ABSTRACT
I. Introduction .................................................................................................. 519 II. Chromatographic Assays .............................................................................. 519
A. Folate Standard Compounds .................................................................... 520 1. Chemical Properties and Sources for Folate Standard Compounds ... 520 2. Preparation and Storage of Calibrators ............................................... 520 3. Folate Interconversions ........................................................................ 521
B. Sample Preparation for Methods Measuring Intact Folates .................... 521 1. Extraction and Cleanup Techniques .................................................... 521 2. Extraction and Cleanup Issues for Different Matrices ........................ 524
C. Measurement of Intact Folates ................................................................. 526 1. High-Performance Liquid Chromatography........................................ 526 2. Liquid Chromatography/(Tandem) Mass Spectrometry ...................... 528
D. Measurement of Folate Breakdown Products as a Surrogate Indicator for Total Folate ......................................................................................... 541 1. Gas Chromatography/Mass Spectrometry .......................................... 541 2. Liquid Chromatography/Tandem Mass Spectrometry ........................ 541
E. Summary .................................................................................................. 542 III. Protein-Binding Assays ................................................................................ 542
A. Factors In uencing Protein-Binding Assays ........................................... 542 1. Response to Different Folate Monoglutamates and Polyglutamyl
Chain Lengths ..................................................................................... 543 2. In uence of pH and Protein Content of the Sample ............................ 543 3. Other Problems Encountered with Protein-Binding Assays ............... 543
B. Sample Preparation ..................................................................................544 1. Radioassays ..........................................................................................544 2. Automated (Nonradioassay) Protein-Binding Assays .........................544
