1、 FORD LABORATORY TEST METHOD AS 002-01 Date Action Revisions 2001 01 31 Revised Editorial no technical change A. Cockman 2000 04 25 Editorial no technical change A. Cockman 1992 05 01 Printed copies are uncontrolled Page 1 of 8 Copyright 2001, Ford Global Technologies, Inc. DETERMINATION OF VOLATILE
2、 CORROSION INHIBITOR IN PACKAGING MATERIALS Application This procedure is used to determine the weight of loading of volatile corrosion inhibitors composed of benzoic acid, urea and sodium nitrite. The calculations at the end of each test for each chemical will give the total weight of loading for a
3、ll three. Any one of the three chemicals may be determined separately to obtain the total weight of loading, assuming that only benzoic acid, urea and nitrite are present. If all three chemicals are determined and the calculations used, the answers should be the same. The water extraction method at
4、the end is much simpler but can only be used if benzoic acid, urea and sodium nitrite are present and other water soluble chemicals are absent. Conditioning and Test Conditions All test values indicated herein are based on material conditioned in a controlled atmosphere of 23 +/- 2 C and 50 +/- 5 %
5、relative humidity for not less than 24 h prior to testing and tested under the same conditions unless otherwise specified. Procedure for Benzoic Acid Summary Total benzoic acid is determined by extraction from the paper with dilute alkali, followed by acidification and extraction of the benzoic acid
6、 from the aqueous solution with chloroform. Upon evaporation of the chloroform, the residue is dissolved in 75 % methanol and titrated with standard caustic. Apparatus Required Mechanical stirrer Buechner funnel Separatory funnel - 250 mL, 1000 mL FORD LABORATORY TEST METHOD AS 002-01 Page 2 of 8 Co
7、pyright 2001, Ford Global Technologies, Inc. Solutions Required Sodium hydroxide - 10 % solution Pydrochloric acid - 3 normal Phenolphthalein - 0.1 % solution in 1 - 1 alcohol Sodium hydroxide - 0.05 N (approx.) - Standardize against Bureau of Standards acid potassium phthalate Methanol - 75 % - Dil
8、ute 75 mL of C.P. methanol to 100 mL with distilled water Chloroform - C.P. grade Procedure Cut ten square inches of the volatile corrosion inhibitor paper into fine pieces and place in a 400 mL beaker with 200 mL of distilled water and 5 mL of NaOH (10 %). Stir mechanically for 30 minutes. Filter t
9、hrough a paper filter on a Buechner funnel. Wash the residue thoroughly with distilled water and transfer the filtrate to a 1000 mL separatory funnel, washing the filter flask with distilled water and adding the washings to the filtrate in the separatory funnel. Acidify the filtrate with 10 mL of HC
10、l (3 N) and add 50 g of NaCl. Extract with seven portions of chloroform in amounts of 70, 70, 50, 50, 40, 40 and 30 mL. After the addition of each portion of chloroform, the mixture is shaken vigorously, swirled, and allowed to stand for a few minutes until clear water and chloroform layers separate
11、, with a relatively small amount of stable emulsion in between. The following extraction scheme is used to minimize emulsion difficulties: Separatory Separatory Funnel “A“ Funnel “B“ Beaker “C“ (1000 mL) (250 mL) (400 mL) Extraction #1 Wash with 70 mL Draw chloroform to C. chloroform. Draw Leave wat
12、er and any chloroform to C. emulsion. Draw emulsion to B. Extraction #2 Wash with 70 mL Shake and settle. chloroform. Draw Draw chloroform to C. chloroform and Leave water and any emulsion to B. emulsion. Extraction #3 Same as Extraction #2, except for amounts of 4, 5, 6, and 7 chloroform taken (#3
13、and 4 = 50 mL each; #5 and 6 = 40 mL each; #7 = 30 mL). Caution must be exercised in all draw-offs of chloroform from Funnel B so that no water or emulsion is transferred to C. FORD LABORATORY TEST METHOD AS 002-01 Page 3 of 8 Copyright 2001, Ford Global Technologies, Inc. Evaporate the final combin
14、ed chloroform extract in the 400 mL beaker on a steam bath. Do not allow the solution to evaporate below 50 mL before removing from the heat. The last 50 mL must be removed at 23 +/- 2 C in order to prevent loss of benzoic acid by sublimation. This final evaporation can be accomplished simply by let
15、ting the 50 mL of chloroform solution stand uncovered over night, or by evaporation in a slow stream of air or nitrogen for one hour after apparent dryness is reached. This evaporation period after dryness should be at least one hour in order to remove any HCl residues. Dissolve the residue after ev
16、aporation in 100 mL of 75 % methanol. Add 1 mL of 0.1 % phenolphthalein and titrate with standard NaOH (approx. 0.05 N). The end point is sharp, but is sometimes difficult to observe since the color change is only from salmon pink to orange. It is advisable to run a blank titration on the methanol (
17、75 %), and deduct from the sample titration. Calculation grams/sq. ft. = 7.91 x (mL NaOH) x (normality of NaOH) Explanation of Factor Conversion of 10 sq. in. to 1 sq. ft. = 14.4 Molecular weight of ethanolamine benzoate = 183 Conversion of ethanolamine benzoate content to total weight of loading =
18、3 Determination of Urea Summary This method is based on the reaction between urea and diacetyl in acid solution, producing a yellow-colored complex. The transmittance of the solution is determined photometrically; and the concentration of urea is read directly from a transmittance curve, previously
19、prepared from measurements on standards of known urea concentration. Because nitrite in the paper affects the color of the urea-diacetyl complex, the paper is also analyzed for nitrite, using standard colorimetric methods; and an empirical nitrite correction is applied to the urea determination. Rea
20、gents and Solutions Acid mixture - a 1:3:4 mixture of concentrated sulfuric acid, 85 % phosphoric acid, and water respectively. Diacetyl in ethyl alcohol - 5 % diacetyl (Eastman #1591) by volume. Acid diacetyl reagent - 0.05 % by volume of diacetyl in the acid mixture. This is made by diluting 1 mL
21、of the 5 % diacetyl solution to 100 mL with the acid mixture. This solution is stable for two weeks or longer if refrigerated and protected from light. FORD LABORATORY TEST METHOD AS 002-01 Page 4 of 8 Copyright 2001, Ford Global Technologies, Inc. Urea Standard Solutions “Stock standard (a)“ - 1.00
22、0 gram of dried reagent grade urea (Mallinckrodt AR), dissolved and made up to 1 liter with distilled water, add 1 mL of chloroform as preservative. This solution is stable for several weeks when refrigerated. “Stock standard (b)“ - 0.100 gram urea per liter, made by diluting 50 mL of stock standard
23、 (a) to 500 mL, adding 1 mL of chloroform as preservative. This solution is stable for about one week under refrigeration. “Working standard solutions“ - 15, 20, 25, 30, 35, 40 and 45 micrograms of urea per mL. These are prepared by diluting 15, 20, etc. mL of stock solution (b) to 100 mL and adding
24、 a few drops of chloroform to each solution as a preservative. These working standards must be used the same day as prepared, although they will keep a few hours if refrigerated. Establishment of Standard Transmittance Curve 1. Five mL of each of the working standard solutions are pipetted into test
25、 tubes, approximately 2 x 14.5 cm. 2. Five mL of the acid-diacetyl reagent are pipetted into each of the urea aliquots. The mixture is thoroughly agitated. Speed in operation and accurate scheduling are important from this point on. 3. Air condensers are placed in the test tubes. These are 3/16 x 4
26、inch glass tubes in corks which are inserted in the test tubes. 4. Within 5 minutes (IMPORTANT) of the addition of the diacetyl reagent, the test tubes are inserted in a boiling water bath with about 2/3 immersion. Note: A four liter stainless steel beaker or an asbestos wrapped glass beaker is used
27、 as the bath, protecting the reacting mixture from light. A lower plate fits inside the beaker. An upper fixed plate acts as a divider and support for the rack. It rests on top of the beaker, acting as a light shield. In addition, a separate aluminum disc drilled in the proper pattern is placed over
28、 the air condensers and rests on the corks, thus protecting the condensers from the steam evolved from the boiling bath. The volume of water in the bath and the heating rate are such that boiling resumes within 1 minute after inserting the test tubes. 5. The mixtures in the test tubes are heated in
29、the bath for 20 +/- 1 minute. 6. Immediately after removal from the boiling water bath, the rack containing the tubes is placed in a second water bath (stainless steel beaker) at about 40 F. This should contain a minimum of 100 mL of cooling water per test tube. They are allowed to cool for about 10
30、 minutes. 7. The condensers are removed, and the test tubes are tilted so as to bring condensed material on the sides of the tube back into solution. FORD LABORATORY TEST METHOD AS 002-01 Page 5 of 8 Copyright 2001, Ford Global Technologies, Inc. 8. The contents are again agitated thoroughly, and th
31、en are evaluated for their transmittance at 480 millimicrons, using a spectrophotometer. Care should be taken to keep the solution above the dew point; otherwise condensation on the cells will cause errors in observed transmittance. 9. The percent transmittance values are plotted against urea concen
32、trations of the working standards (micrograms/mL) on semilogarithmic graph paper, using the logarithmic scale for transmittance. 10. It will be noted that a straight-line relationship exists from about 15 micrograms/mL to 30 micrograms/mL. Thereafter the relationship becomes curvilinear, but is suff
33、iciently reproducible to make the entire graphical relationship usable over the range of 15 to 45 micrograms/mL. Analysis for Urea in Paper 1. Two square inches of paper are extracted at 23 +/- 2 C with 200 mL of distilled water. Five to ten drops of chloroform are added to the extracting solution a
34、s a preservative. 2. After occasional agitation of the water and paper samples over a period of 30 minutes, the extraction should be complete. In the case of certain laminated grades of VCI papers, this period may be inadequate. The completeness of extraction can be checked by testing several aliquo
35、ts after successive extraction periods. 3. A 5 mL aliquot of the extract is taken and used for the urea analysis by the procedure described in the preceding section, reading the urea concentrations directly from the standard transmittance curve. These values are subject to a correction for nitrite a
36、s described in a later section under “Calculations“. Procedure for Nitrite Reagents and Solutions Diazotization reagent - consists of one gram sulfanilamide (Eastman reagent grade No. 4378), 100 mL of C.P. concentrated hydrochloric acid, and 400 mL of distilled water. This reagent contains 0.2 % sul
37、fanilamide and about 8 % HCl. Coupling reagent - consists of a 0.1 % aqueous solution of N-(1-naphthyl) ethylenediamine dihydrochloride (Eastman 4835). Stock standard nitrite solution - 10 micrograms of A.C.S. reagent grade sodium nitrite per mL. Establishment of Standard Transmittance Curve 1. The
38、stock standard solution (10 micrograms/mL) is taken in amounts of 1, 2, 3, 4 and 5 mL, pipetted into separate 50 mL volumetric flasks. This will give 10, 20, 30, 40 and 50 micrograms respectively. Then 10 to 15 mL of distilled water are added to each flask. FORD LABORATORY TEST METHOD AS 002-01 Page
39、 6 of 8 Copyright 2001, Ford Global Technologies, Inc. 2. The procedure for producing the color for intensity measurements is as follows: (a) Add 5 mL of diazotization reagent to each flask. Allow to stand at least 2 minutes with occasional agitation. (b) Add 1 mL of coupling reagent, allow to stand
40、 for at least 15 minutes with occasional agitation to obtain full color development. (c) Fill volumetric flask to 50 mL with distilled water. (d) Determine transmittance of the solution at 540 millimicrons, using a spectrophotometer. (e) Percent transmittance values are plotted against the amounts o
41、f sodium nitrite in micrograms. When semilogarithmic paper is used and transmittance is plotted on the logarithmic scale, a straight line results. This “standard curve“ is used to convert transmittance values for unknown solutions into equivalent amounts of sodium nitrite. Analysis for Nitrite in Pa
42、per 1. The paper extract used for urea analysis is also used for nitrite analysis. As described in the preceding section, this extract consists of two square inches of paper with 200 mL water. 2. For nitrite determination, a 1 mL aliquot of this extract to a 50 mL volumetric flask, 10 to 15 mL of wa
43、ter are added, and the color is developed by diazotization and coupling as described previously. 3. Transmittance is measured at 540 millimicrons, and the nitrite concentration in micrograms for 1 mL of extract is then read directly from the standard curve. Calculation of Urea Results After completi
44、on of the urea and nitrite analysis the total amount of urea in the paper can be calculated by the following equation: U = ( A ) 200 x 144 x 3 1 - 0.0046 B 2 x 10 deg U = 0.0432 A 1 - 0.0046 B where U = grams per square foot of paper FORD LABORATORY TEST METHOD AS 002-01 Page 7 of 8 Copyright 2001,
45、Ford Global Technologies, Inc. A = micrograms urea per mL of extract paper, as obtained from the urea standardization curve. B = amount of nitrite expressed as micrograms of NaNO2 in the 1 mL aliquot of the paper extract, obtained from the nitrite standardization curve. 2 = square inches of paper ta
46、ken for analysis. 200 = mL of extract 144 = in2/ft2 106 = micrograms/gram 0.0046 = empirically determined correction factor for effect of nitrite in reducing color intensity of the urea-diacetyl complex. Notes: 1. The above equation applies only when a 200 mL extracting solution is used. Should a di
47、fferent volume of extracting solution be used, the results are multiplied by the factor V/200. This factor should also be applied to the nitrite correction factor before it is used in the above equation. 2. It should be noted that the standard transmittance curve of the urea is plotted against the c
48、oncentrations of the “working standards“; not against the concentrations of the final colored solutions. For nitrite, the standard transmittance curve is plotted against micrograms of nitrite taken for each analysis. With this scheme, provided 5 mL aliquots are used for urea and 1 mL aliquots for ni
49、trite, the values read from the standard curves will read directly in micrograms per mL of paper extract. 3. Once the standard transmittance curves have been prepared on a particular spectrophotometer, that work need not be repeated until there has been a change in the transmittance components of that instrument. Since each spectrophotometer has individual characteristics, a curve prepared on one instrument cannot be used for other instruments. 4. Instead of using distilled water, control solution
