Determination of Anions in Acid Rain by Ion Chromatography

Transcription

1 Appliction Updte 16 Determintion of Anions in Acid Rin by Ion Chromtogrphy INTRODUCTION The increse in cidity of wet nd dry tmospheric depositions hs been ttributed to the increse of SO 2 nd NO 2 emissions from sttionry nd mobile pollution sources. The cid rin problem hs reched drmtic proportions throughout mny regions of the United Sttes, Europe, Cnd, nd Jpn. Monitoring ir nd rin is essentil, not only for ssessing the effects of pollutnts on globl ecology, but lso for monitoring the progress of pollution control nd btement efforts. Ion chromtogrphy (IC) is convenient nd relible technique for determining low concentrtions of inorgnic nions in cid rin. IC with suppressed conductivity detection offers excellent precision nd ccurcy for the mesurement of such pollutnts nd hs been specified by the U.S. Environmentl Protection Agency (EPA) s the method of choice for determining inorgnic nions in wet deposition smples. 1,2 In this ppliction updte, we describe the use of utomted eluent genertion combined with high-cpcity, hydroxide-selective, nion-exchnge column the Dionex IonPc AS18 for the determintion of inorgnic nions in rinwter. This document updtes Dionex Appliction Note 31 by incorporting electrolytic eluent genertion with the IonPc AS18 to eliminte the need for mnully prepring the eluents offline, nd thereby incresing the IC system s level of utomtion nd ese of use. We evluted the IC method with simulted rinwter smple obtined from High- Purity Stndrds (HPS). The nion concentrtions of this smple re trceble to the Ntionl Institute of Stndrds nd Technology (NIST), Stndrd Reference Mteril No series. EQUIPMENT A Dionex ICS-2000 Regent-Free Ion Chromtogrphy (RFIC) System ws used in this work. The ICS-2000 is n integrted ion chromtogrph tht consists of: Eluent Genertor Column Heter Pump Degs EluGen EGC-KOH Crtridge (Dionex P/N ) Continuously Regenerted Anion Trp Column (CR-ATC) (Dionex P/N 06077) AS50 Autosmpler Chromeleon 6.5 Chromtogrphy Worksttion This ppliction updte is lso pplicble to other RFIC systems. REAGENTS AND STANDARDS Deionized wter, Type I regent-grde, 18 MΩ-cm specific resistnce or better Sodium nd potssium slts, ACS regent-grde or better, for prepring nion stndrds (VWR or other) Fluoride stndrd 1000 mg/l, 100 ml (Dionex P/N ) Chloride stndrd 1000 mg/l, 100 ml (Dionex P/N ) Sulfte stndrd 1000 mg/l, 100 ml (Dionex P/N ) Nitrte stndrd 1000 mg/l, 100 ml (Ultr Scientific, VWR P/N ULICC-00) Phosphte stndrd 1000 mg/l, 100 ml (Ultr Scientific VWR P/N ULICC-005) Bromide stndrd 1000 mg/l, 100 ml (Ultr Scientific, VWR P/N ICC-001) Appliction Updte 16 1

2 CONDITIONS Columns: IonPc AS18 Anlyticl, 250 mm (Dionex P/N 06059) IonPc AG18 Gurd, 50 mm (Dionex P/N ) 38 mm potssium hydroxide Flow Rte: 1.0 ml/min Temperture: 30 C Injection: 25 µl Detection: Suppressed conductivity, ASRS ULTRA, mm (Dionex P/N 05397) AutoSuppression Recycle Mode 100 ma current Bckground Conductnce: ~1. µs System Bckpressure: ~2500 psi Run Time: 10 min PREPARATION OF SOLUTIONS AND REAGENTS Stock Stndrd Solutions Stock Anion Stndrd Solutions (1000 mg/l) For severl nlytes of interest, 1000-mg/L stndrd solutions re vilble from Dionex nd other commercil sources. When commercil stndrds re not vilble, 1000-mg/L stndrds cn be prepred by dissolving the pproprite mounts of the corresponding mss in 1000 ml of deionized wter ccording to Tble 1. Stndrds re stble for t lest one month when stored t C. Working Stndrd Solutions Composite working stndrd solutions t lower nlyte concentrtions re prepred from the 1000-mg/L stndrds described bove. Working stndrds contining less thn 100 mg/l nions should be prepred dily. Five levels of clibrtion stndrds were used in this study to cover the expected concentrtions found in rinwter smples. Tble 2 shows the liner concentrtion rnge, method detection limits (MDLs), nd the concentrtions used to determine the MDLs for ech inorgnic nion investigted. Tble 1. Preprtion of Stock Stndrd Solutions Anion Compound Amount (g) Fluoride Sodium fluoride (NF) Chloride Sodium chloride (NCl) 1.68 Nitrite Sodium nitrite (NNO 2 ) 1.99 Bromide Sodium bromide (NBr) Nitrte Sodium nitrte (NNO 3 ) Phosphte Potssium phosphte, monobsic (KH 2 PO ) 1.33 Sulfte Sodium sulfte (N 2 SO ) 1.79 Tble 2. Liner Concentrtion Rnges nd MDLs Anlyte b Rnge Linerity Clculted MDL (mg/l) (r 2 ) MDL Stndrd (µg/l) (µg/l) Fluoride Chloride Nitrte Sulfte MDL = t S where t = Student s t vlue for 99% confidence level nd stndrd devition estimte with n 1 degrees of freedom (t = 3.1 for seven replictes of the MDL Stndrd), nd S = stndrd devition of the replicte nlysis. b A 25-µL injection volume ws used. Simulted Rinwter Smple, SR-II The simulted rinwter smple, SR-II, ws obtined from High-Purity Stndrds (HPS) nd nlyzed without further tretment by direct injection. 2 Determintion of Anions in Acid Rin by Ion Chromtogrphy

3 25 µs 0 Column: IonPc AG18, AS18, mm 38 mm potssium hydroxide Temperture: 30 C Flow Rte: 1 ml/min Inj. Volume: 25 µl Detection: ASRS ULTRA, mm, recycle mode Peks: 1. Fluoride 2 mg/l 2. Chloride 5 3. Crbonte. Nitrite Sulfte Bromide Nitrte Phosphte Figure 1. Seprtion of common inorgnic nions using the Ion Pc AS18 column Minutes RESULTS AND DISCUSSION The IonPc AS18 is ltex gglomerted column with 7.5-µm-dimeter mcroporous resin bed consisting of ethylvinylbenzene (EVB) cross-linked with 55% divinylbenzene (DVB), which mkes the column solvent comptible with reversed-phse solvents. The outer lyer consists of 65-nm ltex functionlized with lknol quternry mmonium groups. The net result is resin tht hs high cpcity, high pek efficiencies, nd high selectivity towrd hydroxide eluents (i.e., hydroxide-selective). The AS18 column is idel for use with isocrtic hydroxide eluents for fst seprtions (e.g., <10 min) of common inorgnic nions in reltively simple mtrices, such s rinwter. An nion nlysis of rinwter requires the determintion of fluoride, chloride, nitrte, nd sulfte. IC is idel for this nlysis becuse it cn lso be used to determine nitrite, bromide, nd phosphte. Figure 1 shows chromtogrm of seven common inorgnic nions seprted in less thn 10 min on the IonPc AS18. The AS18 hs different selectivity thn conventionl nion-exchnge columns tht use crbonte eluents. Using the eluent conditions described in this ppliction updte, sulfte elutes before bromide, nitrte, nd phosphte. However, if smples contin high mounts of dissolved CO 2, then grdient hydroxide seprtion should be used to improve the resolution between chloride nd crbonte. 3 The ICS-2000 system ws clibrted to cover the expected concentrtions found in rinwter smples. Tble 2 shows the liner concentrtion rnges investigted, the coefficients of determintion (r 2 ), nd typicl clculted method detection limts (MDLs) for ech nion seprted on the IonPc AS18 column. The response of ech nion ws liner, over the concentrtions reported in Tble 2, with r 2 vlues > The MDLs were determined by performing seven replicte injections of the MDL stndrd shown in Tble 2 nd clculting the MDL vlues bsed on the stndrd devition of the men multiplied by 3.13 (Student s t vlue for 99% confidence for n = 7). Simulted rinwter smples were nlyzed nd the results were compred with the vlues reported by HPS (Tble 3). The results were well within the stndrd devition rnges certified by HPS. Figure 2 illustrtes the ppliction of this method to simulted rinwter smple. Tble shows typicl retention time nd pek re precision dt for 20 replicte injections of the simulted rinwter smple. The excellent retention time stbility nd pek re precision cn be ttributed to the consistent genertion of high-purity potssium hydroxide by the ICS Tble 3. Anlysis of Simulted Rinwter, SR-II Anlyte Concentrtion Found HPS Certified Vlue (mg/l) (mg/l) Fluoride 0.10 ± ± 0.01 Chloride 0.99 ± ± 0.03 Nitrte 7.10 ± ± 0.20 Sulfte 10.0 ± ± 0.3 The stndrd devitions were clculted from twenty replicte injections (n = 20). Appliction Updte 16 3

4 25 µs Column: IonPc AG18, AS18, mm 38 mm potssium hydroxide Temperture: 30 C Flow Rte: 1 ml/min Inj. Volume: 25 µl Detection: ASRS ULTRA, mm, recycle mode Peks: 1. Fluoride 0.10 mg/l 2. Chloride Crbonte. Sulfte Nitrte 7.10 Tble. Precision of the Retention Times nd Pek Ares for Anions in Simulted Rinwter Anlyte Retention Time Pek Are RSD (%) RSD (%) Fluoride Chloride Nitrte Sulfte The reltive stndrd devitions (RSDs) were clculted from twenty replicte injections (n = 20) Figure 2. Anlysis of simulted rinwter Minutes The dt presented in Tble re typicl results tht cn be expected when using the IonPc AS18 for environmentl nlyses, such s rinwter smples. The routine use of hydroxide eluents cn further improve the performnce of existing IC methods where crbonte/ bicrbonte eluents hve commonly been used. The dvntges of using hydroxide eluents for IC re improved linerity, lower bckground conductivity, nd improved method detection limits when compred to conventionl IC columns using crbonte/bicrbonte eluents. Electrolytic genertion of potssium hydroxide further enhnces the level of instrument utomtion by requiring the nlyst to merely dd wter to the system. Using only wter, the system utomticlly prepres the eluent, clens the trp column, nd suppresses the eluent for conductivity detection SUMMARY The use of IC with n IonPc AS18 nd electrolytic eluent genertion provides rpid, isocrtic nlysis for the determintion of inorgnic nions in rinwter. The results obtined from the simulted rinwter smples were comprble to the vlues reported by HPS nd were well within the certified stndrd devition rnges. In ddition, electrolytic genertion of potssium hydroxide elimintes the need to mnully prepre eluents, incresing the IC system s level of utomtion, ese of use, nd nlyticl performnce. This pproch lso improves retention time precision nd quntittion relibility, nd llows esy method trnsfer between different opertors nd lbortories. SUPPLIER High-Purity Stndrds, 71 Frnchise Street, Chrleston, South Crolin 2918 USA, Tel: , REFERENCES 1. Chloride, Orthophosphte, Nitrte, nd Sulfte in Wet Deposition by Chemiclly Suppressed Ion Chromtogrphy, EPA Method 300.6; U.S. Environmentl Protection Agency, Stndrd Test Method for the Determintion of Chloride, Nitrte, nd Sulfte in Atmospheric Wet Deposition by Chemiclly Suppressed Conductivity. Method D ; Vol ; Americn Society for Testing nd Mterils: West Conshohocken, PA, Dionex Corportion, Appliction Note 15; Sunnyvle, CA. Determintion of Anions in Acid Rin by Ion Chromtogrphy

5 Regent-Free is trdemrk nd ASRS, AutoSuppression, Chromeleon, EluGen, nd IonPc re registered trdemrks of Dionex Corportion. Dionex Corportion Dionex Corportion Dionex U.S. Regionl Offices Dionex Interntionl Subsidiries 1228 Titn Wy Slt Lke City Technicl Center Sunnyvle, CA (08) Austri (01) Belgium (03) Cnd (905) Chin (852) Denmrk P.O. Box West 2200 South, Suite A Westmont, IL (630) Frnce Germny Itly (06) Jpn (06) The Netherlnds (0161) Sunnyvle, CA Slt Lke City, UT Houston, TX (281) Switzerlnd (062) United Kingdom (01276) Atlnt, GA (770) * Designed, developed, nd mnufctured under n NSAI registered ISO 9001 Qulity System. (08) (801) Mrlton, NJ (856) LPN 151 PDF 9/ Dionex Corportion Appliction Updte 16 5