Spectrophotometric Determination of Total Iron in EASTMAN Color Films, KUL Bleach

Transcription

1 Spectrophotometric Determination of Total Iron in EASTMAN Color Films, Bleach ECN-0006/1 ECP-0006/1 Process ECN-2 ECP-2D VNF-1/LC RVNP Formulas SB-34/ SR-34R SB-34/ SR-34R INTRODUCTION The determination of total iron in Eastman Color Films, Process ECN-2 or Process ECP-2D, Bleach utilizes a spectrophotometric procedure. Total Iron is determined by oxidizing any iron (II) present to iron (III) with persulfate. A thiocyanate complex of the iron (III) is formed in a dilute acid solution. A direct measurement of the iron-thiocyanate complex is made using a calibrated spectrophotometer with wavelength set at 477 nm. The calibration of the spectrophotometer is described in Appendix A. Use of this method requires handling potentially hazardous chemicals. Consult the Material Safety Data Sheet for each chemical before use. MSDS's are available from your chemical supplier. PRECISION AND BIAS Repeatability To obtain the repeatability data, a single skilled analyst performed five (5) replicates on each of the following solutions during methods development: a. A fresh EASTMAN Color Films, Process ECN-2 or Process ECP-2D, bleach prepared with all components at their respective working tank aim concentrations: g/l total iron for Process ECN g/l total iron for Process ECP-2D b. A seasoned EASTMAN Color Films, Process ECP-2, bleach analyzed as received at: g/l total iron for Process ECN g/l total iron for Process ECP-2D c. The same seasoned solution as in letter b, above, analyzed after making an analytically weighed, standard addition of: g/l total iron for Process ECN g/l total iron for Process ECP-2D Repeatability Deviation, 1s r & (not including bias) Repeatability standard deviation is an estimate of the variability one trained analyst should be able to obtain under favorable conditions (analyzing a sample, with one instrument, within one day). The 95 percent confidence estimate (calculated using the repeatability standard deviation) around a single test will include the mean value 95 percent of the time. ECN-2, (4.946 g/l Total Seasoned with Addition ECP-2, (8.728 g/l Total Seasoned with Addition Repeatability Deviation, 1S r ± ± ± 0.11 Repeatability Deviation, 1S r ± ± ± 0.21 Bias Bias is a statistically significant deviation of the mean from the known mix level at a 95 percent confidence level. It is determined for fresh samples only. Bias is not determined for seasoned samples, since the component concentration level was not determined independently of the test method. No statistically significant bias was found for a Process ECN-2, fresh tank bleach sample. A statistically significant low bias ( 1.5 percent) was found for a Process ECP-2, KUL fresh tank bleach sample. This was judged not to be practically significant. Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H

2 Recovery Recovery is used instead of bias for seasoned samples, since the component concentration level was not determined independently of the test method. It is defined as the calculated mean for the seasoned sample, which contains the standard addition minus the mean of the seasoned sample, divided by the actual amount of the standard addition. It is expressed as a percentage. For the Process ECN-2, KUL fresh tank bleach sample, the recovery (96.8 percent) was not statistically different from 100 percent. For the Process ECP-2, KUL fresh tank bleach sample, the recovery (100.3 percent) was not statistically different from 100 percent. Reproducibility Customer Deviation, 1s c & (not including bias) The customer standard deviation (1s c )is an estimate of the variability a customer could expect when submitting a sample to any Photoprocessing Quality Services laboratory, where any trained analyst could test the sample using any instrument on any day. The 95 percent confidence estimate (calculated using the customer standard deviation) around a single test result will include the mean value 95 percent of the time. Two EASTMAN Color Films, Process ECN-2, bleach samples were analyzed by four trained analysts, using multiple calibrated spectrophotometers, on two different days. Duplicate analyses were performed on each sample, on each of two days. These samples were: a. A fresh tank solution prepared at g/l total iron. b. An EASTMAN Color Films, Process ECN-2, seasoned bleach tank sample analyzed, as received, in the same manner as the fresh bleach. ECN-2, (4.937 g/l Total Reproducibility Deviation, 1S c ± ± 0.15 Three EASTMAN Color Films, Process ECP-2, bleach samples were analyzed by four trained analysts, using multiple calibrated spectrophotometers, on two different days. Duplicate analyses were performed on each sample, on each of two days. These samples were: a. A fresh bleach tank solution prepared at g/l total iron with all components at their respective working tank aim concentrations. b. An EASTMAN Color Films, Process ECP-2, seasoned bleach tank sample analyzed, as received at g/l total iron, in the same manner as the fresh bleach. c. The same seasoned solution, as in number b above, analyzed after making an analytically weighed, standard addition of g/l Total Iron. ECP-2, (8.712 g/l Total Seasoned with Addition Reproducibility Deviation, 1S c ± ± ± Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03

3 APPARATUS All volumetric glassware should meet all Class A specifications, as defined by American Society for Testing and Materials (ASTM) s E 287, E 288, and E 969, unless otherwise stated. 1.0-cm silica cell 2.0- and 3.0-mL pipettes 100- and 250-mL volumetric flasks Double-beam spectrophotometer, equipped with a tungsten light source (i.e., Shimadzu Model UV160U) REAGENTS Use ACS Reagent Grade reagents unless otherwise specified. Nitric Acid, HNO 3 (5.0 N) Potassium Persulfate, K 2 S 2 O 8 (40 g/l) Ammonium Thiocyanate, NH 4 SCN (200 g/l) Water, Type I Reagent-This method was developed, and the resulting statistical data were obtained using reagent water equivalent to or purer than Type I Grade, as defined in ASTM D Other grades of water, e.g., reverse osmosis (RO), demineralized, or distilled water, may give equivalent results, but the effects of water quality on method performance have not been studied. PROCEDURE 1. Zero the Spectrophotometer a. Adjust the wavelength on the spectrophotometer to 477 nm. b. Zero the spectrophotometer vs air. 2. Blank a. Prepare a blank solution by adding 10 ml of 5 N nitric acid, 1 ml of 40 g/l potassium persulfate, and 25 ml of 200 g/l ammonium thiocyanate to a 100-mL volumetric flask. b. Swirl to mix reagents, dilute to the mark with reagent water & invert 6 to 10 times to mix. c. Rinse a clean, 1-cm silica cell 3-5 times with blank solution from step b and fill the silica cell with the blank. Rinse the outer surfaces of the cell with reagent water and wipe dry with a tissue. Place the cell into the sample beam cell holder of the spectrophotometer. d. Read the absorbance of the blank within 2 minutes at 477 nm vs. air as (ABS blk ). e. Remove the silica cell and rinse 3 to 5 times with reagent water. 3. Sample a. Add approximately 200 ml of reagent water to a 250-mL volumetric flask. b. Pipette 2.0 ml of the sample into the 250-mL flask. Fill to volume with reagent water. Invert the flask 6 to 10 times to mix. c. To a 100-mL volumetric flask, add 10 ml of 5 N nitric and 1 ml of 40 g/l potassium persulfate. Swirl to mix. d. Pipette 3.0 ml of the diluted sample from step 3b, into the 100-mL flask. e. Add 25 ml of 200 g/l ammonium thiocyanate solution to the 100-mL flask, while swirling the flask. Fill to volume with reagent water. Invert the flask 6 to 10 times to mix. f. Rinse the 1-cm silica cell 3-5 times with the sample from step 3e, and then fill the silica cell with the sample. Rinse the outer surfaces of the cell with reagent water and wipe dry with a tissue. Place the cell into the spectrophotometer s sample beam cell holder. g. Record the absorbance of sample at 477 nm vs. air as (ABS spl ). Absorbance should be recorded within 2 minutes of sample preparation. Note: When using a single-beam spectrophotometer, as opposed to a double-beam spectrophotometer, the procedure is the same. However, a new blank should be prepared for each sample due to the instability of the blank. Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H

4 CALCULATIONS ABS 477 = ABS spl ABS blk Where: If: g/l Fe = Then: ABS 477 x DF Absorptivity DF = dilution factor, e.g., = (250 ml)(100 ml) = (2.0 ml)(3.0 ml) 250 ml = volume of first dilution 2.0 ml = volume of sample pipetted into first volumetric flask 100 ml = volume of second dilution 3.0 ml = volume pipetted from first dilution into second volumetric flask Absorptivity = 205 ABU-L/g-cm * * NOTE: Use the APPENDIX to determine absorptivity of the iron thiocyanate complex, since each spectrophotometer may yield a different absorptivity value. ABS spl = ABS blk = ABS 477 = g/l Iron = g/l Iron = x APPENDIX Calibration of the Spectrophotometer for the Iron-Thiocyanate Complex This appendix should be used to recheck the iron thiocyanate absorptivity at least every 6 months. Also, it is to be used the first time this method is performed and whenever the spectrophotometer has been adjusted or repaired. Reagents Use ACS Reagent Grade reagents unless otherwise specified. Water, Type I Reagent-This method was developed, and the resulting statistical data were obtained using reagent water equivalent to purer than Type I Grade, as defined in ASTM D Other grades of water, e.g., reverse osmosis (RO), demineralized, or distilled water, may give equivalent results, but the effects of water quality on method performance have not been studied. Nitric Acid, HNO 3 (Concentrated) Nitric Acid, HNO 3 (5.0 N) Nitric Acid, HNO 3 (0.5 N) Potassium Persulfate, K 2 S 2 O 8 (40 g/l) Ammonium Thiocyanate, NH 4 SCN (200 g/l) Iron, wire, 0.5 mm diameter, percent pure available from: Aldrich Chemical Company, Inc. 940 West Saint Paul Ave. Milwaukee, WI CAT No. 26,624-8 in either 0.75 g or 7.5 g quantities 4 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03

5 Procedure Preparation of 10 g/l Iron Stock Solution. 1. Measure 200 ml of concentrated nitric acid into a 250-mL graduated cylinder. Slowly pour the acid into a 1-L beaker containing 300 ml of reagent water and a magnetic stir bar. Mix thoroughly. 2. Weigh 2.50 g of iron wire and record the weight to the nearest 0.1 mg. Wear white cotton gloves to keep finger oils and moisture from the wire. Use complete packs of wire to avoid contamination from wire cutting devices. Two or three of the 0.75-g packs will contain a weight close to the stated amount (each typically contains more than the nominal 0.75 g). 3. Place the iron wire into a 1-L beaker with a magnetic stirring bar. Place the beaker on a warm, hot-plate/ stirrer. 4. Slowly add about 125 ml of the diluted nitric acid (prepared in step 1) to the iron wire in the beaker. The iron wire will begin to dissolve and the acid will begin to boil. 5. Once the wire has totally dissolved, immediately allow the solution to cool to room temperature. Quantitatively transfer the cooled solution into a 250-mL volumetric flask. 6. Fill the volumetric flask to the mark with reagent water. Invert the flask 6 10 times to mix. Note: This solution is stable for six months and should be stored in either plastic or colorless glass bottles (do not store in brown glass bottles as extraneous iron will be extracted from the glass). Calculations Conc. of 10 g/l stock standard solution Where: = weight from step 2 x x x = assay value of iron wire supplied by Aldrich 4 = factor to convert 250 ml to 1 L 250 = volume of stock solution (ml) Absorptivity of Iron-Thiocyanate Complex 1. Zero the spectrophotometer as described in the Zero the Spectrophotometer Procedure of the above method. Prepare and record the absorbance of a reagent blank described in the Blank Procedure of the above method (ABS blk ). 2. Pipette 3.0 ml of the 10 g/l iron stock solution into a 1-L volumetric flask containing 500 ml of 0.5 N nitric acid. Dilute to volume with 0.5 N nitric acid, stopper, and invert several times (6-10) to mix. This is the absorptivity stock solution (approximately 30 mg/l Fe). 3. To a 100-mL volumetric flask, add 10 ml of 5 N nitric acid and 1 ml 40 g/l potassium persulfate. Swirl to mix. 4. Pipette 3.0 ml of the stock solution from step 2, into the flask in step 3, with swirling. 5. Add 25 ml of 200 g/l ammonium thiocyanate to the flask (step 4) with swirling. Dilute to volume with reagent water. Stopper and invert 6 10 times to mix. This is Std Rinse the 1-cm silica spectrophotometer cell several times with the sample. Fill the cell and rinse the outer surfaces with reagent water. Wipe dry with a soft tissue and place the cell into the sample beam cell holder of the spectrophotometer. 7. Record the absorbance of Std 1 at 477 nm as ABS std 1. Absorbance should be recorded within 2 minutes of sample preparation. 8. Repeat steps 3 to 7, two more times. 9. Repeat steps 2 to 8, substituting the following pipette sizes into step 4 (see the following table). Record absorbances with the corresponding Std #. Pipette Size (ml) Std # 5.0 Std Std Std The linear nature of the relationship between absorbance at 477 nm and iron concentration is shown in the Typical Absorptivity Table with the accompanying Figure, Calibration of Total Iron in ECN-2 or ECP-2 Bleach. Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H

6 Calculation of Absorptivity Absorptivity (ABU-L/g-cm) = Where: ABS std # x df Iron Stock Conc. Figure 1 Calibration of Total Iron in ECN-2 or ECP-2 Bleach ABS std # df Iron Stock Conc. = recorded absorbance for each standard measured at 477 nm = dilution factor for corresponding standard 1000 ml 100 ml x 3.0 ml pipet size = calculated amount of iron in iron wire stock solution (refer to section on Preparation of 10 g/l Iron Stock Solution.) Example x Absorptivity (ABU-L/g-cm) = = Typical Absorptivity ml Diluted Stock Absorbance Absorptivity x = s = Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03