Simple, sensitive, rapid, selective, and precise reversed-phase liquid chromatography (LC), electrospray ionization mass spectrometry
(ESI-MS), and tandem MS (ESI-MS-MS) methods were developed and validated for the determination of 2-hydroxy-4-(methylthio)-butanoic
acid (HMTBA) in bovine serum and sea water matrix. HMTBA is the α-hydroxy analog of the sulfur-containing amino acid methionine
and is extensively used as a methionine supplement in poultry and bovine feed.
Methods were developed and validated for the determination of 2-hydroxy-4-(methylthio)butanoic acid (HMTBA), which is a water-soluble
hydroxy acid. HMTBA is a commercially available α-hydroxy analogue of the sulfur-containing limiting amino acid methionine.
HMTBA and its isopropyl ester has been shown to be a highly effective dietary methionine supplement in dairy cows, poultry,
and aquaculture (1–10). It has been shown that both the D and L enantiomers are converted to L-methionine (L-Met) through
a stereospecific transamination pathway (11–13). The relative efficacy of uptake of racemic HMTBA and D,L-Met have been investigated
in several studies; efficacies in such studies have been established through growth rate assessment in poultry or milk production
rate in lactating cows. Studies show that HMTBA or its isopropyl ester supplementation yield higher growth rates and higher
milk yields than Met supplementation (13,14). Uptake of HMTBA and its subsequent conversion to methionine has been studied
in lactating dairy cows with infusion of 13C-labeled HMTBA. It was shown that infusion of HMTBA increased whole-body plasma flux of Met (15). It has been postulated
that uptake of Met and HMTBA from the gastrointestinal track involve different mechanisms; Met uptake involves an active transport
across the cell membrane and HMTBA uptake occurs through diffusion, this uptake is more efficient especially when animals
experience stress, for example, heat stress. It has also been shown that HMTBA can lead to increased production of antioxidant
metabolites such as taurine and reduced glutathione (16). However, experiments that link HMTBA supplemented in feed directly
with its concentration in blood serum have not been reported in literature.
HMTBA has also been used in a chelated form such as zinc-HMTBA (Zn-[HMTBA]2) which is an efficient carrier of micronutrients (17,18). Zinc-HMTBA chelate has also been used as an antifouling agent in
marine paints and coatings (19). It has been reported that it minimizes biofouling and is less toxic to the environment than
other Zn and tin-based antifouling agents. It has also been shown that Zn-HMTBA is more effectively retained in the coatings.
However, direct leaching of HMTBA from marine coatings and its stability in the marine environment have not been reported
because of a lack of accurate and precise methods for HMTBA determination in sea water. This article deals with a sensitive,
accurate, and precise method for quantification of HMTBA in blood serum and sea water.