Có 40+ tài liệu thuộc chủ đề "phân tích mẫu"
tailieu.vn Xem trực tuyến Tải xuống
If the column oven does not preheat the mobile phase (generally required only for methods operating at >40 ◦ C), a simple preheater can be fabricated from 0.5 m of 0.005-in i.d. This tubing should be connected to the column inlet and mounted inside the column oven, preferably in contact with a heated surface.. The block heater relies on direct...
tailieu.vn Xem trực tuyến Tải xuống
Typical System Performance Parameters for Tests of Section 3.10.1 Parameter/Test Typical Specification Typical Acceptance Criteria. An additional test of the outlet check valves can be made with a pressure bleed-down test. For this test the outlet tubing from the pump is blocked (by a union and a plug). A larger drop suggests that the outlet check valve(s) should be cleaned...
tailieu.vn Xem trực tuyến Tải xuống
The detector for the first liquid chromatographic separations was the human eye, used by Tswett in his classic experiments [1, 2]. The concentration of analyte in each fraction could be plotted against fraction number, as in Figure 4.1b, resulting in a crude chromatogram. Some of the first applications of on-line liquid chromatographic detection included the refractive index detector reported by...
tailieu.vn Xem trực tuyến Tải xuống
Figure 4.7 Measurement of chromatographic signal (S) and noise (N).. from the middle of the baseline noise to the top of the peak (Fig. The contribution of S/N to precision can be estimated as. where CV is the coefficient of variation (equivalent to %-relative standard deviation,. These values of CV are the contribution of S/N to the overall imprecision of...
tailieu.vn Xem trực tuyến Tải xuống
Figure 4.12 Illustration of spectral deconvolution of analytes. The same dataset collected at 240 and 280 nm could be used to determine peak purity by calculation of the 240/280 ratio at every point across the peak. If the peak were pure X or Y, the ratio would be constant, whereas if the mixture of Figure 4.12a were present, the ratio...
tailieu.vn Xem trực tuyến Tải xuống
Figure 4.19 Response of chemiluminescent nitrogen detector (CLND) for different com- pound types. Adapted from [29].. both the concentration of the chiral compound and its molecular structure. Optical rotary dispersion (ORD) detectors operate on a similar principle to polarimeters, but use lower wavelengths (e.g., the 365-nm mercury emission line), which in theory should give stronger signals. For strong CD signals,...
tailieu.vn Xem trực tuyến Tải xuống
MS detection has become the standard detector system for bioanalytical methods—the analysis of pharmaceutical compounds in biological systems (e.g., plasma or urine). MS detectors are also widely used in the R&D setting to provide structural information or confirmation of unknowns, although it does not have the mass-resolution capability of traditional stand-alone mass spectrometers. (Within a given run, more than one...
tailieu.vn Xem trực tuyến Tải xuống
Figure 4.37 shows an example of the popular post-column derivatization of amino acids with ninhydrin followed by UV detection at 405 nm. THE COLUMN. 5.1 INTRODUCTION, 200 5.2 COLUMN SUPPORTS, 200. 5.3.2 Other Organic-Based Stationary Phases Column Functionality (Ligand Type), 225 5.4 COLUMN SELECTIVITY, 227. 5.4.2 Column Reproducibility and ‘‘Equivalent’’ Columns Orthogonal Separation, 236. 5.4.4 Other Applications of Column Selectivity,...
tailieu.vn Xem trực tuyến Tải xuống
Figure 5.2 Visual appearance of several silica particles for RPC. mobile-phase velocity (mm/sec) 5- μ m totally porous. 3.5- μ m totally porous. 1.8- μ m totally porous. Figure 5.3 Column efficiency as a function of particle size and type. mobile phase is 60% acetonitrile-water mobile phase;. Halo particle-size-distribution Average = 2.77 μ m. Figure 5.4 Narrower particle-size-distribution for the...
tailieu.vn Xem trực tuyến Tải xuống
Figure 5.12 High-temperature separation of a pharmaceutical mixture. low- and high-pH mobile phases (1 ≤ pH ≤ 13), and they can be used at very high temperatures. Figure 5.12 shows a separation on a zirconia column at pH-13 and 140 ◦ C. Early columns packed with polymer-coated zirconia displayed rather poor efficiency, apparently because of poor stationary-phase mass transfer.. Consequently,...
tailieu.vn Xem trực tuyến Tải xuống
Phenyl columns Cyano column “Other”columns. Figure 5.19 RPC columns classified according to the ligand (figures omit the connecting silane group [–Si(CH 3 ) 2. simplified cartoons of Figure 5.19 (the—Si[CH 3 ] group is omitted in Fig. 5.19d), and this gives rise to the additional column types listed at the bottom of Figure 5.19. The nature of the ligand mainly...
tailieu.vn Xem trực tuyến Tải xuống
236 THE COLUMN. Values of H 1 and H 2 refer to values of H for columns 1 and 2, and similarly for the remaining column parameters S*, A, etc. A value of F s ≤ 3 indicates that the two columns are similar in selectivity and can be substituted for each other in any RPC separation (for less challenging...
tailieu.vn Xem trực tuyến Tải xuống
‘‘bad’’ column can be confirmed as the cause of the problem.. Every column used for a routine method has a finite lifetime (number of injected samples before column failure) that depends on separation conditions—especially mobile-phase pH and temperature. The performance and life of the column depend on how it is used and handled.. column, or deterioration of the column packing....
tailieu.vn Xem trực tuyến Tải xuống
Beginning in the early 1970s, RPC columns of the latter type were used increasingly because of their many advantages. In the mid-1970s, the use of RPC underwent an explosive growth in popularity. several hundred separations are cited in [5] for the period 1976 to 1979. samples, the classic paper by Horv ´ath [6] demonstrated that RPC could also be used...
tailieu.vn Xem trực tuyến Tải xuống
A 1:1 blend of the mobile phases of Figure 6.8a (46% ACN) and Figure 6.9a (61% MeOH) was prepared, and used to obtain the separation of Figure 6.9b. Figure 6.7 Variation of log k with %B for regular and irregular samples. (c) irreg- ular sample of Figure 6.6. conditions as in Figure 6.6. While the separation of Figure 6.9b is...
tailieu.vn Xem trực tuyến Tải xuống
We presently have a more complete understanding of the basis of column selec- tivity than for other kinds of selectivity (solvent strength, solvent type, temperature, etc. As discussed in Section 5.4.1, column selectivity can be quantitatively defined by five different characteristics:. For the case of neutral samples, only the first four column parameters (H, S*, A, B) are important. The...
tailieu.vn Xem trực tuyến Tải xuống
RPC (Chapter 6, or Section 7.3) IPC (Section 7.4) IEC (Section 7.5) NPC (Chapter 8). Adjust column conditions (N, Section 2.5.3) Figure 6.21 (Continued). can be varied (step 6) for the purpose of either increasing resolution or reducing run time.. Multiple-variable optimization in each case relies on an experimental design: a plan for the required experiments, as illustrated in Figure...
tailieu.vn Xem trực tuyến Tải xuống
mobile phase is 30% ACN-buffer for (a) and (b). 8% chloroform-ACN mobile phase. From a practical standpoint, if NARP is chosen for a separation, all water must be washed from the HPLC system and column prior to switching to the nonaqueous mobile phase.. Solutes that are very polar may not be retained with k ≥ 1, even when pure water...
tailieu.vn Xem trực tuyến Tải xuống
Figure 7.1 Hypothetical illustration of the RPC separation of an acidic compound HA from a basic compound B as a function of pH. (a) Ionization of HA and B as a function of mobile-phase pH and effect on k. (b) sample separation as a function of mobile-phase pH;. Figure 7.1b shows chromatograms for the separation of HA and B as...
tailieu.vn Xem trực tuyến Tải xuống
Phosphate buffers have been preferred for this application, as long as the mobile-phase pH can be accommodated within the ranges specified in Table 7.1 (pH pH ≤ 8.5, or pH ≥ 11.0). Phosphate, acetate, and formate are the most commonly used buffers for separations with a mobile-phase pH <. 8) as a result of the development of RPC columns that...