93 



scan. The conversion dynode alternated between positive and negative 5 kV for the 



detection of both positive and negative ions with the electron multiplier at -1100 V. 



Solution-based analyses of methanolic lactic acid were also performed. A 100 

 mL methanol stock solution containing 1.206g of (85% w/w L-lactic acid in water) 

 was prepared. This 12 ng/^L L-lactic acid solution was then diluted by a factor of 

 100 to give a 120 ng/^L L-lactic acid solution in methanol, allowing for GC/MS 

 analysis without overloading the sample capacity of the GC column. An 0.5 jiL 

 injection of this solution was made onto a 10.5 m x 0.178 mm i.d. DB-5 column 

 (df=0.4 nm). The GC injection port and transfer line were operated isothermally at 

 250°C and 190°C, respectively. The column was initially held at 30°C for 0.25 min, 

 then ramped at 30°C/min for 4.0 min to 180°C and held at that temperature for 0.25 

 min. Samples were ionized by CI using methane reagent gas at an indicated pressure 

 of 1600 mtorr. Daughter ion spectra were acquired using nitrogen as the collision 

 gas (2.00 mtorr) with collision energies of 2 eV or eV. The ion source and 

 manifold temperatures were 150°C and 70°C, respectively. The filament emission 

 current was set at 200 ^lA vdth and electron energy of 100 eV. The electron 

 multipher was at -1300 V with the dynode at -1-5 kV. Data were collected in the 

 daughter ion mode by scanning Q3 at 0.5 s per scan. 



Some experiments were performed using the apparatus described in figure 2-3. 

 One hundred glass beads were handled for 3 min and then transferred to a 100 mL 

 round bottom flask with a specially fitted stem (described in Chapter 2). The beads 

 were spiked with 2 p,L of a 300 ng/p,L L-lactic acid solution prior to heating. 



