1,5-Diphenylcarbohydrazide Method* Powder Pillows or AccuVac Ampuls (0 to mg/l Cr 6+ )

Transcription

1 DR/4000 PROCEDURE Method ,5-Diphenylcarbohydrazide Method* Powder Pillows or AccuVac Ampuls (0 to mg/l Cr 6+ ) Scope and Application: For water and wastewater;usepa accepted for reporting for wastewater analyses**. The estimated detection limits for program numbers 1560 and 1570 are and mg/l Cr 6+, respectively. * Adapted from Standard Methods for the Examination of Water and Wastewater. ** Procedure is equivalent to USGS method I for wastewater.. Using Powder Pillows HACH PROGRAM HACH PROGRAM: 1560 Chromium, Hex. ENTER 1. Press the soft key under HACH PROGRAM. Select the stored program for hexavalent chromium (Cr 6+ ) by pressing 1560 with the numeric keys. Press: ENTER Note: If samples cannot be analyzed immediately, see Sample Collection, Preservation, and Storage following these steps. Note: The Flow Cell and Sipper Modules can be used for this procedure. Use a 25-mL sample volume and reagents for the Flow Cell Module. 2. The display will show: HACH PROGRAM: 1560 Chromium, Hex. The wavelength (λ), 540 nm, is automatically selected. Note: For best results, determine a reagent blank for each new lot of reagent as follows. Prepare a reagent blank by repeating Steps 3 through 9, using chromium-free deionized water as the sample. Zero the instrument on deionized water by pressing the soft key under ZERO. Insert the reagent blank and the blank value will be displayed. Correct for the reagent blank by pressing the soft keys under OPTIONS, (MORE), and then BLANK:OFF. Enter the reagent blank value and press ENTER. Repeat for each new lot of reagent. 3. Fill a sample cell with 10 ml of sample. Note: For proof of accuracy, use a 0.25 mg/l hexavalent chromium standard solution (preparation given in the Accuracy Check section) in place of the sample. Note: For samples with extreme ph, see the Interferences section. 4. Add the contents of one ChromaVer 3 Reagent Powder Pillow to the sample cell (the prepared sample). Swirl to mix. Note: A purple color will form if hexavalent chromium is present. Note: At high chromium levels a precipitate will form. Dilute sample according to Section Sample Dilution Techniques. ChromiumHex_AVPP_Other_DCH_Eng_4000.fm Page 1 of 8

2 , continued START TIMER ZERO 5. Press the soft key under START TIMER. An 8-minute reaction period will begin. 6. Fill another sample cell with 10 ml of sample (the blank). Note: For turbid samples, treat the blank with the contents of one Acid Reagent Powder Pillow. This will ensure any turbidity dissolved by the acid in the ChromaVer 3 Chromium Reagent also will be dissolved in the blank. 7. When the timer beeps, place the blank into the cell holder. Close the light shield. 8. Press the soft key under ZERO. The display will show: mg/l Cr 6+ Note: If you are using a reagent blank correction, the display will show the correction. Note: For alternate concentration units, press the soft key under OPTIONS. Then press the soft key under UNITS to scroll through the available options. Press ENTER to return to the read screen. 9. Place the prepared sample into the cell holder. Close the light shield. Results in mg/l hexavalent chromium (Cr 6+ ) will be displayed. Note: Results may be expressed as chromate (CrO 2-4 ) or as sodium chromate (Na 2 CrO 4 ), or dichromate (Cr 2 O 7 2-). Press the soft keys under OPTIONS and then FORM: to scroll through the available options. Press ENTER to return to the read screen. Page 2 of 8 ChromiumHex_AVPP_Other_DCH_Eng_4000.fm

3 , continued Using AccuVac Ampuls HACH PROGRAM HACH PROGRAM: 1570 Chromium, Hex. AV ENTER 1. Press the soft key under HACH PROGRAM. Select the stored program for hexavalent chromium (Cr 6+ ) by pressing 1570 with the numeric keys. Press: ENTER Note: If samples cannot be analyzed immediately, see Sample Collection, Preservation, and Storage following these steps. 2. The display will show: HACH PROGRAM: 1570 Chromium, Hex. AV The wavelength (λ), 540 nm, is automatically selected. Note: For best results, determine a reagent blank for each new lot of reagent as follows. Prepare a reagent blank by repeating Steps 3 through 10, using chromium-free deionized water as the sample. Zero the instrument on deionized water by pressing the soft key under ZERO. Insert the reagent blank and the blank value will be displayed. Correct for the reagent blank by pressing the soft keys under OPTIONS, (MORE), and then BLANK:OFF. Enter the reagent blank value and press ENTER. Repeat for each new lot of reagent. Note: For sample with extreme ph, see the Interferences section. 3. Fill the zeroing vial with at least 10 ml of sample (the blank). Collect at least 40 ml of sample in a 50-mL beaker. Note: For turbid samples, treat 25 ml of the blank with the contents of one Acid Reagent Powder Pillow. This will ensure any turbidity dissolved by the acid in the ChromaVer 3 Chromium Reagent also will be dissolved in the blank. Note: For proof of accuracy, use a 0.25 mg/l hexavalent chromium standard solution (preparation given in the Accuracy Check section in place of the sample. 4. Insert the AccuVac Adapter into the sample cell module by sliding it under the thumb screw and into the alignment grooves. Fasten with the thumb screw. ChromiumHex_AVPP_Other_DCH_Eng_4000.fm Page 3 of 8

4 , continued START TIMER 5. Fill a ChromaVer 3 Reagent AccuVac Ampul with sample (the prepared sample). Note: Keep the tip immersed while the ampul fills completely. 6. Quickly invert the ampul several times to mix. Wipe off any liquid or fingerprints. Note: A purple color will form if hexavalent chromium is present. 7. Press the soft key under START TIMER. An 8-minute reaction period will begin. 8. When the timer beeps, place the blank into the cell holder. Close the light shield. ZERO 9. Press the soft key under ZERO. The display will show: mg/l Cr 6+ Note: If you are using a reagent blank correction, the display will show the correction. Note: For alternate concentration units, press the soft key under OPTIONS. Then press the soft key under UNITS to scroll through the available options. Press ENTER to return to the read screen. 10. Place the prepared sample into the cell holder. Close the light shield. Results in mg/l hexavalent chromium (Cr 6+) will be displayed. Note: Results may be expressed as chromate (CrO 4 2-) or as sodium chromate (Na 2 CrO 4 ), or dichromate (Cr 2 O 7 2-). Press the soft keys under OPTIONS and then FORM: to scroll through the available options. Press ENTER to return to the read screen. Page 4 of 8 ChromiumHex_AVPP_Other_DCH_Eng_4000.fm

5 , continued Interferences Table 1 Interfering Substances and Suggested Treatments Interfering Substance Iron Mercurous & Mercuric Ions ph Vanadium Interference Levels and Treatments May interfere above 1 mg/l Interferes slightly Highly buffered samples or extreme sample ph may exceed the buffering capacity of the reagents and require sample pretreatment; see Section ph Interference. May interfere above 1 mg/l. Wait 10 minutes before reading. Sample Collection, Preservation, and Storage Collect samples in a cleaned glass or plastic container. Store at 4 C (39 F) up to 24 hours. Samples must be analyzed within 24 hours. Accuracy Check Standard Additions Method a. Leave the unspiked sample in the sample cell compartment. Verify that the units displayed are in mg/l. Select standard additions mode by pressing the soft keys under OPTIONS, (MORE) and then STD ADD. b. Press ENTER to accept the default sample volume (ml), 25. c. Press ENTER to accept the default standard concentration (mg/l), d. Press the soft key under ENTRY DONE. e. Snap the neck off a Chromium Voluette Ampule Standard, 12.5-mg/L Cr 6+. f. Use the TenSette Pipet to add 0.1, 0.2 and 0.3 ml of standard, respectively to three 25-mL samples and mix each thoroughly (for AccuVac Ampuls, use 50-mL beakers). g. Analyze each standard addition sample as described above. Accept the standard additions reading by pressing the soft key under READ each time. Each addition should reflect approximately 100% recovery. h. After completing the sequence, the display will show the extrapolated concentration value and the best-fit line through the standard additions data points, accounting for matrix interferences. i. See Section Standard Additions for more information. Standard Solution Method Prepare a 0.25-mg/L Cr 6+ standard solution by pipetting 5.00 ml of Hexavalent Chromium Standard Solution, 50-mg/L, into a 1000-mL volumetric flask. Dilute to the mark with deionized water. Prepare this solution daily. Perform the hexavalent chromium procedure as described above. To adjust the calibration curve using the reading obtained with the 0.25-mg/L standard solution, press the soft keys under OPTIONS, MORE then STD: OFF. Press ENTER to accept the displayed concentration, the value of which depends on the selected units. If an alternate concentration is used, enter the actual ChromiumHex_AVPP_Other_DCH_Eng_4000.fm Page 5 of 8

6 , continued Method Performance concentration and press ENTER to return to the read screen. See Section Adjusting the Standard Curve for more information. Precision Standard: 0.25 mg/l Cr 6+ Program 95% Confidence Limits mg/l Cr mg/l Cr 6+ For more information on determining precision data and method detection limits, refer to Section 1.5. Estimated Detection Limit Program For more information on derivation and use of Hach s estimated detection limit, see Section To determine a method detection limit (MDL) as defined by the 40 CFR part 136, Appendix B, see Section Sensitivity Program Number: 1560 EDL mg/l mg/l Portion of Curve Abs Concentration Entire Range mg/l Program Number: 1570 Portion of Curve Abs Concentration Entire Range mg/l See Section Sensitivity Explained for more information. Page 6 of 8 ChromiumHex_AVPP_Other_DCH_Eng_4000.fm

7 , continued Calibration Standard Preparation To perform a hexavalent chromium calibration using the 1,5-Diphenylcarbohydrazide method, prepare a 5.0-mg/L chromium stock solution by pipetting 10.0 ml of a 50-mg/L Chromium Hexavalent Standard Solution into a 100-mL volumetric flask using Class A glassware. Dilute to the mark with deionized water and mix thoroughly. Prepare calibration standards containing 0.05, 0.30, and 0.60 mg/l Cr 6+ as follows: a. Into three different 100-mL Class A volumetric flasks, pipet 1.00, 6.00, and ml of the 5.0 mg/l Cr 6+ stock solution using Class A glassware. b. Dilute to the mark with deionized water and mix thoroughly. c. Using the 1,5-Diphenylcarbohydrazide method and the calibration procedure described in the User-Entered Programs section of the DR/4000 Spectrophotometer Instrument Manual, generate a calibration curve from the standards prepared above. Summary of Method Hexavalent chromium is determined by the 1,5-Diphenylcarbohydrazide method using a single dry powder formulation called ChromaVer 3 Chromium Reagent. This reagent contains an acidic buffer combined with 1,5-Diphenylcarbohydrazide, which reacts to give a purple color when hexavalent chromium is present. Safety Good safety habits and laboratory techniques should be used throughout the procedure. Consult the Material Safety Data Sheet for information specific to the reagents used. For additional information, refer to Section 1. Pollution Prevention and Waste Management The final samples are highly acidic. Neutralize to ph 6 9 and flush down the drain for disposal. For more information on pollution prevention and waste management, refer to Section 1. ChromiumHex_AVPP_Other_DCH_Eng_4000.fm Page 7 of 8

8 , continued REQUIRED REAGENTS AND STANDARDS (Using Powder Pillows) Quantity Required Description per test Unit Cat. No. ChromaVer 3 Chromium Reagent Powder Pillows... 1 pillow /pkg REQUIRED REAGENTS AND STANDARDS (Using AccuVac Ampuls) ChromaVer 3 AccuVac Ampuls... 1 ampul... 25/pkg REQUIRED EQUIPMENT AND SUPPLIES (Using Powder Pillows) DR/ Inch Cell Adapter each REQUIRED EQUIPMENT AND SUPPLIES (Using AccuVac Ampuls) Beaker, 50-mL each DR/4000 AccuVac Adapter each Sample Cell, 10-mL with cap (zeroing vial) each OPTIONAL REAGENTS AND SUPPLIES Description Unit Cat. No. Acid Reagent Powder Pillows... 50/pkg Chromium, Hexavalent, Standard Solution, 50-mg/L Cr ml h Chromium, Hexavalent, Standard Solution, 10-mL Voluette Ampules, 12.5-mg/L Cr /pkg Chromium, Hexavalent, Standard Solution, 2-mL ampule, 5.0-mg/L Cr /pkg Nitric Acid, ACS ml Nitric Acid Solution, 1: ml Sodium Hydroxide Standard Solution, 5.0 N ml* DB Water, deionized... 4 liters OPTIONAL EQUIPMENT AND SUPPLIES AccuVac Snapper Kit... each Ampule Breaker Kit... each DR/4000 Carousel Module Kit... each DR/4000 Flow Cell Module Kit, 1-inch... each DR/4000 Flow Cell Module Kit, 1-cm... each DR/4000 Sipper Module Kit, 1-inch... each Flask, volumetric, Class A, 25-mL... each Flask, volumetric, Class A, 1000-mL, with glass stopper... each ph Paper, ph 1.0 to rolls/pkg ph Meter, sension 1, portable... each Pipet, serological, 2-mL... each Pipet, TenSette, 0.1 to 1.0 ml... each Pipet Tips, for TenSette Pipet... 50/pkg Pipet, volumetric, Class A, 1.00-mL... each Pipet, volumetric, Class A, 5.00-mL... each Pipet, volumetric, Class A, 6.00-mL... each Pipet, volumetric, Class A, mL... each Pipet Filler, safety bulb... each Sample Cells, 1-inch, matched pair... 2/pkg * Contact Hach for larger sizes. 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. 6/03 11ed Page 8 of 8 ChromiumHex_AVPP_Other_DCH_Eng_4000.fm