title: Potential loss of methionine following extended storage of newborn screening samples prepared for tandem mass spectrometry analysis.
abstract: BACKGROUND
  Methionine (Met) is a key metabolite used in the newborn screening of homocystinuria by tandem mass spectrometry (MS/MS). Recently, a loss of ion counts in both Met and its deuterium-labeled internal standard ((2)H(3)-Met) was observed by the CDC's Newborn Screening Quality Assurance Program laboratory. We report on the stability of labeled and unlabeled Met solutions and their storage in two types of 96 well microtiter plates to illustrate the potential loss of Met following storage of samples prior to MS/MS analysis.
  
  
  METHODS
  Neat labeled and unlabeled Met standards were prepared and added (25, 50 and 100 microl) to two different types of microtiter plates, dried under nitrogen and stored for up to 168 h. All samples were reconstituted in mobile phase and analyzed as free acids for simplification of the study.
  
  
  CONCLUSIONS
  Met appears to interact significantly with polystyrene microtiter plates and to a much lesser extent with polypropylene microtiter plates. Furthermore, the loss is greatest for lower concentrations of methionine. While this loss of Met signal may be unimportant due to a presumption of equal loss of (2)H(3)-Met, a significant decline in ion signals will cause greater error in the calculation of concentration. These results suggest that polypropylene may be a better choice for Met analysis. Furthermore, storing prepared samples prior to analysis may impact the quality of the MS/MS analysis for Met and potentially other metabolites. Plates used by newborn screening laboratories should be evaluated periodically if the signal intensity for Met is reduced.
authors.affiliation: Pediatrix Analytical, The Center for Research and Education, Pediatrix Medical Group, Inc., 1301 Concord Terrace, Sunrise, FL 33323, USA. donald_chace@pediatrix.com
authors.forename: Donald H
authors.initials: DH
authors.lastname: Chace
authors.forename: Zuzheng
authors.initials: Z
authors.lastname: Luo
authors.forename: Víctor R
authors.initials: VR
authors.lastname: De Jesús
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Haynes
authors.forename: W Harry
authors.initials: WH
authors.lastname: Hannon
mesh_terms: D006801:Humans; D007231:Infant, Newborn; D008715:Methionine / Q000652:urine*; D015997:Neonatal Screening; D012015:Reference Standards; D013048:Specimen Handling; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D008715:Methionine