TAILIEUCHUNG - HPLC for Food Analysis phần 6

Điều kiện sắc ký để phát hiện UV phương pháp HPLC trình bày ở đây đã được sử dụng trong phân tích của một tiêu chuẩn vitamin. MAU 700 600 500 400 300 200 100 0 2 4 6 8 Thời gian [min] 10 α-tocopherol β-và γ-tocopherol Tiêu chuẩn Vitamin D3 δ-tocopherol | Size-exclusion gels Adsorption media Size-exclusion chromatography is used for sample cleanup and fractionation and is described in more detail in chapter 5 Sample preparation . Adsorption chromatography is used for sampling and cleanup. For example flavonoids from plant material can be cleaned fractionated and enriched on alumina. Other examples are given in chapter 5. The advent of narrow-bore columns Time min Figure 44 Effect of bore dimensions on separation Discussions of HPLC methods often revolve around the internal diameter id or bore of the column to be used. Standard-bore columns have an internal diameter of approximately 4 or 5 mm whereas narrow-bore columns have an internal diameter of approximately 2 mm. When packed with the same materials as the standard-bore column the narrow-bore column can achieve the same resolving power with less solvent because the analytes can be eluted at a lower flow rate ml min than the 2-3 ml min required for standard-bore columns. In addition narrow-bore columns are 4-6 times more sensitive using the injection volume required for a standard-bore column see figure 44 . Narrow-bore columns nonetheless place higher demands on the equipment used than standard-bore columns. First the HPLC pump must yield these low flow rates in a way that is both reproducible and precise. Second all capillary connections that is from injector to column and from column to detector must be kept to a minimum. Third because column frits block more often guard columns are recommended. An HPLC system designed for narrow-bore columns low dead volume and high-performance pumping system can achieve solvent economies of more than 60 as well as improve detection limits with the same injection volume. Moreover under the same conditions a standardbore column may have higher resolving power. 59 Influence of column temperature on separation Many separations depend not only on the column material and mobile phases but also on the column temperature. In such

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