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Selective method for the analysis of perchloratein drinking waters at nanogram per liter levels,using two-dimensional ion chromatography with

suppressed conductivity detection

CHEM 699

Izzat w. Kazi

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outline

Introduction

Experimental

InstrumentationResult & Discussion

Conclusion

Recommendation

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Introduction

Perchlorate can interfere with the uptake of iodide by thethyroid gland

Health effects associated with the presence of perchloratein various food products and drinking water is a cause of

concern since certain populations are particularlysusceptible, such as pregnant women and infants

High doses of perchlorate can affect metabolism, growthand development of the body.

Early in 2005, the National Academy of Sciencesrecommended a maximum perchlorate dose of0.7 mg kg1body weight per day from all sources, including water,milk, vegetables and prepared food

Office of Environmental Health Hazard Assessment, March 11, 2004,http://www.oehha.ca.gov/public info/facts/faqperchlorate.html.National Academy of Science, January 10, 2005, http://www4.nationalacademies.org/news.nsf/isbn/0309095689?OpenDocument

http://www.oehha.ca.gov/public%20info/facts/faqperchlorate.htmlhttp://www.oehha.ca.gov/public%20info/facts/faqperchlorate.html

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Introduction contd

Until recently, U.S. EPA method 314.0 was used fordetermining the level of perchlorate in drinking andgroundwaters

Excellent utility at 4 mg l1 or higher concentration levels,

But Requires offline sample pretreatment using solid phase

extraction (SPE) cartridges

Difficult to determine perchlorate at low levels.

High levels of matrix ions chloride, sulfate or bicarbonate

Labor intensive and cumbersome sample pretreatment

Safe Drinking Water Act Analytical Methods and Laboratory Certification

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Introduction contd

In order to eliminate these more laborintensive procedures, EPAs Office of GroundWater and Drinking Water (OGWDW) and

National Exposure Research Laboratory,initiated method development projects toincrease sensitivity and selectivity using

direct injection techniques for the analysisof perchlorate in drinking water and insimulated high ionic strength matrices.

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Introduction contd

Two-dimensional ion chromatography (2D-IC) with suppressed conductivity detectionmet all OGWDW requirements for

selectivity

sensitivity

precision

accuracy and

method robustness

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Introduction contd

This is essentially an automated heart-cutting, columnconcentration and matrix elimination technique withsecond column confirmation

In the first dimension, a large sample volume is injected

onto a first separation column and the matrix ions arediverted to waste, while the perchlorate and a smallamount of other anions that elute within the cut windoware diverted and trapped onto a concentrator column

In the second dimension, the contents of the concentrator

column are eluted off and diverted onto a secondanalytical, smaller diameter (higher resolution) column forseparation and quantitation of perchlorate.

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Introduction contd

Dionex Corporation and OGWDW worked in partnership todevelop a 2D-IC method in order to simplify the Method

Development of this new

highly sensitive and selective 2D-IC, suppressed conductivitymethod

Drinking water Lowest Concentration Minimum ReportingLevel (LCMRL) of55 ng/L, and has

comparable sensitivity and selectivity

simpler and more economical than IC-MS or ICMSMS techniques.

Revisions to the Unregulated Contaminant Monitoring Regulation for Public Water Systems, Proposed Rule, EPA document #815-R-05-006, November 2004 (http://www.epa.gov/safewater/methods/pdfs/method lcmrl.pdf).

http://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdfhttp://www.epa.gov/safewater/methods/pdfs/method_lcmrl.pdf

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Experimental

ReagentsAll solutions and all dilutions were prepared

using purified reagent water (RW) 18 MW

filtered with a 0.2 mm filter and did not contain any

measurable quantity of the target analyte orinterfering compound

laboratory synthetic sample matrix (LSSM)

fortified with 1000 mg/L of chloride, bicarbonate and

sulfate

This solution was used to simulate a drinking watermatrix containing a total of 3000 mg/L of theseanions

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Standard and sample preparation

Calibration standards,

Continuing calibration check standards and

Perchlorate spiking solutions

prepared using a 1000 mg/L perchlorate (ClO4)

standard stock solution prepared from solid sodium

perchlorate (Sigma, Milwaukee, WI).

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Instrumentation

Dionex Model ICS-3000 dual system Dual pump (DP) module

Eluent generator (EG) module

Detector/chromatography (DC) module

Autosampler (AS)

Continuously-regenerated anion trap columns,

Suppressors Carbonate removal devices

Dual conductivity detectors, and

Computer-based data acquisition and controls stem.

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Instrumental conditions and equipment forfirst dimensions

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Ion chromatograph Dionex ICS-3000 dual system

Sample loop 2.0 or 4.0 mLLoad volume 4.7 mL

Eluent generator Dionex ICS-3000 eluent generator (EG) with dual channel EluGen Catridges

EluentIsocratic 35 mM potassium hydroxide ramped to 100 mM potassium hydroxide

following the elution of perchlorate

(when injection valve system #2 is switched to the inject position)

Eluent flow 1.0 mL/min

AutosamplerAutosampler module (AS) with sequential injection, sample preparation options and

a large volume (8.2 mL) sample needle assembly

Columns Dionex IonPac AG 20 (4 mm 50 mm) Dionex IonPac AS 20 (4 mm 250 mm)

Typical system back-

pressure2500 psi

Conductivitysuppressor

Dionex ASRS Ultra II, 4-mm with 4-mm carbonate removal device (CRD)

Chromatography

module DC-Module maintained at 30 C

Detector Conductivity detector (CD) with integrated cell held at 35 C

Total analysis time 45 min

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Instrumental conditions and equipment forsecond dimensions

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Ion chromatograph Dionex ICS-3000 dual system

Sample loop Dionex UTAC ULP1, 5 mm 23 mm, concentrator column

Load volume Cut-window time set per procedures

Eluent generator Dionex ICS-3000 eluent generator (EG) with dual channel EluGen Catridges

Eluent Isocratic 65 mM KOH

Eluent flow 0.25 mL/min

Autosampler Autosampler module (AS)

Columns Dionex IonPac AG 16 (2 mm 50 mm) Dionex IonPac AS 16 (2 mm 250 mm)

Typical system back-

pressure2500 psi

Conductivity

suppressorDionex ASRS Ultra II, 2-mm with 2-mm carbonate removal device (CRD)

Chromatography

module DC-Module maintained at 30 C

Detector Conductivity detector (CD) with integrated cell held at 35 C

Total analysis time45 min

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Fig. 1 Scheme of 2-D IC. Acronyms defined in above Table

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Results and discussion

Two complete IC systems are integrated toprovide a single IC

Automated analyses that incorporate heart-

cutting, column concentration Matrix elimination techniques

Single injection for the analysis

can accommodate a large sample injectionvolume (up to 4.0-mL)

greatly increases sensitivity

refocus the perchlorate peak that is partially

resolved in the first15

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Setting the cut window

window must be set to ensure that theperchlorate is completely eluted from thecolumn and that the amount of other

potentially interfering species, which mayalso elute during this time, are kept to aminimum

Ideally, a surrogate would be included inthe method to monitor and ensure that thecut window is functioning properly

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Setting the start time for the cut window inthefirstdimension

Since 2D-IC utilizes a large volume injection (up to4 mL)

high ionic matrix concentration on the retention time isa critical factor

address when setting the cut window

injection volume is also a critical factor

retention time for perchlorate determined in

1000 mg/L (LSSM) to set the start time of the cut window and

RW

to set the stop time of the cut window17

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The start time for the cut window 2.0 mL of a 50 mg/L perchlorate standard

prepared in the 1000 mg/L LSSM

injection valve #2 on system #2 is switchedto the load position

pressure spike

baseline deflection occurs after about 30 sstart time for the cut window

1 min before the rise in baseline for the

perchlorate peak in the 1000 mg/L LSSM.18

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Fig 2: start time for the cut window using a 2.0-mL injection volume of a50 mg/L ClO4

fortification in the 1000 mg/L LSSM.

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To ensure the start time is set using theperchlorate peak, not this earlier baselinedeflection

2.0-mL injection of the blank 1000 mg/L LSSM(without the perchlorate) also be injected.

Retention time

19.5 min and, therefore, the cut window starttime was set at

18.5 min.20

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Setting the stop time for the cut window

The stop time for the cut window 2.0 mL of a 25 mg/L perchlorate standard prepared in

the RW

stop time for the cut window is also the time atwhich injection valve #2 on system #2 is switchedto the inject position

elution of perchlorate must be completed at least 60 sbefore injection valve #2 is switched into the injectposition

perchlorate peak returned to baseline at 22.5 min andthe stop time for the cut window was established at23.5 min.

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Fig. 3. Setting the stop time for the cut window using a 2.0-mL injectionvolume of a 25mg/L ClO4

fortification in RW.

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Fig. 4. First- and second-dimension chromatogram using a 2.0-mLinjection volume of a 25mg/L ClO4

fortification in RW.

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Incorporating QC standards to monitor the cutwindow

Column performance can deteriorate aschromatographic columns age

Should monitored on a daily basis, with the use of QC

standardsHighest calibration standard should be prepared in

the 1000 mg/L LSSM as a continuing calibrationcheck standard (CCC)

to ensure the perchlorate is being trapped within the setcut window.

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. Demonstration of method performance using a2.0-mL injection volume

Instrument calibration standards prepared in RW

0.025, 0.050, 0.10, 0.30, 0.50,1.0, 3.0, 5.0 and 10g/L

correlation coefficient was 0.99956LCMRL determination

LCMRL is the lowest true concentration

between 50 and 150% recovery with 99% confidence

seven individual, sterile filtered replicates

0.050, 0.10, 0.20 and 0.30g/L perchlorate fortifiedRW samples

LCMRL of 0.055g/L25

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Precision and accuracy (P&A) data

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Table 2Precision and accuracy (P&A) data (n = 7) using 2.0-

mL injection volume

Matrix

Native

concentration

(

g/L)

Fortified

concentration (

g/L)

Precision

(%RSD)

Accuracy

(%recovery)Reagent

water

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Table 3

Precision and accuracy (P&A) data (n = 7) using 4.0-mL injection volume

Matrix

Native

concentratio

n (g/L)

Fortified

concentration

(g/L)

Precision

(%RSD)

Accuracy

(%recovery)

Reagent water

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Demonstration of method performance using a4.0-mL injection volume

Larger injection volume increases sensitivity.

dramatic effect on retention

Resetting cut window using a 4.0- mLinjection

start time for the cut window was established at20.0 min

stop time was set at 26.0 min

LCMRL is 0.041g/L

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Fig. 5. Setting the start time for the cut window in the first dimensionusing a 4.0-mL injection volume of a 25mg/L ClO4

fortification in the1000 mg/L LSSM.

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Fig. 6. Setting the stop time for the cut window in the first dimensionusing a 4.0-mL injection volume of a 10mg/L ClO4

fortification in RW

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Precision and accuracy data

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Table 3

Precision and accuracy (P&A) data (n = 7) using 4.0-mL injection volume

Matrix

Native

concentration

(g/L)

Fortified

concentration

(g/L)

Precision

(%RSD)

Accuracy

(%recovery)

Reagent water

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Comparison of 2.0 and 4.0 mL injection volumes

Peak areas for the 4.0-mL injection volume

2.0 to 2.1 times the peak area than the 2.0-mLinjection volume for the

low, mid and high-level CCC standards (n 5)

LCMRL was also slightly improved

native concentrations in the three drinking

water matrices ranged from 0.199 to 0.742mg/L

statistically equivalent (95% confidence interval) in

both injection volumes32

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Conclusions

The new two-dimensional IC method withsuppressed conductivity detection

excellent sensitivity

Selectivity

precision

accuracy and

method robustness

Simpler and more economical than IC-MS orIC- MSMS techniques

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Recommendation

Apply method for the determination of otherion like

Bromate (elutes just before chloride)

Nitrate (elutes just after chloride) etc.

In sea water or high matrix water

Simplification of the instrumentation

Replacing two-6port valve by single 10portvalve

Eliminating CD-134

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