How to determine level of Hydrazine

Hydrazine

Hydrazine in boiler water is an effective chemical oxygen scavenger, reacting with dissolved oxygen to produce nitrogen and water. These reaction products do not add solids to the boiler  water and are not corrosive to ferrous metals. For these reasons, hydrazine often is used rather than sodium sulfite as an oxygen scavenger in high pressure boiler.

Theoretically, 1.0 ppm of hydrazine is required to react with 1.0 ppm of dissolved oxygen. Unreacted hydrazine can be composed to form ammonia (which may attack copper or copper- containing alloys). To avoid excessive ammonia concentrations in the steam, the residual hydrazine in the boiler water is usually maintained at 0.1 ppm or less.

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Hydrazine, Photometric Method (0-0.3 ppm) Theory of Test

This photometric method is based on the reaction of pipidiamino benzaldehyde with hydrazine to produce a yellow color. The intensity of the yellow color is proportional to the amount of  hydrazine in the sample.

Apparatus Required

Filter photometer complete with assorted laboratory glassware.

Chemicals Required

Hydrazine Reagents A, B, C, and D Hexyl Alcohol

Hydrochloric Acid

Concentrated Hydrrazine Standard

Methyl Alcohol (absolute)

Calibration Curves

This method for the determination of Hydrazine uses a wavelength of 460 nm and a light path of 20 mm. Prepare a calibration curve in the following manner. Mix 20 ml of reagent B and 25 ml of reagent C, and use this mixture to set the photometer at zero on the dial. Mix 20 ml of reagent A and 25 ml of reagent C and use this mixture to obtain a reference point for hydrazine free water (zero hydrazine).

Reference points for the remainder of the calibration curve are obtained by a series of dilutions of reagent D to a total volume of 200-ml, using a volumetric flask and reagent C as the diluent. For example, 2.0 ml reagent D diluted to 200 ml in a volumetric flask with reagent C is equivalent to 0.01 ppm hydrazine, undiluted reagent D is 1.0 ppm hydrazine. Reference points are obtained by treating 25 ml portions of the dilutions with 20 ml reagent A, as shown below.

Each time a determination is made, the calibration curve should be checked to establish a correction factor. This procedure is necessary to insure that the results are accurate since reagent age and stability as well as temperature can affect the results. The curve should be checked with reagent C and also at a dilution at reagent D that approximates the middle of the hydrazine range covered by the curve. All reagent as well as the check samples and the actual sample to be  analyzed must be at the same temperature.

Procedure for Test Colorless sample

To determine hydrazine in a colorless sample, add 15 ml of concentrated hydrochloric acid to the sample bottle marked at 200 ml and collect the sample with minimum exposure to air until the 200 ml mark is reached. Measure 25 ml of the sample and add 20 ml of the reagent B.  Use this  mixture as a blank to set the photometer at zero absorbance. Measure a second 25 ml portion of the sample and add 20 ml of reagent A. Pour the prepared solution into the optical cell and read the absorbance at the end of one minute.

Colored sample

To determine hydrazine in a colored sample, add 15 ml of concentrated hydrochloric acid to the sample bottle marked at 200 ml and collect the sample with minimum exposure to air until the 200- ml mark is reached. Transfer 50 ml of the collected sample by means of a graduate to a separatory funnel, add 10 ml of the hexylalcohol by means of a pipet, and mix by shaking the funnel. Allow the layers to separate and then drain the bottom layer into a beaker for use as the sample. Add 20 ml of the reagent B to 25 ml of the prepared sample, mix and set the photometer to zero absorbance using this solution as a reference.  Add 20 ml of the reagent A to the remaining 25-ml portion of  the sample. Measure the absorbance of this solution at the end of one minute.

Calculation of Results

The hydrazine content in parts per million as N2H4 is obtained by reference to the calibration curve.

Limitations of Test

Ions normally present in industrial boiler water do not interfere with this test. If oxidizing agents are collected with the sample or absorbed prior to testing, the hydrazine content may be diminished.

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