Determination of oxygen in organic substances by reaction-frontal gas chromatography

Uhdeová, Jitka; Rezl, Vlastimil

doi:10.1021/ac00225a008

Cited by 8 publications

(5 citation statements)

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“…Three milligrams of dried sample from each size fraction were burned and converted into gas containing CO 2 , H 2 O, and NO x . The gases were separated through a column according to the principle of frontal chromatography (Uhdeova and Rezl, 1981). The nitrogen content of each burned sample was measured using a CHN Analyzer sensor.…”

Section: Characterization Of Digested Tofu Samples (1) Classificationmentioning

confidence: 99%

Development of a Human Gastric Digestion Simulator Equipped with Peristalsis Function for the Direct Observation and Analysis of the Food Digestion Process

Kozu

Nakata

Nakajima

et al. 2014

FSTR

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A novel in vitro gastric device, the Gastric Digestion Simulator (GDS), was developed for the direct observation and quantitative analysis of the food digestion process in the human stomach. In addition to simulating the chemical digestion environment, this device provides a physical digestion environment comparable to that found in the stomach by simulating peristalsis, which is assumed to contribute to solid food disintegration. The GDS was successfully used to directly observe the disintegration process of Tofu (bean curd) as a typical solid food containing protein. The size distribution and protein content of Tofu particles during the digestion experiments were investigated. The results demonstrated the difference in particle disintegration between GDS and flask shaking experiments, which may be due to the lack of peristalsis in the latter case. Moreover, the size distribution of Tofu particles after the GDS experiments was affected by the physical properties of Tofu, thus revealing the usefulness of GDS for food digestion analysis.Keywords: GI tract, gastric digestion, in vitro gastric device, peristalsis, direct observation, solid food IntroductionIn the human gastrointestinal (GI) tract, foods are digested by a combination of physical and chemical processes. Chemical digestive processes are catalyzed by digestive enzymes secreted in the stomach and small intestine, and disintegrate foods down to the molecular scale. However, physical digestive processes, which are induced mainly by peristalsis, mix and empty gastric and intestinal contents, and thus play an important role in promoting food digestion in the GI tract. Peristalsis in the GI tract is caused by peristaltic wall motion (e.g., antral contraction waves (ACWs)) in the stomach. Periodically generated ACWs induce the motion of the gastric contents, mix the gastric contents, and grind bulk solid foods to reduce their particle size (Kong and Singh, 2008) Food digestion in the human GI tract has been studied using in vivo, in vitro, and in silico approaches. MRI has been used for in vivo studies on gastric peristaltic motion and the physical properties of gastric contents. The speed of ACWs and the ACW amplitude in the human stomach were calculated using data obtained by real-*To whom correspondence should be addressed. time MRI (King et al., 1984;Pallotta et al., 1998). The timedependent change of the viscosity of the gastric contents was measured using echo planar MRI (Marciani et al., 2000). This study seeks to develop a new in vitro gastric digestion device that focuses mainly on the physical digestion environment of the human stomach, and to assess the device's performance. The gastric digestion simulator (GDS) that we developed here can simulate peristaltic motion in the human stomach and enables direct observation of the digestion process in real time. In this study, two different types of Tofu were used as model solid foods.We investigated food digestion characteristics using GDS to quantitatively understand the dynamic digestion processes in t...

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Section: Characterization Of Digested Tofu Samples (1) Classificationmentioning

confidence: 99%

Development of a Human Gastric Digestion Simulator Equipped with Peristalsis Function for the Direct Observation and Analysis of the Food Digestion Process

Kozu

Nakata

Nakajima

et al. 2014

FSTR

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“…26.1 ± 2.9 (10) 6.9 ± 0.4 range. This good digitization was, in part, due to the use of a 12-bit Á/D converter rather than the more commonly used 8-bit A/D.…”

Section: Resultsmentioning

confidence: 95%

“…The method first reported by Schutze (7) and later modified by Unterzaucher (7) and others (8)(9)(10) consists of thermally decomposing the sample and then reacting the oxygen-containing decomposition products with hot carbon to produ-ce CO. -Th-e CO is ·then detected either---directly by nondispersed infrared absorption (NDIR) or coulometrically after it is converted to C0 2…”

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“…Clemenson (1) used a cyclotron technique to determine the oxygen content of a few atmospheric aerosol samples. His technique is unique in that total oxygen is determined, as compared with a variety of other techniques (2)(3)(4)(5)(6)(7)(8)(9)(10) that, if used to analyze an atmospheric aerosol sample, would only determine a fraction of the oxygen in the sample. For example, a gas-chromatographic technique (2) requires that the substance of interest elutes from a column-a requirement not suitable for nonvolatile substances-and ESCA (4) or Auger (5) spectroscopy is a surface-sensitive technique.…”

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Determination of pyrolyzable oxygen in ambient particulate matter

Benner¹

1984

Anal. Chem.

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A technique is described for the determination of tens of micrograms of oxygen that can be pyrolyzed at T < 1135°C. Standard oxygen-containing compounds and filter samples of ambierit particulate matter are pyrolyzed in purified N 2 , and oxygen in the pyrolysis products is quantitatively converted to CO by passage over carbon at 1135°C. The evolved CO is detected by NDIR spectrometry or by coulometry after conversion to C0 2• The application of the technique for the analysis of ambient particulate matter is shown. packing is between 10 and SO ml/min. Below 10 ml/min it becomes difficult to adjust the flowrate with a rotameter, and above SO ml/min the decomposition products don't have time to react completely with the hot carbon.Gas samples were injected into the pyrolysis tube via a septum. A multipart valve (Condyne, La Canada, California) was used to change the direction of flow through the pyrolysis tube. Solid samples and filter samples were loaded into a small platinum boat (formed from S mil Pt foil) and placed into the cool zone of the pyrolysis tube while backflushing with N 2 so that room air did not contact ,~ 1 5 the hot carbon. After a sample was loaded, the pyrolysis tube was resealed (at the 0-ring seal) and any entrained air was backflushed from the system (~ 4 min).Then the multiport valve was switched; and finally after the CO detector stabilized, the sample boat was slid into the hot zone with a magnetically moved plunger. Results and DiscussionThe digitized analog NDIR detector signal deviated less than 0.5% from the analog signal in the 1.0-99.0 ppm CO range. This good digitization was, in part, due to the use of a 12-bit A/D converter rather than the more commonly used 8-bit A/D. Table 1 shows the results of thedeterminationof oxygen in a variety of oxygenated organic compounds, (NH 4 ) 2 so 4 , and NH 4 No 3 • These chemicals were either weighed into an empty boat or solutions containing these chemicals were evaporated onto 1-cm 2 discs of quartz fiber filter material. Also, several microliter volumes of C0 2 were analyzed and served as a convenient way to check out the system. Direct injections of C0 2 into the coulometer (footnote f, Table 1) shows good recovery (100.4%) with a standard deviation (cr) of 2.3%. Passage of C0 2 through the hot carbon and subsequent conversion of the evolved CO back to C0 2 did not affect the accuracy (footnote g, Table 1). The injection of C0 2 upstream of the hot carbon with NDIR detection of the evolved CO also gave good recovery (100.0 ±0.4%). Each detector offers certain advantages over the other one.The coulometer enables larger samples to be analyzed: 55-400 ~g 0 is a good ope~ating range. Below 55 ~g 0, one is operating below the limit of quantitation (LOQ) (See Table 2 A number of compounds were analyzed to determine the appropriateness of this technique for analyzing samples of ambient particulate matter. The compounds presented in Table 1 have a variety of oxygenJunctionalgroups, some of which have been observed in ambient air and smog c...

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“…Their calculations assumed that poly(oxymethylene) glycols were not present in significant concentrations, although there was no experimental evidence to support this concept. By indirect methods, Iliceto (5) investigated the formation of the dimeric species, oxydimethylene glycol, from formaldehyde and methylene glycol and calculated the enthalpy of formation to be -11.6 kcal/mol in the gas phase. This equilibrium has been supported by the work of Bryant and Thompson (6).…”

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confidence: 99%