Determination of Phosphorus in Highly Alloyed Steels with Quinoline Molybdate Arthur Lench Australian Defence Scientific Sercice, Defence Standards Laboratories, Victoria, Australia AN INVESTIGATION into the elimination of the tedious recovery step for occluded and precipitated P in the quinoline phosphomolybdate (QPMo) method for the determination of P in steels containing W, Nb, Ta, Ti, and Zr ( I , 2), showed that this could be accomplished by the method described. I n this method, H F is used to dissolve insoluble oxides and Z r P 0 4 following decomposition of the sample and supplementary oxidation of P by HC104. The fluoro compounds are converted to tartrates with removal of HF and a n impure Q P M o is precipitated. Purification is achieved by reprecipitation after solvent extraction. W is held in solution as a stable complex with F e and tartaric acid. N b and T a cause contamination of the original QPMo precipitate when present in large amount. Table I demonstrates the wide applicability of the method. EXPERIMENTAL
Reagents. Quinoline Molybdate Reagent Solution (QMoR). Add 180 grams of M o o 3 (100%) to 500 ml of HzO containing 60 grams of NaOH. Heat t o dissolve, adding 0.5 ml of 100 volume % H202to assist solution (solution 1). Dissolve 100 grams of citric acid in a mixture of 250 ml of 1 2 M HC1 and 500 ml of H 2 0 with heating (solution 2). Dissolve 32 ml of distilled quinoline in 100 ml of 1 2 M HC1 and add 300 ml of H 2 0(Solution 3). Add solution 1 t o solution 2 and solution 3 t o the mixture. Heat t o boiling and boil gently until a small amount of precipitate (QPMo) which has formed, darkens in color. Allow t o cool and dilute t o 2 liters. Store the mixture in a borosilicate glass or plastic container. T o use, warm to dissolve material that may have crystallized out, and filter. Iron Solution. Dissolve 20 grams of very low phosphorus iron in 1 2 M HCl, add 75 ml of 1 2 M HC104, evaporate to fumes and then to reflux. Continue refluxing until separation of Fe occurs. Dilute with a little H20, add 20 ml of 1 2 M HC1 and re-evaporate t o fumes of HC104. Cool and dilute to 200 ml. Solvent Mixture. Mix together 100 ml of HzO, 100 ml Acetone purified of acetone, and 5 ml of ISM ",OH. by distillation from a mixture containing K M n 0 4 should be used. Standard Solutions. Solution 1 was approximately 0.084N NaOH and solution 2 was approximately 0.084N "03. The preparation and standardization of these solutions has been described in (2). General Procedure. Transfer a 2-gram sample [P to 0.35 % gravimetric, 0.1 % volumetric determination. For higher P contents see (2)] t o a 400-ml squat-form beaker. Add cautiously a mixture of 25 ml of 1 2 M HC1 and 15 ml of 1 6 M HNOs and, using a cover glass, digest until dissolved. Add 20 ml of 1 2 M HC104 and heat the mixture until all free liquid has been evaporated, washing down material collecting o n the sides of the beaker several times with 1 6 M "01 during the evaporation. Heating should not be continued beyond the stage of evaporation of free liquid, otherwise (1) Australian Standard No. K1,Part 18-1963. (2) A. Lench, ANAL.CHEM., 35, 1695 (1963). 1456
ANALYTICALCHEMISTRY
Table I. Determination of Phosphorus in Standard Analyzed Iron and Steel Samples by Modified Quinoline PhosphomolybdateMethod Phosvhorus content. 7 . 4 Recommended Found NBS samples 50a 18W-4Cr-lV steel 0.020 0.020(4), 0.019(7) 50b 18W-4Cr-lV steel 0.029(2), 0.030(7) 0.029 0.024( 12) 50c 18W-4Cr-lV steel 0.022 0.023(3) 7e high phosphorus cast range 0,850 to 0.850 to 0.865 iron 0. 860b 115 15Ni-6Cu-2Cr cast 0 . 108b range 0.107 to iron 0.110 121 19Cr-9Ni-0.4Tisteel 0.028 0,029(3) 153 1.5W-2V-8.5Co-4Cr 0.025 0.025(2) steel 0.024 125 4Si steel 0.008 0.007(2) 123 18Cr-8Ni-Nb steel 0.007 0.007(3) 0.010h British Chemical standards Sample 206/1 1.38 1.38(3) Standards Association of Australia samples 108 17Cr-8Ni-lNb steel 0.019-0.021b 0.021(2), 0.020 115 2OW-5.5Co high 0.036(2), 0.037b 0.036, 0.037(2) speed steel 101 6W-1.9V-5.25M00.037-0. 038b 0.037(5), 0.038(2) 4.25Cr high speed steel 125 6W-3Nb-13Ni0.033(3)b 0.033(3) 13Cr-12Co-3Mo turbine disk a Numbers in parentheses show individual determinations giving results stated. b Determination by Australian Standard K1 Part 18-1963.
insoluble oxides of W, Nb, Ta, Ti, and Z r P 0 4 may not be dissolved by the subsequent treatment. Allow the beaker t o cool and wash down sides and cover with 1 2 M HCI, and finally with water. Remove the cover, add 30 grams of tartaric acid and warm t o dissolve soluble salts. Transfer the mixture t o a 500-ml polytetrafluoroethylene (PTFE) beaker, washing with 1 2 M HC1 and water. Add 12.5 ml of 26M HF, place a cover on the beaker, heat t o boiling, and simmer until solids have dissolved. The plastic cover should be raised about inch above the beaker by stirrups or a ribbed cover used. Add 10 ml of ethylene glycol, 20 ml of 28M HBr and evaporate until the solution begins t o froth. Quench the reaction quickly by directing a stream of water (about 15-ml volume) into the beaker. Remove the beaker from the hot plate and wash down cover and sides with warm water. The onset of frothing a t the end of the evaporation stage is accompanied by the liberation of small amounts of Brz fumes. If evaporation be continued beyond the light frothing stage, a rapid reaction will take place between the remaining trace of HCIOa and the tartaric acid and the contents of the beaker will become a charred mass. N o danger of explosion exists.
Table 11. Purification of Quinoline Phosphomolybdate by Re-precipitation Weight of precipitate, mg (Blank deducted) Purified Recommended Iron Phosphorus Iron phosphorus added, 1 g. found, omitted content, Original
Sample no. NBS sample 50a 18W-4Cr-lV Steel
NBS sample 50b
0.020
0.029
Standards Assoc. of Australia Sample 101 6W-5Mo-1.9V Hot die steel
0.038
Std dev
z
z
31.3 32.9 31.2 31.3 30.7 32.0 30.9 48.3 47.1 47.4 47.2 47.0 46.1 46.3 54.5 53.9 54.6 55.2
Transfer the solution t o a 500-ml conical beaker, washing with water. Dilute to 200 ml, add 15 ml of 1 2 M HCIO?, bring the solution t o boil and boil gently for a few minutes. Add 120 ml of Q M o R rapidly dropwise until precipitation begins, then slowly add a n additional 25 ml of reagent. Digest a t boiling point until the precipitate has coagulated. Cool slightly, filter under suction through a sintered Gooch crucible (of No. 4 porosity), and wash the precipitate moderately with H20. Extract under suction with solvent mixture*.g., collect the extract in a 250-ml conical beaker held in a Bruhle or Witts jar. Add 5 ml of 1 8 M ",OH t o the contents of the beaker and evaporate t o low volume (5 t o 10 ml). Add 10 grams of tartaric acid, wash down the cover, and sides of the beaker with about 1 0 ml of H 2 0 and warm to dissolve. Add 5 ml of 1 2 M HCI, 3 to 4 ml of 16M H N 0 3 , and evaporate until the solution froths evenly and brown fumes are evolved rapidly. Remove the beaker from the hot plate and quench the reaction by adding 10 t o 20 ml of H20. Add 10 ml of Fe solution, and boil for several minutes. Transfer the solution t o a 500-ml conical beaker, dilute t o approximately 150 ml, add 15 ml of 1 2 M HClO,, and bring to the boil. Add Q M o R rapidly dropwise until precipitation begins, then slowly add a n additional 25 ml of reagent. Digest a t boiling point until the precipitate has coagulated. Cool slightly for convenience in filtration. Gravimetric and Volumetric Determinations. CALCULATIONS. These sections have been described in ( I , 2 ) . BLANK. A blank determination should be carried through all steps of the procedure. One to 2 ml of 1 6 M H N 0 3 should be added to the tartrate solution for the first precipitation of Q P M o before the addition of QMoR. Using low-P reagents, blank values of about 3 mg of Q P M o should be obtained. DISCUSSION
Preliminary work showed that if insoluble products were permitted to form during the decomposition of the sample and supplementary oxidation treatment (to oxidize all P), occlusion of P and separation as ZrPO, could not be prevented. Retention of all elements present in solution from the commencement of sample decomposition was not found feasible, however, because of incomplete solution of phos-
28.1 28.0 28.3 27.6 28.3 27.8
... 46.6 44.4 47.7
... ...
44.9 43.0 52.4 52.2 53.2 53.5
27.8 27.7 27.9 27.0 27.3 27.4 27.1 43.6 42.5 43.0 42.4 43.2 43.6 43.5 51.5 51.8 52.9 52.8
0.0192
0.0002
0,0302
0.0003
0,0365
0.0005
phides in some steels such as NBS (National Bureau of Standards) No. 115 and incomplete oxidation of P. Attention was therefore turned to the dissolution of insoluble products, after oxidation of P by HClO?, without separation and fusion, and retention of all elements present in solution from thereon. Two interdependent factors involved were (i) the precipitation of Q P M o from solutions containing u p t o 400 mg of W, 60 mg of Nb, and smaller amounts of Ta, Ti, Z r (and V) without interference or with little interference, followed by solution and re-precipitation in a pure form, and (ii) dissolution of insoluble products and conversion of the solution to a suitable medium for QPMo precipitation. Formation of a Stable Tungsten-Iron-Tartaric Acid Complex. In an investigation of ( I ) , W was found to form a complex with F e and tartaric acid highly resistant to breakdown by 1 2 M HCI, 16M H N 0 3 , and diluted HCIO,. In illustration, a mixture prepared by dissolving 1.6 grams of NBS sample series 55 in 25 ml of 12M HC1 and 15 ml of 1 6 M "Os, adding 20 grams of tartaric acid and 300 mg of W as sodium tungstate and boiling the whole for 20 minutes, gave a clear solution when boiled with 25 ml of 16M "03. N b and Ta formed soluble complexes with tartaric acid under similar conditions. Consequently, a precipitation medium consisting largely of tartaric acid was employed. Quinoline Molybdate Reagent. The reagent previously used ( I , 2 ) proved unsuitable for QPMo precipitation from tartrate solutions containing much W, such as solutions of the NBS sample series 50. Contamination of the precipitates by W was marked. Increasing the amount of tartaric acid reduced W contamination but gave rise t o incomplete precipitation of Q P M o unless large amounts of reagent were added. Replacement of a large part of the HC1 content by citric acid lessened this effect which was eliminated by further adding 1 2 M HCIOl to the precipitation medium. The HC104 addition also gave a precipitate which coagulated readily. By appropriate adjustment of the composition of the Q V o R and tartaric and HCIO, acid contents of the precipitation medium, P was completely separated from a solution of 9 grams of steel containing up to 2 0 z of W. There was little VOL. 39, NO. 12, OCTOBER 1967
1457
contamination by W a n d this was removed by re-precipitation. was not so satisfactory as 12M HC104. The use of 16M "03 It reacted vigorously with tartaric and citric acids when V was present and tended to cause breakdown of the reagent. Conversion of Oxidized Sample to a Solution in TartaricPerchloric Acids. The use of HF was found essential to dissolve the oxidized sample completely after removing all but minor amounts of HClO?. Unfortunately, the precipitation of QPMo was inhibited by the presence of HF. Its effect could not be eliminated by complexing with borax because of the instability of fluoroboric acid in the boiling precipitation solution. The addition of excess of HBr t o the HF-tartaric acid mixture overcame the difficulty. Tartaric acid tended to char in the concluding stages of the evaporation with some breakdown of the W-Fe-tartaric acid complex. This was overcome by the addition of ethylene glycol. Precipitation of Quinoline Phosphomolybdate. Contamination o f the original Q P M o precipitate by W, Nb, and Ta necessitated the use of solvent extraction and a re-precipitation for its elimination. The effect of different treatments of W-contaminated precipitates is shown in Table 11. The presence of Fe to form the stable W-Fe-tartaric acid complex was found essential to reduce W contamination to negligible proportions, as determined by x-ray fluorescent analysis. Contamination of the original precipitate by N b was considerable at the 3 level, but slight at the 1 level. Almost all N b remained on the sinter disk of the filter as a blue-gray residue after solvent extraction.
z
z
The impossibility of removing QPMo quantitatively from PTFE beaker walls without using solvent mixture made it necessary to use glass beakers for the initial precipitation. A volume of 200 ml was used for precipitation and acidity adjustment as specified in earlier work (3) was no longer necessary because of the presence of the large amounts of organic acids. Complete precipitation of QPMo was achieved only from boiling solutions. About 90 ml of QMoR was required t o start the first QPMo precipitation and 30 ml to complete it. About 45 ml of QMoR was required for the second precipitation of QPMo. Tartaric acid suppressed the formation of a partly insoluble complex between QMoR and ethylene glycol. Blank Determination. For the first QPMo precipitation the use of H N 0 3 instead of iron is specified to avoid an prevents the additional determination of P in iron. " 0 3 reduction of Mo by tartaric acid, which in turn suppresses For the re-precipitation the breakdown of QMoR by "03. of QPMo, 1 gram of Fe and 15 ml of 12M HC104 provided a reasonable margin for the suppression of M o reduction by tartaric acid. RECEIVED for review October 31, 1966. Accepted July 3, 1967. Published with permission of the Chief Scientist, Department of Supply, Australia.
(3) U. Fernlund and S. Zechner, 2. Anal. Chem., 146, 11I (1955).
Determination of Trace Elements in Chromatographic Paper by Neutron Activation and Gamma Spectrometry Peter Patek and Herbert Sorantin Institute of Chemistry, Reactor Centre, Seibersdorf, Austria
MANYE L E M ~ N T Sin various substances have been determined after separation on chromatographic paper by neutron activation. Only a few authors dealt with the impurities in the paper itself (1-3). Staerk and Knorr ( 4 ) made a quantitative assay of the sodium and chlorine content of Whatman No. 1, Schleicher Schull 2043a, and Schleicher-Schull white ribbon 5892 paper, and were able to show that only 10% of the mentioned impurities could be removed by chemical leaching. In one case a n additional uptake of the used reagents was noticed. Therefore, it is important to determine the trace elements in the paper before application. Whatman chromatographic paper No. 3 (185-200 mg/cmz) has a higher loading capacity and was used by us to separate trace elements from their matrix. Before identifying them by neutron activation, we were interested in the kind and amount of impurities in the paper itself, their distribution in different charges, and their influence on the degradation and loss of tensile strength during longer irradiations. -__.-__._____
(1) A. A. Renson, B. Maruo, R. J. Flipse, H. W. Jurow, and W. W. Miller, Proc. Second Intern. Conf: Peaceful Uses At. Energy, Geneca, 19-78, 24, 289 (1958). (2) A. G. Soulitis, ANAL.CHEM., 36, 811 (1964). (3) A. Dimitriadu, P. C . R. Turner, and T. R. Fraser, Nature, 198, 446 (1953). (4) H. Staerk and D. Knorr, Atomkernenergie, 6 , 408 (1961).
1458
ANALYTICAL CHEMISTRY
EXPERIMENTAL
Irradiations. For the detection of short-lived radionuclides, 10- to ZO-granl samples of paper were put into polyethylene containers and irradiated in the pneumatic rabbit system of the ASTRA reactor. The flux was 2 X 1 O I 2 neutrons/cm* second for thermal, and 2 X 1Olo neutrons/cm2 second for fast, neutrons. Longer irradiations were performed in a corner position of the reactor core a t a flux of 6 X 1013 for thermal, and 6 x l O l a neutrons/cm2second for fast, neutrons. I n this position aluminum containers were used. All samples were wrapped in an additional layer of paper to avoid direct contact with the walls of the capsules. Counting Equipment. Gamma spectrometry was performed with a Harshaw 3- X 3-inch NaI crystal and a n Intertechnique 400 channel analyzer with multiscaler, tape recorder, x , y-writer, and a Packard printer. Standard Substances. Because no papers with known amounts of trace elements were available, solutions of different metals o r salts were prepared and standardized by conventional methods. All chemicals were of analytical grade; for gold and aluminum, solutions of metals with 99.9975purity were used. For quantitative assays two strips of the same paper and size were taken. O n one, a known amount of standard solution was applied and distributed by the addition of
