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Determination of formaldehyde via EDTA titration
MICROCHEMICAL
JOURNAL
Determination
(1968)
of Formaldehyde
L.&LO Chemical
13, 227-229
Institute
SZEKERES
AND
AGNES
of the Veterinary Received
via EDTA KELLNER
University,
October
Titration’
Budapest,
Hungary
3, 1967
It has been pointed out by several authors that oxydizing and reducing agents can be determined volumetrically via titration with EDTA (J-8). Th is is possible in two cases. (a) If a polivalent cation is formed in a quantitative redox reaction, which cation forms a stable complex with EDTA, then the cation formed can be titrated with EDTA solution. (b) If a cation which has a stable EDTA complex is converted by a redox reaction into a noncomplex-forming cation or ‘to a metal, then only the nonreacted amount of the cation is measured by the EDTA solution. We have already shown previously, that the mercury( I)-mercury(I1) system can be utilized for the determination of reducing or oxydizing agents, as only mercury ( II ) f orms stable complex with EDTA (4). We applied these principles to the determination of formaldehyde as follows: The solution of formaldehyde was added to a mixture of known concentration of Hg( NOs)a and EDTA, the resulting mixture was made alkaline and allowed to stand. The complex of mercury( II) is reduced and HgzO is formed, which disproportionately converts to mercury metal and HgO. The metallic mercury settles as a black precipitate, while the HgO forms an EDTA complex again. Thus the overall reaction is the following: HgO
+
HCHO
=
Hg
+
HCOOH,
that is, 1 mole of EDTA is equivalent to 1 mole of HCHO, this is liberated during the reaction, and it can be titrated (Table I ). Reagents. A 0.1 M Hg( NO 3) 2 solution, which also contains 63 g of HNOB in 1006 ml; a 0.1 M EDTA soln; 2 N NaOH soln; 2 N HN03 soln; crystalline hexamethylene tetramine; and methylthymol blue as 1: 100 ground mixture with KNOB. 1 Part IV of the series: Chelatometric methods and reductants. Part III of the series was published (1966). 227
in the determination in Chemist-Analyst
of oxidants 55, 77-76
228
SZEKERES
AND
KELLNER
TABLE DETERMINATION Formaldehyde
1
OF FORMALDEHYDE
(mg)
Taken
Found
7.50 7.50 12.75 12.75 19.12 19.12 25.50 25.50
7.58 7.62 12.60 12.36 18.60 18.72 25.95 25.86
Difference
(mg
)
0.08 0.12 0.15 0.39 0.52 0.40 0.45 0.36
Procedure. Add 15-25 ml of 0.1 M EDTA soln to 10-20 ml of 0.1 M Hg(N03)2. Wait until the sohr clears, then add 5-20 ml of 0.1 N formaldehyde soln. Adjust the pH to about 9-10 by the addition of 2 N NaOH, and let it stand for 2 hours. The mercury precipitates in the flask, and this precipitate does not disturb further titration. After 2 hours add the calculated amount of 2 N HNOs adjusting the pH to 44, then adjust to final pH of 6 by the addition of hexamethylene tetramine crystals. Titrate the excess of EDTA in the presence of methylthymol blue with 0.1 A4 Hg( NOa) soln. The change of color (from yellow to blue) can be observed distinctly (9). RESULTS As shown in Table simple method.
1 satisfactory
results
were
obtained
by the application
of this
REFERENCES I. 2. 3.
4.
BEFUCA, A., Indirekte komplexometrische Bestimmung AIkohole und a -Hydroxysauren. 2. Anal. Chem. 195, DOLEZAL, J. AND ZYKA, J., Determination of inorganic using EDTA after amalgam reduction. Chemist-Andyst FLASCHKA, H. AND GARRETT, J., Determination of some by oxydation with permanganate and subsequent EDTA Analyst 52, 101-103 (1963). KELLNER, A. AND SZEKERES, L., Determination of some tants via EDTA titrations. Chemist-Analyst 54, 75-76
einiger mehrwertiger 263-266 ( 1963). and organic systems 53, 63-69 ( 1964). organic compounds titration. Chemistoxidants ( 1965).
and
reduc-
DETERMINATION
5.
6. 7.
8. 9.
OF
FORMALDEHYDE
229
PRIEXL, R., “Komplexone in der chemischen Analyse,” pp. 443, 459. Deut. Verlag. Wiss., Berlin, 1961. SCRIBNER, W. G. AND F~EILLEY, C. N., Indirect complexometric analysis with aid of liquid amalgams. Anal. Chem. 30, 1452-1462 ( 1958). SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Determination of some inorganic ions and oxalate via oxidation with acid permanganate and subsequent EDTA titration. Chemist-Analyst 54, 116-117 ( 1965). SZEICERES, L., KARDOS, E., AND SZEKERES, G. L., notes on the manganese determination. Microch. J. 11, 476480 ( 1966). SZEKERES, L. AND KELLNER, A., Determination of Some Reductants Via EDTA Titrations. Chemist-Analyst 55, 77-78 ( 1966).
JOURNAL
Determination
(1968)
of Formaldehyde
L.&LO Chemical
13, 227-229
Institute
SZEKERES
AND
AGNES
of the Veterinary Received
via EDTA KELLNER
University,
October
Titration’
Budapest,
Hungary
3, 1967
It has been pointed out by several authors that oxydizing and reducing agents can be determined volumetrically via titration with EDTA (J-8). Th is is possible in two cases. (a) If a polivalent cation is formed in a quantitative redox reaction, which cation forms a stable complex with EDTA, then the cation formed can be titrated with EDTA solution. (b) If a cation which has a stable EDTA complex is converted by a redox reaction into a noncomplex-forming cation or ‘to a metal, then only the nonreacted amount of the cation is measured by the EDTA solution. We have already shown previously, that the mercury( I)-mercury(I1) system can be utilized for the determination of reducing or oxydizing agents, as only mercury ( II ) f orms stable complex with EDTA (4). We applied these principles to the determination of formaldehyde as follows: The solution of formaldehyde was added to a mixture of known concentration of Hg( NOs)a and EDTA, the resulting mixture was made alkaline and allowed to stand. The complex of mercury( II) is reduced and HgzO is formed, which disproportionately converts to mercury metal and HgO. The metallic mercury settles as a black precipitate, while the HgO forms an EDTA complex again. Thus the overall reaction is the following: HgO
+
HCHO
=
Hg
+
HCOOH,
that is, 1 mole of EDTA is equivalent to 1 mole of HCHO, this is liberated during the reaction, and it can be titrated (Table I ). Reagents. A 0.1 M Hg( NO 3) 2 solution, which also contains 63 g of HNOB in 1006 ml; a 0.1 M EDTA soln; 2 N NaOH soln; 2 N HN03 soln; crystalline hexamethylene tetramine; and methylthymol blue as 1: 100 ground mixture with KNOB. 1 Part IV of the series: Chelatometric methods and reductants. Part III of the series was published (1966). 227
in the determination in Chemist-Analyst
of oxidants 55, 77-76
228
SZEKERES
AND
KELLNER
TABLE DETERMINATION Formaldehyde
1
OF FORMALDEHYDE
(mg)
Taken
Found
7.50 7.50 12.75 12.75 19.12 19.12 25.50 25.50
7.58 7.62 12.60 12.36 18.60 18.72 25.95 25.86
Difference
(mg
)
0.08 0.12 0.15 0.39 0.52 0.40 0.45 0.36
Procedure. Add 15-25 ml of 0.1 M EDTA soln to 10-20 ml of 0.1 M Hg(N03)2. Wait until the sohr clears, then add 5-20 ml of 0.1 N formaldehyde soln. Adjust the pH to about 9-10 by the addition of 2 N NaOH, and let it stand for 2 hours. The mercury precipitates in the flask, and this precipitate does not disturb further titration. After 2 hours add the calculated amount of 2 N HNOs adjusting the pH to 44, then adjust to final pH of 6 by the addition of hexamethylene tetramine crystals. Titrate the excess of EDTA in the presence of methylthymol blue with 0.1 A4 Hg( NOa) soln. The change of color (from yellow to blue) can be observed distinctly (9). RESULTS As shown in Table simple method.
1 satisfactory
results
were
obtained
by the application
of this
REFERENCES I. 2. 3.
4.
BEFUCA, A., Indirekte komplexometrische Bestimmung AIkohole und a -Hydroxysauren. 2. Anal. Chem. 195, DOLEZAL, J. AND ZYKA, J., Determination of inorganic using EDTA after amalgam reduction. Chemist-Andyst FLASCHKA, H. AND GARRETT, J., Determination of some by oxydation with permanganate and subsequent EDTA Analyst 52, 101-103 (1963). KELLNER, A. AND SZEKERES, L., Determination of some tants via EDTA titrations. Chemist-Analyst 54, 75-76
einiger mehrwertiger 263-266 ( 1963). and organic systems 53, 63-69 ( 1964). organic compounds titration. Chemistoxidants ( 1965).
and
reduc-
DETERMINATION
5.
6. 7.
8. 9.
OF
FORMALDEHYDE
229
PRIEXL, R., “Komplexone in der chemischen Analyse,” pp. 443, 459. Deut. Verlag. Wiss., Berlin, 1961. SCRIBNER, W. G. AND F~EILLEY, C. N., Indirect complexometric analysis with aid of liquid amalgams. Anal. Chem. 30, 1452-1462 ( 1958). SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Determination of some inorganic ions and oxalate via oxidation with acid permanganate and subsequent EDTA titration. Chemist-Analyst 54, 116-117 ( 1965). SZEICERES, L., KARDOS, E., AND SZEKERES, G. L., notes on the manganese determination. Microch. J. 11, 476480 ( 1966). SZEKERES, L. AND KELLNER, A., Determination of Some Reductants Via EDTA Titrations. Chemist-Analyst 55, 77-78 ( 1966).