The HT5011 solutions are advertised as 10% Neutral Buffered Formalin. The formaldehyde content, however, is expected to be in the range of 3.7% to roughly 4.0%. This can be rather confusing because the terms formaldehyde and formalin are often used interchangeably by some. For many histology laboratories, formaldehyde is used to describe formaldehyde content. Some laboratories do consider the terms interchangeable. Formalin is used to describe a dilution from the 37% to 40% stock bottle of the saturated solution. If the 37% to 40% solution is diluted 1 to 10, this is the origin of the term 10% formalin. But the formaldehyde content is still just 3.7% to 4.0%.
If a simple 2% solution of HT501 is desired, then simply dilute 1 part of HT501 with 4 parts of water. This would result in a formaldehyde content ranging from 0.74% to 0.8%. If you dilute with water, there is a chance the expiration dating could be affected. A better way to dilute 10% formalin would be to create a salt solution used for the original product. To prepare a suitable diluent for dilution, combine 4 grams of sodium phosphate monobasic and 6.5 grams of sodium phosphate, dibasic (anhydrous) in 1 liter of water. The water can be diluted in either distilled or deionized water. If 1 liter of diluent is not required, simply scale down in a proportional amount the amount of chemicals and water used. If the salts are used for dilution, it would probably be best to prepare a 2% solution and use it immediately. If a 2% formaldehyde solution is required, simply dilute the stock HT501 one to one with either water or the salt solution mentioned above. If using water, the same recommendation for immediate use is appropriate.