LITERATURE CITED
resulting in oxidation of ascorbic acid to dehydroascorbic acid and partial reduction of DMDQ t o the "Indigoid" quinhydrone (III),as shown here.
Ascorbic acid
(1) H. Elsourdy, Ph.D. Thesis, University of Assiut, 1968. (2) Takeru Higuchi and Einar Brochmann-Hanssen. Pharmaceutical Analysis," lnterscience Publishers, New York. London, 1961, p 689. (3) W. H. Sebrell. Jr., and Robert Harris, "The Vitamins," 2nd ed., Vol. I, Academic Press, New York and London, 1967, p 305. (4) "The United States Pharmacopeia" 18th rev., Mack Publishing Co., Easton, Pa., 1970, pp 51-53. (5) British Pharmacopeia, 1968, pp 64-65. (6) G. G. Rao and G. S. Sastry, Anal. Chim. Acta, 56, 325 (1971). (7) R. Aragones-Apodaca, lnform. Quim. Anal. 21, 224 (1967); Chem. Abstr., 68, 722792 (1968). 18) Y. Kochi and Y. Kaneda, Bitamin. 41 (3), 240-4 (1970); Chem. Abstr., 73, 289582 (1970). (9) Basch Serrat, Ars. Pharm., 11, 267 (1970); Chem. Abstr., 75, 25466t (1971). (10) Rusu et a/., Univ. Timisoara, 9 (2), 109 (1971); Chem. Abstr. 78, 1435569 (1973). (1 1) A. S. Hammam M.Sc. Thesis, Univ. of Assiut, 1961. (12) M. A. Eldawy, Abstracts of papers, 12th Congress of Pharmaceutical Sciences. Cairo. Nov. 1971. D 31. _.. M. A. Eldawy, A. S. TawfiK,'and S. R . Elshabouri, Abstracts of papers 33rd International Congress of Pharmaceutical Sciences, Stockholm, September 3-7, 1973, p 153. Erdtmann, Roc. Roy. Soc., Sec. A, 143: 211 (1934). "The United States Pharmacopeia" 18th rev., Mack Publishing Co.. Easton, Pa., p 939. J. Davidek et ab, Scientific papers of the institute of Chemical Technology, Prague ESO, 1971, p 17. M. P. Lamden, And. Chem., 22, 1139 (1950). A. Robertson et a/., J. Chem. SOC., 11 (1955).
I11
~I
Structure I11 is assigned to the violet intermediate reduction product of DMDQ (18). However, this assumption is far from conclusive, and a thorough investigation of the chemistry of this reaction, which is beyond the scope of this manuscript, is currently being undertaken and will be the subject matter of a future report.
SUMMARY A fast, facile, spectrophotometric method for determining ascorbic acid is described. The procedure is based on interaction between DMDQ and vitamin C to give a stable reddish violet color. The method is sensitive and offers a good degree of specificity to allow determination of ascorbic acid in the presence of other substances likely to be present along with vitamin C in pharmaceutical dosage forms. Single component and multivitamin formulations are satisfactorily analyzed by this method. Ordinary tablet excipients, antioxidants, preservatives, and stabilizers do not interfere. Dehydroascorbic acid also does not interfere.
RECEIVEDfor review June 13, 1974. Accepted October 8, 1974. Abstracted from a thesis presented by S.R. Elshabouri in partial fulfillment of the Ph.D. Degree, University of Assiut. Presented, in part, a t the 33rd International Congress of Pharmaceutical Sciences, Stockholm, Sept. 3-7, 1973. Abstracts p 153.
Improved Rhodanine Method for the Spectrophotometric Determination of Gold 1. E. Lichtenstein Corning Glass Works, Corning, N. Y. 14830
Drawbacks of the rhodanine specfrophotometric method for gold currently in use are limited solubility of the reagent and instability of the reaction product. These disadvantages have been overcome by dissolution of the reagent in pyridine and by use of a mixed aqueous-pyridine reaction system. At 515 nm, a plot of absorbance vs Au concentration Is linear In the range 0.2-0.8 X 10-5M Au. The molar absorptivity based on Au concentration is 3.8 X l o 4 in the waterpyridine system, or about twice that In the 0.12M HCI medium commonly used. The effects on color development of significant reaction variables have been studied, as well as interference by associated noble metals. An analytical procedure utilizing the improved rhodanlne method, applicable to the determination of gold In various matrices, has been developed.
A popular spectrophotometric method for gold ( 1 ) utilizes the reagent p - dialkylaminobenzylidenerhodanine (the alkyl can be methyl or ethyl). whose name shall be shortened to "rhodanine" from now on in this article.
NH-C=O
s=c,
I
I LH3 , C = C H ~ N'CH3
S RHODANINE (DIMETHYL DERIVATIVE)
In acidic medium, tetrachloroaurate ion reacts with rhodanine to form an intensely red product whose absorbance, as measured a t 515 nm, is proportional to the concentration of gold present. The reaction product is obtained as a colloidal suspension, as are most colored gold-organic compounds that have been reported for the spectrophotometric determination of gold in aqueous medium (2, 3 ). As is generally the case with colloidal systems, the intensity of color developed in the Au-rhodanine reaction is very sensitive to reaction conditions, notably electrolyte concentration and pH. Color maximizes within 1-2 minutes of initiation of reaction, but fades rapidly after that; hence, color stability is a problem. Another serious drawback of the recommended method is limited solubility of the reagent in aqueous medium. Rhodanine is very soluble in pyridine and in mixed aqueous-pyridine media. Further, an aqueous solution of
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
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AuC14- reacts with rhodanine in pyridine to give a n apparently true solution of a red product similar t o the Aurhodanine colloid described above. T h e intensity of color developed by this reaction is about twice that reported for the reaction in acid medium, and absorbance relative t o a blank is constant for more than 20 hours. A study of variables affecting color development in the reaction of gold with rhodanine in aqueous pyridine medium has been carried out. Interference by other species, with emphasis on the other noble metals, has been investigated. Optimal conditions have been incorporated into a recommended analytical procedure which, when suitably modified to take into account the presence of certain interferences, can be applied to the determination of gold in complex matrices.
EXPERIMENTAL Reagents. The rhodanine reagent, obtained from Aldrich Chemical Company (product 11, 458-81, proved to be satisfactory for use as received. Recrystallization of this material from methyl ethyl ketone yielded a product whose properties (infrared spectrum and reaction with gold) were indistinguishable from those of the original. Reagent grades of pyridine from various suppliers were purified by distillation over potassium hydroxide. Purification of this solvent is recommended, as some lots of reagent grade pyridine contained an impurity that hindered full color development in the Au-rhodanine reaction. Solutions of rhodanine in pyridine are stable for at least a week, as judged by absorbance data. A gold stock solution containing approximately 1000 Fg Au/ml was prepared by dissolution of HAuC14 xHlO in dilute hydrochloric acid. This solution was standardized gravimetrically by the thioglycollic acid method of Mukherji ( 4 ) . Less concentrated gold solutions were prepared as needed by suitable dilutions of the stock solution. Solutions of other noble metals for ,interference studies were prepared as follows. Palladium, as PdC142-, and platinum, as PtC1G2-: the pure metals were dissolved in HCl + HNO:+ evaporated to dryness evaporated again with HC1 to remove nitrate, and taken up in dilute HCI. Rhodium, as RhCl&, and ruthenium, as RuCls3-: the anhydrous trichlorides were dissolved in concentrated HC1 and diluted to suitable volumes. Silver, as Ag+: a reagent grade of silver nitrate was dissolved in dilute "03. Other chemicals were of reagent grade quality or the equivalent. Distilled and deionized water was used Lhroughout. A Hitachi Model 139 spectrophotometer was used for absorbance measurements. Recommended Procedures. Calibration Curue. Aliquots containing 20-80 fig of Au are pipetced from a dilute gold solution into 50-ml beakers. One ml of 6M HC1 is added to each and to a blank. One ml of 0.01 M EDTA is added as a general masking agent for small amounts of interferences. Solution pH's are adjusted to 3.0 f 0.1 with dilute NaOH. Exactly 10.0 ml of 0.0075% (w/v) rhodanine in pyridine reagent is added with stirring. The resultant solutions are transferred to 50-ml volumetrics and are diluted to volume with water. The solutions are allowed to stand for at least 1 hour, then the absorbances of the standards us. the blank are measured at 515 nm, using 1-cm path length cells. Analysis of S a m p l e . Siliceous materials are decomposed with HF, HCl, and "03, fumed to dryness, and evaporated again with 6M HCl to remove nitrate. Noble metal films are leached from substrates with HCl + "03, evaporated several times with HC1, dissolved in dilute HCl, and analyzed for gold by the calibration procedure or a suitable modification thereof. If the material contained macro amounts of base metals other than the alkalies and alkaline earths, it is recommended that gold (and associated noble metals) be separated from them directly after the HC1 evaporations of sample decomposition. Mercurous chloride can be used as a carrier for gold. The residue from sample decomposition is dissolved with 1 ml of 6M HC1. 1 ml of 10% tartaric acid, and water to about 15 ml with heating. Then about 200 mg of Hg2C12 is added as the solid reagent. The mixture is brought to a boil, digested for half an hour, then allowed to cool to room temperature. The mixture is filtered through Whatmaa No. 42 or equivalent paper, and the residue is washed with 0.5M HC1 saturated with HgZC12. The filter paper and its contents are transferred to a Vycor brand crucible or dish and ignited t o 600 'C under a hood to remove mercury by volatilization. The residue from this treatment is dissolved with HC1 + HNO:j, evaporated to 466
dryness, evaporated several times to dryness with 6M HC1, and dissolved in dilute HC1. Analysis of this solution, or of a convenient portion of it. is then carried out by the calibration procedure. Modifications of the basic procedure are necessary when certain other noble metals are present in amounts comparable to that of gold. If palladium or platinum are present, absorbance readings are best taken within an hour of addition of the rhodanine reagent, preferably within a half hour for palladium. A standard should be run concurrently to compensate for the lesser amount of color developed by Au at times less than l hour after initiation of reaction. If silver is known to be present, or if a turbidity develops in the sample solution on adding 1 ml of 6M HC1 en route t o the rhodanine finish, the following modification is recommended. Adjust pH's to 4.0 rather than 3.0. Add 1.0 ml of 0.1M potassium iodide (approximately 2% w/v KI in water) after pH adjustment. Add 10.0 ml of the rhodanine reagent with stirring. Let stand for 15-30 minutes. Then filter via 30-ml, fine porosity, sintered glass crucibles into 50-ml filter flasks. Wash residues (if any) with sparing quantities of a freshly prepared 10 vol % pyridine-10-3M KI wash solution. Transfer contents of the filter flasks to 50-ml volumetrics. dilute to volume with water, and measure absorbances as in the calibration procedure.
RESULTS AND DISCUSSION Calibration Curve. The system developed in the basic calibration procedure contains 20% pyridine by volume, is 6 X 10-jM in rhodanine, 2 X 10-4M in EDTA, 0.1M in C1-, and has a p H of about 8.4. A satisfactorily linear plot, passing through the origin, is obtained for the range 0.2-0.8 x 10-jM Au using the recommended procedure. The molar absorptivity, e , based on gold concentration, is 3.8 X lo4. This is about twice as great as 6 for the Au-rhodanine reaction carried out in 0.12M HC1 ( I ). Net absorbance relative to the blank maximizes in the 510-513 nm region, as is indicated by the data of Table I. The strong absorption by the blank in the region of interest precludes increasing the concentration of the reagent appreciably, as this would result in decreased analytical precision for gold concentrations a t the lower end of the calibration curve. Since, as will be shown, a large mole ratio of rhodanine:Au is necessary for complete color development, the 6 X 10-jM reagent concentration chosen for this procedure sets a n effective upper limit of about 1 X 10WM Au for which the linear relationship of net absorbance and gold concentration is valid. A measure of the reproducibility of the method was obtained by analysis of data accumulated from twelve independent experiments. The average net absorbance for 4.7 x 10-6M Au using the recommended procedure was 0.180, with a standard deviation of 0.0025. Rate of Color Development and Color Stability. Typical data for the rate of color development at room temperature by the recommended procedure are shown in Table 11. Ninety-five percent of the maximum color is attained within a half hour of initiation of reaction ( t o ) . Full color is developed by to 1M hours, and the absorbances of both the blank and the gold solution are stable for a t least 20 hours after that. Mild heating of the reaction system, e g . , for 15 minutes a t 50-60 "Cin a water bath, serves to bring about complete color development within half an hour, and has no deleterious effect on color stability. Prolonged heating at steam bath temperatures appears t o result in some deterioration of the colored product of the gold-rhodanine reaction, however, and is not recommended. T h e absorbance of the blank was not affected by either heat treatment. The reaction product does not appear t o be sensitive to diffuse light, and it is not necessary t o store solutions in the dark if it is desired to await full color development before taking absorbance readings. Percent Pyridine in the System. T h a t pyridine may be an integral part of the reaction system and not merely a ve-
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
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Table I. Absorbance of B l a n k a n d of 4.7 X 10-6M A u at Various Wavelengths Using Recommended Procedure Ab sorb anc e A, nm
505 510 515 520
Hlank
Au
Net
0.575 0.425 0.304 0.209
0.750 0.610 0.488 0.384
0.175 0.185 0.184 0.175
05/
15
20
ADJUSTED pH’s
25
30
35-40
I
70
Table 11. R a t e of Color Development for 4.7 X 10-6M Au at Ambient Temperature Using Recommended Procedure T i m e from initiation
N e t absorbance
of reaction, hr
us. blank
0.5 1.5 3 .O 5 .O 7.5 23.
0.175 0.184 0.184 0.184 0.182 0.180
Table 111.Variation of Color Developed a n d Wavelength of AhfaximumAbsorbance (Amax) with Percent Pyridine at 4.7 X 10-6M Au a n d 4 X lO-5M Rhodanine Yo Pyridine (v/v)
Amax, nm
6 10 12 16 22
Net absorbance a t Amax
530 520 5 15-520 510-515 510
0.070 0.167 0.175 0.186 0.180
Table IV. Variation of Color Developed by 4.7 X 10-6M Au as a Function of t h e Rhodanine: Gold Mole Ratio Rhodanine:Au, mole ratio
Net absorbance US. blank
1.5 4.8 7.9 11.8 15.8
0.064 0.154 0.176 0.186 0.186
Table V. Effect of Chloride Concentration on Color Developed by 4.7 x 10-6M A u IC1-I,
M
0.006 0.03 0.12 0.6
Xet absorbance
0.171 0.177 0.180 0.168
hicle for keeping rhodanine in solution is indicated by the data of Table 111. Maximum color is obtained in the 15-20 vol % pyridine region. Absorbance falls off drastically when there is less than 10% pyridine in the system. Further evidence for interaction of pyridine with the Au-rhodanine reaction product is the shift in the wavelength of maximum toward the UV as the percent pyridine in absorption, A,, the system increases.
ICORRELATION APPROXI L
7.4
7.8
82
8.6
9.0
F I N A L pH OF SYSTEM (CORRELATED WITH PBSORBANCES)
Figure 1. Correlation of adjusted and final pH’s with net absorbances of 3.8 X 10-6M Au (1) and Blank (2). Initial rhodanine concentrations of each, 4 X 10-5M
Effect of Rhodanine :Gold Concentration Ratio. In Table IV is shown the dependence of color development on the mole ratio of rhodanine to gold in the system. Evidently, a substantial excess of the reagent is necessary for complete color development. A mole ratio of a t least 1 O : l is desirable for attaining maximum color development. Below 8:l the reduction in color becomes analytically significant. Effect of Chloride Concentration. The color developed by the Au-rhodanine reaction in aqueous pyridine medium is only slightly affected by substantial changes in sodium chloride concentration, as can be seen from Table V. The recommended procedure results in a final chloride concentration in the system of about 0.1M. This is quite convenient from a practical standpoint, as it permits the use of a reasonably concentrated HCl solution in the dissolution of residues obtained on decomposition of gold-containing materials. Effect of pH. A study was made of the effect on color development of the p H to which the gold solution was adjusted prior to addition of the reagent. Although it is the final p H of the system that ultimately affects color development, for practical purposes we are interested in establishing the optimal p H t o which the sample should be adjusted before initiating reaction. It is therefore useful to correlate adjusted as well as final pH’s of the system with color development, as well as with each other, if possible. Figure 1 illustrates this kind of correlation graphically. With regard to the gold-containing solution, net absorbance is essentially constant for final pH’s in the range 7.88.6, which correspond to initially adjusted pH’s in the range 2.0-4.0. For a final p H of 7.3, the absorbance falls off appreciably, so an initial p H of 1.5 for the system is clearly unsatisfactory. Initial pH’s greater than 4.0 were not investigated, as it did not seem wise to risk loss of gold on standing in near-neutral solutions ( 5 ) . The blank is quite insensitive to variation in final pH in the region 8.2-8.8 (and probably above). Appreciable increase in the blank is noted in going from pH 8.2 to 7.8, and the blank increases very rapidly for final pH’s below 7.8. Since even a small uncertainty in the blank is magnified in the uncertainty of the net absorbance of the gold-containing solution, blank uncertainty must be kept to a minium. In conjunction with other requirements for this system, it is felt that a target for the final p H of 8.4 f 0.2 is desirable, and that this can best be met by using initially adjusted pH’s in the 2.5-4.0 region. The procedure recommended calls for an adjustment to 3.0. In special cases (as for silver interference, to be discussed later), other pH’s in the optimal range can of course be used. ANALYTICAL C H E M I S T R Y , VOL. 47, NO. 3 , M A R C H 1975
467
Siluer. Silver must be masked or otherwise removed from the system, as it forms a highly insoluble orange-red precipitate with rhodanine in aqueous pyridine, similar to its behavior in acidic media ( 7 ) . Chloride does not suffice to mask Ag+ here. Iodide is an excellent masking agent for Ag+ in the aqueous pyridine system, however, and does not interfere with the Au-rhodanine reaction a t concentrations of 4 X 10-3M or less. A t higher iodide concentrations, less Au-rhodanine color is developed. This may be due to unfavorable equilibria involving AuI2- and rhodanine a t the higher I- concentrations (8). Excellent recovery of Au is obtained in the presence of a fivefold mole excess of Ag+, using 2 or 4 X 10-3M I-. When iodide masking is called for, as in this case, it is prudent to adjust the gold-containing solution to the highest practical pH prior to adding KI to avoid air oxidation of I-. Hence, a pH of 4.0 is recommended. The "iodide procedure" yields a blank identical with one developed by the general procedure (pH 3.0, no I-), and no change in the iodide blank is noted over a period of many hours. An alternative to masking Ag is to separate gold from it. In Mizuike's method ( 9 ) , mercury in ammoniacal solution is used to collect Au selectively and thus to separate it from relatively large amounts of silver and macro amounts of copper. Summary. Results of the studies on masking of noble metal interferences are summarized in Table VI. E x t r a c t i o n Studies. In an effort to improve the sensitivity and calibration range of the method by separation of the Au-rhodanine reaction product from excess reagent, extractions of the aqueous pyridine system were carried out with a number of organic solvents (e.g., chloroform, toluene). However, the strongly absorbing excess rhodanine reagent was extracted into these media along with Au-rhodanine, and could not be successfully removed from them by scrubbing or back-extraction. Thus extraction, although useful for concentrating the Au-rhodanine reaction product ( I O ) , is not capable of reducing the reagent blank correction. Nor is it likely to be generally useful for separating Au from interferences (11, 1 2 ) . Applications. The rhodanine method developed in the course of this work has been successfully applied to the determination of gold in noble metal (Au-Pt) films and in certain glasses.
Table VI. Masking of Noble Metal Interferences Mole ratio, Species
,MjAua
PtCI6-*
6.4 3.6 4.2 4.0 4.7
PdCI,-' RhC1,-3 RuC&-~
Ag+
Masking agent and concn,
2 X lo4 4 X lo4 2 X lo4 2 X lo4 Iodide: 2-4 X EDTA: EDTA: EDTA: EDTA:
Ai. recovery, %
b99,105, 110 '110, 118, 143 '101 '106 elOl
a Au (as A u C l d - ) a t 4.7 X 10-6M in a l l cases. b , c Calculated from absorbance of same solution relative t o one containing no Pt (Pd) at, respectively, 0.5, 1, or 2 hours after a d d i t i o n of rhodanine reagent. d Recoveries did n o t v a r y with t i m e . e Calculated relative to a n Au standard containing EDTA. Recovery relative t o a n Au
standard containing iodide was 106%.
Masking of Interferences. E D T A as a General Masking Agent. EDTA in mole excess of Au by as much as 100fold has relatively little effect on the color developed by the Au-rhodanine reaction. A decrease in net absorbance of about 5% relative to that of a system containing no EDTA is obtained using either 2 or 4 X 10-4M EDTA. Base Metal Interferences. T h e recommended procedure utilizes EDTA a t 2 X 10-4M as a general masking agent. This should suffice to mask sub-milligram amounts of many base metal cations. Significantly, the following ions a t the 250-pg level do not change the net absorbance of 50 pg Au by more than lt3 relative percent, and are therefore considered not to interfere with the Au-rhodanine reaction as carried out by the recommended procedure: Fe3+, Cu2+, Ni2+, Cr3+, Cr6+. Up to 1.5mg of Pb2+ can be present without interfering. As gold is rather easily separated from macro amounts of base metals, primary attention was devoted to the problem of eliminating interference from other noble metals. Noble Metal Interferences. Platinum. Platinum, as PtC1S2-, reacts slowly with rhodanine, giving high results for Au. EDTA masking reduces or a t least delays Pt interference markedly. At a 6:l Pt:Au mole ratio, the error is no more than +5 relative percent if absorbances are measured within an hour from addition of rhodanine reagent. Citrate fails to mask platinum against reaction with rhodanine. Palladium. Palladium, as PdCld", reacts rapidly with rhodanine. The resultant color is stable, and might be corrected for if the P d content of the system were known independently. EDTA masking of P d is not as effective as for Pt. A t a 4:l Pd:Au mole ratio, the error in the Au determination can be held to within +10 relative percent only by measuring the absorbance of the system within a half hour of rhodanine addition. Thus, large amounts of P d interference should be separated before attempting to determine Au. Dimethylglyoxime ( I ) or 2-nitroso-1-naphthol (6) precipitation or extraction separations of P d may be feasible. Acetylacetone is unsatisfactory here as a masking agent for palladium, and also appears to interfere with full color development in the Au-rhodanine reaction. Rhodium. Rhodium does not appear to react with rhodanine with or without EDTA present, and thus its interference with the Au determination is minimal. Ruthenium. Ruthenium does not seem to react with rhodanine, either. However, the color of RuC1& itself is such as to contribute slightly to the net absorbance a t 515 mp. EDTA masking reduces but does not eliminate this interference. At 2:1 mole ratio of Ru to Au (1:l weight ratio), the positive error in Au recovery is no greater than 3 relative percent. 468
ACKNOWLEDGMENT Helpful discussions with D. E. Campbell, M. Lynn, Y.-S. Su, and B. A. Swinehart of these laboratories is gratefully acknowledged. LITERATURE CITED E. 8 . Sandell, "Colorimetric Methods of Analysis," 3rd ed., Interscience, New York, N.Y., 1959, pp 496-502. F. E. Beamish, "The Analytical Chemistry of the Noble Metals," Pergamon, New York, N.Y., 1966, p 470. F. E. Beamish and J. C. VanLoon. "Recent Advances in the Analytical Chemistry of the Noble Metals," Pergamon, New York. N.Y., 1972, pp 324-3321 A. K. Mukherji, Anal. Cbim. Acta, 23,325 (1960). A. E. Smith, Analyst (London),98, 209 (1973). L E G. Kesser. L. E. Ross. Ross, __. Kesser, and E. T. Kucera. Kucera, Anal. Cbem., 32, 1367 (1960). Ref. 1. OD 805-812. A: M. Ksnburg and E. I. Peshchevitskii, Russ. J. horg. Cbem., 14, 485 (1969) (Eno. transl). A. Mizu'iker Talanta, 9, 948 (1962). T. M. Cotton and A. A. Woolf, Anal. Cbim. Acta, 22, 192 (1960). N. K. Podverczskaya, E. A. Shilenko, and D. P. Shcherov, Zavod. Lab, 36. - - , 661 - - (1970) IEno. transl.). R. B Doycheva. PTA. Mosheva, and E. K. Topalova, Bulg. Akad, Nauk Sofia (Doklady), 25 (5), 649 (1972).
RECEIVEDfor review June 26, 1974. Accepted November 11, 1974. Presented a t the 167th National Meeting, American Chemical Society, Los Angeles, Calif., April 3, 1974.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
