Non-dispersive Infrared Analyzer Research Articles

Discrepancy in infrared measurement results of carbon monoxide in nitrogen mixtures due to variations of the 13C/12C isotope ratio

Significant errors in the non-dispersive infrared (NDIR) analyses of carbon monoxide (CO) can be made when the 13C/12C isotope ratio in the sample and the calibrant differ significantly. This paper shows that variations in the 13C/12C isotope ratio of 5×10−2 mol/mol CO in nitrogen mixtures on three different NDIR CO analysers may lead to serious deviations in the instrument response, whereas the instrument response using GC-TCD is unaffected. The observed deviations in the assigned amount-of-substance fraction CO for a 13C depleted mixture vary from +2 to −5% relative to the gravimetric amount-of-substance fraction for different NDIR analysers. A GC-MS method has been developed to perform a pre-screening of the isotopic composition of CO in nitrogen mixtures. This method proved to be an adequate tool to measure differences in the 13C/12C ratio. Based on the GC-MS results a suitable measurement technique can be selected, or information about a possible error in NDIR analysis can be given to the producer or user of the calibration gas mixture.

Quad quantum cascade laser spectrometer with dual gas cells for the simultaneous analysis of mainstream and sidestream cigarette smoke

A compact, fast response, infrared spectrometer using four pulsed quantum cascade (QC) lasers has been applied to the analysis of gases in mainstream (MS) and sidestream (SS) cigarette smoke. QC lasers have many advantages over the traditional lead-salt tunable diode lasers, including near room temperature operation with thermoelectric cooling and single mode operation with improved long-term stability. The new instrument uses two 36 m, 0.3 l multiple pass absorption gas cells to obtain a time response of 0.1 s for the MS smoke system and 0.4 s for the SS smoke system. The concentrations of ammonia, ethylene, nitric oxide, and carbon dioxide for three different reference cigarettes were measured simultaneously in MS and SS smoke. A data rate of 20 Hz provides sufficient resolution to determine the concentration profiles during each 2 s puff in the MS smoke. Concentration profiles before, during and after the puffs also have been observed for these smoke constituents in SS smoke. Also, simultaneous measurements of CO 2 from a non-dispersive infrared (NDIR) analyzer are obtained for both MS and SS smoke. In addition, during this work, nitrous oxide was detected in both the MS and SS smoke for all reference cigarettes studied.

Comparison of the Flame Characteristics of Turbulent Circular and Elliptic Jets in a Crossflow

This study was directed to understand the coupling effects of the noncircular geometry of the burner and a crossflow on the combustion of gas jets. This paper compares the characteristics of turbulent propane jet flames from circular (diameter=0.45 cm) and elliptic (major axis/minor axis=3) burners of equivalent exit area in a crossflow. The elliptic burner was oriented with its major axis or minor axis aligned with the crossflow. Experiments were conducted in a wind tunnel provided with optical and probe access and capable of wind speeds up to 12.5 m/s. The burners were fabricated with metal tubes. Instrumentation included a Pt-Pt/13% Rh thermocouple, a quartz-probe gas sampling system, chemiluminescent and nondispersive infrared analyzers, a video-recorder, and a computer data acquisition system. The measurements consisted of the upper and lower limits of jet velocity for a stable flame, flame configuration, and visible length. Flame structure data including temperature profiles and concentration profiles of CO2,O2, CO, and NO were obtained in a two-zone flame configuration (at jet to crossflow momentum flux ratio=0.11), where a planar recirculation exists in the wake of the burner tube followed by an axisymmetric tail. The relative emission indicators of CO and NO were estimated from the composition data. Results show that the upper and lower limits of the fuel jet velocity increase with the crossflow velocity for all burners, and the rate of increase is highest for the elliptic burner with its minor axis aligned with the crossflow. That burner configuration also produces the longest flame. The relative emission indicators show that the CO production is lower and NO production is higher with elliptic burners than with circular burners in crossflow.

An experimental study on the thermal decomposition of catechol

In order to better elucidate the role of thermal decomposition products in the formation of polycyclic aromatic hydrocarbons (PAH) from complex fuels, we have performed pyrolysis experiments in a tubularflow reactor, using the model fuel catechol ( ortho -dihydroxybenzene), a, phenol-type compound representative of structural entities in biomass, coal, and wood. Catechol pyrolysis at temperatures of 700–1000°C and a residence time of 0.4 s produces a range of C 1 −C 6 products, which have been analysed by nondispersive infrared analysis and by gas chromatography with flame-ionization detection. Quantification of product yields versus temperature reveals that the major products are CO, acetylene, 1.3-butadiene, phenol, cyclopentadiene, benzene, and ethylene, minor products are methane, ethane, propyne, propadient, and propylene. CO is the highest yield catechol pyrolysis product at all temperatures. Among the hydrocarbons, 1,3-butadiene is the highest yield product at temperatures up to 800°C; above 800°C acetylene is. The structural features of catechol and the experimental product yield data—considered with the established reactions for phenol decomposition—suggest that the major products of catechol decomposition come from the following routes: (1) phenol and benzene from H displacement of OH on catechol and phenol, respectively, (2) cyclopentadiene from unimolecular decomposition of the phenoxy radical, and (3) 1,3-butadiene, acetylene, and CO from decomposition of the hydroxy-substituted phenoxy radical (but with different oxygenated C 5 intermediates). The remaining, C 1 −C 3 products appear to arise chiefly from the decomposition of key radicals such as cyclopentadienyl, propargyl, and 1,3-butadienyl. The results presented in this work, in concert with those from a complementary study of the C 7 −C 28 catechol products, provide the basis for the development of a detailed kinetic model for both pyrolytic catechol decomposition and PAH formation and growth.

A carbon dioxide gas sensor based on solid electrolyte for air quality control

A practical CO 2 gas sensor for air quality control is developed by using a combination of a Na 3Zr 2Si 2PO 12 (NASICON) as a solid electrolyte and Li 2CO 3 as a carbonate phase. The sensor's electromotive force (emf) shows a linear relationship with the logarithm of CO 2 concentration. Zeolite is chosen as a filter material in order to minimize the effect of interfering gases on the sensor's emf and shows very little sensor response deterioration to CO 2. Under continuous energizing, both the emf and a change in the emf (defined as Δemf) are stable over a period of 2 years. However, after the sensor is exposed to a high humidity atmosphere in an unpowered state, the emf decreases, but Δemf stays constant. A new data selection method for renewing the standard of the emf is investigated in order to monitor CO 2 concentration using Δemf. The output of the CO 2 monitor corresponds to a conventional non-dispersive infrared (NDIR) analyzer.

A Design for Unattended Monitoring of Carbon Dioxide on a Very Tall Tower

Abstract Unattended measurements of carbon dioxide (CO2) mixing ratio at three altitudes up to 496 m above the surface on a television transmitter tower in the southeastern United States have been made for a period of 4 yr. This report describes the design of the automatic tower measuring system in detail. A nondispersive infrared (NDIR) analyzer is used to measure the CO2 concentration continuously. Real-time control and data collection uses a PC 486 running under the multitasking operating system QNX. The CO2 data show strong diurnal and seasonal variations, and large vertical gradients. A comparison of this study’s continental tower data with data from “background” sites should provide a strong constraint for regional and global models of terrestrial CO2 fluxes.

An Experimental Evaluation of Remote Sensing-Based Hydrocarbon Measurements: A Comparison to FID Measurements.

The purpose of this study was to intercompare hydrocarbon (HC) measurements performed by a number of different instruments: a gas chromatograph (GC), a flame ionization detector (FID), a fourier transform infrared spectrometer (FTIR), a commercially produced non-dispersive infrared analyzer (NDIR), and two remote sensors. These instruments were used to measure total HC concentrations in a variety of samples, including (1) ten different individual HC species, (2) 12 different vehicle exhaust samples, and (3) three different volatilized fuel samples. The 12 exhaust samples were generated by operating two different vehicles on a dynamometer. Each vehicle was operated at different times with three different fuels. The vehicles were operated fuel rich, i.e., with low air/fuel ratios to encourage elevated exhaust HC levels. Some of the exhaust samples were obtained while operating each vehicle at a stoichiometric air/fuel ratio with one spark plug wire disconnected. To quantify the degree to which the various instruments agreed with the FID, a parameter called the response factor was used, where the response factor was defined as the HC/CO2 ratio measured by each instrument divided by the HC/CO2 ratio measured by the dynamometer bench. Of the various instruments, only the GC yielded response factors that were consistently at or close to one. The other instruments typically had values at or below one. For the ten individual HC species studied, the NDIR and remote sensors obtained response factors between 0.05 and 1.0, with the highest response factors being obtained for the alkanes and the lowest response factors obtained for toluene and ethylene. For the exhaust samples, the NDIR and remote sensors obtained response factors between 0.23 and 0.68. For raw fuel samples, the response factors were between 0.44 and 0.68. NDIR and remote sensor measurements correlated very poorly with total HC in exhaust.

Experimental and Numerical comparison of extractive and in situ laser measurements of non-equilibrium carbon monoxide in lean-premixed natural gas combustion

Measurements of carbon monoxide (CO) in the high-temperature combustion product stream of an atmospheric pressure, lean-premixed combustion, natural gas reactor were obtained using line-of-sight tunable diode laser absorption and extractive probe sampling in conjuction with nondispersive infrared analyzers over various equivalence ratios and flow residence times. The measurements are compared with (1) a numerical model using comprehensive chemical kinetics for methane combustion in conjunction with perfectly stirred reactor (PSR) and plug-flow reactor (PFR) modeling approaches, and (2) chemical equilibrium at the measured temperatures. Temperatures ranging from 1500 to 2000 K were measured using a radiation corrected thermocouple and also by a diode laser thermometry technique. The laser based in situ measurements of CO concentration ranged from 50 to 5000 ppm depending on the equivalence ratio and flow residence time. Results of the numerical model were consistent with the laser-based measurements. The extractive probe measurements were found to be as much as 10 times less than the laser-based measurements. However, laser and probe measurements for fuel-rich equivalence ratios agreed. In an effort to improve the performance of extractive sampling probes, we tested several aerodynamic quench probe designs. We were unable to achieve an aerodynamic quench of the CO in a high-temperature combustion product stream. A model of the sampling probe as a PFR indicates that extractive sampling of [CO] is increasingly inaccurate at gas temperatures above 1000 K.

High-accuracy measurements of total dissolved inorganic carbon in the ocean: comparison of alternate detection methods

High-accuracy measurements of total dissolved inorganic carbon in the ocean are currently performed using an automated coulometric system based on that described by Johnson et al. (1987). These measurements require highly-trained technicians and the manipulation of expensive and hazardous chemicals. We tested an alternate detection method based on non-dispersive infra-red analysis. All of the dissolved carbonate species from a seawater sample were extracted as CO 2 gas by acidification and nitrogen stripping. The CO 2 gas was then quantitatively detected with either a coulometric system or an infra-red analyzer. The reproducibility of the two detection methods is similar. Although the infra-red system requires further testing, it holds promise as an alternative to coulometry. The detection of the CO 2 gas by infra-red analysis presents several advantages over coulometric detection: it simplifies and reduces the cost of the measurements, shortens the analysis time, reduces the sample size requirement by at least a factor of five, and allows us to consider complete automation of the system for underway surface seawater measurements.

Progress in the development of a test method for fireplace particulate matter and carbon monoxide emissions

Progress in the development of a test method for determining carbon monoxide (CO) and particulate (PM) emissions from fireplaces is described. Such a method must specify fueling and measurement procedures for determination of both emission rates (g h −1) and factors (g kg −1). The current version of the test method starts with a room temperature fireplace and monitors emissions for six and a half hours. The fuel load size and fueling intervals are dependent on the width of the firebox. Emission samples are extracted from a dilution tunnel with a set flow rate and configuration. Particulate matter sampling is similar to U.S. EPA Method 5G for woodstoves, and CO concentration is measured by a nondispersive infrared (NDIR) analyzer. Emissions from a range of fireplaces, including both factory-built and masonry fireplaces, were measured using various versions of the test method. The fueling protocol was not able to sustain a fire in some of the fireplaces. Modifications to the fueling protocol, fuel composition, and/or fueling rate scaling will be necessary before the test method can be used for fireplace emissions certification purposes.

Development of a Coulometric Method for Assessing the Concentration of Ambient Levels of CO2/Air in Compressed Gas Mixtures.

The coulometric method presented here is a reliable method for the direct analysis of CO2/air cylinder gas mixtures. It is based on Faraday’s laws of electrolysis and therefore no external standardization is required. A series of CO2/air cylinder gas mixtures ranging in concentration from 300 to 375 µmol/mol (ppm) were analyzed and the results compared to those results obtained by non-dispersive infrared (NDIR) analysis with traceability to gravimetric standards. The coulometric method is rapid, sensitive, precise, and with the proper experimental controls, will yield accurate results.

Body and organ weights of rats exposed to carbon monoxide at high altitude.

Although chronic exposure to carbon monoxide (CO) or high altitude produces pronounced cardiovascular changes in humans as well as animals, there is little information on the effects elicited by these stressors combined. Theoretical considerations, as well as data from acute studies, suggest that CO inhaled at high altitude may be more detrimental than CO inhaled at low altitude. The purpose of these studies was to construct a system in which CO and altitude could be controlled precisely, and to investigate the effects of continuous exposure to CO and high altitude on body weights and hematocrit ratios, as well as heart, spleen, adrenals, kidneys, and pituitary weights. Male, laboratory rats were exposed for 6 wk in steel barometric chambers to (1) 100 ppm CO, (2) 15,000 ft simulated high altitude (SHA), and (3) CO at SHA. Altitude was simulated by a system of gate valves and a vacuum pump, and measured by an altimeter. CO, from high-pressure cylinders, was introduced into the air supplying each chamber through a mass flow controller and measured by a nondispersive infrared (NDIR) analyzer. Although SHA had no affect on left ventricle plus septum (LV + S), adrenal, spleen, or kidney weights, SHA decreased body weights, and increased hematocrit ratios, as well as right ventricle (RV), total heart (HT), and pituitary weights. CO had no affect on body weights, RV, HT, adrenal, spleen, or kidney weights, but CO increased hematocrit ratios and LV + S weights. There was no significant interaction between SHA and CO on any parameter except kidney weight. These results indicate that, in general, the effects produced by 15,000 ft SHA are not intensified by exposure to 100 ppm CO.

The NOAA/GMCC continuous CO2 record at the South Pole, 1975–1982

Hourly carbon dioxide concentrations at the south pole were obtained by nondispersive infrared analyzers for the years 1975–1978 and 1980–1982. A spectral analysis of the ambient CO2 variability showed very little power for periods shorter than 5 days. Our data showed good agreement with other data sets for the range of the annual fluctuation from 1977 to 1982 and disagreements for 1976. The estimated annual CO2 increase (about 0.6 to 2 ppm yr−1) and ranges of seasonal fluctuation were insensitive to the data selection methods used. After 1979, seasonal fluctuations apparently decreased.

Calibration of Nondispersive Infrared CO2Analyzers with CO2-in-Air Reference Gases

A set of eight CO2-in-air secondary standard calibration gases has been established by NOAA/Geophysical Monitoring for Climatic Change (GMCC) for use in its global CO2 monitoring program. Use of these gases obviates the need for pressure broadening corrections that arises when CO2 air sample analyses are performed with nondispersive infrared analyzers using CO2-in-N2 calibration gases. The gases are composed of clean mountain air, with suitably adjusted CO2 content, pumped into 49 1 chrome-molybdenum steel tanks to 150 atm pressure. Five of the tank gases have been calibrated manometrically at the Scripps Institution of Oceanography (SIO) to an accuracy of about ±0.10 parts per million (ppm). Calibration of the remaining gases is traceable to manometric primary standards maintained at SIO. The secondary standards are used periodically in Boulder, Colorado, to calibrate tertiary CO2 standards with which, in turn, field station standards and working reference gases are calibrated. Both the tertiary standards and the field station gases are commercially available CO2-in-synthetic-air gases which contain natural proportions of nitrogen, oxygen and argon. Calibrations by SIO since 1978 suggest that the CO2 of NOAA/GMCC secondary standard gases may be drifting at a rate of 0.05.ppm yr−1. Several CO2-in-air tanks used in Boulder for CO2 flask air sample analyses have exhibited drifts of up to 0.39 ppm yr−1. The CO2-in-synthelic-air reference gases appear to be more stable, generally exhibiting CO2 concentration drift rates of from 0 to 0.10 ppm yr−1.

Hygrometry

To meet the many different requirements of gas humidity and water vapour measurement, a wide variety of measurement techniques has been developed. The criteria for deciding which technique to use are the range of concentration, the accuracy of measurement required, the sensitivity, and the pressure or even the corrosiveness of the gas sample. For measuring traces of moisture, sensors are used in which the admittance of an arrangement of electrodes changes with the partial pressure of the water vapour. Another method measures desorption due to Joule heat after absorption of the water by phosphorus pentoxide. Devices for measuring high humidities are equipped with capacitive, temperature-controlled sensing elements which measure the dew point. For special application, units have been developed which make use of the dielectric absorption of microwaves by the water. For hygrometrical problems requiring a high degree of accuracy, good discrimination and continuous measurement, a method is discussed below which uses the absorption of IR radiation by molecules in gaseous phase: Non-Dispersive Infra-Red Analysis.

The determination of tropospheric nitrous oxide

A two‐step technique, in which the N2O/CO2 ratio is measured by ultrasonic phase‐shift gas chromatography and the dry air CO2 concentration is measured by nondispersive infrared analysis, has been developed for the determination of the mole fraction of nitrous oxide in dry air. The N2O concentration is given by the product of these two independent measurements and has a precision (±1 standard deviation) ranging between 0.3 and 0.5%. The absence of systematic errors has been verified by extensive standard intercomparisons and by independent cross checks of the sample extraction procedures. The results of extensive measurements by this technique, reported in a companion paper, fix the mean tropospheric dry air mole fraction of nitrous oxide in the northern hemisphere as of January 1, 1978 at 300.2±0.6 parts per billion, including systematic uncertainties.

The Determination of Nitric Oxide in Gas Phase Cigarette Smoke by Non-dispersive Infrared Analysis

AbstractNitric oxide in cigarette smoke was conveniently determined by non-dispersive infrared analysis (NDIR). Recoveries of 95 % were obtained with standard gas-air mixtures but recoveries from smoke increased from 87% for high-yield to 91 % for low-yield cigarettes. Relative error was about 4 %. A reduction in the dead volume of Cambridge filter cassettes, to reduce the amount of NO reacted between puffs, increased NO deliveries of cigarettes by 4%. Deliveries of NO were estimated to average 4 % lower due to oxidation, but reaction with other smoke components reduced them further depending upon concentrations. The NO deliveries of cigarettes increased as blend nitrate increased and as the flow of air around cigarettes decreased. Nitric oxide in smoke and in standard gas-air mixtures, determined by non-dispersive infrared (NDIR) spectroscopy, was substantiated by an automated colorimetric analysis. Interfering smoke species were determined and circumvented in both methods.

Simultaneous DTA-EGA of minerals and natural mineral mixtures

A DTA apparatus has been linked to non-dispersive infrared H2O and CO2 analyzers and an SO2 analyzer based on an electrochemical cell, enabling evolution profiles of these three volatiles to be recorded simultaneously with the DTA curve. Examples are given of the use of the combined DTA-EGA method in the determination of the quantitative mineralogical composition of potential industrial raw materials.

An automated photochemical method for the determination of dissolved organic carbon in sea and estuarine waters

An improved version of Ehrhardt's (1969) method for the analysis of dissolved organic carbon is described. The method, which is automated, determines the carbon dioxide with a non-dispersive infra-red analyser. The conditions of photo-oxidation have been examined in order to achieve maximum performance. It was found that careful attention needed to be paid to U-V source, “oxygen source”, pH and time or irradiation. The completeness of the method was examined by three independent procedures. We concluded that in all cases the extent of oxidation of organic material was in excess of 98%. Typical performance figures were: precision ±2.5% above 2.0 mg C l −1, approaching 0.03 mg C l −1 below 1.0 mg Cl −1; blank, equivalent to 0.3 mg C l −1; sampling frequency, 10 samples per hour. The lower limit of sensitivity is mainly governed by the blank. The upper limit of the method is greater than 40 mg C l −1. A wholly continuous modification of the method has been devised which permits on line analyses. An attentuated version of the method has been used for the analysis of total carbonate. The present and other published methods for the analysis of dissolved organic carbon in natural waters are discussed in relation to one another.

An Automated Procedure for CO in Cigarette Smoke, Using a 20-Port Syringe Smoking Machine

AbstractA procedure for the determination of CO in the gas phase of cigarette smoke has been developed. Cigarettes are smoked on a 20-port syringe-type smoking machine and the gas phase is sampled by a specially designed sampling unit without appreciably affecting the level of particulate phase components or the operation of the smoker. After mixing, the concentration of CO in the gas phase is measured by nondispersive infra-red analysis. All operations are carried out automatically except the initial start-up, calibration of the analyser, and calculation of results. The procedure has been applied to a variety of cigarette brands with results ranging from 1.2 to 2.0 ml of CO per puff. The precision of the procedure was determined by repeated analysis of a standard cigarette over a four-month period. For a single value representing 100 cigarettes, the relative standard deviation was found to be 2.2 % for ml of CO per cigarette and 1.1 % for ml of CO per puff.