2011_aca (han)

Analytica Chimica Acta 692 (2011) 96–102 Contents lists available at ScienceDirect Anal yt ica Chimica Acta journal homepage: www.elsevier.com/locate/aca Surface-enhanced Raman scattering for arsenate detection on multilayer silver nanofilms Mei-Juan Han 1 , Jumin Hao 1 , Zhonghou Xu, Xiaoguang Meng ∗ Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, United States a r t i c l e i n f o Article history: Received 19 October 2010 Received in revised form 17 February 2011 Accepted 24 February 2011 Available online 4 March 2011 Keywords: Surface-enhanced Raman scattering Arsenate detection Silver nanofilm Electroless deposition Groundwater Sensor a b s t r a c t Surfa ce-en hanc ed Rama n scat terin g (SERS ) hasrecentlyemergedas a promi singmethodfor chemicaland biomolecular sensing. SERS quantification analysis of arsenate (As(V)) was investigated using multilayer Ag nanofilms deposited on glass slides as SERS-active substrates (Ag/GL substrates) by an electroless deposition process. The As(V) limit of detection (LOD) was determined to be ∼5 g L −1 or lower with or with out coexi sting multip le back groun d elect rolyte s (Na + , K + , Ca 2+ , Mg 2+ , Cl − , NO3 − , SO4 2− an d H2PO4 − ). The presence of the background electrolytes at low concentrations was observed to enhance the SERS sensi tivity of thesubst rate toward s As( V) more tha n twofol d. Sta nda rd cal ibr ati oncurveswere pre par ed in the absence and presence of the background electrolytes. Excellent linear relationships between the peak heights of the As(V) SERS band at ∼780cm −1 and the As(V) concentrations were obtained in a conce ntra tion rang e of 0–250g L −1 . The selectivit y of the Ag nano filmtowar ds oxyan ionswas examined to be in the order of As(V) phosphate nitrate, sulphate. A low sample-to-sample relative standard deviation (RSD) of 5.2% was also determined, suggesting the Ag/GL substrate was uniform and highly repro ducibl e. Exper imen tal resul ts indic atedthat the SERSmethod couldbe usedfor quan titat ive anal ysis of As(V) in groundwater samples. © 2011 Elsevier B.V. All rights reserved. 1. Intro ducti on Arsenic (As) is one of the most toxic contaminants found in the environment, and long-term exposure to arsenic can cause vari- ous cancers and other serious disease s [1,2]. Based on the World Health Organization (WHO) guideline, many countries including the US have promulgated a more stringent drinking water stan- dar d for arsenic wit h a max imum contaminant level (MCL) of 10 g L −1 (ppb) [2,3]. The new drinking water standard has a sig- nificant impact on the management of arsenic-contaminated sites, and promotes technological innovations for sensitive, rapid, and inexpensive field assays of arsenic. It is well known that the main species of arsenic found in the environment are the inorganic arsenite (As(III)) and arsenate (As(V)). Since the toxicity of arsenic depends on its chemical form (generally, As(III) > As(V)), both analysis o f total arsenic concentra - tion and speciation analysis of arsenic are important. Currently, the commonly used laboratory methods such as atomic fluores- cence spectroscopy (AFS), atomic absorption spectroscopy (AAS), induct ivelycoupled plas ma-at omicemission spectrometry or mass spectr ome try (IC P-AES or ICP-MS) all ow the det ect ion of low ∗ Corresponding author. Tel.: +1 201 216 8014; fax: +1 201 216 8303. E-mail addresses: [email protected] , [email protected] (X. Meng). 1 These authors equally contributed to the work. arsenic concentration. However, these techniques are expensive, bulky, and usually involved in sophisticated and time-consuming prepa rations of the samples, making them infeasible for field assay s, especi ally in develo ping count ries [4]. In recent yea rs,some field-compatible techniques including colorimetric methodology, anodi c strip ping volt amme try (ASV), and laserinduced break down spectroscopy (LIBS) have shown promise and even been applied in the arsenic field assays, nevertheless they either require the use of reagents, complicated pretreatment of samples and laborious fab ric ati on of ana lys is pla tfo rms, or suf fer from pro duc tion of tox ic substances , low sensit ivity , poorreproduci bilit y and extreme inter - ference of matrix [4]. Furthermore, most of the above-mentioned methods have no selectivity for arsenic species, which only give total arsenic amount unless coupled with effective separation processes inclu ding ion chromatog raphy (IC) techni que. Undou bted ly, the combination of detection methods with separation processes (e.g., IC-AFS and IC-MS) aggravates their above-mentioned disad- vantages deviating from field application. As a kind of colorimetric method (UV–Vis spectrophotometric method), the “arsenomolyb- denum blu e” met hod can sel ect ive ly det ect As( V) based on the fac t that As( V) for ms a complex (ar senomo lyb date ani on) with reduced molybdate to produce an intense blue color that can be measured easily, while As(III) does not. However, it suffers strong interfer- ences from phosphates and silicate [4]. Therefore, there exists an urgentneed forthe develo pme nt of new fiel d-c ompati blemethods for arsenic detection and speciation analysis. 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.02.054

2011_aca (han)

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