An Improved Ion Chromatography Method for …

1 Air quality monitoring for acetic and formic acid vapours inmuseum galleries and storage environments is commonlyconducted using passive sampling and ion Chromatography (IC). We report development of a rapid IC Method with 2 to60-fold improvement in detection limits for acetate and for-mate. Baseline resolution is achieved in min using anAS11-HC anion exchange column with 4 mM NaOH eluent mL/min flow rate. The detection limits are 12 g/mL( ng) for acetate and 11 g/mL ( ng) for Method was successfully used for air quality monitor-ing in a Los Angeles museum indoor and outdoor air quality requires accurate collection andquantification of volatile organic compounds. Acetic and formic acids arethe most abundant carboxylic acids in the troposphere, having both anth-ropogenic and biogenic Anthropogenic sources include vehicleemissions resulting from incomplete combustion of ethanol-based fuel,3,5-7biomass burning,3,4,6,8industrial heat generation7 and synthetic ,10 Biogenic sources include emissions from vegetation, forests, andoceans,3,4,6,7,11-13photochemical synthesis involving ozone and olef-ins,2,3,6,14-16and secretions from and formicacids have been linked to increased cloud and fog formation,4,17,18incre-ased acidity of rain water,5,19-22and to the corrosion of cultural heritageobjects,23-32historical buildings and collectionsare at risk when acetic and/or formic acid are present at low ,37,38At these concentrations, the corrosion of metals and cal-careous objects such as limestone.

2 Ceramics, and fossils has been ,25-32,39-43 Over time, this corrosion can lead to complete deteri-oration of the and formic acid vapours are collected by active sampling or passi-ve ,5,7,37,44-56 Quantitative analysis can be performed directly ongas phase samples obtained by active sampling using gas chromatogra-phy mass ,12,16,55 Alternatively, the acid vapours can becollected and trapped passively as solid salts. Some passive samplerscan be read directly, while others must be analyzed in a salts in laboratory-analyzed passive samplers are usually extrac-ted in water and quantified by ion Chromatography (IC).3,17,48,50-54,57 Passive sampling is often preferred in museums because it requires neit-e-PRESERVATIONS ciencepublished byMORANARTD E. Hodgkins1*, Cecily M. Grzywacz2, Robin L. Garrell1AN Improved ION Chromatography METHODFOR ANALYSIS OF ACETIC AND FORMIC ACIDVAPOURSTECHNICAL PAPER1.

3 Department of Chemistry andBiochemistry & California NanoSystemsInstitute (CNSI), University of California,Los Angeles, Box 951569, Los Angeles,CA 90095-1569, USA2. National Gallery of Art, 6th Street &Constitution Ave NW, Washington DC20565, USA, formerly at The GettyConservation Institutecorresponding : words:Ion Chromatography , acetic acid, formicacid, passive sampling, indoor air quali-ty, museums environmentse-PS, 2011, 8, 74-80 ISSN: 1581-9280 web editionISSN: 1854-3928 print by M O R A N A RTD 74is calculated based on Fick s law of diffusion, usingequation 1: C=Lm/DAt(1)where Lis the length of the tube, mis the mass ofacid collected, Dis the vapour phase diffusion coeffi-cient, Ais the cross-sectional area of the diffusionpath, and tis the collection time. Since Gibson s work, further improvements in organicacid vapour analysis have been obtained by modi-fying the passive sampler and the IC Method , as sum-marized in Table 1.

4 The fastest elution times withbaseline resolution reported to-date are min foracetate45and min for lowestdetection limits obtained without the use of organicsolvents are 28 ng/mL for acetate and 26 ng/mL detect low concentrations, baseline resolution,short elution times and detection limits less than 100ng/mL are desirable. The Method in Table 1 that pro-vides low detection limits requires longer elutiontimes, while the methods that provide shorter elutiontimes do not give baseline resolution. The IC methodreported in this paper combines low detection limitsand baseline resolution with fast elution times toquantify acetic and formic acid vapours collected byMDTs exposed to museum storage environments. 2 Materials and chemicals were ACS reagent grade unless other-wise stated and were used as received. Sodium ace-tate, sodium formate, and potassium hydroxide pel-lets were from JT Baker (Phillipsburg, NJ, USA).

5 Sodium hydroxide 50 wt% was from Fisher Scientific(Pittsburg, PA, USA). Ethylene glycol dimethyl ether( HPLC grade) was from Sigma-Aldrich ( , MO, USA). Glacial acetic acid (HPLC grade)was from VWR International, LLC (West Chester, PA,USA). Formic acid (88% in water) was from EMScience (Gibbstown, NJ, USA). All solutions weremade using deionized reverse osmosis water filteredwith a MilliQ system (Millipore, Billerica, MA, USA),referred to as MilliQ water. of Museum Diffusion TubesMDTs were assembled using clear poly(methylmethacrylate) tubes ( x cm), acrylic caps, andstainless steel mesh disks (Gradko International Ltd.,Hampshire, United Kingdom). The trapping solution,40 L of 5 M KOH with 10% ethylene glycol dimethylether in MilliQ water, was pipetted into coloured capscontaining two stainless steel mesh disks and allo-wed to air dry for 3 h.

6 The MDTs were assembled bypushing a clear tube onto the coloured cap andsealing with a clear cap. The MDTs were divided intothree categories for analysis: laboratory blank MDTs,monitoring blank MDTs, and exposure MDTs. Thelaboratory blank MDTs were unexposed tubes usedto evaluate potential contamination of the MDTsduring preparation. Monitoring blank MDTs wereunexposed tubes that remained sealed inside theher high-level skills nor special equipment, it is lessexpensive than active sampling, and the samplerscan be placed discreetly in exhibitions for extendedperiods of , commercial passive samplers are availablefor detecting acetic acid in the parts per million byvolume (ppmv) or acid can bequantified with the same direct-read sampler, but onlyin the absence of acetic acid. In 1997, Gibson and co-workers developed passive samplers based onPalmes diffusion tubes, to detect acetic and formicacids simultaneously in the parts per billion by volu-me (ppbv) or passive samplers,referred to as museum diffusion tubes (MDTs), usepotassium hydroxide (KOH) to trap the organic acidvapours by forming deprotonated acid are dissolved in water and analyzed by IC.

7 Thetime-weighted average acid vapour concentration, C, by M O R A N A RTD Determination of Acetic and Formic Acid in Air, e-PS, 2011, 8, 74-8075a) Retention times were taken from chromatogram, b) Values weredetermined using densities of acetic and formic 1: Analytical figures of merit of IC methods using conductivitydetection for analyzing formic and acetic acid vapours collectedwith passive (min)Limit ofdetection(ng/mL)Calibrationstandards( g/mL)Upper limitof dynamicrange( g/mL) Correlationcoefficient(r2)Dionex IonPac AS4A51,525 mM Na2B4O7at mL/minAcetate1-10 Formate1-10 Dionex IonPac AS11450-50 mM NaOH gradient at IonPac mM Na2B4O7at Allsep mM NaHCO3 mM Na2CO3at IC SI-50 mM NaHCO3 mM Na2CO3at Allsep A-2 mM NaHCO3 mM Na2CO3at IonPac AS11-HC531-32 mM NaOH gradient at IonPac AS11-HC (this work)4 mM NaOH at during exposure and were used todetermine if there was contamination during transpor-tation to the site or during Warehouse EnvironmentAcetate and formate-induced efflorescence was iden-tified on fossils in the Invertebrate Paleontology (IP)warehouse at the Natural History Museum (NHM) ofLos Angeles County.

8 The IP collection is stored inmetal cabinets with wooden drawers. Air qualitymonitoring (AQM) was conducted in multiple loca-tions within the warehouse to determine whether ace-tic acid and/or formic acid vapours were present andwhether they present an ongoing risk to the collec-tion. Two storage cabinets containing fossils withefflorescence were chosen and the ambient warehou-se environment was monitored as a control. Sampling Using MuseumDiffusion TubesMDTs were exposed by removing the clear caps andplacing the tubes in the microclimate to be monitoredfor an appropriate length of time, based on the expec-ted acid vapour concentrations. Each environmentwas sampled with three exposure MDTs and twomonitoring blank MDTs. Monitoring blank MDTs wereleft sealed inside the sampled environment duringexposure. Exposure MDTs were capped at the end ofexposure by replacing the clear caps, and all MDTswere stored in a refrigerator at 5 C until results from replicate MDTs were averaged andused in the final times for the samplers are planned basedon the most likely concentration ranges.

9 Ambient con-centrations are usually in the low g/m3range, whilemicroclimates can range from 1 to 2500 ,9,17-22,37,38,58To obtain more representative air qualitymonitoring results, microclimates should be closedfor at least one month prior to exposing the microclimate dilutes any analytes pre-sent with external air. Once MDTs have been placedin the microclimate, they should remain for a periodlong enough to allow for re-equilibration of the envi-ronment and to ensure enough analyte is collected foranalysis. With this in mind, MDTs are usually expo-sed for at least 28 MDTs exposed in the ware-house and storage cabinets at the Natural HistoryMuseum of Los Angeles County were collected after33 IC Sample PreparationIon Chromatography samples were prepared in dispo-sable 15 mL BD Falcon polypropylene centrifugetubes (VWR International, LLC, West Chester, PA,USA).

10 The coloured MDT cap containing the trappingagent was removed and the steel mesh disks weretapped into a disposable centrifuge tube. The MDTcap was rinsed five times with 1 mL aliquots of MilliQwater, the centrifuge tube was sealed, and the solu-tion was sonicated for 1 min using a Bransonic 1510ultrasonic cleaner (Branson, Danbury, CT, USA). TheIC autosampler vials were 1 mL polypropylene withPTFE clear snap caps (Agilent, Foster City, CA,USA). Before adding sample for analysis, the vialswere rinsed twice with the sample extract to removeinherent unidentified contaminates, described inSection and AnalysisA Dionex DX-500 ion chromatograph (Dionex Corp.,Sunnyvale, CA, USA) was used for all analyses. Itconsisted of an AS3500 autosampler, EO1 mobilephase station, GP40 pump, ED40 conductivity detec-tor, and LC20 column compartment.