Journal of Chromatography A, 1109 (2006) 214–221

Determination of levoglucosan in atmospheric aerosols using highperformance liquid chromatography with aerosol charge detection

Roy W. Dixon ∗, Gregor Baltzell 1

Chemistry Department, California State University, 6000 J Street, Sacramento, CA 95819-6057, USA

Received 1 July 2005; received in revised form 1 January 2006; accepted 10 January 2006Available online 31 January 2006

Abstract

A sensitive method for analysis of levoglucosan (1,6-anhydro-�,d-glucopyranose) and other monosaccharide anhydrides, compounds presentin biomass combustion smoke, was investigated employing high-performance liquid chromatography (HPLC) with recently developed aerosolcharge detection. Aerosol charge detection involves the conversion of the column effluent to an aerosol, which is charged to produce a current.Use of a cation-exchange column and a pure water eluent was found to separate levoglucosan and mannosan from other aerosol components witha detection limit of about 90 ng mL−1 for levoglucosan or 5 ng injected. This method was demonstrated by successful analysis of aerosol filters©

K

1

af[cbc1ipbm(ifft

C

0d

amples from three locations.2006 Elsevier B.V. All rights reserved.

eywords: HPLC detection; Aerosol charge detection; Levoglucosan; Atmospheric aerosols; Biomass combustion; Monosaccharide anhydrides

. Introduction

Atmospheric aerosols are known to affect health, visibility,nd climate [1,2]. Organic compounds make up a significantraction of aerosol mass in the important “fine” particle size3–6] but are not well characterized [7]. Determination of theoncentrations of individual organic compounds is challengingecause of the large number of compounds present at lowoncentrations, typically in the ng m−3 range. Levoglucosan, or,6-anhydro-�,d-glucopyranose, (Plate 1) has been measuredn atmospheric aerosols where it has been identified as arevalent organic compounds in smoke from biomass com-ustion [8–14]. Related monosaccharide anhydrides (MAs),annosan (1,6-anhydro-�,d-mannopyranose) and galactosan

1,6-anhydro-�,d-galactopyranose), also have been detectedn atmospheric aerosols [10,11,13,14]. Since no other sourceor these compounds is known and the compounds appearairly stable [9], monosaccharide anhydrides appear to be goodracers for biomass combustion smoke [3].

Having the high resolution and sensitivity needed for anal-ysis of complex mixtures, gas chromatography (GC) has beena commonly used method for analysis of organic compoundsin atmospheric aerosols [7,15]. The most common methods ofmeasuring MAs in atmospheric aerosols have involved extrac-tion with organic solvents, derivatization to trimethylsilyl ethers,and analysis by GC or GC–MS [8,10–12]. Direct analysis by GCis also possible, but peak tailing in the chromatograms has beenobserved, leading to reduced sensitivity and greater interferences[8,9–11]. While derivatization results in improved chromatogra-phy, it adds complexity to the analysis procedure. Additionally,since MAs are highly water soluble, methods using aqueoussolvents would have advantages because aqueous extracts ofaerosol samples are commonly used for analysis of the majorionic constituents and because real-time aerosol instrumenta-tion is available that converts an aerosol stream into an aqueousliquid stream [16].

The goal of this work is to develop a simple method forthe analysis of the main MAs in atmospheric aerosols usinghigh-performance liquid chromatography (HPLC) with recentlydeveloped aerosol charge detection (ACD) [17]. Aerosol charge

∗ Corresponding author. Tel.: +1 916 278 6893; fax: +1 916 278 4986.E-mail address: rdixon@csus.edu (R.W. Dixon).

1 Present address: California Department of Fish and Game, Water Pollutionontrol Laboratory, 2005 Nimbus Rd., Rancho Cordova, CA, USA.

detection is in a class of detection methods including evaporativelight scattering detection (ELSD) and condensation nucleationlight scattering detection (CNLSD) in which the liquid streamis converted to an aerosol and detected (see [18] and [19] for

021-9673/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.chroma.2006.01.021

R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221 215

Plate 1.

reviews of ELSD and CNLSD). These detection methods are“universal” (detect any compounds provided the volatility is lowenough) and offer greater sensitivity than absorption detectionfor compounds such as carbohydrates with weak chromophores.The universal detection is expected be useful in this applicationsince the peak areas should be dependent on mass concentra-tions. HPLC–ELSD has been used extensively for analysis ofcarbohydrates [20,21]. A recent study has shown that monosac-charides can be separated and detected with good sensitivityusing HPLC–CNLSD employing either an ion-exchange col-umn designed for carbohydrates and 100% aqueous eluents ornormal phase chromatography (using amino and diol columns)[22]. ACD is expected to have sensitivity similar to CNLSDand better sensitivity and linearity than ELSD [17]. Whilethe ACD instrument described here was laboratory built, aninstrument based on the method, the charged aerosol detec-tor or CADTM, recently has become commercially available[23].

In addition to this work, a number of recent studies alsohave investigated new methods for aerosol MA analysis usingaqueous extraction and analysis involving liquid separations.One method used both electrospray ionization mass spectrom-etry (ESI–MS) and ion chromatography with pulsed amper-ometric detection [24]. Both of the methods suffered fromselectivity problems due to overlapping peaks (HPLC method)and inability to discriminate between the different MAs (usingEowbragAtsHsnoaevmrbcos

2. Experimental methods

2.1. Experimental apparatus

The HPLC system used for this study used a Waters (Mil-ford, MA, USA) 6000A pump, a Rheodyne (Cotati, CA, USA)Model 7125 injection valve, a Benson (Reno, NV, USA) BC-100Ca2+ 7.8 mm × 300 mm column, and an ACD system describedin more detail in the next paragraph. An injection loop of 57 �Lwas used. The Benson column is a cation exchange columndesigned for separation of carbohydrates and separation is basedon interactions with the Ca2+ ion (ligand exchange). This col-umn was heated using a Merck (Darmstadt, Germany) T6300column heater or a Phenomenex (Torrance, CA, USA) TS-130column heater. The Phenomenex column heater was run 5 ◦Cwarmer than the Merck column heater to obtain similar reten-tion times. Data from the aerosol charge detector was collectedusing a personal computer with an analog to digital board andwith Chromperfect software (Justice Laboratory Software, PaloAlto, CA, USA).

The ACD system used in this study is described in greaterdetail in Dixon and Peterson [17]. The HPLC effluent is neb-ulized using heated nitrogen into a spray chamber containingan impactor to remove large droplets. The spray is then evapo-rated as it flows through heated tubing and an oven to a TSI (St.Paul, MN, USA) Model 3030 Electrical Aerosol size Analyzer(wp

bnOfic0ae1ft1s

ptisaaw

2

Uf

SI–MS). More recently, a novel method for analyzing lev-glucosan has employed microchip capillary electrophoresisith pulsed amperometric detection (CE–PAD) [25]. A borateuffer was used to produce charged complexes. This methodesulted in low mass detection limits for levoglucosan and fastnalysis (under a minute), although interference from inor-anic compounds precluded its use for atmospheric samples.nother study has shown that HPLC with electrospray ioniza-

ion/mass spectrometry detection (HPLC–MS) can be used forensitive analysis of MAs [26]. In that study, reversed-phasePLC was used, the analysis run took an hour and very good

ensitivity was achieved. Baseline separation between man-osan and levoglucosan was not achieved, requiring the usef less abundant ions to quantify these compounds if bothre present. Another HPLC method was developed using ion-xclusion chromatography with low wavelength (194 nm) ultra-iolet detection (UVD) [27]. This method, however, had aodest detection limit, levoglucosan was not baseline sepa-

ated from mannosan, and solid phase extraction was requiredefore sample analysis. For these two HPLC methods twoolumns in series were used. The limits of detection (LODs)f these methods are discussed in greater detail in the resultsection.

EAA). The EAA charges and detects aerosol particles [28] andas used without any voltage on the charged rod to remove smallarticles.

One improvement in the ACD system from that describedy Dixon and Peterson [17] was the use of a more efficientebulizer. This nebulizer consisted of a stainless steel 1.59 mm.D. × 0.51 mm I.D. outer tube, which was soldered to a modi-ed stainless steel compression fitting attached to the same sprayhamber described previously. Inserted into the outer tube was a.31 mm O.D. × 0.16 mm I.D. stainless steel capillary (Poppernd Sons, New Hyde Park, NY, USA) through which the liquidffluent from the HPLC passed. A Valco (Houston, TX, USA).59 mm stainless steel tee connector was used with a Valcoused silica adapter to allow the stainless steel capillary to passhrough the tee. The stainless steel capillary was connected to.59 mm HPLC tubing using a union fitting with another fusedilica adapter.

This nebulizer had a smaller annular area (0.13 mm2) com-ared to the past fused silica nebulizer (0.31 mm2) allowing ito be run at a higher pressure of 4.1 bar nitrogen pressure result-ng in smaller droplet production. With the new nebulizer, theignal and signal to noise ratios, measured using flow injectionnalysis with sodium sulfate standards, were found to be aboutfactor of three higher (not shown) than in the previous systemith the fused silica nebulizer.

.2. Chemicals used

Deionized water purified with Barnstead (Dubuque, IA,SA) cartridges was used. Ammonium sulfate was purchased

rom Aldrich (Milwaukee, WI, USA). Levoglucosan was from

216 R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221

both Sigma (St. Louis, MO, USA) and Fluka (Milwaukee,WI, USA). Mannosan, mannose, methyl �-d-mannopyranoside,and galactosan were from Sigma (St. Louis, MO, USA),and glucose (dextrose) was from Spectrum (Redondo Beach,CA, USA). Methanol (HPLC grade) was from Fisher Sci-entific (Pittsburgh, PA, USA). The reagents used for prepar-ing quantitative standards had a minimum purity of atleast 98%.

2.3. Aerosol sampling

Three sets of aerosol filter samples that were used as testsamples in this study will be discussed. The first two sets,one set collected in Socorro, New Mexico (NM set) and oneset collected in Davis, California (Davis set) were used forinitial development and will only be discussed for develop-ment purposes. Following analysis of these samples, subse-quent samples were collected from Sacramento, California (Sacset). The equipment used to collect the NM set samples hasbeen previously described [29] with the exception of usingof 47 mm Whatman (Maidstone, England) quartz fiber filtersthat had been cleaned by extraction successively with ace-tone, ethanol and water. The NM set consisted of two 24 hsamples (65 m3), which were collected starting on 10 Januaryand 11 January 1999, and a blank. The second set of sam-ples (Davis set) was collected from an interagency monitor-iDdTacsfsbqs

sSMacsarrdFaMBiEfifi

2.4. Sample extraction and treatment

Sample filters were cut into halves with each segment trans-ferred to Whirlpak (NASCO, Ft. Atkinson, WI, USA) bags, andfor the last 5 Sac Set samples, 5 mL tapered glass vials (FisherScientific) for storage and extractions. One half of the NM set fil-ters was extracted with 2.0 mL of deionized water. The other halfwas extracted with 0.5 mL of methanol and 4.5 mL of deionizedwater to test for differences in the extraction methods. Methanolwas added first to “wet” the filters and to serve as a microbial bio-cide. Filter halves from the Davis set were extracted using 0.2 mLof methanol and 1.8 mL of water. The Sac set samples wereextracted using 0.2 mL of methanol, 0.1 mL of 100 �g mL−1

methyl �-d-mannopyranoside (MMP, added as an internal stan-dard) and 1.7 mL of water. Following the addition of solventsand the internal standard, the containers were briefly shaken andthen placed in an ultrasound bath for about 20 min. Followingextraction, samples were stored in a refrigerator or freezer andwere analyzed within two weeks of extraction. Sample extractswere filtered using 10 mm, 0.2 �m Anotop syringe filters (What-man, Maidstone, England) while loading the injection loop. Anumber of tests were performed on the extraction, recovery andidentification of compounds in the samples that will be discussedin detail in the next section.

3

3

tc0e5iAitie

Fc

ng for protected visual environments (IMPROVE) test site inavis, California. The sampling site and air samplers have beenescribed in other publications [30,31]. The 25 mm stretchedeflo brand Teflon filters (Pall, NY, USA) from the IMPROVEir samplers [31] were used for this study. These samples wereollected between February and August, 1997, with sampleizes of 85–120 m3. These first two sample sets are consideredor method development only because of the limited sampleize (NM set), samples of low concentrations (Davis set) andecause of the incorporation of improvements in the subse-uent sample set (use of other MA standards and an internaltandard).

The Sac set samples were collected from the roof of thecience building on the campus of California State Universityacramento at various times between 14 August 2002 and 31arch 2003 with sample sizes of 25–80 m3. This site is located

bout 5 km east of downtown Sacramento. The air sampleronsisted of a BGI (Waltham, MA, USA) inlet with PM2.5ize-cut cyclone and a BGI filter holder mounted on a tripodnd a pump with critical orifices for flow control. Air-flowates were measured at the start and finish using a calibratedotometer. The filters consisted of 1.0 �m pore size, 47 mmiameter Cole-Parmer (Vernon Hills, IL, USA) Teflon filters.ilters were weighed before and after sample collection onCahn 25 Microbalance (ThermoElectron Corp., Beverly,A, USA). Filters were stored in a freezer until extraction.lank filters were collected at each site by loading filters

nto cassettes and turning the pump on for about a minute.xcept for the amount of time the pump was on, the blanklters were handled under the same conditions as the samplelters.

. Results and discussion

.1. Method optimization

Optimization of this method was performed by varying theemperature and percent acetonitrile while analyzing a set ofommon sugars and levoglucosan. The selected flow rate of.7 mL min−1 was based on a back pressure of 34 bar (high-st recommended by manufacturer) at a column temperature of0 ◦C (the lowest investigated). Up to 7.1% acetonitrile was usedn the eluent but resulted in only small changes in performance.s a result, 100% water was used as the eluent. As expected,

ncreasing the temperature to 80 ◦C resulted in improved separa-ion efficiency (Fig. 1). Analysis of monosaccharides normallys preferred at higher temperatures because of better columnfficiency and, for reducing sugars, because of faster exchange

ig. 1. Plot of plate number and signal to noise ratio for 10 �g mL−1 levoglu-osan as a function of column temperature.

R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221 217

between isomers (mainly � and � forms). Increasing the tem-perature also reduced the retention time of levoglucosan from18.3 min at 50 ◦C to 14.9 min at 80 ◦C as has been observedpreviously [32].

Fig. 1 also shows the decrease in the signal to noise (3�) ratiowith increasing temperature. This has been observed previouslyusing a similar column and CNLSD [33]. The reduction in thesignal to noise ratio was attributed to an increase in the baselinedue to greater column bleed at high temperature. A temperatureof 60 ◦C was selected and used in subsequent analyses as anoptimal temperature in providing good signal to noise ratios andsufficient resolution, primarily for the MAs (higher temperaturesmay be optimal for more common sugars). It should be notedthat the baseline continued to drop over the first ∼50 h of useof the column, and this may shift the optimum temperature tohigher values.

3.2. Method performance

Much of the method performance evaluation is based on cali-bration standards used for the Sac set that contained ammoniumsulfate (for identification of unretained compounds), glucose,MMP, galactosan, levoglucosan and mannosan with MA andglucose standards in the range of 0.5–10 �g mL−1. Sac set chro-matograms were processed using a Hamming filter (8 s timecc

wAcaopi

tcaapfsoao

Fig. 2. A chromatogram of MA standards. The chromatogram is for a standardcontaining 4.0 �g mL−1 ammonium sulfate (off scale), 2.0 �g mL−1 glucose,galactosan, levoglucosan, mannosan, and 5.0 �g mL−1 MMP (off scale) at reten-tion times of 4.8, 8.6, 12.1, 16.8, 22.6, and 11.0 min, respectively. The responseshown is the EAA response after attenuation by a factor of 10.

chamber to the EAA was increased. Peak height was favored foranalyzing samples for MAs because of smaller integration errorsfor many of the samples with low levoglucosan and mannosanconcentrations.

For some of the analysis runs, slow drifts in the detectorsensitivity (e.g. a 30% change over several hours) were observedby repeated analysis of a standard over the run period. Basedon more recent work, these drifts are believed to be from aninsufficient warm up time for the detector (it was recognizedduring this study that complete warm up required two hours).To attempt to compensate for detector drift, MMP was selectedas an internal standard and was added to standards and samples ata concentration of 5.0 �g mL−1. Although around twenty sugarsand related compounds were tested for possible use as an internalstandard, no ideal internal standard was found. MMP appearedto be one of the better candidates based on narrow peaks, goodresponse, and elution at times away from the monosaccharideanhydrides and contaminants and interferences. MMP was notideal because of some peak overlap with galactosan and becausethe Sac set filter blanks and samples produced broad peaks underthe MMP peak. Use of peak area ratios or peak area heights werefound to result in improved R2-values and better analyses inanalysis runs with observable detector response drift. For manyof the analysis runs (five of eight analysis runs of the Sac set) nodrift was observable, and in all these runs the relative standarddeviation in the MMP peak height in standards was less than 5%.

t

TL

P C

S 34I 2RL 18

T peakb LOD

onstant) that reduced higher frequency noise without signifi-antly affecting peak width.

Fig. 2 shows a calibration standard chromatogram associatedith the Sac set samples with all components eluted in 25 min.ll of the MAs are shown to be well resolved using a single

olumn in contrast to recent studies using HPLC or CE to analyzeerosol MAs [24–27]. A small amount of peak overlap only isbserved for MMP and galactosan. The greater peak width andoorer peak shape for glucose is a result of partial separation ofsomers that occurs at the column temperature used.

A set of least squares linear regression parameters for calibra-ion lines based on peak areas and average detection limits for thealibration standards are given in Table 1. Whether using peakrea or peak height, calibration lines generally had R2-valuesbove 0.995 for all monosaccharides. The sensitivity (based oneak area) for the MAs was low relative to glucose and variedrom compound to compound. Most other sugars tested had sen-itivity similar to glucose (within ∼10%). The lower sensitivityf the MAs may be due to the greater volatility of the MAs;reduction in levoglucosan peak area relative to glucose was

bserved when the temperature of the tube connecting the spray

able 1east squares regression parameters and average limits of detection (LODs)

arameter (NH4)2SO4 Glucose

lope 1657 1019ntercept −1955 −552 0.9970 0.9997OD 100

he calibration line parameters are given for a representative calibration usingased on a signal to noise (1�) ratio of 3. The units for the slope, intercept and

The 3� limits of detection listed in Table 1 were based onhe Sac set. The LODs for this set were lower than earlier

ompound galactosan Levoglucosan Mannosan

5 784 6459 −33 −930.9996 0.9998 0.99870 90 150

areas from a set consisting of 5 different concentrations. The average LOD isare mV s mL �g−1, mV s, and ng mL−1, respectively.

218 R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221

Fig. 3. Chromatograms of extracted aerosol samples from: (a) Socorro, NMand (b) Sacramento, CA. The chromatograms were collected under similarconditions except for the use of a Hamming filter in the processing of the Sacra-mento sample. The full-scale chromatogram is shown in the bottom half withthe expanded fraction of the chromatogram shown in the top half. The peaksobserved at 16.9 min are from levoglucosan. The higher baseline in the NMsample is due to greater column bleed in the initial operations.

LODs due to a decrease in the baseline from column bleed overtime (also shown in Fig. 3 which is discussed below). The con-centration LODs for glucose and levoglucosan were about thesame as and the mass LODs (about 5 ng) were a factor of twolower than the lowest LODs listed by Wang et al. [22] usingHPLC-CNLSD with a similar column. As shown in Table 2, thismethod’s concentration LODs are lower than HPLC–UVD andCE–PAD values, similar to GC–MS values, and a little higherthan ESI–MS and HPLC–MS values. Mass detection limits,however, were higher than other methods where they could becalculated.

3.3. Aerosol samples—application of method

This method was initially applied to the NM and Davis sam-ple sets. Following some changes to the procedure mentionedpreviously, Sac set samples then were analyzed. Fig. 3 showsexample chromatograms from the NM and Sac sets. In thesechromatograms, peaks near 16.9 min match the retention timeof levoglucosan in the standard. Although the retention timesfor compounds varied somewhat (e.g. from 16.7 to 17.7 min forlevoglucosan), the peak retention times were close to retentiontimes for standards analyzed the same day. A peak at 22.6 minin the Sac sample also matches the retention time of mannosanin the standard.

To demonstrate that the observed peak was levoglucosan,part of two Sac sample extracts were treated with 0.1 M HClat 85 ◦C for 28 h to hydrolyze levoglucosan to glucose. Testswith galactosan, levoglucosan, and mannosan standards undersimilar conditions showed that this hydrolysis method wouldconvert nearly all of these compounds to galactose, glucose,and mannose, respectively. The levoglucosan peak in SampleSac 17, which appeared at 17.6 min in the Fig. 4a, disappearedcompletely in the hydrolyzed sample (Fig. 4b) and a peak at thetime of glucose (9.2 min) appeared. While overlap of the largeunretained peak makes integration of the glucose peak difficult,this test confirms the presence of levoglucosan.

Also observed in chromatograms (e.g. in Fig. 3) were largeuO8tUbs1w

sFntbhdfo

Table 2Comparison of method limits of detections for levoglucosan

Method GC–MS ESI–MS CE–PA

Concentration LOD 100 50 2700Mass LODb a 0.5 0.004Reference [12] [24] [25]

Units for concentration LOD (concentration LOD) and mass LOD are ng mL−1 and na Not able to calculate.b Mass LOD is the product of the volume of sample injected and the concentrationc Based on use of smaller ion fragments to be able to resolve overlapping peaks. W

nretained peaks and an elevated baseline (in most samples).ther peaks, such as the peaks observed in the NM sample at.3 and 12.6 min were contaminants present in some blanks andhe peak at 14.1 min in the Sac sample originated from methanol.nfortunately, the peak at 12.5 min interferes with galactosan,ut the source has not been identified. The filters used in the Sacamples also produced a small, but broad peak from about 8 to2 min. No peaks at the times of levoglucosan and mannosanere observed in the blank filters.Most of the air samples were observed to have peaks or

houlders shortly after the unretained peak (as can be seen inig. 3b) as well as an elevated baseline that was most promi-ent between 8 and 12 min but extended out to as far as 18 minhat could not be attributed solely to contaminants. The elevatedaselines were prevalent in summer samples and samples withigh levoglucosan concentrations. The elevated baseline may beue to dicarboxylic acids, which were observed to give broad,ronting peaks between 7 and 10 min, unresolved carbohydrates,r other water soluble organic compounds. This “unclassified

D HPLC–MS HPLC–UV HPLC–ACD

51c 500 900.25c a 5[26] [27] This paper

g, repectively.

LOD.ith the main ion, the LODs are a factor of 5 lower.

R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221 219

Fig. 4. A winter Sacramento sample: (a) following the standard extraction and(b) following hydrolysis. The hydrolyzed sample was diluted by a factor of two.

mass” (UCM) was estimated through integration as it may beequivalent to a water soluble organic mass reported previously[33] provided most of the components elute from the columnand are non-volatile.

Both the elevated baseline and the contaminant peak in Sacsamples overlapped with the MMP peak. The overlap appearedto cause systematic errors in the integrated area of the MMPpeak, since the MMP peak areas were observed to be up to 25%larger than expected. For this reason, MMP peak areas werenot used in calibrations except for samples Sac 9 through Sac

15, all of which had levels of levoglucosan below the level ofquantification (0.3 �g mL−1).

Tests were undertaken on aerosol samples to determine if lev-oglucosan was efficiently being extracted, for potential matrixeffects on analysis and for precision. To test for the efficiencyof the extraction, three of the four NM filter halves and one Sacfilter half were extracted a second time. The second extractionwas performed in the manner of the first extraction after firstremoving as much liquid as possible from the extraction bag.Assuming all of the mass is extracted in the first two extrac-tions, the extraction efficiency was calculated as the ratio oflevoglucosan mass extracted the first time to the extracted lev-oglucosan mass from both extractions. In one of the secondextractions performed on a NM filter half, levoglucosan wasbarely detectable giving an estimated extraction efficiency of94%. The other samples extracted a second time showed nodetectable levoglucosan indicating minimum extraction efficien-cies (based on the LODs) of 90 and 96% for the NM samplesand 97% for the Sac sample. The measured extraction effi-ciency for levoglucosan using water or water and methanol ishigh. Additionally, one Sac filter also was tested for recoveryof galactosan, levoglucosan and mannosan by extracting thesecond half and spiking the extract with 5.0 �g mL−1 of eachcompound. The percent recoveries were found to be 79, 96, and93% for galactosan, levoglucosan and mannosan. The percentrecoveries for levoglucosan and mannosan were not signifi-cawp

icisot2T

d unre

Fig. 5. Aerosol concentrations of the Sac samples. The estimate

antly different than 100%. The average relative standard devi-tion from replicate analysis of six samples, including three inhich separate halves were analyzed was 6.7% indicating goodrecision.

An initial concern in using the ion exchange column was thatt would degrade rapidly following use because of higher con-entrations of inorganic compounds in sample extracts. Approx-mately 40 filter extracts were injected over the course of thistudy along with an even larger number of standards. No obvi-us degradation in column performance was observed duringhe course of this study, which included the injection of about0 samples containing between 0.01 and 1.0 M of strong acids.he ACD baseline and noise did decrease considerably during

tained mass concentrations are also reported on the left Y-axis.

220 R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221

the first ∼50 h of use, probably due to removal of compoundscausing the bleed.

3.4. Aerosol samples—ample concentrations

The results of the Sac set filters are shown in Fig. 5. Sampleswithout levoglucosan shown had concentrations below the limitof quantification (five times the LOD or 15–7 ng m−3). Man-nosan had quantifiable concentrations only for sample Sac 17although mannosan was between the limit of detection and thelimit of quantification in other samples. Samples Sac 2 throughSac 8 were collected in August during a time in which the airquality appeared to be influenced from forest fires in southwest-ern Oregon. Samples Sac 9 through Sac 15 were collected inSeptember during a period of good air quality. Samples Sac 16and Sac 17 were collected during stagnant conditions in Januaryand the high levoglucosan concentrations appear to be from localresidential wood burning, while samples Sac 18 and Sac 19, col-lected in March, are thought to be less influenced by wood smokedue to higher wind speeds.

Also shown in Fig. 5 is an estimate of the unretained mass(using ammonium sulfate as a surrogate standard) for samples inwhich the peak area was in the calibration range (less than thatof the 50 �g mL−1 standard). This should be related to the totalinorganic ion concentration in the aerosol. The UCM leading toelevated baselines between roughly 8 and 15 min also was esti-mTa

4

mesndmtstbfgesteotwti

sm

when air samples of reasonable air volume were impacted fromsmoke from wood burning for heat or from regional forest firesmoke.

Acknowledgements

We would like to thank Cort Anastacio (UC Davis) for sup-plying us with IMPROVE air samples collected at UC Davis.We also received assistance from the CSU Sacramento MachineShop in the construction of the improved nebulizer, from TiffanyHester, Matt Jauregui, and Jonathon Pollack (CSU Sacramento)in the collection of air samples, from Kizzy Whitfield, AndroRios and Jennifer Cruz (CSU Sacramento) in the development ofthe method for acid hydrolysis of monosaccharide anhydrides,and Brian Bergamaschi (USGS) for review of the document.This work was supported by CSUS 2001-2002 and 2002-2003RCA Awards.

References

[1] S.E. Manahan, Environmental Chemistry, sixth ed., CRC Press, BocaRaton, FL, 1994, p. 306.

[2] J.H. Seinfeld, S.N. Pandis, Atmospheric Chemistry and Physics, JohnWiley and Sons Inc., New York, 1998, p. 1113.

[3] T. Novakov, J.E. Penner, Nature 365 (1993) 823.[4] W.F. Rogge, M.A. Mazurek, L.M. Hildemann, G.R. Cass, B.R.T.

[

[

[[

[

[[[[

[

[[[[

[

[

[[

ated using glucose as the surrogate standard (but not shown).he estimated UCM ranged from 0.15 to 1.92 �g m−3 with anverage of 0.60 �g m−3.

. Conclusions

A method was devised for analysis of levoglucosan andannosan in atmospheric aerosols using HPLC with an ion-

xchange column, 100% water eluent, and ACD. Galactosan iseparated from the other MAs but can be affected by contami-ants and interferences. This method has similar concentrationetection limits, although poorer mass detection limits, thanore commonly used GC–MS methods [12]. The main advan-

age, however, is simpler sample handling because it involvesimple extraction of filters into aqueous solutions with no deriva-ization or concentration steps. Compared to more recent liquidased analysis methods [24–27], this method appears to compareavorably in terms of simplicity of sample treatment, chromato-raphic selectivity and concentration detection limits with thexception of the HPLC–MS method [26] which had superior sen-itivity and selectivity. HPLC–MS instrument costs are expectedo be higher, however. This method also may provide ways tostimate total inorganic ion concentrations and water solublerganic mass as well. The precision of the method was foundo be good, provided sufficient time was allowed for detectorarm-up. It was found that an internal standard could be used

o correct for detector drift, although MMP was not an idealnternal standard.

This method was successfully applied to samples from threeites collected at different times of the year. The sensitivity of theethod was sufficient so that levoglucosan could be measured

Simoneit, Atmos. Environ. 27A (1993) 1309.[5] W.C. Malm, J.F. Sisler, D. Huffman, R.A. Eldred, T.A. Cahill, J. Geo-

phys. Res. 99D (1994) 1347.[6] T. Novakov, D.A. Hegg, P.V. Hobbs, J. Geophys. Res. 102D (1997)

30,023.[7] P. Saxena, L.M. Hildemann, J. Atmos. Chem. 24 (1996) 57.[8] B.R.T. Simoneit, J.J. Schauer, C.G. Nolte, D.R. Oros, V.O. Elias, M.P.

Fraser, W.F. Rogge, G.R. Cass, Atmos. Environ. 33 (1999) 173.[9] M.P. Fraser, K. Lakshmanan, Environ. Sci. Technol. 34 (2000) 4560.10] C.G. Nolte, J.J. Schauer, G.R. Cass, B.R.T. Simoneit, Environ. Sci. Tech-

nol. 35 (2001) 1912.11] Z. Zdrahal, J. Oliveira, R. Vermeylen, M. Claeys, W. Maenhaut, Environ.

Sci. Technol. 36 (2002) 747.12] M.W. Poore, J. Air Waste Manage. Assoc. 52 (2002) 3.13] B. Graham, A.H. Falkovich, Y. Rudich, W. Maenhaut, P. Guyon, M.O.

Andreae, Atmos. Environ. 38 (2004) 1593.14] B.R.T. Simoneit, V.O. Elias, M. Kobayashi, K. Kawamura, A.I. Rushdi,

P.M. Medeiros, W.F. Rogge, B.M. Didyk, Environ. Sci. Technol. 38(2004) 5939.

15] B.J. Turpin, Environ. Sci. Technol. 33 (1999) 76A.16] P.K. Simon, P.K. Dasgupta, Anal. Chem. 67 (1995) 71.17] R.W. Dixon, D.S. Peterson, Anal. Chem. 74 (20022930).18] J.A. Koropchak, S. Sadain, X. Yang, L.-E. Magnusson, M. Heybroek,

M. Anisomov, S.L. Kaufman, Anal. Chem. 71 (1999) 386A.19] J.A. Koropchak, L.-E. Magnusson, M. Heybroek, S. Sadain, X. Yang,

M. Anisomov, Adv. Chromatogr. 40 (2000) 275.20] R. Macrae, J. Dick, J. Chromatogr. 210 (1981) 138.21] M. Dreux, M. Lafosse, J. Chromatogr. Lib. 58 (1995) 515.22] Q. Wang, S. Sadain, J. Koropchak, Am. Biotechnol. Lab. 19 (2001) 22.23] P.H. Gamache, R.S. McCarthy, S.M. Freeto, D.J. Asa, M.J. Woodcock,

K. Laws, R.O. Cole, LCGC North Am. 23 (2005) 150.24] S. Gao, D.A. Hegg, P.V. Hobbs, T.W. Kirchstetter, B.I. Magi, M. Sadilek,

J. Geophys. Res. -Atmos. 108 (2003), doi:10.1029/2002JD002325.25] C.D. Garcia, G. Engling, P. Herckes, J.L. Collett Jr., C.S. Henry, Environ.

Sci. Technol. 39 (2005) 618.26] C. Dye, K.E. Yttri, Anal. Chem. 77 (2005) 1853.27] G. Schkolnik, A.H. Falkovich, Y. Rudich, W. Maenhaut, P. Artaxo, Env-

iron. Sci. Technol. 39 (2005) 2744.

R.W. Dixon, G. Baltzell / J. Chromatogr. A 1109 (2006) 214–221 221

[28] B.Y.H. Liu, D.Y.H. Pui, J. Aerosol Sci. 6 (1975) 249.[29] R.W. Dixon, H. Aasen, Atmos. Environ. 33 (1999) 2,023.[30] Q. Zhang, C. Anastacio, M. Jiminez-Cruz, J. Geophys. Res. 107D

(2002), doi:10.1029/2001JD000870.[31] W.C. Malm, J.F. Sisler, D. Huffman, R.A. Eldred, T.A. Cahill, J. Geo-

phys. Res. 99D (1994) 1347.

[32] R. Pecina, G. Bonn, E. Burtscher, O. Bobleter, J. Chromatogr. 287 (1984)245.

[33] S. Zappoli, A. Andracchio, S. Fuzzi, M.C. Facchini, A. Gelncser, G.Kiss, Z. Krivacsy, A. Molnar, E. Meszaros, H.-C. Hansson, K. Rosman,Y. Zebuhr, Atmos. Environ. 33 (1999) 2733.