The composition of the cleaning solution for the minicolumn regeneration was also studied. Several solutions were tested: water, 5% HNO3, 5% ascorbic acid, 50% ethanol, 50% ethanol1% HNO3, 50%
ethanol1% HCl, 80% ethanol1% HNO3 and
80% ethanol1% HCl. Best results were achieved
by using 50% ethanol in 1% HCl solution. Required time for an ef®cient cleaning (assessed by on line
spectrophotometric measurements of the iron-thiocya-nate complex) was 1.6 min, with a ¯ow rate of 3.51 ml/min. In the proposed procedure the washing time was 2 min to guarantee the total regeneration of the minicolumn. Flow rates over 3.51 ml/min did not increase the cleaning and gave rise a small overpres-sure inside the minicolumn. Also, in solutions contain-ing more than 50% ethanol the lifetime of the Tygon tubes decreased too much.
The composition of the cleaning solution for the minicolumn regeneration was also studied. Several solutions were tested: water, 5% HNO3, 5% ascorbic acid, 50% ethanol, 50% ethanol1% HNO3, 50%ethanol1% HCl, 80% ethanol1% HNO3 and80% ethanol1% HCl. Best results were achievedby using 50% ethanol in 1% HCl solution. Required time for an ef®cient cleaning (assessed by on linespectrophotometric measurements of the iron-thiocya-nate complex) was 1.6 min, with a ¯ow rate of 3.51 ml/min. In the proposed procedure the washing time was 2 min to guarantee the total regeneration of the minicolumn. Flow rates over 3.51 ml/min did not increase the cleaning and gave rise a small overpres-sure inside the minicolumn. Also, in solutions contain-ing more than 50% ethanol the lifetime of the Tygon tubes decreased too much.
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