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17.3.5 Module Substitution Put It Back, 821. 17.4 Common Symptoms of HPLC Problems Leaks, 822. 17.4.1.1 Pre-pump Leaks Pump Leaks, 823. 17.4.1.3 High-Pressure Leaks Autosampler Leaks Column Leaks Detector Leaks Abnormal Pressure, 830. 17.4.2.1 Pressure Too High Pressure Too Low Pressure Too Variable Variation in Retention Time, 833. 17.4.3.1 Flow-Rate Problems Column-Size Problems Mobile-Phase Problems Stationary-Phase Problems Temperature Problems Retention-Problem....
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Figure 2.16a AU absorbance units (UV detection). Equation (9.4) B column hydrogen-bond basicity. CEC capillary electrochromatography CCC countercurrent chromatography CLND chemiluminescent nitrogen detector C m solute concentration in mobile phase CMPA chiral mobile-phase additive. Equation (2.19) DMSO dimethylsulfoxide. F opt optimum mobile-phase flow rate (mL/min) (Section 2.4.1) F s column-comparison function. Equation (6.3) G gradient compression factor. Equation (9.15a) H...
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Figure 1.4 Recent examples of HPLC capability. (a) Fast separation of six proteins, using gra- dient elution with a 150 × 4.6-mm column packed with 1.5-μm-diameter pellicular particles [5]. (b) initial separation of peptides and proteins from human fetal fibroblast cell by gradi- ent cation-exchange chromatography. (c) further separation of fraction 7 (collected between 24–28 min) on a second column...
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Zlatkis, eds., 75 years of Chromatography—A Historical Dialog, Elsevier, Amsterdam, 1979.. Gehrke, ed., Chromatography—A Century of Discovery Elsevier, Amsterdam, 2001.. 81), Dekker, New York, 1999.. BASIC CONCEPTS AND THE CONTROL OF SEPARATION. 2.3.2 Role of Separation Conditions and Sample Composition, 28 2.4 PEAK WIDTH AND THE COLUMN PLATE NUMBER N, 35. 2.5.3 Optimizing the Column Plate Number N, 61 2.5.4...
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where K = (C s /C m ) is the equilibrium constant for Equation (2.2), and = (V s /V m ) is the phase ratio—the ratio of stationary and mobile-phase volumes within the column. values of k can help us interpret and improve the quality of a separation. A solute molecule must be present in either the mobile or...
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Figure 2.10 Origin and measurement of peak width. (b) peak 3 of Figure 2.6 as a function of %B, shown with the same time scale for each peak.. Because an ideal chromatographic peak has the shape of a Gaussian curve (Section 2.4.2), peak width is sometimes described in terms of the standard deviation σ of the Gaussian curve, where. (2.9c)...
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Figure 2.13 Knox equation. (a) Plot of reduced plate height h versus reduced velocity ν with A = 1, B = 2, and C = 0.05. All plots based on Equation (2.17) with A = 1, B = 2, and C = 0.05.. Column conditions can be defined as column length and diameter, particle size, and flow rate. Together these...
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Figure 2.18 Separation as a function of mobile phase %B. methanol-water mixtures as mobile phase. a shorter run time.. However, the term ‘‘optimized’’ is often used in the literature to indicate a relatively improved or preferred separation rather than an absolute best separation.. We will continue this usage in the present book. Sample retention k in isocratic elution is usually...
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present, it will be necessary to add a buffer to the mobile phase so as to control its pH. pK a values for sample compounds, if available, can be useful during method development (Chapter 7). The molecular weight of the sample may also affect the choice of separation conditions for initial experiments (Sections . Depending on the equipment that is...
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Gradient elution refers to a continuous change in the mobile phase during separation, such that the retention of later peaks is continually reduced. An illustration of the power of gradient elution is shown in Figure 2.25c, where all peaks for the sample of Figure 2.25a, b are separated to baseline in a total run time of slightly more than 7...
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3.2.2 Mobile-Phase Filtration, 91 3.3 MOBILE-PHASE DEGASSING, 92. Today there is less distinction between HPLC systems than in the past, and it can be safely said that there are no ‘‘bad’’ HPLC systems currently on the market. Users in the past often would select specific equipment modules from different vendors and, in a mix-and-match approach, would design their own ‘‘ideal’’...
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If reasonable care is taken in the selection and use of tubing and fittings, problems will seldom be encountered. Note that the following discussion refers to the dimensions and thread sizes of tubing and fittings in English units (usually fractional or decimal inches), because this is the way they are commonly supplied in the United States.. 3.4.1.1 Low-Pressure Tubing. The...
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Figure 3.12 Check-valve designs. Operation of the ball-type check valve is quite simple. When the pressure on the inlet side of the valve (below the ball in Fig. 3.12a) is higher than that on the outlet side, the ball will be displaced from the seat and solvent will flow through the valve. As described above, and illustrated in Figure 3.11,...
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Figure 3.19 Effect of laminar flow on injection accuracy. (b) laminar flow profile of sample. ≥200% of the loop volume for maximum accuracy.. Injection-volume accuracy may fall short of this level because of errors in calibration of the sample syringe or injection loop.. Usually the precision of injection is more important than accuracy because of the compensating use of standards...
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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...
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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...
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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...
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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...
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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...
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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,...