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A previous cLC method, involving large injection volumes (20 μL) and on-column focusing techniques, provided a suitable sensitivity using an Inertsil? C8 capillary column, DAD and gradient elution. This method showed that composition of the focusing solution, mobile phase and pH have remarkable effects on HA separation. In order to improve this separation, an isocratic cLC method compatible with MS detection was developed and the influence of several chromatographic factors on separation quality evaluated. Different reversed-phase packings such as Luna? C8, Luna? C18, Synergi? Max-RP (C12) and Synergi Fusion (C18 and polar embedded group) were tested using UV-DAD detection. These columns were chosen due to their high efficiencies and bonded phase surface coverage. Considering the different particle sizes, flow rate was set at 15 μL min?1 for both Synergi Fusion? and Synergi? Max-RP, 12 and 9 μL min?1 for Luna? C8 and Luna? C18 columns respectively. Chromatographic conditions were optimized using experimental design methodologies such as central composite design. Factors and ranges selected for the optimization of mobile phase composition were ACN (11.6–28.4%), ammonium acetate concentration (13.2–46.8 mM) and buffer pH (3.6–4.4). Response variables were expressed in terms of resolution, calculated at baseline, between the worst resolved peak pair NH–H (Rs,min), and retention time of the last eluting peak (tend). From the obtained equations, it could be concluded that Rs,min was significantly affected by both ACN percentage and pH while tend only by ACN. In addition, the ammonium acetate concentration had no significant effect on separation. Chromatographic separation efficiency was optimized for Rs,min ≥ 2 and minimum tend value. Luna? C8 capillary column provided poor resolution. Luna? C18 and Synergi? Max-RP columns provided similar Rs,min to Synergi? Fusion but higher efficiencies. However, Synergi? Max-RP column provided poor peak symmetry. Therefore, Luna? C18 column was selected for further optimization with the quadrupole MS detector. Taking into account the instrumental limitations of the MS capillary nebulizer, the ammonium acetate concentration in the mobile phase was fixed to 5 mM. Chromatographic separation was optimized using multifactorial design. Factors and ranges selected were ACN (12–18%) and pH (3.6–4.1). For the injection, buffered focusing solutions with 5% MeOH were used. Table 1 includes the values of the experimental responses (Rs,min and tend), which were fitted into the following normalized polynomial equations: (1)Rs,min=1.74?0.51pH?1.35ACN?0.06pH2+0.39pH ACN+0.40ACN2 (2)tend=12.18+0.18pH?11.02ACN+0.76pH2?0.94pH ACN+4.83 ACN2 Determination coefficients were 0.988 and 0.992 for Rs,min and tend respectively, showing the reliability of the equations. In the studied domain, both ACN percentage and pH affected significantly to Rs,min (p values 0.0000 and 0.0002 respectively) (Eq. (1)) while ACN (%) affected only tend (p value 0.0000 and 0.0005 for the single and quadratic term respectively) (Eq. (2)). As can be expected, the interactions between factors (ACN-pH) were significant only for Rs,min response (p = 0.0033). In Fig. 1 it can be observed that the ACN percentage decrease in the mobile phase increases Rs,min and tend. However, when pH decreases, Rs,min increases and tend does not change significantly. The chromatographic separation efficiency was optimized by maximizing Rs,min and minimizing tend values which maximized the desirability function over the selected region. The maximum desirability function yielded a tend = 13.6 min and Rs,min = 2.2 at pH 3.6 and 14.5% ACN. The estimated response surfaces predicted that Rs,min > 2 and tend in the range 12.5–15.0 min could be obtained at pH 3.6–3.7 and 13–15% ACN. As a compromise, pH 3.6 and 13% ACN were selected as optimum values. Under these conditions tend = 15.0 min and Rs,min = 2.3 were expected and experimentally assessed. Finally, ammonium formate 5 mM was also tested and selected to avoid problems into the capillary MS nebulizer. |
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7楼2010-12-07 17:28:31
★ ★
ringzhu(金币-2):本版严禁机器翻译。。。。 2010-12-08 13:07:33
zxc578642(金币+35, 翻译EPI+1): 2010-12-11 00:08:34
ringzhu(金币-2):本版严禁机器翻译。。。。 2010-12-08 13:07:33
zxc578642(金币+35, 翻译EPI+1): 2010-12-11 00:08:34
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先前的分类号方法，涉及到大注射量（20μL）和柱上聚焦技术，提供了合适的灵敏度使用Inertsil？ C8的毛细管柱，爸爸和梯度洗脱。这种方法表明，聚焦解决方案，流动相组成和pH值对医管局分离成效显着。为了改善这种分离，一等度分类号兼容MS检测法的开发和几种因素对色谱分离质量的影响进行评估。 不同的反相填料，如Luna？ C8的，Luna？ C18时，Synergi？马克斯反相（十二）和Synergi融合（C18和极性嵌入组）进行了测试使用紫外二极管阵列检测。这些列被选为由于其高效率和键合相表面覆盖。考虑到不同颗粒大小，流量率定为15微升分钟？Synergi融合为1？和Synergi？马克斯余段，12分钟和第9微升？负责卢纳1？ C8和卢娜？ C18柱分别。 色谱条件进行了优化，采用中心组合设计，如实验设计方法。因素和流动相组成的优化选择范围为乙腈（11.6-28.4％），醋酸铵浓度（13.2-46.8毫米）和缓冲液pH值（3.6-4.4）。响应变量中表达了在基准计算的决议而言，最糟糕的解决高峰之间的配对的NH -的H（卢比，分钟），并保留最后洗脱峰（倾向）的时间。从得到的方程，可以得出结论，卢比，最小显着比例都乙腈和pH的影响，而往往只乙腈。此外，醋酸铵浓度无显着影响的分离。 色谱分离效率进行优化卢比，≥2分和最低倾向于价值。卢纳？ C8的毛细管柱提供的分辨率较低。卢纳？ C18和Synergi？马克斯反相柱提供了类似的卢比，分钟，以Synergi？融合，但更高的效率。然而，Synergi？马克斯穷人提供的反相柱峰的对称性。因此，卢娜？ C18柱被选定为四极杆质谱检测器的进一步优化。 考虑到MS的毛细管雾化器的工具的限制，在流动相中醋酸铵浓度为5毫米。色谱分离采用多因素进行了优化设计。被选定的因素和范围乙腈（12-18％）和pH值（3.6-4.1）。对于注射液，缓冲聚焦5％甲醇被用来解决方案。 表1包括对实验的反应值（卢比，min和靠拢），分为以下规范化多项式拟合方程： （1）卢比，最小= 1.74？0.51pH？1.35ACN？0.06pH2 0.39 pH值乙腈+0.40 ACN2 （2）= 12.18 +0.18 pH值趋向？11.02ACN 0.76 pH值为2？0.94pH乙腈4.83 ACN2 决定系数分别为卢比，最小为0.988和0.992，往往分别显示了该方程的可靠性。在所研究的领域，都乙腈率和pH值的影响显着卢比，分（P值分别为0.0000和0.0002）（式（1）），而乙腈（％）仅影响往往（P值0.0000和0.0005为单和二次任期分别）（式（2））。正如可以预料，因素之间（乙腈- pH值）有显着的相互作用只有卢比，最小反应（P = 0.0033）。在图。 1可以观察到，在增加流动相乙腈比例下降卢比，min和趋向。然而，当pH值降低，卢比，最小升幅，而且往往没有明显变化。 色谱分离效率的最大化卢比，min和价值观趋于优化，最大限度地减少对选定的区域最大化的可取性功能。最大的可取性功能产生了往往和Rs = 13.6分，3.6分，在pH = 2.2和14.5％乙腈。估计响应面预测，遥感，分“2和范围12.5-15.0分钟往往可以在pH值3.6-3.7和13-15％乙腈获得。作为一种妥协，pH值3.6和13％乙腈被选定为最佳值。在这种情况往往和Rs = 15.0分钟，2.3分=预期和实验评估。最后，甲酸铵5毫米进行了试验，并选择了避免陷入毛细管质谱雾化器的问题。 |
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9楼2010-12-14 21:32:45
