Basic Analytes sample loading

Relative extraction efficiencies of polar polymeric neutral, cation, and anion exchange sorbents (HLB, MCX, and MAX) for 11 beta antagonists and 6 beta agonists in human whole blood were probed.109 Initial characterization of MCX and MAX for acidic and basic load conditions, respectively, showed that both the agonists and antagonists were well retained on MCX, while they were recovered from MAX in the wash with either methanol or 2% ammonia in methanol (see Table 1.6). Blood samples were treated with ethanol containing 10% zinc sulfate to precipitate proteins and the supernatants loaded in 2% aqueous ammonium hydroxide onto the sorbents. After a 30% methanol and 2% aqueous ammonia wash, the analytes were eluted with methanol (HLB), 2% ammonia in methanol (MCX), or 2% formic acid in methanol (MAX). The best recoveries were observed with MCX under aqueous conditions or blood supernatant (after protein precipitation) spiked sample load conditions (see Table 1.7). Ion suppression studies by post-column infusion showed no suppression for propranolol and terbutaline with MCX, while HLB and MAX exhibited suppression (see Figure 1.6). 

Figure 1.25 illustrates the principle underlying LLE in the solid-supported LLE format. In order to facilitate elution with a water-immiscible organic solvent, it is imperative that analytes are in their neutral form during sample load. Thus, for basic analytes, loading should be done in a high pH (9 to 10) buffer and for acidic analytes, a low pH (2 to 3) buffer. 

Increasing the load of basic analytes in order to increase analyte sensitivity can lead to a decrease in apparent peak efficiency and increase in peak tailing. However, if an analysis must be performed at a relatively high sample load, the addition of a chaotropic additive may be employed to increase the apparent peak efficiency and symmetry. Much higher loading capacities could be obtained by operating columns with these mobile-phase additives without substantial deterioration in efficiency. 

HPLC injectors serve two basic functions to load a precise volume and to enable the use of high pressure. The small particle and column diameters used in analytical and microfluidic HPLC can cause large backpressures, requiring high pressure for moving the sample solution and mobile... 

CE presents potential advantages in forensic science to carry out the analysis of opium alkaloids, as it can be in the different applications being published. Nevertheless, the lack of the sensitivity required for this type of analysis is always a great problem. One of the most basic approach for sensitivity enhancement is based on increasing analyte mass loading via online sample preconcentration techniques. The most widely employed in the analysis of major alkaloids is FASI that basically consists in a mismatch between the electric conductivity of the sample and that of the miming buffer. It is achieved by injecting the sample diluted in a solvent of lower conductivity than that of the carrier electrolyte. Upon the application of the... 

These adsorbants are typically used for polar compounds that are not well retained by reverse-phase adsorbants. The colunms are conditioned by washing with 5-10 bed-volumes of the solvent which will be used to elute the analyte. The sample is loaded onto the column in a solvent, which is not sufficiently strong to elute it. Washing of the column is often carried out with a moderate polarity organic solvent, e.g. alcohol-free methylene chloride. Polar compounds are then eluted with methanol or mixtures of methanol and acidic buffer (for basic compounds) or methanol and alkaline buffer (for acidic compounds). Diol columns have been used to good effect in the extraction of polar drugs from pharmaceutical creams. ... 

The column is packed with the required amount of a sorbent and loaded with the sample extract. Elution of the analytes is effected with a suitable solvent, leaving the interfering compounds on the column. The packing material may be an inorganic substance such as Florisil (basic magnesium silicate) or one of many commercially available SPE stationary phases. The eluate may be further concentrated if necessary. A Florisil column is shown in Figure 1.9. Anhydrous sodium sulfate is used to dry the sample [8],... 

The basic equipment required for an HPLC system includes a solvent reservoir, a pump, an injector, an analytical column, a detector, and a recorder. The analysis of the sample is displayed as a chromatogram, with detector deflection presented usually as a function of time after loading the sample. By virtue of the shape of the curves, the distance between them, and their... 

Mobile-Phase Overload There are two basic types of mobile-phase overload. One is due to the solubility limits of the analyte in the mobile phase the other is due to the presence of the sample solvent or sample matrix components, which may interfere with the adsorption of the sample on the column top. Both can result in significant peak distortions. In the case of analyte insolubility, only the analyte peak will be distorted. In the case of a disturbance of the loading of the sample onto the top of the column, it is possible that only some peaks are affected or that all peaks are affected equally. For example, if the pH of the sample is different from the pH of the mobile phase, only those analytes whose retention changes with pH could be affected, while other analytes remain unchanged. 

The main analytical instrumentation in the vehicle is a benchtop GC/MS by Hewlett Packard, HP 5890 GC/5970 MSB (mass selective detector). A basic configuration for analyzing liquid samples includes a heated injection port and a capillary fused-silica column interfaced directly to the MS via a heated transfer line. The MS is a quadrupole design operated under vacuum provided by a diffusion pump and backed by a mechanical rotary pump. System operation and data analysis are performed by a Pentium-level personal computer loaded with proprietary software and a NBS spectral library to aid with identification of unknowns. Depending on the mission, a simpler installation may consist of a GC equipped with an appropriate detector such as the electron capture detector (ECD). 

---