Taurodeoxycholic acid is a

bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primary b ...

. This compound is a closely related isomer of

Taurochenodeoxycholic acid Taurochenodeoxycholic acid is a bile acid formed in the liver of most species, including humans, by conjugation of chenodeoxycholic acid with taurine. It is secreted into bile and then into intestine. It is usually ionized at physiologic pH, altho ...

and

Tauroursodeoxycholic acid Ursodoxicoltaurine is the international nonproprietary name (INN) for the pharmaceutical form of tauroursodeoxycholic acid (TUDCA). It is also known as taurursodiol. Tauroursodeoxycholic acid is a naturally occurring hydrophilic bile acid which ...

sharing the exact molecular formula and molecular weight. Mass Spectrometry Interference with PFOS Benskin and colleagues (https://pubs.acs.org/doi/pdf/10.1021/ac070802d) published in 2007 an article identifying Taurodeoxycholic acid and isomers as mass spectrometry interferents with PFOS (

Perfluorooctanesulfonic acid Perfluorooctanesulfonic acid (PFOS) (conjugate base perfluorooctanesulfonate) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group and thus a perfluorosulfonic acid. It is an anthropogenic (man-ma ...

) as the two compounds share the m/z transition of 498-80. The molecular weight of PFOS and taurodeoxycholic acid and isomers are similar enough in molecular weight that most low resolution

Triple quadrupole mass spectrometer A triple quadrupole mass spectrometer (TQMS), is a tandem mass spectrometer consisting of two quadrupole mass analyzers in series, with a (non-mass-resolving) radio frequency (RF)–only quadrupole between them to act as a cell for collision-in ...

are unable to distinguish these two chemicals from each other. Additionally both compounds share a

Sulfonate In organosulfur chemistry, a sulfonate is a salt or ester of a sulfonic acid. It contains the functional group , where R is an organic group. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-ox ...

group (leading to the ''m/z'' 80 loss) in the common mass spectrometry transition. Reiner and colleagues https://pubs.acs.org/doi/pdf/10.1021/es800770f found these bile acid compounds in chicken eggs and suggest that monitoring for ''m/z'' 99 (FSO3 loss) as does Benskin and colleagues noted above. Compounding the issue is PFOS is widely distributed in global wildlife, and analysis of blood, liver and flesh of monitored wildlife will likely also contain these bile acids. Therefore caution must be taken in sample cleanup, analysis and mass spectra interpretations. Strynar and colleagues
ASMS Strynar et al., 2009
demonstrated the presence of these cholic acids in a number of biological samples. Additionally they gave suggestions for removal of this interferent issue during PFOS analysis including the use of high resolution mass spectrometry (

Time-of-flight mass spectrometry Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which an ion's mass-to-charge ratio is determined by a time of flight measurement. Ions are accelerated by an electric field of known strength. This acceleration res ...

) that is able to resolve PFOS (monoisotopic mass 498.9302) from cholic acids (monoisotopic mass 498.2895) easily. Additional suggestions included removal of cholic acids through the

Solid-phase extraction Solid-phase extraction (SPE) is an extractive technique by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties. Analytical labor ...

cleanup of methanolic extracts using Supelco's ENVI-Carb cartridge or monitoring for the presence of cholic acids via ''m/z'' 498-124 and 498-107 which PFOS does not respond to.

References

{{steroid-stub Bile acids Sulfonic acids Cholanes