Multiple reaction monitoring sample preparation

LC coupled with detection by mass spectrometry (MS) offers the potential for excellent sensitivity and specificity. Sample preparations suitable for niacin analysis by LC-UV and other methods should also be suitable for LC-MS. However, chromatographic methods developed for LC-UV or LC-fluorescence methods would in most cases have to be modified due to issues such as ion suppression and problems created by non-volatile species in commonly used mobile phases. Niacin has a relatively low molecular mass (123 Da), and thus in selected ion recording (SIR) mode, there may still be significant interference problems. With instruments that allow a multiple reaction monitoring mode (MRM), however, interference problems can potentially be avoided even without optimized chromatography or sample clean-up. 

Optical detection methods have a suite of attractive features for many in situ monitoring and reaction optimization applications. These features include nondestructive measurement capabilities, fast response, low detection limit, means to analyze materials with no sample preparation, ease of multiplexing for parallel measurements of multiple compounds in the library, and spatial-mapping capabilities. One or several lightwave parameters (amplitude, wavelength, polarization, phase, and temporal property) can be measured and related to a material property of interest. Complementing direct measurements, in which the spectroscopic features of the material are measured, an indirect material determination can be used in which an auxiliary reagent is employed. ... 

A general procedure is described for preparation of copolymer 4-(Leu-6)o.5o-Lys(Bz)o.5o.. A 0.1 mole of a bis-nucleophile monomer II (here, a mixture of 0.05 mol. of L-Leu-6 and 0.05 mol. of II.3), 0.1 mol of di-p-nitrophenyl adipate (monomer I) stirred in 52 mL of N,N-dimethylformamide (DMF) at 60"C and dry triethylamine (NEts) added (30.8 mL, 0.22 mol.) corresponded to total monomer concentration 1.2 mol/L. The reaction was conducted over 24 h and crude samples monitored by GPC. The purification of co-PEAs was achieved by multiple precipitation from solvent (ethanol, dichloromethane) into non-solvent (water or cold ethylacetate) until no p-nitrophenol was detected in the UV spectrum. 

---