Pretreatment procedures

Increase inhibitor concentration to 2-3 times its normal level. 

Circulate the high inhibitor concentration slurry for 4-12 hours. Maintain pH between 6 and 7 and temperatures between 49 and 60°C. if ambient temperatures must be used, increase the pretreatment period to 24-48 hours, 

After passivation, the system should be deconcentrated. Reduce the inhibitor concentration to normal maintenance levels. 

Thoroughly clean system of all dirt, oil, scale, organics and corrosion by-products. 

After system cleaning, refill with fresh water. Add the pretreatment formulation to the required concentration level. 

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Hall and Hassell (50) continued these studies with the intention of proving that possible traces of oxide dissolved in the metal play no significant role in the poisoning or promoting effects arising from hydrogen which had been presorbed during the pretreatment procedure. The catalysts were prepared in essentially the same manner as before. The kinetics... 

For this purpose we studied a temperature-programmed interaction of CH with a-oxygen. Experiments were carried out in a static setup with FeZSM-5 zeolite catalyst containing 0.80 wt % Fe203. The setup was equipped with an on-line mass-spectrometer and a microreactor which can be easily isolated from the rest part of the reaction volume. The sample pretreatment procedure was as follows. After heating in dioxygen at 823 K FeZSM-5 cooled down to 523 K. At this temperature, N2O decomposition was performed at 108 Pa to provide the a-oxygen deposition on the surface. After evacuation, the reactor was cooled down to the room temperature, and CH4 was fed into the reaction volume at 108 Pa. 

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

FIGURE 11.12 TSA method using the conventional ABC method, together with pretreatment procedures and optimal antigen retrieval. Source www.hmds.org.uk/ histology.html... 

Girardon J.-S., Constant-Griboval A., Gengembre L., Chemavskii P.A., and Khodakov A.Y. 2005. Optimisation of the pretreatment procedure in the design of cobalt silica supported Fischer Tropsch catalysts. Paper presented at the Gas-Fuel 05 Conference, Bruges, Belgium. 

An essential step in the analysis of trace pollutants in environmental matrices is the pretreatment procedure. Methods that are more efficient have been developed in the last few years, facilitating subsequent chromatographic analysis. Because of the complexity of the matrices, the sample pretreatment procedure includes both extraction and purification of the target analytes. 

Repeated visual examination and impedence measurements indicated no degradation of the electrode over the course of the experiments (3 weeks). During this time, the selected electrodes were stored in the inert-atmosphere glove box in which the electrochemical experiments were performed. No electrode pretreatment procedures were used and the crystals were not recleaved. 

The liquid stationary phase in a GLC packed column is adsorbed on the surface of a solid substrate (also called the support). This material must be inert and finely divided (powdered). The typical diameter of a substrate particle is 125 to 250 ft, creating a 60- to 100-mesh material. These particles are of two general types diatomaceous earth and Teflon . Diatomaceous earth, the decayed silica skeletons of algae, is most commonly referred to by the manufacturer s (Johns Manville s) trade name, Chromosorb . Various types of Chromosorb, which have had different pretreatment procedures applied, are available, such as Chromosorb P, Chromosorb W, and Chromosorb 101-104. The nature of the stationary phase as well as the nature of the substrate material are both usually specified in a chromatography literature procedure, and columns are tagged to indicate each of these as well. 

Figure 3 shows the effect of reaction temperature on the liquefaction reactivity of methylated (3 hrs, 100/1 methanol/HCl wt. ratio) and untreated Wyodak coals using DHP solvent. Mildly treating the coal (approx. 0.2 methyl groups added/100 carbon atoms) resulted in THF conversion improvements of about 21 wt% at 315 C, 23 wt% at 350 C, and 14 wt% at 400 C. Clearly, mild pretreatment enhances reactivity over the entire range of observed conversion levels. This result is very significant since it shows that our pretreatment procedure is beneficial at conversion levels of commercial interest, and thus, represents more than a laboratory curiosity. 

Wang F, Ji Z, Wang D. 1991. A rapid pretreatment procedure for determining trace organochlorine compounds in biological samples by capillary gas chromatography. Microchemical Journal 44 67-71. 

Hoogvliet et al. [9] have proposed a pulsed-potential pretreatment procedure, which allows one to decrease, in a reproducible manner, surface roughness of mechanically polished polycrystalline gold electrodes by a factor of 2. 

Li, S.H., He, C.Y., Liu, H.W., Li, K., and Liu, Ionic liquid-based aqueous two-phase system, a sample pretreatment procedure prior to high-performance liquid chromatography of opium alkaloids, /. Chromatogr. B, 826, 58-62, 2005. 

The complexity of the pretreatment procedure chosen is largely determined by the nature of the sample and the information required. Most present-day analytical instruments are designed to process gas and/or liquid samples. These could, therefore, be used with the minimum of pretreatment. Solid samples, on the other hand, have to be brought first into solution. This can be accomplished by homogenisation of the sample. However, as already emphasised it is important to separate the various compartments. 

It is not possible to prescribe specific pretreatment procedures here because these can only be decided upon when the system and the purpose of the experiments has been properly defined. However, a wealth of information exist in various biochemical reference books on how to isolate various biological compounds. The recommended techniques and methods could be used as part of the trace element speciation protocol often after slight modification, taking into consideration the following points First, the trace element blank levels have to be low, less than 10% of the total concentration in the sample. Second, the regents used should not interfere with subsequent analytical determinations. Third, the experimental conditions should not deviate markedly from those found in vivo, especially the pH and ionic strength of the medium. 

Both types of detector systems can be used in two modes of applications, i.e., on-line and off-line. In the on-line mode the fractionation and detection systems are directly coupM. It is possible to use more than one detector either in series or in parallel. Examples of this mode of detection will be given in the section dealing with combined techniques. The off-line mode involves the collection of the fractions with subsequent determination of the constituents. The advantage of this approach is that further sample pretreatment procedures could be applied where necessary before the constituents are detected. In addition, quantitative estimates of the recoveries can be made. 

It has been shown that every step of a particular surface preparation may be of significance with respect to the resulting bond strength of an adhesion system47. Therefore, it is imperative that pretreatment procedures be followed exactly if the experimental results from various laboratories are to be rightfully compared. 

Liquid samples such as urine, plasma, bile, or milk are normally incubated in the presence of -glucuronidase/sulfatase at 37 C for 2 h to deconjugate glucuronide and sulfate conjugates of the analytes (427-430). The most common preparation for this purpose is the juice of the snail Helix pomatia, which has sulfatase and glucuronidase activity. In some instances, dilution of urine with water (431), or dilution of plasma with phosphate buffer and centrifugation (432), may constitute the only pretreatment procedure applied. 

Liquid samples such as milk do not normally require application of any pretreatment procedure. Semisolid samples such as muscle, liver, and fat tissues usually require more intensive sample pretreatment for tissue break-up. The most popular approach is grinding the sample in a food chopper or homogenization in a Waring blender to expose residues to the extraction solvent. Fatty tissue samples are usually warmed at 35 C until fat melts (491-493), or sometimes blended with immersion blender (494). A fat sample that has been blended with immersion blender melts to produce yellow oil, whereas oil does not separate... 

In addition to solid-phase extraction and chemical vapour generation, other sample pretreatment procedures (including liquid-liquid extraction, precipitation, dialysis and even distillation) can be automated and coupled to the spectrometer. 

We have found that rigorous sorbent pretreatment procedures (e.g., Soxhlet extraction and thermal desorption) in concert with a well-established quality control program will successfully control potential contamination effects arising from the sample collection media. Furthermore, a well-executed quality control program will permit identification of spurious data points attributable to media contamination when and if they do occur. 

Figure 3. Temperature dependence of proton relaxation time Ti of water in NaPtY. Pore filling factor 6 0.8. Pretreatment procedure for 20 hours at 100° Ifi0°C. For comparison the results for NaY without platinum are also plotted.

Solid electrode performance can be affected by the electrode s previous history. A freshly polished electrode surface is virtually free of functional groups. To what extent its electrochemical behaviour changes in use depends very much on the electrode material and electrochemical pretreatment procedures [98]. 

Offline passivation involves treatment of equipment currently out of service. Treatment levels are typically higher consequently, passivation is completed more quickly. Passivation of nonchromate treatment generally uses either a polyphosphate, zinc, molybdate or other nonchromate-based inhibitor in combination with various surface-active cleaning agents. The passivation solution should be disposed of after the pretreatment stage, rather than dumped back into the cooling system where the potential for fouling can exist due to the precipitation of pretreatment compounds such as zinc or phosphate. Table 8.1 outlines both online and offline pretreatment procedures. 

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