Method (0.2 to 6.0 mg/l Fe) TNTplus 858

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2 , Phenanthroline Method 1 DOC Method (0.2 to 6.0 mg/l Fe) TNTplus 858 Scope and Application: For drinking water and wastewater. Digestion may be required for determining total iron. 1 Adapted from Standard Methods for the Examination of Water and Wastewater. Test preparation How to use instrument-specific information The Instrument-specific information table displays requirements that may vary between instruments. To use this table, select an instrument then read across to find the corresponding information required to perform this test. Table 1 Instrument-specific information Instrument Light shield Adapter DR 5000 DR 2800 LZV646 Before starting the test: DR 2800: Install the light shield in Cell Compartment #2. Read the safety information and expiration date on the package label. Color or turbidity in the sample can cause incorrect results. To correct for color or turbidity, measure a Sample blank. Perform this test at C (59 77 F) and store reagents at 2 8 C (35 46 F) for best results. The recommended sample ph is A sample digestion may be necessary to measure undissolved iron or iron bound in complexes. The digestion can be performed with the Metals Prep Set TNT890 or by the USEPA mild or vigorous digestion procedure. TNTplus methods are activated from the Main Menu when a vial is inserted into the sample cell holder. Collect the following items: Description Quantity Light Shield (see Instrument-specific information) 1 Iron TNT858 Reagent Set 1 Pipette, variable volume, 1-5 ml 1 Pipette Tips for 1-5 ml Pipette 1 Disposable wipes 1 See Consumables and replacement items for reorder information. Page 1 of 4

3 Iron TNTplus method 1. Pipet 2.0 ml of sample into the vial. 2. Cap and invert the vial until the contents are completely dissolved. 3. Wait 15 minutes. 4. After the timer expires, wipe the sample vial and insert it into the cell holder. The instrument reads the barcode, selects the method and makes the measurement. No zero is necessary. Results are in mg/l Fe. Interferences Ions that do not cause an interference up to the concentrations that were tested are shown in Table 2. Combinations of ions were not tested. Table 2 Interfering substances and levels Interfering substance Cadmium, Cd 2+ Calcium, Ca 2+ Carbonate, CO 2-3 Chloride, Cl Chromium, Cr 3+, Cr 6+ Cobalt, Co 2+ Color Copper, Cu 2+ Lead, Pb 2+ Mercury, Hg 2+ Nickel, Ni 2+ Nitrate, NO 3- Potassium, K + Sodium, Na + Silver, Ag + Sulfate, SO 2-4 Tin, Sn 2+ Turbidity Zinc, Zn 2+ Interference levels and treatments No effect at 70 mg/l. No effect at 1000 mg/l. Can cause high results. To make a correction for the interference, measure a Sample blank. No effect at 10 mg/l. Higher concentrations cause high results. No effect at 25 mg/l. Higher concentrations cause high results. No effect at 100 mg/l. No effect at 1000 mg/l. No effect at 5 mg/l. Higher concentrations cause high results. Can cause high results. To make a correction for the interference, measure a Sample blank. Page 2 of 4

4 Sample blank If the sample has color or turbidity, measure a sample blank to correct the test result for the interference. Required: TNTplus 919 sample blank vial Procedure 1. Complete the test procedure for iron. 2. Pipet 2.0 ml of fresh sample into a TNTplus 919 sample blank vial. 3. Wipe the vial and insert it into the cell holder. The instrument will read the barcode of the sample blank vial and subtract the value from the original test result. Sample collection, preservation and storage Accuracy check Collect samples in acid-cleaned glass or plastic containers. No acid addition is necessary if analyzing the sample immediately. To preserve samples, adjust the ph to 2 or less with concentrated nitric acid (about 2 ml per liter). Preserved samples may be stored up to six months at room temperature. Before analysis, adjust the ph to between 3 and 5 with 5.0 N Sodium Hydroxide Standard Solution. Correct the test result for volume additions. If only dissolved iron is to be determined, filter the sample before acid addition. To validate the method, use a standard solution in place of the sample. The standard solution must be prepared by dilution. Required for accuracy check * : Iron Standard Solution, 100 mg/l Fe Volumetric Flask, 100-mL glass Pipet, variable volume Pipet tip Deionized water Standard solution method 1. Prepare a 2.00-mg/L Fe standard solution as follows: a. Use a pipet to add 2.0 ml of the 100-mg/L standard solution into the volumetric flask. b. Dilute to the mark with deionized water. Stopper and mix well. Prepare this solution daily. 2. Follow the test procedure to measure the concentration of the diluted standard (refer to the Iron TNTplus method). Use the diluted standard solution in place of the sample. 3. Compare the measured concentration to the expected concentration. Acceptable results are typically within 10% of the expected. * See Optional reagents and apparatus. Page 3 of 4

5 Summary of method Ferrous iron (Fe 2+ ) forms an orange-red complex with the 1,10-phenanthroline indicator in the reagent. Any ferric iron (Fe 3+ ) present in the water sample is reduced to ferrous iron (Fe 2+ ) by ascorbic acid before the complex is formed. Test results are measured at 510 nm. Consumables and replacement items Required reagents Description Quantity/Test Unit Catalog number Iron TNT 858 Reagent Set 1 25/pkg TNT858 Required apparatus Light Shield (DR2800) each LZV646 Pipet, variable volume, ml each BBP065 Pipet Tips, for variable volume pipet 75/pkg BBP068 Wipes, disposable, 11 x 22 cm 280/pkg Recommended standards and apparatus Iron Standard Solution, 100 mg/l 100 ml Iron Standard Solution, 1 mg/l 500 ml Water, deionized 4L Optional reagents and apparatus Flask, volumetric, Class A, glass, 100 ml, w/ stopper each Nitric Acid, ACS 500 ml Sodium Hydroxide, 5.0 N 100 ml TNT 890 Metals Prep Set for digestions 50/pkg TNT890 TNTplus 919 sample blank vials 5/pkg TNT919 FOR TECHNICAL ASSISTANCE, PRICE INFORMATION AND ORDERING: In the U.S.A. Call toll-free Outside the U.S.A. Contact the HACH office or distributor serving you. On the Worldwide Web techhelp@hach.com HACH COMPANY WORLD HEADQUARTERS Telephone: (970) FAX: (970) Hach Company, All rights reserved. Printed in the U.S.A. Updated May 2008 Edition 1