Titer (or titre) is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive reading. For example, positive readings in the first 8 serial twofold dilutions translate into a titer of 1:256 (i.e., 2−8). Titers are sometimes expressed by the denominator only, for example 1:256 is written 256.
The term has also two other, conflicting meanings. In titration, the titer is the ratio of actual to nominal concentration of a titrant, e.g. a titer of 0.5 would require 1/0.5 = 2 times more titrant than nominal. This is to compensate for possible degradation of the titrant solution. Second, in textile engineering, titer is a synonym for linear density.
A specific example is a viral titer, which is the lowest concentration of virus that still infects cells. To determine the titer, several dilutions are prepared, such as 10−1, 10−2, 10−3, ... 10−8.
The titer of a fat is the temperature, in degrees Celsius, at which it solidifies. The higher the titer, the harder the fat. This titer is used in determining whether an animal fat is considered tallow (titer higher than 40 °C) or a grease (titer below 40 °C).
- Michael G. Kaplitt; Arthur D. Loewy (1 August 1995). Viral vectors: gene therapy and neuroscience applications. Academic Press. p. 304. ISBN 978-0-12-397570-6. Retrieved 18 March 2012.
- Morag Crichton Timbury (1994). Notes on medical virology. Churchill Livingstone. p. 27. ISBN 978-0-443-04872-2. Retrieved 18 March 2012.
- Harold E. Fox; Jessica Bienstock (21 December 2010). The Johns Hopkins Manual of Gynecology and Obstetrics. Lippincott Williams & Wilkins. p. 226. ISBN 978-1-60547-433-5. Retrieved 18 March 2012.
- Richard D. O'Brien (5 December 2008). Fats and oils: formulating and processing for applications. CRC Press. p. 207. ISBN 978-1-4200-6166-6. Retrieved 18 March 2012.
- van Gerpen, Jon Harlan; Rudy Pruszko; Davis Clements; Gerhard Knothe; Brent Shanks (2006). Building a Successful Biodiesel Business (2nd illustrated ed.). Biodiesel Basics. p. 93. ISBN 0-9786349-0-X. Retrieved 2009-07-11.