Purge Vessel Research Articles

Comparative Evaluation of Chemical and Photolytic Denitrosation Methods for Chemiluminescence Detection of Total N-Nitrosamines in Wastewater Samples.

N-Nitrosamines form as byproducts during oxidative water treatment and occur as impurities in consumer and industrial products. To date, two methods based on chemiluminescence (CL) detection of nitric oxide liberated from N-nitrosamines via denitrosation with acidic triiodide (HI3) treatment or ultraviolet (UV) photolysis have been developed to enable the quantification of total N-nitrosamines (TONO) in environmental water samples. In this work, we configured an integrated experimental setup to compare the performance of HI3-CL and UV-CL methods with a focus on their applicability for TONO measurements in wastewater samples. With the use of a large-volume purge vessel for chemical denitrosation, the HI3-CL method achieved signal stability and detection limits comparable to those achieved by the UV-CL method which utilized a microphotochemical reactor for photolytic denitrosation. Sixty-six structurally diverse N-nitroso compounds (NOCs) yielded a range of conversion efficiencies relative to N-nitrosodimethylamine (NDMA) regardless of the conditions applied for denitrosation. On average, TONO measured in preconcentrated raw and chloraminated wastewater samples by the HI3-CL method were 2.1 ± 1.1 times those measured by the UV-CL method, pointing to potential matrix interferences as further confirmed by spike recovery tests. Overall, our comparative assessment of the HI3-CL and UV-CL methods serves as a basis for addressing methodological gaps in TONO analysis.

An improved device for continuously measuring dimethyl sulfide and isoprene in the air and seawater

The oceanic short-lived trace gases, such as dimethyl sulfide (DMS) and isoprene, play important roles between the surface ocean and the lower atmosphere. Once emitted into the atmosphere, these gases were rapidly oxidized, and their by-products could influence the atmospheric physical and chemical properties by forming particles. However, it is still challenging to collect these trace gases data efficiently due to the lack of a fully automatic measurement method. Therefore, we improved our previous home-made purge and trap system, including the controlling system, purge vessel and heating and cooling device, for measuring DMS and isoprene in the air and seawater respectively. The parameters, such as purge flow, split ratio and heating power rate (for controlling desorption temperature), were investigated by coupling with a gas chromatography–mass spectrometry (GC–MS). Under the conditions of split ratio 8:1, heating power rate 85% and purge flow 50 mL min−1, the peaks and intensities of DMS and isoprene standards were found to be sharp and significant. The standard curves were also established with high linear correlations (R2 > 0.97). The system was reliable and stable with small uncertainty (<5%) and low detection of limit (0.1 ppb and 4 ppt for the DMS and isoprene respectively in air sample, 0.2 nmol L−1 and 6 pmol L−1 for the DMS and isoprene respectively in water sample). Finally, the developed measurement method was successfully used to continuously detect the seawater and air samples. It is anticipated that our method could be widely spread because there are still many labs employing the traditional low automatic purge and trap system.

324 - Sodium Nitrate Attenuates the Acute Antihypertensive and Vascular Effects of Sodium Nitrite by Inhibiting Nitrite-Reductase Activity of Xanthine Oxidoreductse

The antihypertensive effects of nitrite are at least in part attributable to tissue reduction of nitrite to nitric oxide (NO) by xanthine oxidoreductase (XOR). XOR also reduces nitrate to nitrite, however, at a much lower rate than it reduces nitrite to NO. Here, we examined whether nitrate decreases the formation of NO from nitrite by XOR, and therefore attenuates its antihypertensive and vascular effects. Methods Blood pressure effects were studied in rats receiving Nω-nitro-L- arginine methyl ester (L-NAME) 100 mg/Kg orally to increase the mean of arterial pressure (MAP). Forty min later, they received nitrate (40 µmol/kg) or vehicle. Then increasing doses of sodium nitrite were infused into the femoral vein. Invasive MAP was assessed in the femoral artery. Vascular reactivity studies: The vasorelaxant effects of sodium nitrite (0.3 nMto 10 mM concentrations) were examined in aortic rings pre-contracted with phenylephrine 10-7M in the presence or absence of sodium nitrate 300 µM. In addition, mesenteric arterial bed preparations infused continuously with phenylephrine (3 µM to 8 µM). Sodium nitrate 300 µM or vehicle was added to the perfusion liquid and a concentration-response curve to nitrite (0.1 µM to 1 mM) was constructed. Nitrite reductase activity was measured by injecting XOR 100 mU/ml into a purge vessel containing nitrite 1 mM, NADPH 1 mM and NADH 1 mM in the presence or absence of sodium nitrate 30 mM, and NO was detected by chemiluminescence. Results Pretreatment with sodium nitrate attenuated nitrite-induced decreases in MAP. Pre-incubation of aortic rings with nitrate shifted the concentration-response curve in response to sodium nitrite to the right and reduced the maximum response. Adding sodium nitrate to the solution perfusing the mesenteric bed attenuated the fall in perfusion pressure induced by nitrite. Nitrate decreased nitrite-induced NO formation by XOR in the purge vessel. Conclusion Our results show that nitrate attenuates the acute blood pressure responses to nitrite by mechanisms that involve reduced nitrite-derived NO formation by XOR.

Markedly Enhanced Purge‐and‐Trap Performance and Efficiency for the Determination of Ammonium Ion in High‐Salinity Water Samples

AbstractWe have previously developed a purge‐and‐trap (P&amp;T) preconcentrator, useful for the determination of trace amounts of ammonium ion in high‐salinity water samples by ion chromatography (IC). In this study, we succeeded in improving the P&amp;T system to markedly enhance performance and efficiency for the determination of ammonium in high‐salinity water samples. Compared to the previous work, the background signal was reduced by a factor of 9. The maximum overall collection efficiency increased greatly from 64% to 97%. With the modified P&amp;T system, this method can be applied to a wide ammonium concentration range of 5 orders of magnitude. These were attributed to the substitution of polypropylene vessels for glass ones, the improvement of the gastight of the P&amp;T system, the increase of the liquid depth in the purge vessel, and the use of 10 mM sulfuric acid as the trapping solution for high ammonium concentration samples. Interferences of 20 native amino acids to the ammonium determination are slightly positive, but also negligible except asparagine and glutamine. The proposed method has been successfully applied to the accurate determination of wide levels of ammonium in seawater and sweat samples.

Quantitation of dissolved gas content in emulsions and in blood using mass spectrometric detection

Quantitation of dissolved gases in blood or in other biological media is essential for understanding the dynamics of metabolic processes. Current detection techniques, while enabling rapid and convenient assessment of dissolved gases, provide only direct information on the partial pressure of gases dissolved in the aqueous fraction of the fluid. The more relevant quantity known as gas content, which refers to the total amount of the gas in all fractions of the sample, can be inferred from those partial pressures, but only indirectly through mathematical modeling. Here we describe a simple mass spectrometric technique for rapid and direct quantitation of gas content for a wide range of gases. The technique is based on a mass spectrometer detector that continuously monitors gases that are rapidly extracted from samples injected into a purge vessel. The accuracy and sample processing speed of the system is demonstrated with experiments that reproduce within minutes literature values for the solubility of various gases in water. The capability of the technique is further demonstrated through accurate determination of O 2 content in a lipid emulsion and in whole blood, using as little as 20 μL of sample. The approach to gas content quantitation described here should greatly expand the range of animals and conditions that may be used in studies of metabolic gas exchange, and facilitate the development of artificial oxygen carriers and resuscitation fluids.

A simplified screening procedure for determination of total N–NO groups (TNG) and nitrite (NO2−) in commercial low-molecular-weight heparins (LMWH) by selective chemical denitrosation followed by high-sensitivity chemiluminescence detection (NO-analyzer, NOA)

Aim of this work was to set up a method for the sensitive and selective determination of nitrite (NO2−) and total N-nitroso groups (TNG) in dalteparin and nadroparin, commercial low- molecular-weight heparins (LMWH), prepared by deaminative depolymerization of heparin with nitrous acid. The European Pharmacopoeia VI ed. indicates respectively 5ppm as the maximum content for contaminant NO2− in the former and 0.25ppm for TNG in the latter and no clear indication is given for N–NO groups in dalteparin, i.e. TNG must be absent because of the specific manufacturing process.The proposed technique is based on the development of a pre-analytical device, coupled to a chemiluminometer, constituted by three sequentially connected and commercially available purge vessels, where selective reagents are employed for the conversion of NO2− and N–NO to nitric oxide (NO). In detail, NO2− was determined in the first chamber and non-volatile and volatile TNG in the second and third. This method was validated for selectivity, sensitivity, linearity, accuracy and precision. The method was shown to be selective, with a quantitative linear range of 1–1000ppb). The bias, intra- and inter-day percent relative error was lower than 1%. The contamination of NO2− and TNG in nadreparin was below the limits; for dalteparin NO2− fell within the limit, but there was a huge amount of TNG (15.80±0.05ppm–6.69±0.02ppm). Preliminary investigation on the solvent-extractable material from dalteparin showed the majority of chemiluminescence retained in the aqueous residue to indicate that this N–NO groups may belong to solvent unextractable material or be tightly bound to the dalteparin backbone.

Sample-introduction systems coupled to ion-mobility spectrometry equipment for determining compounds present in gaseous, liquid and solid samples

This article reviews available sample-introduction systems (SISs) for coupling to ion-mobility spectrometry (IMS) equipment. A wide variety of devices are currently in use to introduce gas, liquid and solid samples into IMS instruments. The systems reviewed in this work include permeation tubes, purge vessels, dilution glass flasks, headspace samplers, evaporator units, membrane inlets, solid-phase microextraction units, stir-bar sorptive extractors, thermal desorption units, chromatographic columns and supercritical fluid chromatographs, in addition to electrospray ionization and matrix-assisted laser desorption/ionization ion sources. Currently available SISs perform far from ideally, so there is still a need to develop new, more efficient choices for introducing samples into IMS equipment in a reliable manner.

Concerted Nitric Oxide Formation and Release from the Simultaneous Reactions of Nitrite with Deoxy- and Oxyhemoglobin

Recent studies reveal a novel role for hemoglobin as an allosterically regulated nitrite reductase that may mediate nitric oxide (NO)-dependent signaling along the physiological oxygen gradient. Nitrite reacts with deoxyhemoglobin in an allosteric reaction that generates NO and oxidizes deoxyhemoglobin to methemoglobin. NO then reacts at a nearly diffusion-limited rate with deoxyhemoglobin to form iron-nitrosyl-hemoglobin, which to date has been considered a highly stable adduct and, thus, not a source of bioavailable NO. However, under physiological conditions of partial oxygen saturation, nitrite will also react with oxyhemoglobin, and although this complex autocatalytic reaction has been studied for a century, the interaction of the oxy- and deoxy-reactions and the effects on NO disposition have never been explored. We have now characterized the kinetics of hemoglobin oxidation and NO generation at a range of oxygen partial pressures and found that the deoxy-reaction runs in parallel with and partially inhibits the oxy-reaction. In fact, intermediates in the oxy-reaction oxidize the heme iron of iron-nitrosyl-hemoglobin, a product of the deoxy-reaction, which releases NO from the iron-nitrosyl. This oxidative denitrosylation is particularly striking during cycles of hemoglobin deoxygenation and oxygenation in the presence of nitrite. These chemistries may contribute to the oxygen-dependent disposition of nitrite in red cells by limiting oxidative inactivation of nitrite by oxyhemoglobin, promoting nitrite reduction to NO by deoxyhemoglobin, and releasing free NO from iron-nitrosyl-hemoglobin.

Measurement of plasma nitrite by chemiluminescence without interference of S-, N-nitroso and nitrated species

Recent studies have demonstrated that plasma nitrite (NO 2 −) reflects endothelial nitric oxide synthase activity and it has been proposed as a prognostic marker for cardiovascular disease. In addition, NO 2 − itself has been shown to have biological activities thought to be triggered by reduction back to NO in blood and tissues. The development of sensitive and reproducible methods for the quantitative determination of plasma NO 2 − is, therefore, of great importance. Ozone-based chemiluminescence assays have been shown to be highly sensitive for the determination of nanomolar quantities of NO and NO-related species in biological fluids. We report here an improved direct chemiluminescence method for the determination of plasma NO 2 − without interference of other nitric oxide-related species such as nitrate, S-nitrosothiols, N-nitrosamines, nitrated proteins, and nitrated lipids. The method involves a reaction system consisting of glacial acetic acid and ascorbic acid in the purge vessel of the NO analyzer. Under these acidic conditions NO 2 − is stoichiometrically reduced to NO by ascorbic acid. Fasting human plasma NO 2 − values were found in the range of 56–210 nM (mean = 110 ± 36 nM). This method has high sensitivity with an accuracy of 97% and high precision (CV < 10%) for determination of plasma nitrite. The present method is simple and highly specific for plasma NO 2 −. It is particularly suited for evaluating vasculature endothelial NO production that predicts the risks for cardiovascular disease.

Detection of Human Red Blood Cell-bound Nitric Oxide

Major disparities in reported levels of basal human nitric oxide metabolites have resulted in a recent literature focusing almost exclusively on methods. We chose to analyze triiodide chemiluminescence, drawn by the prospect of identifying why the most commonly employed assay in nitric oxide biology typically yielded lower metabolite values, compared with several other techniques. We found that the sensitivity of triiodide was greatly affected by the auto-capture of nitric oxide by deoxygenated cell-free heme in the reaction chamber. Potential contaminants and signal losses were also associated with standard sample purification procedures and the chemistry involved in nitrite removal. To inhibit heme nitric oxide auto-capture, we added potassium ferricyanide to the triiodide reagent, reasoning this would provide a more complete detection of any liberated nitric oxide. From human venous blood samples, we established nitric oxide levels ranging from 0.000178 to 0.00024 mol nitric oxide/mol hemoglobin. We went on to find significantly elevated nitric oxide levels in venous blood taken from diabetic patients in comparison to healthy controls (p < 0.0001). We concluded that the lack of signals reported of late by several groups using triiodide chemiluminescence for the detection of hemoglobin-bound nitric oxide may not represent levels on the border of assay sensitivity but rather underestimated values because of methodological limitations. We therefore stress the need for assay systems to be developed that differentiate between individual nitric oxide metabolite species and overcome the limitations we outline, allowing accurate conclusions to be drawn regarding physiological nitric oxide metabolite levels.

Uniform purging of resins in contact bed purge vessels

AbstractResin storage vessels such as bins, silos, and tanks often double as purge vessels, in which products are purged of volatiles or polymerization reactions are controlled. Processing is achieved by gas flowing among resin particles or pellets. Problems associated with these purge vessels include typical bin flow problems such as flow stoppages due to arching or ratholing, erratic discharge, particle segregation, and flooding or flushing. In addition, purging may be non‐uniform or incomplete, and cross contamination between grades may occur. These problems are often the result of either a funnel flow pattern, where some of the material in the vessel moves while the rest remains stationary, or a non‐uniform velocity profile, where some parts of the vessel flow much faster than others. Also, the location and the manner in which gas is injected into the vessel contents affect the uniformity of exposure of polymer particles to the gas. This paper describes methods of designing purge vessels to eliminate stagnant regions. Also, velocity gradients of solids in mass flow vessels (where all of the material is in motion whenever any is withdrawn) are discussed. Considerations of the gas introduction schemes that do not disturb the resin flow patter are also described.

Rapid Ultratrace Analysis of Tributyltin in Aqueous Matrixes by Purge-and-Trap Gas Chromatography with Flame Photometric Detection

Abstract A simplified purge-and-trap technique for detecting subnanogram amounts of the biocide tributyltin (TBT) and its degradation products dibutyltin (DBT) and monobutyltin (MBT) in aqueous environmental samples is described. Butyltin chlorides present in the sample were derivatized to volatile butyltin hydrides with NaBH4 and simultaneously purged by drawing ambient air through the purge vessel. Butyltin hydrides were trapped on a Porapak-N cartridge, eluted with dichloromethane, and analyzed by gas chromatography with flame photometric detection. Recoveries of the butyltin species ranged from 46 to 101%. Method detection limits for MBT, DBT, and TBT were 1.28, 0.39, and 0.24 ng/L, respectively. The major advantages of this technique are sensitivity, reduced analysis time, and a significant reduction in the amount of dichloromethane used. Results from the analysis of various surface water samples collected in New York are presented.

Determination of selected chlorinated benzenes in water by purging directly to a capillary column with whole column cryotrapping and electron-capture detection

The purge with whole column cryotrapping (P/WCC) method for the determination of volatile organic compounds (VOCs) in aqueous samples is adapted for use with an electron-capture detector. In this method, VOCs are stripped from an aqueous sample with an inert purge gas and transferred directly to the head of a capillary column for subsequent GC analysis. To prevent the column from plugging with ice during the purge step, and to reduce the chromatographic interference caused by the reaction of small amounts of water with thermal electrons in the detector, a glass-bead water trap is placed in-line between the purge vessel and the gas chromatograph. The water trap is constructed of a short length of 0.32 cm O.D. stainless-steel tubing filled with 0.5 mm diameter glass beads. By maintaining the trap at − 10°C during the purge, most of the water can be removed from the purge gas. Transmission of the analytes to the column is then achieved with a subsequent, short purge of the trap at 25°C. The method was tested with the chlorinated benzenes. Despite their high molecular masses, the more chlorinated members of this group have large enough Henry's law constants that they can be determined with a purge technique. Experimental purging efficiencies were determined and compared to theoretical values. This method allows the simplicity and the high reliability of the P/WCC method to be combined with the exceptionally high sensitivity of an electron-capture detector.

Reduction of biological effluents in purge and trap micro reaction vessels and detection of endothelium-derived nitric oxide (edno) by chemiluminescence

Various analytical approaches have been used to measure endothelium-derived nitric oxide (NO) [ 1, 3, 4, 7, 10, 12]. We have detected NO in perfusates with a sample size as low as 2 ml after acidification with 4 N HCl to pH < 2 at 25°C by using a Nitric Oxide Analyser (Sievers, Colorado) [ 7]. This procedure had the advantage that the detectable level of NO was enhanced by the self-decomposition of HNO 2 when the PH < pK a of NHO 2 (pKa = 3.15) and also the reaction temperature of 25°C substantially increased the half-line of NO [ 2]. Palmer, et al., [ 10] measured NO released by cultured porcine endothelial cells by chemiluminescence after passing cell effluents continyously at a rate of 5 ml/min into 75 ml of 1% sodium iodide in glacial acetic acid. The larger volumes involved in this method for continuous refluxing, made it less desirable for the detection of endothelium-derived nitric oxide. Feelisch et al. [ 1] utilized the activation of soluble guanylate cyclase, as well as, the quantitative oxidation of oxyhemoglobin to methemoglobin in aqueous solutions by NO as a means of measuring nitric oxide. We describe here a modification of our earlier micromethod which now enables us to detect NO after complete reduction with glacial acetic acid and sodium iodide. A comparison of the two procedures indicate that while freshly prepared NO standard solutions gave identical chemiluminescence response with and without reduction, effluents from bovine intrapulmonary artery under basal conditions gave substantially higher values upon reduction.

Analysis of volatile organic chemicals in aqueous samples by purge/GC with selective water removal

AbstractA gas chromatographic method for volatile organic chemicals in which an aqueous sample is purged directly to a cryogenically cooled, fused silica column uses a Nafion tube drier between the purge vessel and GC column. The Nafion strips water from the gas stream during the purge step while allowing volatile halocarbons and aromatics to continue to the GC column. Examples of this technique are presented on 0.53 mm and 0.25 mm fused silica columns coated with a variety of stationary phases.

A modified purge-and-trap/gas chromatography method for analysis of volatile halocarbons in microbiological degradation studies

A modification of a purge-and-trap unit is described for use in microbiological studies concerning degradation of aliphatic halogenated hydrocarbons (halocarbons). Sealed serum tubes containing bacteria, aqueous medium, headspace, and volatile halocarbons are used as purge vessels to monitor the disappearance of the halocarbons. Data are presented to show the loss of volatile halocarbons that occurred when these systems were analyzed by standard purge-and-trap. An application of this method is shown with methane-utilizing bacteria. The modified purge-and-trap method resulted in a total measurement of halocarbons in the sample without making a transfer to a separate purge vessel.

Determination of picogram quantities of methyltins in sediment

An extremely sensitive purge and trap method is described for the determination of methyltins in complex matrices. Organotins were determined directly from sediments and culture medium as the volatile methylstannanes. Hydride derivatives were prepared with NaBH/sub 4/ in a closed, flow-through system consisting of a purge vessel, gas chromatograph, and mass spectrometer. Borate buffer added to samples generated H/sub 2/ from NaBH/sub 4/, resulting in high purge efficiencies for mono-, di-, and trimethyltin. Selected ion mode monitoring with the mass spectrometer gave detection limits for methyltins of 3-5 pg as Sn. The concentration detection limits for a 5-g sediment sample were < pg/g with a standard deviation of 6-18%, depending upon the methyltin species and sample type. Sensitivity achieved was 2 orders of magnitude lower than previously reported for methyltins in sediment. The method reported is both selective and specific, eliminating most interferences while permitting positive identification of individual methyltin species.

Determination of polar volatiles in water by volatile organics analysis

The applicability of the Volatile Organics Analysis technique to the determination of polar volatile compounds in water was investigated. Purge vessels smaller than the commonly-used Bellar & Lichtenberg device were used in the study. Purgeability as a function of temperature was measured for a number of compounds, including several phenols. Sample chromatograms are presented.

Purge vessel design in determinations of volatile organic compounds

Five purge vessels are described for use in determinations of volatile organics. Less conventional designs permit extension of the technique to untraditional samples, including soil and viscous glues.