DR/4000 PROCEDURE. HARDNESS, Total

Transcription

1 Method 8374 DR/4000 PROCEDURE Calcium and Magnesium; Chlorophosphonazo Colorimetric Method ULR (0 to 1,000 µg/l Ca & Mg as CaCO 3 ) Scope and Application: For ultra pure water. The estimated detection limit for program number 2000 is 4 µg/l. HACH PROGRAM HACH PROGRAM: 2000 Hardness, Tot. ULR. ENTER 1. Press the soft key under HACH PROGRAM. Select the stored program for ultra low range hardness by pressing 2000 with the numeric keys. Press: ENTER Note: If samples cannot be analyzed immediately, see Sample Collection, Storage and Preservationfollowing these steps. Note: The Flow Cell and Sipper Modules cannot be used for this procedure. Plastic sample cells must be used. 2. The display will show: HACH PROGRAM: 2000 Hardness, Tot. ULR The wavelength (λ), 669 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 11, using deionized water as the sample. The value displayed after Step 11 will be the reagent blank value. 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. Rinse a plastic sample cell and the cap three times with the water to be tested. Do not allow the underside of the cap to come in contact with surfaces that may contaminate it. Note: Plastic sample cells must be used. Glass will contaminate the sample. 4. Fill the plastic sample cell to the 25-mL mark with sample. HardnessTot_PP_ULow_CPZ_Eng_4000.fm Page 1 of 6

2 , continued ZERO 5. Add the contents of one Chlorophosphonazo Solution Pillow to the sample cell. Note: A small amount of solution may remain in the pillow. This will not affect results. Note: One ml of Chlorophosphonazo Solution (Cat. No ) may be used instead of the solution pillow. 6. Cap the cell and swirl to mix. 7. Place the sample cell into the cell holder. Close the light shield. 8. Press the soft key under ZERO. The display will show: 0 µg/l CaCO 3 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. Remove the cell from the instrument. Add one drop of CDTA Reagent for Ultra Low Range Hardness. Note: Complete steps within 1-2 minutes. 10. Cap the cell and swirl to mix. 11. Place the sample cell into the cell holder. Close the light shield. The result in µg/l as CaCO 3 (or chosen units) will be displayed. Note: The results can be expressed as µg/l calcium (Ca 2+ ) or magnesium (Mg 2+ ). Press the soft key under OPTIONS, then FORM: to scroll through the available options. Page 2 of 6 HardnessTot_PP_ULow_CPZ_Eng_4000.fm

3 , continued Interferences Interference studies were conducted at various hardness levels between 0 and 500 µg/l as CaCO 3. Various cations and anions were evaluated at levels in the range appropriate for ultra pure water applications. An ion is said to interfere when the resulting concentration is changed by ±10%. Table 1 Interfering Substances and Suggested Treatments Interfering Substance Aluminum Ammonium Copper Formaldehyde Nitrate Potassium Silicon Sodium Interference Levels and Treatments Negative interference above 150 µg/l No interference at or below 1000 µg/l Positive interference above 250 µg/l No interference at or below 47,000 µg/l Positive interference above 250 µg/l No interference at or below 1,000 µg/l Positive interference above 1,000 µg/l Negative interference above 79,000 µg/l Sample Collection, Storage and Preservation Do not use glass containers. Collect samples in clean plastic containers, preferably with screw-type closures. Rinse containers several times with the water to be analyzed before collecting final sample. Seal to avoid contamination during transport. Analyze as soon as possible. Accuracy Check Standard Additions Method a. Leave the unspiked sample in the sample cell compartment. Verify that the units displayed are in µg/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 (µg/l), 20,000. d. Press the soft key under ENTRY DONE. e. Obtain a Calcium Chloride Standard Solution, 20,000-µg/L as CaCO 3. f. Use the TenSette Pipet to add 0.1 ml, 0.2 ml and 0.3 ml of standard, respectively to three 25-mL samples and mix each thoroughly. 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 Use the Calcium Chloride Standard Solution 500-µg/L (as CaCO 3 ) listed under OPTIONAL REAGENTS AND STANDARDS. Perform the total hardness procedure as described above. HardnessTot_PP_ULow_CPZ_Eng_4000.fm Page 3 of 6

4 , continued Method Performance To adjust the calibration curve using the reading obtained with the 500-µg/L Calcium Chloride 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 concentration and press ENTER to return to the read screen. See Section Adjusting the Standard Curve for more information. Precision Standard: 100 µg/l Program For more information on determining precision data and method detection limits, refer to Section 1.5. Estimated Detection Limit 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: % Confidence Limits µg/l Program EDL µg/l Portion of Curve Abs Concentration Abs µg/l 500 µg/l µg/l 900 µg/l µg/l See Section Sensitivity Explained for more information. Summary of Method Calcium and magnesium combine equivalently with the chlorophosphonazo III indicator to form a complex which absorbs light very strongly at 669 nm. One drop of the CDTA reagent breaks up this complex, and the resultant decrease in absorbance is related to the amount of calcium and magnesium in the sample (as CaCO 3 ). 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 For information on pollution prevention and waste management, refer to Section 1. Page 4 of 6 HardnessTot_PP_ULow_CPZ_Eng_4000.fm

5 , continued REQUIRED REAGENTS AND STANDARDS Description Cat. No. ULR Hardness Reagent Set (100 tests) Includes: (1) , (1) , (1) , (1) ULR Hardness Reagent Set (500 tests) Includes; (1) , (2) , (1) , (1) Quantity Required Description per test Unit Cat. No. Chlorophosphonazo Indicator Solution Pillows... 1 pillow /pkg CDTA Solution... 1 drop ml SCDB REQUIRED EQUIPMENT AND SUPPLIES Clippers (Shears) for opening solution pillows each DR/ Inch Cell Adapter each Sample Cell, 1-inch, polystyrene w/ cap /pkg OPTIONAL REAGENTS AND STANDARDS Calcium Chloride Standard Solution, 20,000-µg/L as CaCO ml Calcium Chloride Standard Solution, 500-µg/L as CaCO ml Chlorophosphonazo Indicator Solution ml OPTIONAL EQUIPMENT AND SUPPLIES Dispenser, 1.0-mL, Repipet Jr... each DR/4000 Carousel Module Kit... each Pipet, TenSette, 0.1 to 1.0 ml... each Pipet Tips, for TenSette Pipet... 50/pkg HardnessTot_PP_ULow_CPZ_Eng_4000.fm Page 5 of 6

6 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 HACH COMPANY WORLD HEADQUARTERS Telephone: (970) FAX: (970) Hach Company, All rights reserved. Printed in the U.S.A. 6/03 11ed Page 6 of 6 HardnessTot_PP_ULow_CPZ_Eng_4000.fm