Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or...
Reexamination Certificate
2000-02-22
2002-07-30
Leary, Louise N. (Department: 1623)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
C435S975000, C435S970000
Reexamination Certificate
active
06426182
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disposal of wastes containing formaldehyde, and more particularly to a test device, method, and indicators for confirming the neutralization of formaldehyde by the calorimetric determination of excess formaldehyde neutralizer in aqueous solution.
2. Description of the Related Art
Formaldehyde is used in a wide variety of industrial and laboratory applications. Disposal of formaldehyde waste through sewer systems is inexpensive and convenient because formaldehyde is very soluble in water and is degraded by a variety of microorganisms. However, because formaldehyde is toxic, disposal of wastes containing formaldehyde requires special procedures.
The United States Environmental Protection Agency (EPA) regulations require that solutions containing formaldehyde are neutralized before being disposed into a sewer system. More specifically, the EPA requires neutralized formaldehyde solutions to be tested to verify that residual formaldehyde is below 10 ppm and that the pH is in the neutral range 6.0 to 8.0.
The safest and most practical commercial method for the neutralization of formaldehyde is by exposure of formaldehyde to sulfite ion, usually by adding sodium sulfite, sodium bisulfite, or a mixture thereof to the aqueous solution containing formaldehyde. The reactions of formaldehyde with sodium sulfite and sodium bisulfite, respectively, are the following equilibrium reactions:
whereby sodium sulfite and sodium bisulfite each react with formaldehyde to yield sodium formaldehyde bisulfite (HOCH
2
NaSO
3
), a very stable compound in aqueous solution. The equilibrium for this reaction is shifted strongly to the right (towards the formation of sodium bisulfite formaldehyde) and the relative concentrations of sulfite ion and the free formaldehyde in the solution are very low after the reaction which forms sodium bisulfite formaldehyde.
Known methods for the determination of whether formaldehyde has been neutralized in an aqueous solution have been directed toward the direct detection or measurement of the amount of free formaldehyde in the solution, and have proven problematic for several reasons. Several prior known methods are impractical and difficult to use, such as several qualitative methods for determining formaldehyde in aqueous solutions described in Walker, J. F.,
Formaldehyde,
3
rd
ed., 483-488 (1964). For example, one such method is to measure the specific gravity and refractivity of the solution, and then estimate the formaldehyde content of the solution from those measurements using a ternary diagram, such as that described in Natta, G., Baccaredda, M.,
Giorn. chim. ind. applicata,
15, 273-81 (1933). This method is not useful from a practical standpoint, as it requires the measuring of both the specific gravity and refractivity of the solution, yields only an estimate of formaldehyde concentration, is cumbersome to perform in the laboratory, and is only effective for pure aqueous formaldehyde solutions, or aqueous formaldehyde solutions containing only a very small percentage of impurities.
A more accurate method of determining formaldehyde in aqueous solutions is the sodium sulfite titration method, described by Walker, pp. 486-488. While useful in the analytical laboratory for determining the concentration of formaldehyde in aqueous solution, the sodium sulfite titration method is cumbersome to perform, both in large scale and in small scale disposals, as a qualitative method of determining whether aqueous solutions of formaldehyde have been neutralized. The sodium sulfite titration method is also time-consuming to perform, and may require multiple titrations.
Other qualitative calorimetric tests for the direct determination of formaldehyde are disadvantageous because they require acidic conditions. The accuracy of these methods is questionable, because the sodium bisulfite formaldehyde product, while stable in neutral conditions, becomes unstable in acidic conditions and decomposes to form free formaldehyde and sulfurous acid. Noller, C. R.,
Chemistry of Organic Compounds,
2
nd
ed., 201-202 (1957). Not surprisingly, these types of tests do not give meaningful results.
For example, a prior known method for the determination of formaldehyde in acidic conditions involves reacting formaldehyde with 3-methyl-2-benzothiazolone hydrazone (MBTH), followed by oxidizing the resulting adduct with ferric chloride in 1.6% sulfamic acid. Hauser, T. H. and Cummins, R. L.,
Anal. Chem.
36, 679-681 (1964). Sulfamic acid is a strong acid that will disrupt the sodium bisulfite formaldehyde complex to yield free formaldehyde, as noted by Noller, p. 202. In addition, any excess sulfite/bisulfite present in the neutralized formaldehyde solution reduces the ferric chloride and blocks the oxidation of the MBTH/formaldehdye adduct. As a result, this method is ineffective for the determination of whether formaldehyde has been neutralized with sodium sulfite/bisulfite in an aqueous solution.
Another known method for the determination of formaldehyde in acidic conditions involves the reaction of Fuchsin, a pink triphenylmethane dye, with sulfurous acid to yield the colorless leucosulfonic acid, also known as “Schiffs reagent.” Schiffs reagent is unstable, and reacts with aldehydes to form a violet-purple quinoid dye, known as the Fuchsin-aldehyde reagent. Shriner, R. L., Fuson, R. C., and Curtin, D. Y.,
The Systematic Identification of Organic Compounds,
4
th
ed., 114-115 (1956). The colored Fuchsin-aldehyde reagent is not useful for the determination of formaldehyde because, as described above, the acidic conditions needed for the assay disrupt the sodium bisulfite formaldehyde complex to yield free formaldehyde. Noller, pp.201-202; Shriner et al., pp.149-150.
Still other qualitative calorimetric methods for the direct determination of formaldehyde are disadvantageous because they require alkaline conditions. Similar to acidic conditions, alkaline conditions also affect the stability of sodium bisulfite formaldehyde. For example, one test for the direct determination of formaldehyde uses 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, supplied under the commercial name Purpald® by Sigma-Aldrich Co., Inc., (Purpald® is a registered trademark of Aldrich Chemical Co., Inc.) or a variant of this compound, as a calorimetric indicator in alkaline solution. This test is supplied by Sakura Finetek U.S.A., Inc. under the commercial name Tissue-Tek® NEUTRALEX™ Aldehyde Test Kit. (NEUTRALEX™ is a registered trademark of Scigen, and Tissue-Tek® is a registered trademark of Sakura Finetechnical Co., LTD). In this test, the 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole reacts with aldehydes, and is oxidized by oxygen in air to yield a purple-to-magenta-colored 6-mercapto-s-triazolo-[4,3-b]-s-tetrazine, as described in Technical Information Bulletin Number AL-145 from Aldrich Chemical Co. (citing Dickinson, R. G., Jacobsen, N. W.,
Chem. Commun.,
1719 (1970)). As demonstrated in Example I and described below, this assay is of doubtful utility.
First, the strong alkaline conditions necessary for the 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole to react with aldehydes adversely affect the stability of sodium bisulfite formaldehyde, such that the assay result is not indicative of the actual amount of free formaldehyde present in the test solution.
In addition, as demonstrated in Example I, the Tissue-Tek® test strips indicate relatively low formaldehyde levels in standard solutions actually known to have relatively high levels of formaldehyde. It is believed that the sulfite ion in the aqueous solution blocks the oxidation of the formaldehyde/4-amino-3-hydrazino-5-mercapto-1,2,4-triazole adduct which is required to form the purple-to-magenta colored triazine.
Furthermore, in solutions with relatively low formaldehyde levels, consumption of the small amount of free formaldehyde by the colorimetric indicator causes the equilibrium between free formaldehyde and sodium bisulfite formaldehyde to shift to th
Baker & Daniels
Leary Louise N.
Serim Research Corporation
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