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On January 22, 2001 the U.S. Envi-ronmental Protection Agency(EPA) replaced the 50 parts per

bil lion (ppb) standard for arsenic indrinking water with a new standard at10 parts per billion. The rule became ef-fective on February 22, 2002 and a sys-tem compliance date was set for January23, 2006. Ever since, arsenic has been an

analyte of interest and the subject ofmany articles, discussions and meetings.The change in the standard has launchedmany initiatives in product developmentand inspired many commercial under-takings. This new standard affects 54,000community water systems and 20,000non-community water systems in theU.S.1

Arsenic is considered a metalloid orsemimetal, having distinct properties

between metals and non-metals. Arsenicoccurs naturally in rocks and soil. Con-sequently, it can be found as a contami-

nant in both ground water and surfacewater sources, although higher levels arefound in ground water. Arsenic is gener-ally present in drinking water at levels

between two and 10 ppb, but regional dif-ferences in both ground and surface wa-ter sources can result in levels muchgreater that 10 ppb. According to the EPAdocument Arsen ic in Drinking Water ,short- and long-term health effects canresult from human exposure to arsenic.Short-term exposure to high doses of ar-senic can have adverse effects, but long-

term or chronic exposure has been linkedto cancer of the bladder, lungs, skin, kid-neys, nasal passages, liver and prostrate.Much has been written about arsenic asa contaminant in drinking water, so Iwont spend too much time on it here.Suffice it to say that the change in thestandard to 10 parts per billion has fo-cused attention on the various laboratory

methods used to analyze arsenic to thisnew low level. Most routine laboratorymethods are used to determine the totalamount of arsenic in a sample. Arseniccan exist as various compounds, bothorganic and inorganic. In drinking wa-ter, arsenic is generally found in two spe-cific species or valence states, namelyArsenite (also referred to as trivalent ar-senic, As+3, or As[III]) and arsenate (alsoreferred to as pentavalent arsenic, As+5,or As[V]). In some cases, an analysis todetermine the precise form of arsenic(speciation) is required in addition to the

total arsenic.A search of The National Environ-

mental Methods Index (www.nemi.gov)lists 36 specific methods for the analysisof arsenic. Most of the list refers to meth-ods utilizing spectroscopy, specificallymass, emission or absorption spectros-copy. One method references the use oftest strips to determine the total amountof arsenic. There are several commer-cially available products that utilize thesetest strips. These products are referred toas semi-quantitative because the results

are determined by comparing the pro-cessed strips against a color chart withvarious increments from zero to 500 ppb.These test strips cannot be used for spe-ciation. When using these products,make sure you understand the limits ofdetection and the reporting units.

The three most common methodsemployed in the analysis of drinking

water are EPA 200.8, Determination of TraceElements in Waters by Inductively CoupledPlasmaMass Spectrometry; EPA 200.7,Determination of Metals and Trace Elementsin Water and Wastes by Inductively CoupledPlasma-Atomic Emission Spectrometry andStandard Method 3113 B, Electrothermal

Atomic Absorption Spectrometric Method.Emission and absorption spectroscopy areclosely related. Both technologies relyupon the fact that characteristic frequen-cies of electromagnetic radiation (spectra)are produced by elements like arsenicwhen they are vaporized and ionized us-

ing either an inductively coupled plasma(Methods 200.7 and 200.8) or a graphitefurnace (Method 3113 B). Figure 1 illus-trates a typical emission spectrum pro-duced when an element is vaporized atextremely high temperatures. Each uniquespectrum acts like a fingerprint that theanalyst can use to identify and quantifythe element that is of interest. Most of thelab instruments being used in a moderndrinking water laboratory can simulta-neously detect and quantify many ele-ments. The ICP-AES instrument used with

The

Analysis

ofArsenic

By Stephen R. Tischler

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S E P T E M B E R 2 0 0 6Water Conditioning & Purification

Method 200.7 makes use of these charac-teristic atomic-line emission spectra. Thespectra are dispersed by a grating spec-trometer, and the intensities of the linespectra are monitored at specific wave-lengths by a photosensitive detector. Theintensities are converted to concentrationsand reported by the laboratory generallyin parts per million (ppm) per mg/L.

Our laboratory analyzes arsenic by

Method 200.8, Inductively Coupled Plasma Mass Spectrometry or ICP/MS. Method200.8 is used to determine the concentra-tion of 21 different elements, includingaluminum, antimony, arsenic, barium,

beryllium, cadmium, chromium, cobalt,copper, lead, manganese, mercury, mo-lybdenum, nickel, selenium, silver, thal-lium, thorium, uranium,vanadium and zinc. TheICP/MS method is fa-vored because its methoddetection level is belowtwo parts per billion for arsenic, well be-

low the new EPA maximum contaminantlevel (MCL) of 10 parts per billion. Thereare three primary parts to the ICP/MSinstrument. The first part is the induc-tively coupled plasma ion source, whichis used to vaporize and ionize elementsin a water sample. The second part is themass analyzer, which is used to separate

elements based on their mass-to-chargeratio. Essentially, the mass analyzer sepa-rates the elements based on the relativeweight and electric charge of each ele-ment. The third component is the detec-tor, which measures the intensity of eachspecific element that strikes the detectorand indicates the amount of the elementin the sample.

An accurate analysis using this

method begins with the proper collection,preservation, handling and storage of thesample. For the determination of totalrecoverable arsenic, a 500 mL sample col-lected in a clean plastic container (pref-erably supplied by the laboratory doingthe analysis) is filled and delivered to thelab within two weeks of taking the

sample. Upon arrival at the lab, the

sample is acidified with nitric acid, mixedand held for 16 hours. After that, the pHis checked to assure that it is less thantwo. If not, the sample is re-acidified andheld for an additional 16 hours until veri-fied to be less than two. Acid preserva-tion can be done at the time of collection;however, to avoid using strong acids in

Figure 1. Typical emission spectrum

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Water Conditioning & PurificationS E P T E M B E R 2 0 0 6

Ions that are too heavybend too little

Ions that are too lightbend too much

Only ions of the right masscan enter the detector

Detector slits

Flight tube

Detector

Recorder

Slits

Insulator

SampleProbe

Ionbeam

ElectronbeamIon

source

Acceleratorplate

To vacuumpump

Magnet

Figure 2. Basic

mass spectrometer

configuration

SOURCE: http://en.wikipedia.org/wiki/Image:Mass_spectrom.gif

the field, transportation restrictions, andpossible contamination issues, themethod recommends that this be done in

the laboratory.As with all methods, rigorous qual-ity control is employed to make sure thatthe instrument is working properly andis capable of delivering accurate results.Calibration curves are developed for eachmetal or metalloid being analyzed. Cali-

bration standards in the range from one

to 100 parts per billion are typically used,in addition to a series of blanks.

A single analysis for one metal us-

ing EPA method 200.8 can cost anywherefrom $10 to $30 dollars per sample, whilea full analysis for all 21 metals will costaround $150 to $200 dollars.

If you are responsible for determin-ing treatment options for the removal ofarsenic, you may want to discuss specia-tion testing with your laboratory. In most

cases, treatment options require the con-version (oxidation) of arsenite (As+3) toarsenate (As+5) prior to applying removaltechniques such as ion exchange or re-verse osmosis. Knowing the preciseamount of each species of arsenic mayassist you in selecting proper treatmentoptions. Speciation of arsenic requiresspecial testing that is available througha few commercial laboratories

References1. http://www.epa.gov/safewater/arsenic/

basicinformation.html#six

About the author Stephen R. Tischler is Vice President ofBusiness Development for National TestingLaboratories and a member of WC&Ps Tech-nical Review Committee. A former analyticalchemist at NASA, he has a long history in theaerospace industry with expertise in qualitycontrol and analytical testing method devel-opment. Tischler has a bachelors degree in

chemistry from John Carroll University anda masters degree in business from Baldwin-Wallace College. National Testing Labs pro-vides assistance to POU/POE dealers involvedin the analysis of drinking water for custom-ers using private wells or municipal sources.For more information, call (440) 449-2525 orvisit www.ntllabs.com