PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 1 of 12 

Standard Operating Procedure 

for PM2.5 Anion Analysis 

Environmental and Industrial Sciences Division
 

RTI International*
 

Research Triangle Park, North Carolina
 

Prepared by: Date: g /:2&/09

I 

Date: R/z tP /t?f 77 1

Date: ¢Z6/o? 7 I 

_RTI 

INTERNATIONAL 

Reviewed by:---,.£-f-=---_---L----::7L.....:~_ __jL--=----­

Approved bY:-6/'l--t6'4.,;'LJ4,"-h~7-I-!LU~'L-f~--

* RTI International is a trade name of Research Triangle Institute. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 2 of 12 

Contents 

Section Page 

1.0 Procedural Section ...............................................................................................................3 

2.0 Quality Assurance and Quality Control.............................................................................12 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 3 of 12 

Standard Operating Procedure for PM2.5 Anion Analysis 

1.0 Procedural Section 

1.1 Purpose and Applicability 

This document outlines procedures for the extraction and subsequent determination of anions in 

filter extracts. Analytical procedures outlined are specific to the ion chromatographs used in 

RTI’s Ion Analysis Laboratory. 

1.2 Summary of Method 

Collected aerosol filter samples are extracted by a method appropriate for the analyte of interest. 

Sample extracts are passed through a resin consisting of polymer beads coated with quaternary 

ammonium active sites. Anion separation is due to the different affinities of the anions for the 

active resin sites. Following separation, the anions pass through a suppressor column, which 

exchanges all cations for H+ ions. An eluent that yields a low-conducting acid is used. Species 

are detected and quantified as their acids by use of a conductivity meter. 

In a laboratory evaluation of the accuracy of the method, spiked PM2.5 filter extracts and quality 

assurance/quality control (QA/QC) samples were analyzed for sulfate and nitrate ions. The 

accuracy (expressed as % recovery) achieved using the subject method is presented in Table 1. 

To test the precision of the method, PM2.5 filter extracts were analyzed in duplicate, and the 

blank extracting solution and a low-level QC sample were analyzed seven times each. The 

results are summarized in Table 2. 

Table 1. Accuracy Values for QA/QC Samples and Spiked PM2.5 Filter Extracts 

Analyte 

QA/QC Sample 

Average % Recovery* (range) 

Spiked Extract 

Average % Recovery* (range) 

SO4 100.5 (97.5–104.2) 

n = 187 

99.9 (98.2–100.7) 

n = 61 

NO3

-

 99.6 (96.9–103.0) 

n = 187 

99.3 (97.5–103.3) 

n = 61 

* % Recovery = (concentration found/concentration expected) H 100 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 4 of 12 

Table 2. Precision Values for PM2.5 Filter Extracts, Extracting Solution, and QC Samples 

Sample Type 

Analyte 

PM2.5 Filter Extracts 

Average RSD** 

(range) 

Blank Extracting 

Solution Average 

(Standard Deviation), 

n = 7 

QC Sample 

(0.600 ppm NO3, 

1.200 ppm SO4) 

RSD, n = 7 

SO4

=

 0.2 (0.0–1.4) 0.000 (0.000) 0.3 

NO3

-

 0.3 (0.0–1.7) for 86 

duplicates 

for 86 duplicates 

0.000 (0.000) 0.2 

** RSD = relative standard deviation (the standard deviation divided by the average value and expressed as a 

percentage) 

1.3 Health and Safety Warnings 

The PM2.5 ion analysis operations do not involve unusual risks from electrical equipment or 

chemical exposures. Standard RTI laboratory health and safety precautions will be followed. 

1.4 Cautions 

Laboratory personnel should always wear clean clothes and wash hands thoroughly before 

performing filter handling and analysis procedures. The use of gloves is required and will 

minimize the potential for laboratory contamination. 

1.5 Interferences 

Large amounts of anions eluting close to the ions of interest will result in an interference. No 

interferences have been observed in nylon filters samples or Teflon filter samples analyzed to 

date. If interferences are observed, several steps to increase separation can be taken, such as 

reducing eluent strength and/or flow rate or replacing the guard and/or separator column. 

1.6 Personnel Qualifications 

Personnel employed to perform ion analysis operations will have at least an associate’s degree in 

a laboratory science and will be trained by a supervisor before being allowed to process client 

samples for the PM2.5 program. 

1.7 Apparatus and Materials 

1. Disposable centrifuge tubes with screw caps, 50 mL (polypropylene). 

2. Calibrated Rainin electronic pipette (10 mL capacity) and adjustable Eppendorf 

pipette (10–100μL). 

3. Tweezers. 

4. Ultrasonic bath fitted with epoxy-coated test-tube rack to hold centrifuge tubes. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 5 of 12 

5. Mechanical shaker. 

6. Ion chromatograph complete with workstation (see Table 3). 

7. Pressurized eluent and regenerant reservoirs. 

8. Volumetric flasks (an assortment of sizes). 

9. Dionex autosampler vials with filter caps. 

10. Coldroom at ≤4oC. 

11. Refrigerators. 

Table 3. Configurations of Ion Chromatographs Used for Anion Analysis 

Instrument ID A1 A2 A3 A4 A5 A6 

Dionex Model DX-500 DX-500 DX-500 DX-600 DX-600 ICS-2000 

Chromatography 

Module 

LC20 LC20 LC20 LC30 LC30 None 

Pump GP50 IP25 IP20 IP25 IS25 IS2000 

Conductivity 

Detector 

CD20 

DS3 Cell 

CD20 

DS3 Cell 

CD20 

DS1A Cell 

CD20 

DS3 Cell 

CD25 

DS3 Cell 

Built-in DS6 

Autosampler AS40 AS40 AS40 AS40 AS40 AS40 

Software Windows 

2000 

Dionex 

PeakNet 5.2 

Windows 

2000 

Dionex 

PeakNet 5.2 

Windows 

2000 

Dionex 

PeakNet 5.2 

Windows 

2000 

Dionex 

PeakNet 5.2 

Windows 

2000 

Dionex 

Chromeleon 

Windows XP 

Dionex 

Chromeleon 

Guard Column AG12A AG12A AG12A AG12A AG12A AG12A 

Separator 

Column 

AS12A AS12A AS12A AS12A AS12A AS12A 

Suppressor 

Column 

AMMSIII AMMSIII AMMSIII AMMSIII ASRS Ultra 

 Auto-regen 

mode 

ASRS Ultra 

Auto-regen 

mode 

Other — — — — — Built-in eluent 

generator (not 

used) 

1.8 Ion Chromatography Reagents 

Use ACS reagent-grade chemicals and 18.2MΩ-cm deionized water for the preparation of all 

solutions. 

1. Concentrated eluent (100X), 30mM NaHCO3/270mM Na2CO3: Dissolve 2.5209 g 

NaHCO3 and 28.6178 g Na2CO3 in 1 L of deionized water (Note: Do NOT dry the 

salts that are used to prepare the eluent). 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 6 of 12 

2. Working eluent, 0.3mM NaHCO3/2.7mM Na2CO3: Dilute 200 mL concentrated 

eluent to 20 L with deionized water. 

3. Regenerant, 0.025N H2SO4: Dilute 100 mL 5.0N H2SO4 to 20 L with deionized 

water (Note: This reagent is not used for an IC system equipped with a selfregenerating suppressor.). 

1.9 Calibration Standards 

Use ACS reagent-grade chemicals and 18.2MΩ-cm deionized water for the preparation of all 

solutions. Dry the salts used for the preparation of calibration standards at 105EC for 2 hours and 

cool in a desiccator immediately before use. 

1. Mixed Stock Solution, 1000 mg/L NO2

-

, NO3

-

, and SO4

2-, and 200 mg/L C1-

: 

Dissolve 1.4998 g NaNO2, 1.3708 g NaNO3, 1.8142 g K2SO4, and 0.3297 g NaCl in 

1 L of deionized water (Note: These are the four anions typically analyzed in the 

Ion Analysis Laboratory. PM2.5 filter extracts will be analyzed using standards 

prepared from this mixed-stock solution.). 

2. Standard Solution A (100 mg/L NO2

-

, NO3

-

, SO4

2-, and 20 mg/L C1-

): Dilute 10 mL 

mixed-stock solution to 100 mL with deionized water. 

3. Standard Solution B (10 mg/L NO2

-

, NO3

-

, and SO4

2-, and 2 mg/L C1-

): Dilute 

10 mL Standard Solution A to 100 mL with deionized water. 

4. Calibration Standards: Using Standard Solutions A and B, prepare calibration 

standards with deionized water in 100 mL volumetric flasks as shown in Table 4. 

Prepare fresh calibration standards weekly. 

Table 4. Preparation of Anion Calibration Standards 

Standard NO3

-

, SO4

2- (mg/L) 

mL of Standard 

Solution/100 mL 

Standard Solution A 

1 25.0 25.0 

2 10.0 10.0* 

3 3.0 3.0 

Standard Solution B 

4 1.0 10.0* 

6 0.5 5.0 

7 0.2 2.0 

1 mg/L STANDARD (Standard 4) 

8 0.1 10.0* 

9 0.05 5.0* 

Note: Higher concentration standards can be prepared from Standard A or from the mixed-stock solution if needed. 

*For these solutions, use two times the stated mL of standard solution in a 200 L flask. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 7 of 12 

1.10 Quality Control Solutions 

Use ACS reagent-grade chemicals and 18.2MΩ-cm deionized water for the preparation of all 

solutions. Dry the salts used for the preparation of calibration standards at 105EC for 2 hours and 

cool in a desiccator immediately before use. Quality control solutions must be prepared 

independent of the calibration solutions. 

1. Chloride Stock Solution, 1000 mg/L C1-: Dissolve 0.8243 g NaCl in 500 mL of 

deionized water. 

2. Nitrite Stock Solution, 1000 mg/L NO2

-

: Dissolve 0.7499 g NaNO2 in 500 mL of 

deionized water. 

3. Nitrate Stock Solution, 1000 mg/L NO3

-

: Dissolve 0.6854 g NaNO3 in 500 mL of 

deionized water. 

4. Sulfate Stock Solution, 1000 mg/L SO4

2-: Dissolve 0.9071 g K2SO4, in 500 mL of 

deionized water. 

5. QC-Intermediate Solution, 10 mg/L C1-, 20 mg/L NO2

-

, 30 mg/L NO3

-

, and 60 

mg/L SO4

2-: Pipette 1 mL of 1000 mg/L C1-

, 2 mL of 1000 mg/L NO2

-

, 3 mL of 

1000 mg/L NO3

-

, and 6 mL of 1000 mg/L SO4

2- into a 100 mL volumetric flask and 

dilute to the mark with deionized water. 

6. QC Samples: Using the QC-intermediate solution, prepare calibration standards 

with deionized water in 100 mL volumetric flasks as shown in Table 5. Prepare 

fresh calibration standards weekly. 

Table 5. Preparation of Anion Quality Control Samples 

QC Sample ID 

mL QC-Intermediate 

Solution 

Final Volume, mL 

(Volumetric Flask 

Size) 

NO3

- Conc 

(mg/L) 

SO4

2- Conc 

(mg/L) 

QC-LOW 2.0 100 0.6 1.2 

QC-MED 5.0 100 1.5 3.0 

QC-HIGH 10.0 50 6.0 12.0 

1.11 Quality Assurance Solutions 

Use commercially prepared, NIST-traceable solutions to prepare an intermediate quality 

assurance solution known concentrations of C1-, NO2

-

, NO3

-

, and SO4

2-. Solutions can be 

purchased from CPI (www.cpichem.com) or GFS Chemicals (www.gfschemicals.com). 

1. QA-Intermediate Solution, 10 mg/L C1-

, 20 mg/L NO2

-

, 30 mg/L NO3

-

, and 60 

mg/L SO4

2-: Pipette 1 mL of 1000 mg/L C1-

, 2 mL of 1000 mg/L NO2

-

, 3 mL of 

1000 mg/L NO3

-

, and 6 mL of 1000 mg/L SO4

2- into a 100 mL volumetric flask and 

dilute to the mark with deionized water. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 8 of 12 

2. Using the QA-intermediate solution, prepare calibration standards with deionized 

water in 100 mL volumetric flasks as shown in Table 6. Prepare fresh quality 

assurance samples as needed. 

Table 6. Preparation of Anion Quality Assurance Samples 

QC Sample ID 

mL QAIntermediate 

Solution 

Final Volume, mL 

(Volumetric Flask 

Size) 

NO3- Conc 

(mg/L) 

SO42- Conc 

(mg/L) 

QA-CPI_LOW 2.0 100 0.6 1.2 

QA-CPI_MED-HI 10.0 100 3.0 6.0 

1.12 Sample Collection 

Sample collection is not applicable to this SOP because samples are acquired by the state agency 

responsible for exposing the filters. 

1.13 Sample Handling 

Note: Additional information on this topic can be found in the Standard Operating 

Procedure for the Sample Handling and Archiving Laboratory (SHAL), Research 

Triangle Institute, Center for Environmental Measurements and Quality Assurance, 2001. 

RTI will provide chain-of-custody documentation with all sample shipments to track and ensure 

that samples are collected, transferred, stored, and analyzed by authorized personnel; sample 

integrity will be maintained during all phases of sample handling and analysis; and an accurate 

written record will be maintained of sample handling and treatment from the time of its 

collection, through the laboratory analytical process, to the eventual relinquishing of all data to 

the client. 

Upon initial receipt of filters, RTI will prepare a Filter Inventory Sheet containing the filter 

identification numbers, box numbers, date received, date inspected, and the number of filters 

rejected. This sheet will allow laboratory personnel to select and use the filter boxes in the 

proper sequence. 

1.14 Filter Extraction Procedure 

1.14.1 Nylon Filters 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 9 of 12 

Note: Nylon filters to be analyzed for nitrate only will be extracted with the eluent used 

for IC analysis, a dilute sodium carbonate/sodium bicarbonate buffer. Filters to be 

analyzed for anions and cations will be extracted with 18.2MΩ-cm deionized water. The 

anion eluent produces a large sodium peak in the cation chromatogram that precludes 

quantitation of the sodium ion in the filter extract and interferes with the quantitation of 

ammonium ion. 

To extract the filters, the analyst will do the following: 

1. Remove filters to be extracted from the freezer and allow them to equilibrate to 

room temperature. 

2. Using gloved hands and tweezers, place each filter in a polypropylene centrifuge 

tube that has been labeled with the sample ID printed on a durable (water-resistant) 

label. 

3. Label two 50-mL extraction tubes as Reagent Blank DI H2O and Reagent Blank 

Eluent. The eluent blank will not be prepared if there are no “nitrate only” samples 

to be analyzed with the batch. 

4. Add 25.0 mL of extraction solution (2.7 mM Na2CO3/0.3 mM NaHCO3 for 

subsequent anion analysis or deionized water for subsequent anion and cation 

analysis) using a calibrated automatic pipette. 

5. Screw the cap tightly on the centrifuge tube. 

6. Ensure that the filter is completely submerged in the extraction solution. 

7. Place the batch of centrifuge tubes in an epoxy-coated wire test-tube rack and place 

the extraction rack in the ultrasonic bath. Make sure that the water level of the 

ultrasonic bath is higher than the extraction solution level but below the screw cap. 

Sonicate for 60 minutes. 

CAUTION: Monitor the bath temperature during sonication. The temperature 

should not exceed 27EC. Add ice initially to lower the temperature, 

and add ice as necessary during the sonication to maintain an 

acceptable temperature. 

8. Install the extraction racks on the mechanical shaker and shake overnight in a cold 

room (≤4EC) at approximately 60 cycles per minute. 

9. Record the date of extraction on the RTI Sample Log Form. 

10. Store the extracts in a refrigerator until analysis. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 10 of 12 

1.14.2 Teflon Filters 

1. Remove filters to be extracted from the freezer and allow them to equilibrate to 

room temperature. 

2. Using gloved hands and tweezers, place each filter in a polypropylene centrifuge 

tube that has been labeled with the sample ID printed on a durable (water-resistant) 

label. 

3. Label one 50-mL extraction tube as AReagent Blank DI H2O.” Remove the caps 

from all 50-mL extraction tubes. To prevent contamination place the caps in an 

upside-down position. 

4. Using an Eppendorf 100-FL pipette, wet the entire surface of each Teflon filter with 

100 FL of nanopure ethanol. This is done by very slowly pipetting the ethanol on 

the center of the filter. Capillary action will distribute the ethanol over the entire 

surface. The Areagent blank@ tube will not contain a filter. Add the 100 FL of 

ethanol directly to the bottom of the tube. 

Note: Before proceeding, visually inspect each filter to be sure that the entire filter 

surface is wet. 

5. Using a calibrated automatic pipette, add 25.0 mL of deionized water to each 

extraction tube. The deionized water must have a resistance of at least 18.2MΩ-cm. 

6. Recap all extraction tubes tightly to prevent leakage during the extraction 

procedure. Be sure that the exposed area of the filter is completely immersed in the 

extraction solution. 

7. Place the extraction rack in the ultrasonic bath. Make sure that the water level of the 

ultrasonic bath is higher than the extraction solution level but below the screw cap. 

CAUTION: Monitor the bath temperature during sonication. The temperature 

should not exceed 27EC. Add ice initially to lower the temperature, 

and add ice as necessary during the sonication to maintain an 

acceptable temperature. 

8. Install the extraction racks on the mechanical shaker and shake overnight in a cold 

room (≤4EC) at approximately 60 cycles per minute. 

9. Record the date of extraction on the RTI Sample Log Form. 

10. Store the extracted filters in the refrigerator prior to analysis. 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 11 of 12 

1.15 IC Procedure 

1. Fill the eluent reservoirs with the eluent and the regenerant reservoirs with 

regenerant and pressurize the reservoirs. 

2. Start the eluent flow at 1.5 mL/min, and if using a self-regenerating suppressor, 

activate it. Allow the baseline to stabilize. 

3. Inject two deionized water blanks to flush the system and to ensure that the system 

is operating properly. 

4. Using the calibration schedule, perform the daily multipoint calibration over the 

range 0.05 to 25.0 ppm NO3

-

 and SO4

2- followed by QA/QC samples listed below. 

 A QC sample containing concentrations of NO3

-

 and SO4

2- typical of those 

found in the mid-range of actual filter extract concentrations (QC-MED). 

 A QC sample containing concentrations of NO3

-

 and SO4

2- typical of those 

found at the lower end of actual filter extract concentrations (QC-LOW). 

 A commercially prepared, NIST-traceable QA sample containing known 

concentrations of NO3

-

 and SO4

2- (QA-CPI_LOW). 

 If the observed value for nitrate or sulfate differs by more than 10% from the 

known values, identify and correct the problem before analyzing samples. 

5. Remove sample extracts from the refrigerator and allow to equilibrate to room 

temperature (Note: This should be performed while the system is stabilizing and the 

calibration is being conducted.) 

6. Load the sample extracts into the autosampler vials according to the schedule 

prepared for that day. Typically, 50 field samples are analyzed per day. The daily 

schedule includes, at a minimum, 3 duplicate samples, 2 spiked samples, and 5 

QA/QC samples. 

7. Begin the analysis run, occasionally checking to ensure that the system is operating 

properly. 

8. Examine the data at the end of the run. If the concentration of any ion exceeds the 

upper end of the calibration curve, dilute the sample appropriately and include with 

the samples to be analyzed the following day. 

1.16 Calculations and Data Reduction 

Peak areas are entered into the computer where calculations are performed using a quadratic fit 

to the calibration data. The quadratic fit yields the following: 
PM2.5 Anion Analysis 

Revision 7 

Date: August 26, 2009 

Page 12 of 12 

 yi = axi

2

 + bxi + c 

where: 

y = the calculated anion concentration, μg/L 

x = the instrument response 

Initially, the calibration curve from 0.05 to 10.0 ppm is used for the calculation of the extract 

nitrate and sulfate concentrations. All sulfate and/or nitrate concentrations that exceed 10 ppm 

are recalculated with the 25.0 ppm standard added to the calibration curve. If a recalculated 

nitrate or sulfate concentration exceeds 25 ppm, the extract is diluted appropriately (usually 

5-fold) to bring the ion concentration into the calibration range and reanalyzed. 

2.0 Quality Assurance and Quality Control 

Compare the regression parameters (a, b, c, and correlation coefficient) for the standard curves 

with those obtained in the past. If they exceed the control limits, stop the analysis and identify 

the problem. 

Analyze QA/QC samples (see Sections 1.10 and 1.11) at the beginning of every analytical run. 

Compare the results with those obtained during previous QA/QC tests. If the observed 

concentration of any ion differs from the known value by greater than 10%, stop the analysis 

until the problem is identified and corrected. Analyze a duplicate sample, a QA/QC sample, and 

a spiked sample after at least every 20 field samples.