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Semi-micro determination of silicon and phosphorus in organic compounds
389
Short communications
15 ml 0,Ol m Komplexonlosung, 20 ml Pulferlijsung und ca. 30 mg des Mischindikators zugegeben und mit 0,Ol m ~~~iumchloridl~sung von blaugriin iiber grau auf rot titriert. Bei dem Blindversuch werden 10 ml dest. Wasser mit dem F~llungsr~genz bis zur 100 ml Marke wfgefiillt und dam-r weiter wie oben beschrieben verfahren. Da zur AusfXlhmg von 2 Mol. Borslure 5 Mol. Bariumchlorid und zur Umsetzung von 1 Mol. Borax sogar 10 Mol. Bariumchlorid benotigt werden, entspricht 1 ml 0,Ol m Komplexonlosung 1 ml 0,Ol m Komplexonlijsung
= 0,04328 mg Bor = 0,38143 mg Borax (Na2Bd0,) 10 HO,
A$beit~vorschr~t~~r bariumbalt~e Salve 10 g Salz genau abgewogen werden in dest. Wasser gel&t und die Ldsung bis zur 100 ml Marke aufgefiillt. Losung 1: 10 ml dieser Losung werden in einen Messkolben pipettiert und mit dem Fallungsreagenz 2 bis zur Marke aufgeftillt. Nach 2 Std. wird dann wie oben beschrieben weiter verfahren. 10 ml der Losung 1 werden in einem Der Blindversuch wird folgendermassen durchgeftihrt: 100 ml Messkolben mit destilliertem Wasser bis zur Marke aufgef~llt und dann, wie bereits beschrieben, weiter verfahren. Der Verbrauch an Komplexon III kann hierbei gleich auf BaCla umgerechnet werden. Es ist also moglich, in einer Einwaage neben dem Borax-Gehalt such gleich ben Bariumchloridgehalt zu bestimmen. OTTO BORCHERT
SchiinebeckjElbe
LITERATUR 1 H. Ballczo und G. Doppler, Mikvochim. Acta, 1954, 403. ibid., 1956, 734. e J. A. Gautier und P. Pignard, Mikrochem. Mikrochim. Acta, 1951, 36137, 793.
Semi-micro determination of silicon and phosphorus in organic compounds (Received 30 May 1959) No method applicable when both silicon and phosphors were present in a compound has been mentioned in recent reviews of methods for the determination of silicon’,2 and phosphor&r* in organic compounds. In the analysis of silicon in rocks, Brabson et aL5 precipitated phosphorus with the silicon and corrected for the phosphorus content; and Wilson6 prevented co-precipitation of silicate with phosphate without separation when analysing fertilisers. It is, perhaps, relevant to note here that, during some preliminary experiments, it was found that silicon could not be determined in the presence of phosphorus-containing materials by simple wet oxidation of the organic material in a platinum crucible followed by weighing the silica,produced. Very high results were obtained. In order to permit analysis of some high-boiling liquids containing silicon and phosphorus, two semi-micro methods used in our laboratory for the determination of phosphorus have been modified to allow the determination of phosphorus and silicon on one individual sample. Acid digestion method The method of Belcher and God~rt’~igestion with nitric and sulphur~c acids followed by gravimetric determination of phosphate after precipitation with JGrgensen’s reagent-although shown not to be universally applicable ,a had given satisfactory results for the determination of phosphorns in a variety of organic compounds. It was established that, after acid digestion of compounds containing silicon and phosphorus, the phosphate-containing acid liquid could be quantitatively separated from the silica precipitated in the glass boiling tube by use of an elongated
390
Short communications
glass filter stick (porosity 4). However, it was found impossible to dry the residue of silica in the glass tube so as to give consistent weights (in situ) for the determination of silicon. In order to overcome this difficulty, a reasonably non-hygroscopic form of silica was prepared by removing the digestion liquid and then washing the residue with nitric acid (1 + 1) followed by alcohol. The residue was t’hen dried at 100” under reduced pressure, cooled in a desiccator and weighed. The majority of this silica was then tipped into a platinum crucible, weighed, ignited to bright red heat and weighed again. The correction factor (weight after ignititionlweight of silica ignited) was applied to the original total weight of silica in the boiling tube and the silicon content c&ulated from this corrected figure. TABLE I
Compound
% Si calculated
% Si found
13.09
13.22 13.18 13.14 12.94 8.50 8.52 7.17 7.49 7.53 7.59
8.84 I,28
%P
%P
calculated
found
9.75
9.15 9.76 7.80 7.80 7.78
8.04
The results obtained for the analysis of three research compounds (one not containing phosphorus) by this method are shown in Table I. Peroxide
bomb method
The second, and more universally succeSsfu1, methods used in our laboratory‘for phosphorus determination involves decomposition of the organic material (in a micro bomb) with sodium peroxide followed by precipitation of phosphate in the acidified bomb leachings as quinoline phosphomolybdate. Co-precipitation of silicomolybdate could be avoided by complexing with citric acid6 or by removal of the silicons by volatilisation as tetrafluoride or precipitation as silica. The latter procedure was found to provide a means for the determination of silicon. The normal procedure for the determination of phosphorus8 was followed except that the acidified bomb leachings were evaporated to dryness and baked at 110”. After cooling, the crystals were moistened with concentrated hydrochloric acid, dried and baked again. The soluble salts were dissolved in hot water and filtered through a paper-pulp pad, the filtrate and washings being collected in a conical flask for precipitation of phosphate in the usual way. All the insoluble residue was collected on the paper pad during the filtration and the whole was quantitatively transferred into a platinum crucible. The paper was ashed and the residue was weighed, treated with hydrofluoric acid and reweighed. From the loss in weight, the silicon content of the organic material was calculated. Results obtained for the analysis of three organic compounds are shown in Table II. A gravimetric finish9 for the determination of phosphorus was used. Discussion
From the limited number of samples available, both methods have produced results which are within the normally accepted limits (ho.3 ‘A)for organic analysis but it is considered that the procedure following peroxide bomb fusion is superior, being manipulatively simpler, more precise and, probably, more universally applicable.
Short communications
391
TABLE II
Compound
% Si calculated
% Si found
12.03
11.81 11.91 8.68 8.74 7.15 7.15
8.84 7.28
13.28 9,75 8.04
/
13.16 13.18 9.72 9.75 8.00 7.99
. Both methods suffer from the disadvantage that the conversion factor for silicon (Si/SiO, = 0.4672) is poor, requiring a sample containing at least 2.5 mg of silicon to provide a reasonable Precipitation as the silicomolybdate of an organic baser0-r2 might weight of silica for determination. provide a better means for determining silicon after separation from phosphate. Interference in the determination of silicon by fluoride, after mineralisation in the peroxide bomb, can be overcome by the addition of boric acid to the bomb leachings before acidification. Acknowledgements-We are indebted to Mr. E. J. P. Fear and Dr. I. M. White for the provision of sample:, and to Mrs. M. W. Roberts for experimental work on the acid digestion procedure. I
T. R. F. W. FENNELL
Royal Aircraft Establishment Farnborough, Ha&s, England
J. R. WEBB
REFERENCES 1 R. Belcher, D. Gibbons and A. Sykes, Mikrochem., 1952, 76. 2 A. Sykes, Mikrochim. Acta, 1956, 1155. s J. E. Fildes, Znd. Chem., 1955, 31, 412. 4 A. M. G. Macdonald, ibid., 1957,33, 360. 5 J. A. Brabson, H. C. Mattraw, G. E. Maxwell, A. Darrow and M. F. Needham, Analyt. Chem., 1948,20, 504. 6 H. N. Wilson, Analyst, 19.54,79, 535. ’ R. Belcher and A. L. Godbert, ibid., 1941, 66, 184. 8 T. R. F. W. Fennell, M. W. Roberts and J. R. Webb, ibid., 1957, 82, 639. 9 T. R. F. W. Fennel1 and J. R. Webb, Talanta, 1959, 2, 105. lo H. N. Wilson, Analyst, 1949, 74, 243. I1 H. Armand and J. Berthoux, Analyt. Chim. Acta., 1953, 8, 510. I2 C. C. Miller and R. A. Chalmers, Analyst, 1953, 78,24.
Short communications
15 ml 0,Ol m Komplexonlosung, 20 ml Pulferlijsung und ca. 30 mg des Mischindikators zugegeben und mit 0,Ol m ~~~iumchloridl~sung von blaugriin iiber grau auf rot titriert. Bei dem Blindversuch werden 10 ml dest. Wasser mit dem F~llungsr~genz bis zur 100 ml Marke wfgefiillt und dam-r weiter wie oben beschrieben verfahren. Da zur AusfXlhmg von 2 Mol. Borslure 5 Mol. Bariumchlorid und zur Umsetzung von 1 Mol. Borax sogar 10 Mol. Bariumchlorid benotigt werden, entspricht 1 ml 0,Ol m Komplexonlosung 1 ml 0,Ol m Komplexonlijsung
= 0,04328 mg Bor = 0,38143 mg Borax (Na2Bd0,) 10 HO,
A$beit~vorschr~t~~r bariumbalt~e Salve 10 g Salz genau abgewogen werden in dest. Wasser gel&t und die Ldsung bis zur 100 ml Marke aufgefiillt. Losung 1: 10 ml dieser Losung werden in einen Messkolben pipettiert und mit dem Fallungsreagenz 2 bis zur Marke aufgeftillt. Nach 2 Std. wird dann wie oben beschrieben weiter verfahren. 10 ml der Losung 1 werden in einem Der Blindversuch wird folgendermassen durchgeftihrt: 100 ml Messkolben mit destilliertem Wasser bis zur Marke aufgef~llt und dann, wie bereits beschrieben, weiter verfahren. Der Verbrauch an Komplexon III kann hierbei gleich auf BaCla umgerechnet werden. Es ist also moglich, in einer Einwaage neben dem Borax-Gehalt such gleich ben Bariumchloridgehalt zu bestimmen. OTTO BORCHERT
SchiinebeckjElbe
LITERATUR 1 H. Ballczo und G. Doppler, Mikvochim. Acta, 1954, 403. ibid., 1956, 734. e J. A. Gautier und P. Pignard, Mikrochem. Mikrochim. Acta, 1951, 36137, 793.
Semi-micro determination of silicon and phosphorus in organic compounds (Received 30 May 1959) No method applicable when both silicon and phosphors were present in a compound has been mentioned in recent reviews of methods for the determination of silicon’,2 and phosphor&r* in organic compounds. In the analysis of silicon in rocks, Brabson et aL5 precipitated phosphorus with the silicon and corrected for the phosphorus content; and Wilson6 prevented co-precipitation of silicate with phosphate without separation when analysing fertilisers. It is, perhaps, relevant to note here that, during some preliminary experiments, it was found that silicon could not be determined in the presence of phosphorus-containing materials by simple wet oxidation of the organic material in a platinum crucible followed by weighing the silica,produced. Very high results were obtained. In order to permit analysis of some high-boiling liquids containing silicon and phosphorus, two semi-micro methods used in our laboratory for the determination of phosphorus have been modified to allow the determination of phosphorus and silicon on one individual sample. Acid digestion method The method of Belcher and God~rt’~igestion with nitric and sulphur~c acids followed by gravimetric determination of phosphate after precipitation with JGrgensen’s reagent-although shown not to be universally applicable ,a had given satisfactory results for the determination of phosphorns in a variety of organic compounds. It was established that, after acid digestion of compounds containing silicon and phosphorus, the phosphate-containing acid liquid could be quantitatively separated from the silica precipitated in the glass boiling tube by use of an elongated
390
Short communications
glass filter stick (porosity 4). However, it was found impossible to dry the residue of silica in the glass tube so as to give consistent weights (in situ) for the determination of silicon. In order to overcome this difficulty, a reasonably non-hygroscopic form of silica was prepared by removing the digestion liquid and then washing the residue with nitric acid (1 + 1) followed by alcohol. The residue was t’hen dried at 100” under reduced pressure, cooled in a desiccator and weighed. The majority of this silica was then tipped into a platinum crucible, weighed, ignited to bright red heat and weighed again. The correction factor (weight after ignititionlweight of silica ignited) was applied to the original total weight of silica in the boiling tube and the silicon content c&ulated from this corrected figure. TABLE I
Compound
% Si calculated
% Si found
13.09
13.22 13.18 13.14 12.94 8.50 8.52 7.17 7.49 7.53 7.59
8.84 I,28
%P
%P
calculated
found
9.75
9.15 9.76 7.80 7.80 7.78
8.04
The results obtained for the analysis of three research compounds (one not containing phosphorus) by this method are shown in Table I. Peroxide
bomb method
The second, and more universally succeSsfu1, methods used in our laboratory‘for phosphorus determination involves decomposition of the organic material (in a micro bomb) with sodium peroxide followed by precipitation of phosphate in the acidified bomb leachings as quinoline phosphomolybdate. Co-precipitation of silicomolybdate could be avoided by complexing with citric acid6 or by removal of the silicons by volatilisation as tetrafluoride or precipitation as silica. The latter procedure was found to provide a means for the determination of silicon. The normal procedure for the determination of phosphorus8 was followed except that the acidified bomb leachings were evaporated to dryness and baked at 110”. After cooling, the crystals were moistened with concentrated hydrochloric acid, dried and baked again. The soluble salts were dissolved in hot water and filtered through a paper-pulp pad, the filtrate and washings being collected in a conical flask for precipitation of phosphate in the usual way. All the insoluble residue was collected on the paper pad during the filtration and the whole was quantitatively transferred into a platinum crucible. The paper was ashed and the residue was weighed, treated with hydrofluoric acid and reweighed. From the loss in weight, the silicon content of the organic material was calculated. Results obtained for the analysis of three organic compounds are shown in Table II. A gravimetric finish9 for the determination of phosphorus was used. Discussion
From the limited number of samples available, both methods have produced results which are within the normally accepted limits (ho.3 ‘A)for organic analysis but it is considered that the procedure following peroxide bomb fusion is superior, being manipulatively simpler, more precise and, probably, more universally applicable.
Short communications
391
TABLE II
Compound
% Si calculated
% Si found
12.03
11.81 11.91 8.68 8.74 7.15 7.15
8.84 7.28
13.28 9,75 8.04
/
13.16 13.18 9.72 9.75 8.00 7.99
. Both methods suffer from the disadvantage that the conversion factor for silicon (Si/SiO, = 0.4672) is poor, requiring a sample containing at least 2.5 mg of silicon to provide a reasonable Precipitation as the silicomolybdate of an organic baser0-r2 might weight of silica for determination. provide a better means for determining silicon after separation from phosphate. Interference in the determination of silicon by fluoride, after mineralisation in the peroxide bomb, can be overcome by the addition of boric acid to the bomb leachings before acidification. Acknowledgements-We are indebted to Mr. E. J. P. Fear and Dr. I. M. White for the provision of sample:, and to Mrs. M. W. Roberts for experimental work on the acid digestion procedure. I
T. R. F. W. FENNELL
Royal Aircraft Establishment Farnborough, Ha&s, England
J. R. WEBB
REFERENCES 1 R. Belcher, D. Gibbons and A. Sykes, Mikrochem., 1952, 76. 2 A. Sykes, Mikrochim. Acta, 1956, 1155. s J. E. Fildes, Znd. Chem., 1955, 31, 412. 4 A. M. G. Macdonald, ibid., 1957,33, 360. 5 J. A. Brabson, H. C. Mattraw, G. E. Maxwell, A. Darrow and M. F. Needham, Analyt. Chem., 1948,20, 504. 6 H. N. Wilson, Analyst, 19.54,79, 535. ’ R. Belcher and A. L. Godbert, ibid., 1941, 66, 184. 8 T. R. F. W. Fennell, M. W. Roberts and J. R. Webb, ibid., 1957, 82, 639. 9 T. R. F. W. Fennel1 and J. R. Webb, Talanta, 1959, 2, 105. lo H. N. Wilson, Analyst, 1949, 74, 243. I1 H. Armand and J. Berthoux, Analyt. Chim. Acta., 1953, 8, 510. I2 C. C. Miller and R. A. Chalmers, Analyst, 1953, 78,24.