The gradient started at 5% B. After a linear increase to 10% B in 5 min and holding this condition for 5 min, another linear increase to 15% B during 10 min and to 50% B in 2 min, which was maintained for 2 min. Within 2 min B was decreased linearly to 5% and the column was equilibrated for 9 min.
Concentration of the single vitamers in the food samples was calculated using the response factors reported recently . For more experimental details see