Formaldehyde
 
 
Visual Kits
Range MDL Method Kit Catalog No. Refill Catalog No.
0-1 & 1-5 ppm 0.1 ppm Purpald K-4605 R-4605
0-30 & 30-150 ppm 5 ppm Purpald K-4605D R-4605D
0-60 & 60-300 ppm 10 ppm Purpald K-4605A R-4605A
0-120 & 120-600 ppm 20 ppm Purpald K-4605B R-4605B
0-1200 & 1200-6000 ppm 200 ppm Purpald K-4605C R-4605C
0.5-5% 0.50% Acid Titrant with Thymolphthalein Indicator K-4250 N/A
Instrumental Kits
Range Method Kit Catalog No.
0.40-8.00 ppm Purpald K-4203

Methods

Formaldehyde, a toxic substance, is used in the following applications: metal plating baths, textile treatments, biological specimen preservatives, and disinfectants of medical equipment. Commercial formaldehyde gas is readily soluble in water.

 

The Purpald Method

Reference: Purpald® developed by Aldrich Chemical Co.


Purpald® is subject to fewer interferences than Shiffs' reagent or chromotropic acid procedures. A purple-colored complex is formed when Purpald in alkaline solution reacts with formaldehyde. Results are expressed as ppm (mg/L) CH2O.

 

Shelf-life of the Purpald Reagent: five months. We recommend stocking quantities that will be used within four months.

 

The Acid Titrimetric Method


Reference: ASTM D 2194-79, Concentration of Formaldehyde Solutions.


CHEMetrics offers a titrimetric method for formaldehyde, which uses sulfuric acid and sodium sulfite. The end point indicator, thymolphthalein, provides a sharp color change from colorless to bright blue. Results are expressed as percent (%) formaldehyde.