2008 Progress Report: Aethalometric Liquid Chromatographic Mass Spectrometric Instrument

EPA Grant Number: R831074
Title: Aethalometric Liquid Chromatographic Mass Spectrometric Instrument
Investigators: Dasgupta, Purnendu K.
Institution: The University of Texas at Arlington
EPA Project Officer: Chung, Serena
Project Period: September 1, 2003 through December 31, 2007 (Extended to December 31, 2008)
Project Period Covered by this Report: January 1, 2008 through December 31,2008
Project Amount: $450,000
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text |  Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter

Objective:

To fabricate, evaluate and field test new instrumentation that can provide more information on the speciation of carbonaceous compounds in the atmosphere.

Progress Summary:

In the present period a paper on a technique that addresses the mathematical resolution of incompletely resolved peaks that is directly relevant to chromatographic characterization of atmospheric particles was published. Two other papers that are related to the present project in an auxiliary fashion were published: these relate to a special class of carbonaceous particles, namely bacterial spores. A further relevant paper that relates to the affordable simultaneous measurement of NO2, O3 and relative humidity was submitted.

Resolution of overlapped chromatographic peaks is generally accomplished by modeling the peaks as Gaussian or modified Gaussian functions. It is possible, even preferable, to use actual single analyte input responses for this purpose and a nonlinear least squares minimization routine such as that provided by Microsoft ExcelTM Solver can then provide the resolution. In practice, the quality of the results obtained varies greatly due to small shifts in retention time. It is shown that such deconvolution can be considerably improved if one or more of the response arrays are iteratively shifted in time.

Bacterial spore determination by Terbium(III)-dipicolinate luminescence has been reported by several investigators. We collected spore samples with a cyclone and extracted dipicolinic acid (DPA) in-line with hot aqueous dodecylamine, added Tb(III) in a continuous-flow system and detected the Tb(III)- DPA with a gated liquid core waveguide fluorescence detector with a flashlamp excitation source. The absolute limit of detection (LOD) for the system was equivalent to 540 B. subtilis spores (for a 1.8 m3 sample volume (t = 2 h, Q = 15 L/min), concentration LOD is 0.3 spores/L air). Extant literature suggests that, from office to home settings, viable spore concentrations range from 0.1 to 10 spores/L; however, these data have never been validated. Previously reported semi-automated instrumentation had an LOD of 50 spores/L. The present system was tested at five different location settings in Lubbock, Texas. The apparent bacterial spore concentrations ranged from 9 to 700 spores/L and only occasionally exhibited the same trend as the simultaneously monitored total optical particle counts in the g0.5 μm size fraction. However, because the apparent spore counts sometimes were very large relative to the 0.5+ μm size particle counts, we investigated potential positive interferences. We show that aromatic acids are very likely large interferents. This interference typically constitutes ~70% of the signal and can be as high as 95%. It can be completely removed by prewashing the particles.

We also described an affordable gated fluorescence detection system to measure fluorescent compounds with long-lifetimes that uses a tuning fork chopper to block the intense excitation pulse from a flash lamp or short-lived fluorescence. A conventional non-gated inexpensive photosensor module was used to collect the luminescence signal. Using the long-lived luminescence from the terbium(III)–dipicolinic acid (DPA) chelate, we demonstrated a limit of detection (LOD) of 120 pM for DPA. This system was not only an order of magnitude less expensive than an electronically gateable phototomultiplier tube (GPMT), it exhibited no evidence of gradual loss of sensitivity, due likely to photocathode fatigue and deterioration, observed with a GPMT.

We described a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxide (NO2), ozone (O3) and relative humidity (RH). A silica gel thin layer chromatographic (TLC) plate with transparent backing and impregnated with 8-Amino-1-naphthol-5-sulfonic acid (ANS) is used as the collection/sensor element. The plate transmittance is probed by three discrete light emitting diodes (LEDs) centered respectively at 442, 525 and 850 nm. The transmission of the plate changes reversibly at all three wavelengths as the RH around the plate changes; this is the basis for a RH sensor. The ANS on the plate reacts to form a brown and a pink colored product when it respectively reacts with NO2 and O3. The sample air impinges on the plate via an  entrance nozzle. The LEDs are alternately turned on and the light is brought to the impregnated face of the plate by a three-legged fiber optic. The transmitted light is detected on the obverse side of the plate. The 850 nm signal provides the RH value and optionally serves as the reference measurement for the other two wavelengths; the NO2 and O3 reaction products do not absorb at 850 nm. The absorbance values at 442 and 525 nm are used to obtain NO2 and O3 concentrations from a pair of simultaneous equations. For a sampling period of 5 min, the limits of detection (LOD) based on 3 times the standard deviation of blank responses were 0.64 and 0.42 ppbv for NO2 and O3, respectively. Data obtained with collocated commercial instruments (O3 induced chemiluminescence analyzer for NO2 and UV-absorption for O3) show good agreement.

Future Activities:

This project ends on Dec 31, 2008. However, on our own we will complete two different projects that we have embarked on and which have been centerpieces of this project.

A fully automated measurement system for total carbon in aerosol samples has been developed. The instrument operates over prolonged periods with minimal attention. Particles down to 0.1 μm are collected in the bottom reservoir of a cyclone and transferred periodically to an annular quartz reactor. The transfer is accomplished by a syringe pump using a 5 mL holding loop that prevents the sample itself from getting into the syringe. The sample in the reactor undergoes sequential treatment that liberates CO2. Minimally, three stages of treatment are used while oxygen is bubbled through the reactor at a low flow rate (10 standard cubic centimeters per minute). The first treatment step involves the addition of dilute H2SO4; this results in the liberation of dissolved CO2 and the decomposition of other inorganic carbonates into CO2. Next the UV lamp (that contains both 254 and 185 nm lines) is turned on (this also leads to the formation of ozone) and easily photochemically oxidizable compounds (carbohydrates, e.g. levoglucosan are typical examples) are next decomposed and lead to CO2 formation. As the final step, acidic persulfate is added that leads to the oxidation of all organic compounds we have tested (it is also a standard method of the measurement of organic carbon in water samples). Even in this final step, which appears to follow a first order oxidation process, different compounds discernibly oxidize at different rates from which further information can be gleaned about their nature. It is to be noted that elemental carbon, either in the form of graphite, activated carbon or buckminsterfullerene (C60) are resistant to oxidation by any of the above steps and are not measured by this system.

The CO2 produced is sensed by two sequential short-long diffusion scrubber (DS)-conductivity detectors operated in the stop-flow mode. Each contains a length of a hydrophobic porous membrane tube in a jacketed enclosure with stainless steel tubular termini that function as the detector electrodes. The short sensor, filled with a low concentration of LiOH solution, is the first in the gas flow stream and captures a relatively small amount of the CO2 in the gas stream while the long sensor contains a higher concentration of LiOH. In both sensors, as the CO2 absorbed by the LiOH, Li2CO3 is formed and the conductivity decreases. The short sensor provides a S/N=3 LOD of 83 ng C while the long sensor provides a large linear dynamic range.


Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 46 publications 22 publications in selected types All 22 journal articles
Type Citation Project Document Sources
Journal Article Dasgupta PK, Campbell SW, Al-Horr RS, Ullah SMR, Li J, Amalfitano C, Poor ND. Conversion of sea salt aerosol to NaNO3 and the production of HCl:analysis of temporal behavior of aerosol chloride/nitrate and gaseous HCl/HNO3 concentrations with AIM. Atmospheric Environment 2007;41(20):4242-4257. R831074 (2006)
R831074 (2007)
R831074 (2008)
R831074 (Final)
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  • Journal Article Dasgupta PK. Chromatographic peak resolution using Microsoft Excel Solver. The merit of time shifting input arrays. Journal of Chromatography A 2008;1213(1):50-55. R831074 (2008)
    R831074 (Final)
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  • Journal Article Li Q, Dasgupta PK, Temkin HK. Airborne bacterial spore counts by terbium-enhanced luminescence detection:pitfalls and real values. Environmental Science & Technology 2008;42(8):2799-2804. R831074 (2008)
    R831074 (Final)
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  • Journal Article Li Q, Dasgupta PK, Temkin H. A time-gated fluorescence detector using a tuning fork chopper. Analytica Chimica Acta 2008;616(1):63-68. R831074 (2008)
    R831074 (Final)
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  • Supplemental Keywords:

    Aethalometry, Ion Chromatography, Liquid Chromatography, Carbonaceous Particles, Atmospheric Aerosols, Oxidation to CO2, Membrane Transfer, Conductometry, Bacterial Spores, Gated Fluorescence Detection, Chromatographic Resolution, Chromatographic Overlap, Multiwavelength Size-discriminated Aethalometry., RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, air toxics, Environmental Chemistry, Air Pollution Effects, Risk Assessments, Monitoring/Modeling, Analytical Chemistry, Environmental Monitoring, Physical Processes, Engineering, Chemistry, & Physics, Environmental Engineering, air quality modeling, health effects, particle size, carbon aerosols, atmospheric particulate matter, human health effects, PM 2.5, atmospheric particles, aerosol particles, mass spectrometry, ambient air monitoring, air quality models, exposure, air modeling, emissions, thermal desorption, molecular markers, gas chromatography, air sampling, carbon particles, air quality model, human exposure, ambient particle health effects, particulate matter mass, aethalometric liquid chromatographic mass spectrometry, aersol particles, monitoring of organic particulate matter, aerosol analyzers, human health risk, measurement methods

    Relevant Websites:

    No specific website solely devoted to the project has been established but the PI’s website contain detailed information: http://www3.uta.edu/faculty/dasgupta/index.htm

    Progress and Final Reports:

    Original Abstract
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006 Progress Report
  • 2007 Progress Report
  • Final Report