Tri-State Laboratories Inc.

Standard Operating Procedure

Procedure No.:4400Revision Date:8/2001

Subject: (EPA 353.2) Nitrates-Nitrites for Public Drinking Water Analysis

Approved By:

Laboratory Director______

Bari Lateef, Ph.D.Date

Dept. Supervisor______

John PflughDate

QA Coordinator ______

Scott Bolam Date

Nitrates-Nitrites in Public Drinking Water

Method EPA 353.2

Description

This method is used to determine nitrate-nitrite in public drinking water. NO3- is reduced to NO2- by passage through a copperized cadmium column, which is then measured colorimetrically. Public drinking water samples are reported as a combined total of NO3-NO2 according to EPA guidelines. NO2 can be determined individually on an unpreserved sample by removing the cadmium column.

Sample Preservation

  • Samples must be collected in a clean glass or plastic screw top container (250-1000 mL).
  • Preserve with concentrated H2SO4 to obtain a pH of less than 2 and refrigerate at 2-10 C. The sample must be checked for preservation prior to 48 hours after collection.
  • Holding time for preserved samples is 28 days.

Interferences

Suspended matter in column can restrict sample flow. Filter turbid samples. Concentrations of iron, copper, or other metals above several mg/L can lower reduction efficiency. High amounts of residual chlorine can interfere by oxidizing the cadmium column, reducing its efficiency.

Apparatus and Materials

  • Lachat QuickChem AE Automated Analyzer/XYZ Sampler/Pump
  • Lachat Nitrate board with Cadmium column
  • Nitrate 17 cm sample loop
  • 520 nm flow cell
  • 13 x 100 mm test tubes
  • Class “A” volumetric flasks and pipets for standard and reagent preparation.
  • 1000 mL Erlenmeyer flask

Reagents and Standards

  • Stock nitrate solution (1000 ppm), obtained commercially.
  • Nitrate working standard (10 ppm):

Dilute 1 ml stock nitrate solution to 100 mL with deionized water.

  • Chloroform
  • Stock nitrite solution (100 ppm):

In a 1-L volumetric flask, dissolve 0.493 g sodium nitrite (NaNO2) in approximately 800 mL of water. Add 2 mL of chloroform. Dilute to the mark and refrigerate.

  • 1.0 mg/L NO2 column efficiency check standard:

Dilute 1 mL of stock NO2 solution to 100 mL with deionized water.

  • QC check standard obtained commercially. For example, quality control samples from Environmental Resource Associates.
  • Following prepartion instuctions for the commercially available QC standards prepare a low-range check standard (approx. 0.10 mg/L) and a high range check standard (approx. 1.0 mg/L).
  • Deionized water, degassed with Helium: obtain water that has been degassed with helium, fill a 1000-mL Erlenmeyer flask.
  • 10 N sodium hydroxide:
  • Ammonium Chloride buffer, pH = 8.5:

In a 1 L volumetric flask, dissolve 85.0 g of ammonium chloride (NH4CL) and 1.0 g disodium ethylenediamine tetracetic acid dihydrate (Na2EDTA*2H2O) in approximately 800 mL of deionized water. Adjust pH up to 8.5 with 10 N sodium hydroxide. Dilute to mark.

  • Sulfanilamide color reagent:

In a 1 L volumetric flask add about 600 mL of water. Then add 100 mL of 85% phosphoric acid (H3PO4), 40.0 g sulfanilamide, and 1.0 g

N-(1-naphthyl)ethylenediamine dihydrochloride (NED). Shake to wet, stir and dissolve for 30 minutes. Dilute to mark. Store in dark bottle, solution is stable for 1 month.

Procedure:

  1. Installing the NO3 board:

The follwing procedures are general guidelines for installing the NO3 board and column. For further information, consult the Lachat QuikChem AE methods manual and Lachat QuickChem AE operations manual.

1.1.Place the board on Channel Two (Front Channel). Remove the carrier hose and union connector from the hose going to the board.

1.2.Connect this union connector to the empty hose on port 2 of the valve.

1.3.Connect the line the carrier hose was removed from to the union fitting going to port 3 of the valve.

1.4.The carrier hose should now be going to port 2 of the valve. The board should be connected to port 3 of the valve.

1.5.Connect the 17 cm NO3 sample loop across port 1 and 4 of the valve.

1.6.Place the 520 flow cell into the detector.

1.7.Connect the empty hose at the end of the second 2” coil on the board to the union fitting going to the flow cell.

1.8.Place hoses across the pump; Snap hoses down with pump cartridges, leaving cartridge tension loose.

1.9.Place hoses in their proper reagents; hoses should be marked according to which reagent they go to. The carrier line is placed in helium degassed water. An additional rinse line (green-green hose) is also placed in the degassed water.

1.10.Turn on the pump; use the override standby button to pump at full speed. Check hoses for flow; tighten tension on the pump cartridges until all reagents are flowing smoothly and continuously. DO NOT connect the cadmium column at this time. After all reagents are flowing, press the override standby button again to return pump to standby speed.

  1. Connecting the cadmium column:

2.1.After all the reagents are flowing through, and all air bubbles have been flushed out of the reagent lines, it is time to connect the cadmium column. DO NOT allow air bubbles into the cadmium column, as this will reduce the life and effectiveness of the column.

2.2.On the left-most union fitting on the column, disconnect the hose from the right-end of the connector.

2.3.On the right-most t-junction fitting on the board, disconnect the hose from the right side of the t-junction. The board has a label marked Cd column pointing to the right side of the t-junction. Connect this hose to the left-most union fitting on the column.

2.4.Connect the hose from the right-most union fitting on the column to the right end of the t-junction where the hose was removed in step 2.3.

2.5.Follow the hose connections. Sample and buffer should be pumping into the left-end of the column, flowing through, being reduced to NO2, and out the right end of column. The reduced sample will flow into the right-most t-junction where it will mix with the color reagent before pumping the detector.

2.6.See the following diagram for clarification:

  1. Instrument Calibration
  2. From the Main Menu on the computer, select Methods, then Analysis Select & Download.
  3. Choose the NO3LOW2 method- Nitrate low on channel 2. The method will load and display the Tray Definition & Submit screen.
  4. Prepare the following standards for calibration:

High Range Standards: use 10 ppm working standard to prepare

2.0 mg/L:10 mL 10 ppm working standard → 50 mL

1.0 mg/L:5 mL 10 ppm working standard → 50 mL

0.5 mg/L:2.5 mL 10 ppm working standard → 50 mL

Low Range Standards: use 1.0 mg/L standard prepared with high range standards

0.1 mg/L:5 mL 1.0 mg/L standard → 50 mL

0.05 mg/L:2.5 mL 1.0 mg/L standard → 50 mL

0.02 mg/L:1 mL 1.0 mg/L standard → 50 mL

3.4. Place the six calibration standards and a blank on the Standards Rack in Slots A-G. Note: Samples are placed in the tray from highest to lowest.

3.5. On the Submit menu, select Calibrate Now.

3.6. A calibration will begin. At the end of the calibration, you will be informed if the calibration passed or failed. Calibration passes if the r-value of the curve is 0.995 or greater.

3.7. From the menu, go to Reports. Select the calibration tray just used, and print the report and print the calibration statistics. After printing, return to Tray Definition and Submit.

  1. Running Samples

4.1.After a calibration has been approved, you are ready to run samples. At the Tray Definition and Submit menu, select Edit, then Identification. Enter in the sample numbers and QC standards. Follow the QA/QC requirements for this method to determine what QC standards should be run.

4.2.From the Edit menu, select Replicates. Set 2 replicates on a sufficient number of samples to fulfill the 20% replicate limit of the method.

4.3.Load tray with samples; from Submit, select Submit Current Tray. If an approved calibration has already been done, select N for perform calibration. Select Y to start the tray.

4.4.Tray will be submitted, and the analysis will begin. Use [CTRL]-[SHIFT]-[1] to view real-time analytical results. Use [CTRL]-[SHIFT]-[2] to exit real-time results.

4.5.After the tray has finished it’s analysis, go to Reports. Select the current sample tray and print the results of the report.

  1. Documentation

5.1.Record all calibration information, QC results, and sample results in the Nitrate analytical logbook. The record must be correctly dated and accompanied by the analysts’ initials.

5.2.Document all calibration results and QC checks on Form 4400-A.

5.3.Record standard information: Date Received, Expiration Date, Date Opened, Date Prepared.

5.4.Record any maintenance or replacement of apparatus.

QA/QC Requirements

  • A calibration curve is prepared for each sample run, in the range of 0.02 mg/L to 2.0 mg/L. Correlation coefficient (r-value) should be 0.995 or greater for an acceptable calibration.
  • A blank sample is run at the beginning and end of each sample run. Blank values should be below the Method Detection Limit. If blanks are above the MDL, check for contamination or possible carry-over problem.
  • To determine if the column is working properly, a column efficiency check is performed with each sample run. To peform, run a 1.0 mg/L NO3 standard, and the 1.0 mg/L NO2 standard. Calculate the efficiency with the following equation:

A = Measured mg/L, NO3 standard

B = Mesured mg/L, NO2 standard

The % efficiency must be within 90-110%.

  • Validation of the calibration curve is performed using a high-range and low-range standard prepared from a second standard source. Low-range standard should be <0.10 mg/L; High-range should be > 1.0 mg/L. Acceptability is 90-110%. These two standards should be run at the beginning and end of each sample run. Standard recoveries are calculated as follows:

A = Measured value of check standard

B = Known value of check standard

  • Duplicates are run at a 20% sample frequency. Duplicates calculated as the difference as a percentage of the mean:
  • Precision of low-level duplicates should be within 25%. Precision of high-level duplicates should be within 10%. Low-level refers to less than 20 times the MDL. High-level refers to greater than 20 times the MDL. If less than 5 samples are analyzed, perform at least one duplicate.
  • Matrix spiking, also called known additions, is required at a 10% sample frequency. If the sample is negative (below MDL) the recovery must be 80-120%. For positive samples, recovery must be 85-115%. Poor recoveries can indicate a complex matrix interference. Dilution can be used provided the dilution does not exceed the required minimum reporting limit. If less than 10 samples are analyzed, always do at least one spike. Use the following equation to calculate spike recoveries:

A = Measured value of spiked sample

B = Measured value of unspiked sample

C = Concentration of spike added to sample

  • Continuing calibration verifications (CCV) are required at 10% sample frequency. CCV is performed using 0.50 mg/L standard. It should be within 90-110% of the original calibration.

References:

Standard Methods for the Examination of Water and Wastewater 18th Edition

Ohio EPA Laboratory Manual for Chemical Analyses of Public Drinking Water, 2000 ed.

Lachat QuickChem AE Methods Manual

Lachat QuickChem AE Training Manual

Lachat QuickChem AE Operations Manual

Lachat QuickChem AE Software Reference Manual

Procedure 4200 Procedure 6600

Revised 8/01