Có 95+ tài liệu thuộc chủ đề "sắc ký lỏng HPLC"
tailieu.vn Xem trực tuyến Tải xuống
Figure 15.9 Isocratic separation of a two-component sample as a function of sample size.. If there is any doubt as to the identity of the product peak in these initial separations, this can be confirmed by a separate injection of pure product.. Step 2 of Figure 15.8. Following the adjustment of %B in step 1, separation conditions are varied for...
tailieu.vn Xem trực tuyến Tải xuống
SAMPLE PREPARATION. 16.1 INTRODUCTION, 758 16.2 TYPES OF SAMPLES, 759. 16.3 PRELIMINARY PROCESSING OF SOLID AND SEMI-SOLID SAMPLES, 760. 16.3.1 Sample Particle-Size Reduction Sample Drying, 762. 16.3.3 Filtration, 763. 16.4 SAMPLE PREPARATION FOR LIQUID SAMPLES, 764 16.5 LIQUID–LIQUID EXTRACTION, 764. 16.5.1 Theory Practice Problems, 768. 16.5.4 Special Approaches to Liquid– Liquid Extraction, 770 16.6 SOLID-PHASE EXTRACTION, 771. 16.6.1 SPE and...
tailieu.vn Xem trực tuyến Tải xuống
16.5.1 Theory. The Nernst distribution law states that any species will distribute between two immiscible solvents so that the ratio of the concentrations remains constant.. (16.1) where K D is the distribution constant, C o is the concentration of the analyte in the organic phase, and C aq is the concentration of the analyte in the aqueous phase.. For one-step...
tailieu.vn Xem trực tuyến Tải xuống
16.2c) permits the handling of submicroliter amounts of sample, such as biological fluids. Solid-phase extraction (SPE) has been performed with various packings that are placed in the pipette tip, or embedded in, or coated on the internal walls of the tip. With coatings on or embedded in the internal surface of the tip, liquid samples can be drawn up and...
tailieu.vn Xem trực tuyến Tải xuống
Figure 16.5 Isolation of albuterol from human plasma by means of solid-phase extraction (SPE).. RAM are most often selected for the analysis of low-molecular-weight drugs, their impurities, and metabolites [50–52]. Dual-mode porous packings are used in the most popular RAM columns.. These packings are used typically for the analysis of drugs in blood, because proteins present in these samples will...
tailieu.vn Xem trực tuyến Tải xuống
organic solvents requires indirect heating via the placement of a microwave-absorbing device in the extraction vessel. These devices are usually rods or a powder of a microwave-absorbing material such as carbon black coated with an inert polymeric substance (e.g., PTFE) that will not contaminate the sample. Multiple samples can be simultaneously processed in a microwave oven, so the sample throughput...
tailieu.vn Xem trực tuyến Tải xuống
Bland, Proceedings of the 3rd Annual International Symposium on Sample Prepara- tion and Isolation using Bonded Silicas, Analytichem International, Harbor City, CA, 1986, pp. 17.1 INTRODUCTION, 810 Quick Fix, 809. 17.2 PREVENTION OF PROBLEMS System Performance Tests Periodic Maintenance System-Suitability Testing Historical Records Tips and Techniques, 814. 17.3 PROBLEM-ISOLATION STRATEGIES Divide and Conquer, 819. 17.3.2 Easy versus Powerful, 820. 17.3.3...
tailieu.vn Xem trực tuyến Tải xuống
In our experience, this will fix leaky check valves most of the time, presumably by removing unwanted contaminants from the ball and/or seat of the seal. See Section 17.4.2.2 for additional discussion on the possible causes of and corrections for check-valve sticking.. 17.2.5.5 Leak Detection. Drips, puddles, and leak alarms usually make location of the leak simple. 17.2.5.6 Repairing Fitting...
tailieu.vn Xem trực tuyến Tải xuống
Figure 17.2 Schematic of low-pressure needle-seal. Failure of the injection rotor-seal can result in leaks at the injection valve. The rotor typically is made of a hard polymer, such as PEEK, Vespel, or one of the fluoropolymers, and contains tiny passages that connect the fluid passages in the stator. The stator may consist of the stainless-steel valve body, or it...
tailieu.vn Xem trực tuyến Tải xuống
17.4.3.5 Temperature Problems. A 1 ◦ C increase in column temperature will normally decrease retention by 1–2% (Section 2.3.2.2), so a method that is operated without column-temperature control will be subject to changes in retention as the temperature of the laboratory changes during the day. 17.4.3.6 Retention-Problem Symptoms. Re-installation of the previous column should confirm this. Legacy methods may require...
tailieu.vn Xem trực tuyến Tải xuống
isolation of the HPLC system from the electrical circuit, as well as pump and detector troubleshooting, could not solve the problem. Rather, movement of the system away from its original location reduced the frequency of the noise, and with sufficient distance eliminated it. An example of this is shown in Figure 17.11a for a gradient of 5–80% ACN-phosphate buffer (pH-7)...
tailieu.vn Xem trực tuyến Tải xuống
Figure 17.22 Separation of tipredane epimers. In Figure 17.22a, the pure S-epimer was injected, and peaks for both the R- and S-epimers are observed in the chromatogram (i..e, reaction of S-epimer to R). The injection of the pure R-epimer (Fig. 17.22b) shows a similar, but reduced conversion to the alternate epimer. When the column was changed to Resolve C 18...
tailieu.vn Xem trực tuyến Tải xuống
Leaks (Section 17.4.1): Symptoms and Sources. Location Sub-location/Symptom Possible Source Solution Pre-pump. Fitting Loose fitting Tighten or replace. Loose or damaged valve. Tighten valve or replace manifold. Pump Fittings Loose or damaged Tighten or replace. Tighten or replace. Stainless steel Loose or contaminated. clean or replace. PEEK Loose or. Fittings Loose or damaged See fittings adjustments, Sections Low-pressure needle. Worn...
tailieu.vn Xem trực tuyến Tải xuống
Degas mobile phase. clean or replace check valve, replace pump seal. Clean or replace check valve, replace pump seal. Mobile-phase solvents are of primary concern, because their properties must often fall within narrow limits for acceptable performance. However, these same properties also influence the choice of the sample-injection solvent and solvents used for sample preparation. Table I.1 lists several solvent...
tailieu.vn Xem trực tuyến Tải xuống
II.1 SEQUENCE OF OPERATIONS. combine the buffer ingredients with water to obtain the aqueous buffer (solution A). confirm or adjust the pH of solution A with a pH meter. combine a given volume (e.g., 200 mL) of organic buffer (solution B) with a given volume (e.g., 800 mL) of solution A from step 2 to obtain the final mobile phase...