DR/4000 PROCEDURE LEAD. 2. The display will show: 3. Fill a 250-mL graduated cylinder to the 250-mL mark with sample.

Transcription

1 Method 8033 DR/4000 PROCEDURE Dithizone Method* (0 to 300 µg/l) Scope and Application: For water and wastewater; USEPA accepted for reporting for wastewater analysis (digestion is required).** See Section 1 for digestion procedure. The estimated detection limit for program number 2200 is 3 µg/l Pb. * Adapted from Snyder, L. J., Analytical Chemistry, (1947) ** Procedure is equivalent to Standard Method 3500-Pb D for wastewater analysis. HACH PROGRAM HACH PROGRAM: 2200 Lead, Dithizone ENTER 1. Press the soft key under HACH PROGRAM. Select the stored program number for lead (Pb) by pressing 2200 with the numeric keys. Press: ENTER Note: If sample cannot be analyzed immediately, see Sample Collection, Storage and Preservationfollowing these steps. Adjust the ph of preserved samples before analysis. Note: The Flow Cell and Sipper Modules cannot be used with this procedure. 2. The display will show: HACH PROGRAM: 2200 Lead, Dithizone The wavelength (λ), 515 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 14, using deionized water as the sample. Zero the instrument on chloroform 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 250-mL graduated cylinder to the 250-mL mark with sample. Note: Clean all glassware with a 1:1 Nitric Acid Solution. Rinse with deionized water. Note: Cloudy and turbid samples may require filtering before running test. Results should be reported as soluble lead. Use a glass membrane filter to avoid loss of lead by adsorption on filter paper. Note: For proof of accuracy, use a 200 µg/l lead standard solution (preparation given in the Accuracy Check section) in place of the sample. 4. Transfer the sample into 500-mL separatory funnel. Lead_PP_Other_DTZ_Eng_4000.fm Page 1 of 8

2 , continued 5. Add the contents of one Buffer Powder Pillow, citrate type for heavy metals. Stopper the funnel. Shake to dissolve. Note: Spilled reagent will affect test accuracy and is hazardous to skin and other materials. 6. Add 50 ml of chloroform to a 50-mL graduated mixing cylinder. Add the contents of one DithiVer Metals Reagent Powder Pillow. Stopper. Invert repeatedly to mix. Pour 30 ml of this dithizone solution into a second graduated cylinder. Note: Use adequate ventilation (i.e. a fume hood). The DithiVer Powder will not all dissolve in the chloroform. For further notes see Dithiver Solution Preparation, Storage and Reagent Blank. 7. Add the 30 ml of the dithizone solution to the separatory funnel. Stopper. Invert. Open stopcock to vent. Close the stopcock and add 5 ml of 5.0 N Sodium Hydroxide Standard Solution. Stopper. Invert. Open stopcock to vent. Close the stopcock and shake the funnel once or twice and vent again. Note: Add a few drops of 5.25 N Sulfuric Acid Standard Solution if the solution turns orange on shaking. The blue-green color will reappear. To avoid higher blanks, repeat procedure on new sample and use less sodium hydroxide in this step. 8. Continue adding 5.0 N Sodium Hydroxide Standard Solution dropwise and shaking the funnel after every few drops until the color of the solution being shaken changes from blue-green to orange. Then add 5 more drops of 5.0 N Sodium Hydroxide Standard Solution. Note: A pink color in the bottom (chloroform) layer at this point does not necessarily indicate lead is present. Only after shaking with potassium cyanide in next step will a pink color in the chloroform layer confirm the presence of lead. Note: Large amounts of zinc cause the color transition at the end point to be indistinct. Note: For more accurate results, adjust the sample to ph using a ph meter, omitting the five additional drops of Sodium Hydroxide Standard Solution. Page 2 of 8 Lead_PP_Other_DTZ_Eng_4000.fm

3 , continued 9. Add 2 heaping 1.0-g scoops of potassium cyanide to the funnel. Stopper. Shake vigorously until the potassium cyanide is all dissolved (about 15 seconds). Note: Wait one minute for the layers to separate. The bottom (chloroform) layer will be pink if lead is present. Warning: Cyanide is a deadly poison. Use a fume hood. Maintain cyanide solutions at ph 11 or greater to prevent formation of cyanide gas. 10. Insert a cotton plug the size of a pea into the delivery tube of the funnel. Slowly drain the bottom (chloroform) layer into a dry 25-mL sample cell. Stopper the sample cell. Note: The lead-dithizone complex is stable for at least 30 minutes if the sample cell is kept tightly capped and out of direct sunlight. 11. Fill another sample cell with chloroform (the blank). Stopper. 12. Place the blank into the cell holder. Close the light shield. ZERO 13. Press the soft key under ZERO. The display will show: 0.00 µg/l Pb 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. 14. Place the prepared sample into the cell holder. Close the light shield. The results in µg/l lead (or chosen units) will be displayed. Note: See Dithiver Solution Preparation, Storage and Reagent Blank for information on preparing a reagent blank. Note: See Pollution Prevention and Waste Management for proper disposal of chloroform solutions. Lead_PP_Other_DTZ_Eng_4000.fm Page 3 of 8

4 , continued Interference The following do not interfere: Aluminum Calcium Magnesium Antimony Chromium Manganese Arsenic Cobalt Nickel Cadmium Iron Zinc Interfering Substance Bismuth Copper Mercury Silver Tin Highly buffered samples or extreme sample ph Interference Levels and Treatments May exceed the buffering capacity of the reagents and require sample pretreatment; see Section ph Interference. Eliminate interference from the metals listed above by the following treatment, beginning after procedure Step 6. a. Measure about 5 ml of the prepared dithizone solution into the separatory funnel. Stopper the funnel, invert and open the stopcock to vent. Close the stopcock and shake the solution vigorously for 15 seconds. Allow the funnel to stand undisturbed until the layers separate (about 30 seconds). A yellow, red, or bronze color in the bottom (chloroform) layer confirms the presence of interfering metals. Draw off and collect the bottom (chloroform) layer for proper disposal. b. Repeat extraction with fresh 5-mL portions of prepared dithizone solution (collecting the bottom layer each time in appropriate waste collection vessel) until the bottom layer shows a pure dark green color for three successive extracts. Extractions can be repeated a number of times without appreciably affecting the amount of lead in the sample. c. Extract the solution with several 2 or 3 ml portions of pure chloroform to remove any remaining dithizone, again collecting the bottom layer each time for proper disposal. d. Continue the procedure, substituting 28.5 ml of prepared dithizone solution for the 30 ml in Step 7. Dithiver Solution Preparation, Storage and Reagent Blank Store DithiVer Powder Pillows away from light and heat. A convenient way to prepare this solution is to add the contents of 10 DithiVer Metals Reagent Powder Pillows to a 500-mL bottle of chloroform and invert several times until well mixed (carrier powder may not dissolve). Store dithizone solution in an amber glass bottle. This solution is stable for 24 hours. A reagent blank using deionized water should be carried out through the entire method to obtain the most accurate results. The amount of reagent blank determined on each lot of DithiVer Metals Reagent Powder Pillow can be subtracted automatically from the sample reading by pressing the soft keys under Page 4 of 8 Lead_PP_Other_DTZ_Eng_4000.fm

5 , continued OPTIONS, (MORE) and then BLANK: (OFF). Enter the blank value and press ENTER to return to the read screen. Sample Collection, Storage and Preservation Collect samples in acid-cleaned glass or plastic containers. Adjust the ph to 2 or less with nitric acid (about 2 ml per liter). Preserved samples can be stored up to six months at room temperature. Before analysis, adjust the ph to with 5.0 N Sodium Hydroxide. Correct the test result for volume additions; see Section Correcting for Volume Additions. 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), 250. c. Press ENTER to accept the default standard concentration (µg/l), 50,000 (equivalent to 50-mg/L). d. Press the soft key under ENTRY DONE. e. Snap the neck off a Lead Voluette Ampule Standard, 50-mg/L Pb. f. Use the TenSette Pipet (do not use a glass pipet) to add 0.1 ml, 0.2 ml and 0.3 ml of standard, respectively to three 250-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 Prepare a 10-mg/L lead standard solution by pipetting ml of Lead Standard Solution, 100-mg/L, into a 100-mL volumetric flask. Add 0.2 ml of concentrated nitric acid using a TenSette Pipet to prevent the adsorption of lead onto the container walls. Dilute to the mark with deionized water and mix thoroughly. To make a 200-µg/L standard, pipet 5.00 ml of the 10.0-mg/L standard into 245 ml of deionized water in the 500-mL separatory funnel in Step 4 of the Dithizone procedure. Prepare these solutions daily. Perform the lead procedure as described above. To adjust the calibration curve using the reading obtained with the 200-µg/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 concentration and press enter to return to the read screen. See Section Adjusting the Standard Curve for more information. Lead_PP_Other_DTZ_Eng_4000.fm Page 5 of 8

6 , continued Method Performance Precision Standard: 200 µg/lpb 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 Pb Program EDL µg/l Pb Portion of Curve Abs Concentration Abs µg/l 150 µg/l µg/l 270 µg/l µg/l See Section Sensitivity Explained for more information. Calibration Standard Preparation To perform a lead calibration using the Dithizone method, prepare a 10,000-µg/L lead stock solution by pipetting ml of a 100-mg/L Lead Standard Solution (Cat. No ) into a 100-mL volumetric flask using Class A glassware. Add 0.2 ml of concentrated nitric acid using a TenSette pipet to prevent the adsorption of lead onto the container walls. Dilute to the mark with deionized water and mix thoroughly. Prepare calibration standards containing 40, 80, 120, 160, 200, 240, 280, and 300 µg/l lead as follows: a. Prepare the standards in 500-mL separatory funnels to minimize lead loss in intermediate glassware due to adsorption. b. Into eight different 500-mL separatory funnels, pipet 1, 2, 3, 4, 5, 6, 7, and 8 ml of the 10,000-µg/L lead stock solution using Class A glassware. Add enough deionized water to bring the final volume to exactly 250 ml. For example, use 3 ml of the 10,000-µg/L lead stock solution and 247 ml of deionized water to prepare the 120-µg/L standard. c. Using the Dithizone 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. Page 6 of 8 Lead_PP_Other_DTZ_Eng_4000.fm

7 , continued Summary of Method The DithiVer Metals Reagent is a stable powder form of dithizone. Lead ions in basic solution react with dithizone to form a pink to red lead-dithizonate complex, which is extracted with chloroform. 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 Both chloroform (D022) and cyanide (D003) solutions are regulated as hazardous wastes by the Federal RCRA. Do not pour these solutions down the drain. Chloroform solutions and the cotton plug used in the delivery tube of the separatory funnel should be collected for disposal with laboratory solvent waste. Collect the cyanide solution as a reactive waste. Be sure that cyanide solutions are stored in a caustic solution with a ph >11 to prevent potential release of hydrogen cyanide gas. See Section 3 for more information on proper disposal of these materials. REQUIRED REAGENTS AND STANDARDS Cat. No. Lead Reagent Set (100 Tests) Includes: (1) , (2) , (1) , (2) , (1) , (2) , (1) Quantity Required Description per test Unit Cat. No. Buffer Powder Pillows, Citrate... 1 pillow /pkg Chloroform ml...4 L DithiVer Metals Reagent Powder Pillows... 1 pillow /pkg Potassium Cyanide, ACS... 2 g g Sodium Hydroxide Solution, 5.0 N... 5 ml ml Sodium Hydroxide Standard Solution, 5.0 N...varies ml DB REQUIRED EQUIPMENT AND SUPPLIES QuantityRequired Description per test Unit Cat. No. Clippers, for opening powder pillows each Cotton balls, absorbent /pkg Cylinder, graduated mixing, 50-mL each Cylinder, graduated, 5-mL each Cylinder, graduated, 50-mL each Cylinder, graduated, 250-mL each DR/ Inch Cell Adapter each Funnel, separatory, 500-mL each ph Meter, sension 1, portable each Ring, support, 4-inch each Sample Cells, matched pair, 1-inch, glass, with stoppers pair Spoon, measuring, 1.0-g each Support, Ring Stand, 5 x 8 in. base each Lead_PP_Other_DTZ_Eng_4000.fm Page 7 of 8

8 , continued OPTIONAL REAGENTS AND STANDARDS Description Unit Cat. No. Chloroform, ACS ml Lead Standard Solution, 100 mg/l Pb ml Lead Standard Solution, 10-mL Voluette Ampules, 50-mg/L Pb... 16/pkg Nitric Acid Solution, 1: ml Nitric Acid, ACS ml Sodium Hydroxide Standard Solution, 5.0 N ml SCDB Sodium Hydroxide Standard Solution, 5.0 N ml MDB Sulfuric Acid, 5.25 N ml MDB Water, deionized... 4 liters OPTIONAL EQUIPMENT AND SUPPLIES Ampule Breaker Kit... each DR/4000 Carousel Module Kit... each Filter Discs, glass membrane, 47-mm /pkg Filter Holder, glass, 47-mm... each Flask, Erlenmeyer, 500-mL... each Flask, filtering, 500-mL... each Flask, volumetric, Class A, 100-mL... each ph Paper, ph 1.0 to rolls/pkg Pipet Filler, safety bulb... each Pipet, TenSette, 0.1 to 1.0 ml... each Pipet Tips, for TenSette Pipet... 50/pkg Pipet, serological, 2-mL... each Pipet, volumetric, Class A, 1.00-mL... each Pipet, volumetric, Class A, 2.00-mL... each Pipet, volumetric, Class A, 3.00-mL... each Pipet, volumetric, Class A, 4.00-mL... each Pipet, volumetric, Class A, 5.00-mL... each Pipet, volumetric, Class A, 6.00-mL... each Pipet, volumetric, Class A, 7.00-mL... each Pipet, volumetric, Class A, 8.00-mL... each Pipet, volumetric, Class A, mL... each 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 Lead_PP_Other_DTZ_Eng_4000.fm