Markes International Inc.

Wilmington, DE, United States

Markes International Inc.

Wilmington, DE, United States
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Peng Z.,University of Colorado at Boulder | Day D.A.,University of Colorado at Boulder | Ortega A.M.,University of Colorado at Boulder | Ortega A.M.,University of Arizona | And 10 more authors.
Atmospheric Chemistry and Physics | Year: 2016

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define "riskier OFR conditionsg" as those with either low H2O (< 0.1 %) or high OHRext (≥100 s-1 in OFR185 and > 200 s-1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm-2 s-1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors. © 2016, Author(s). All rights reserved.


Watson N.M.,Markes International Inc. | Thaxton K.,Markes International Inc.
Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA | Year: 2011

The CIA Advantage™ is designed to allow samples comprising a wide range of concentrations to be analyzed without the need for dilution. Using a combination of loop sampling, large volume sampling, and the ability to split, ppt levels to % levels can be analyzed on one instrument, thereby considerably increasing the dynamic range. Automated canister analysis can also be carried out at high concentrations, e.g., benzene, tetrachloethene, and trichloroethene. The CIA Advantage provides a convenient way of running a low volume screening method on a number of canisters and, if necessary, a second larger volume sample can be analyzed to accurately assess lower sample concentrations. This is an abstract of a paper presented at the 104th AWMA Annual Conference and Exhibition (Orlando, FL 6/21-24/2011).


Watson N.M.,Markes International Inc.
Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA | Year: 2011

The series 2 UNITY-Air Server™, a new, cost-effective system for round-the-clock speciated measurement of multiple trace-level VOC in air or pure gases was presented. The system was validated for on-line monitoring of the 27 ozone precursors specified by European regulators, including ethane, ethylene, toluene, n-butane, o-, m-, p-xylene, and isoprene. A reliable, semi-continuous, cryogen free sampling and GC/FID analysis system has been demonstrated for this challenging and complex mix of volatile and very volatile hydrocarbons. The design of the focusing trap and the sorbent choice within increased the maximum sample volume and along with the complete transfer of the whole sample to the GC system, allowing for greater sensitivity. Reliability and stability of the system was excellent, achieving < 0.3% RSD in retention time shift and > 98% of compounds having linearity of ≥ 0.99. This is an abstract of a paper presented at the 104th AWMA Annual Conference and Exhibition 2011 (Orlando, FL 6/21-24/2011).


Watson N.,Markes International Inc. | Davies S.,Markes International Inc. | Wevill D.,Markes International Inc.
TheScientificWorldJournal | Year: 2011

As the harmful effects of low-level exposure to hazardous organic air pollutants become more evident, there is constant pressure to improve the detection limits of indoor and ambient air monitoring methods, for example, by collecting larger air volumes and by optimising the sensitivity of the analytical detector. However, at the other end of the scale, rapid industrialisation in the developing world and growing pressure to reclaim derelict industrial land for house building is driving the need for air monitoring methods that can reliably accommodate very-high-concentration samples in potentially aggressive matrices. This paper investigates the potential of a combination of two powerful gas chromatographybased analytical enhancementssample preconcentration/thermal desorption and time-of-flight mass spectrometryto improve quantitative and qualitative measurement of very-low-(ppt) level organic chemicals, even in the most complex air samples. It also describes new, practical monitoring options for addressing equally challenging high-concentration industrial samples. Copyright © 2011 Nicola Watson et al.


Watson N.M.,Markes International Inc. | Widdowson C.,Markes International Inc.
Air and Waste Management Association - Air Quality Measurement Methods and Technology Conference 2016 | Year: 2016

Each step from field deployment through to tube conditioning for re-use has been covered. They cycle of which can be shown graphically in this simple schematic (Figure 7).


Barden D.,Markes International Inc.
American Laboratory | Year: 2013

The detection of volatile organic compounds (VOC) is important for a variety of reasons, many of which stem either from the need to ensure that damaging chemicals are controlled or eliminated, or the desire to understand more about the chemicals that affect the enjoyment of the world around. These applications range from environmental monitoring to material emissions testing, but one area in particular has recently seen large advances-the analysis of VOCs in food. The large number of compounds released from food and the need to separate and identify them presents a particular challenge for the analyst, and one that demands techniques with the ability to identify the widest possible range of compounds from a single sample. In this respect, sulfur compounds appear often in the literature, primarily because of their disproportionately strong odors, even at trace levels. They are often of key importance in food aromas, although not only as indicators of decay, since they can be contributors to the distinctive aromas of certain foods.


Widdowson C.,Markes International Inc.
12th International Conference on Indoor Air Quality and Climate 2011 | Year: 2011

New 'green chemistry' regulations and increased consumer awareness of product safety issues are driving global demand to test intentional and unintentional release (emission) of chemicals from everyday products. The new EC Construction Product Regulation (CPR), REACH and new US building codes are key examples of regulatory developments which will increase the need for chemical emissions testing as part of product labelling. Reference methods require chemical emissions from representative samples to be tested under simulated real-world conditions using small chambers or emission test cells. The method is carried out at a prescribed, near-ambient temperature and under a flow of pure, humidified air. Volatile and semi-volatile organic chemicals emitted by the sample pass into the chamber/cell air and are collected at specific times - typically 3, 10 or 28 days - using sorbent tubes. DNPH cartridges with HPLC analysis are also used for formaldehyde tests. This paper describes innovative new technologies to simplify the chemical emission testing and data analysis process.


Barden D.,Markes International Inc. | McGregor L.,Markes International Inc.
American Laboratory | Year: 2014

SelecteV technology from Markes International, enables low energy (soft) ionization without compromising sensitivity and without any need for reagents or hardware changes. The required SelecteV ionization energy is software controlled and requires no change to system hardware or configuration. This means that analyses can be carried out at different ionization energies simply by changing a parameter in the TOFDS acquisition sequence. At ionization energy of 11 eV, the improvement in molecular ion intensity, coupled with a reduction in fragmentation, results in overall fivefold improvements of the signal-to-noise ratios for the molecular ions. Limits of detection are therefore extended, which would allow ultra-trace analysis of these challenging environmental contaminants.


Watson N.M.,Markes International Inc.
Air and Waste Management Association - Air Quality Measurement Methods and Technology Conference 2012 | Year: 2012

These examples have shown how recent advances in air monitoring technology have extended the range and robustness of GC-based analytical procedures for air samples collected using either canisters or sorbent tubes. Some of the potential applications and advantages that have been explored here, include automated screening of uncharacterized canister samples, reliable detection of very low-concentration species and technologies to facilitate transition from canisters to sorbent tubes, with the employment of simple grab sampling devices. With the advancement of air sampling techniques and technology excellent linearity and detection methods are available to ensure laboratory inaccuracies are minimized. The greatest area for inaccuracy when making ambient air measurements now lies with the sample collection itself. This paper has discussed the two main sampling types for VOC collection, canister sampling and absorbent tube sampling and it is important to ensure that when taking the sample the correct collection method is employed. These new technologies lend themselves to sampling smaller air volumes on to sorbent tubes, which can dispel user worries about breakthrough volumes and humidity effects. Taking small sample volumes and combining this with powerful detection techniques, such as time-of-flight mass spectrometry, allows detection of trace compounds to be achieved either at the same level or at much lower limits of detection when compared to less sensitive detection techniques. However, more work is required to identify the limits of new time-of-flight mass spectrometer technologies when used in combination with TD-GC systems for real-world air monitoring.


Watson N.M.,Markes International Inc. | Wevill D.,Markes International Inc.
Air and Waste Management Association - Air Quality Measurement Methods and Technology Conference 2013 | Year: 2013

These examples have shown how recent advances in air monitoring technology have extended the range and robustness of GC-based analytical procedures for air samples collected using either canisters or sorbent tubes. Some of the potential applications and advantages that have been explored here, include automated screening of uncharacterized canister samples, reliable detection of very low-concentration species and technologies to facilitate transition from canisters to sorbent tubes, with the employment of simple grab sampling devices. With the advancement of air sampling techniques and technology excellent linearity and detection methods are available to ensure laboratory inaccuracies are minimized. The greatest area for inaccuracy when making ambient air measurements now lies with the sample collection itself. This paper has discussed the two main sampling types for VOC collection, canister sampling and absorbent tube sampling and it is important to ensure that when taking the sample the correct collection method is employed. These new technologies lend themselves to sampling smaller air volumes on to sorbent tubes, which can dispel user worries about breakthrough volumes and humidity effects. Taking small sample volumes and combining this with powerful detection techniques, such as time-of-flight mass spectrometry, allows detection of trace compounds to be achieved either at the same level or at much lower limits of detection when compared to less sensitive detection techniques. However, more work is required to identify the limits of new time-of-flight mass spectrometer technologies when used in combination with TD-GC systems for real-world air monitoring.

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