and 9 sulfur compounds were identified in three samples by GC-FPD, respectively. Combining physicochemical and sensory properties, T1 presented fatty, green and rotten cabbage odor; T2 exhibited mushroom, sulfuric and musty odor notes; T3 had nutty, floral and roasted potato odor. Dimethyl sulfide, 3-methylbutanal, dimethyl disulfide, 3-octanone, bis(methylthio) methane, octanal, 1-octen-3-one, 1-octen-3-ol and benzeneacetaldehyde played indispensable roles in the overall aroma of three truffles. Finally, based on quantitative concentration in T1, odorous compounds (OAV) > 1 were mixed to recombine aroma, demonstrating that these key aroma compounds based on OAV can successfully recombine pretty similar aroma of each variety.

A flame photometric detector with a silicon photodiode assembly for sulfur detection

A flame photometric detector with a silicon photodiode assembly instead of a photomultiplier tube for sulfur detection was developed and evaluated. The photosensitive area of photodiode, the optical design, and band-pass filters, were optimized. It was found that the optimal photosensitive area of the photodiode was 100 (mm)2, and three focus lenses combined with a broad band-pass filter of 378/52 nm and a QB21 glass yielded the best result. This design fully utilized the wide emission spectrum of S2*, the response characteristics of silicon photodiode, and effective absorption of strong emission spectrums of OH* at wavelength around 310 nm by QB21 glass. The limits of detection for nine kinds of sulfur containing compounds were between 5.8 × 10−12 to 9.5 × 10−12 g s−1. This mode provided a linear response of 3 orders of magnitude for compounds being tested and a selectivity of sulfur over carbon of 105. It is demonstrated for the first time that the overall performance of the flame photometric detector integrated with a silicon photodiode assembly work at room temperature was comparable to a conventional detector coupled with a photomultiplier tube, with advantages of short equilibration time, robust to electromagnetic interference and vibration, and low cost. The new detector can find wide application in gas chromatography and on-line monitoring instruments for sulfur measurement.

Identification of the source of volatile sulfur compounds produced in milk during thermal processing

Volatile sulfur compounds in ultra-pasteurized (UP) milk are the major contributors to sulfur/burnt and eggy flavors, and these flavors are disliked by consumers. Previous research has established distinct differences in flavor profiles of fluid milk processed by high temperature, short time pasteurization (HTST) and UP by direct steam injection (DSI-UP) or indirect heat (IND-UP). An understanding of the contribution of the individual milk proteins to sulfur off-flavors would clarify the source of sulfur flavors in UP milks. The objective of this study was to determine the source of volatile sulfur compounds in fluid milk with a specific focus on the comparison of heat treatment effects on milks by HTST and UP. Formulated skim milks (FSM) were manufactured by blending micellar casein concentrate and serum protein isolate (SPI). Three different caseins as a percentage of true protein (FSM95, FSM80, and FSM60) were formulated to determine the source of sulfur/burnt and eggy flavors. Freshly processed micellar casein concentrate or SPI were blended to achieve a true protein content of about 3.2%. Raw skim milk served as a control. Skim milk and FSM were pasteurized at 78°C for 15 s (HTST) or 140°C for 2.3 s by IND-UP or DSI-UP. The experiment was replicated twice. Sensory properties of milks and FSM were documented by descriptive sensory analysis. Volatile sulfur compounds in milks and FSM were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry combined with a sulfur selective flame photometric detector. The FSM with higher SPI as a percent of true protein had higher sensory sulfur/burnt and eggy flavors along with elevated concentrations of hydrogen sulfide and carbon disulfide compared with skim milk or FSM with lower proportions of SPI. Sulfur compounds including dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, dimethyl sulfoxide, and methional were not associated with sulfur/burnt and eggy flavors, which suggests that these compounds may not specifically contribute to the sulfur/burnt and eggy off-flavors of UP milks. Sensory panelists found higher overall aroma impact, and cooked, sulfur/burnt, and eggy flavors for DSI-UP, followed by IND-UP and HTST. The combination of sensory and instrumental methods used in the current study effectively identified that milk serum proteins are the source of sulfur compounds in milk, and further confirmed the contribution of hydrogen sulfide and carbon disulfide to eggy and sulfur/burnt flavors, respectively.