Nebulization efficiency

The aerosol then passes along the plastic expansion chamber. Large droplets collect on the walls of the chamber and, to ensure that only the smallest particles reach the flame, spoilers or baffles may be placed in the path of the gases. The chamber also allows for mixing of the gases and tends to damp fluctuations in nebulization efficiency. Some loss of solvent by evaporation will also occur. The chamber requires a drain tube which must be sealed to provide a back-pressure for the flame. This is usually... 

Inductively coupled plasma-atomic emission spectrometry was investigated for simultaneous multielement determinations in human urine. Emission intensities of constant, added amounts of internal reference elements were used to compensate for variations in nebulization efficiency. Spectral background and stray-light contributions were measured, and their effects were eliminated with a minicomputer-con-trolled background correction scheme. Analyte concentrations were determined by the method of additions and by reference to analytical calibration curves. Internal reference and background correction techniques provided significant improvements in accuracy. However, with the simple sample preparation procedure that was used, lack of sufficient detecting power prevented quantitative determination of normal levels of many trace elements in urine. 

Ute intensities of flame emission lines can be influenced by a variety of instrumental factors, including flame temperature, flow rate of solution, and nebulizer efficiency. We can compensate for variations in these factors by using the inteihal standard method. Here, we add the same amount of internal standard to mixtures containing known amounts of the analyte and to the samples of unknown analyte con-... 

Nebulizers such as these have high nebulization efficiencies and a low sample consumption (down to 0.1-0.5 mL/min). In particular, they have been shown to be useful for plasma spectrometry in the case of organic solutions or for coupling with liquid chromatography [119]. However, in comparison with the other types of nebulizers they suffer from memory effects. Indeed, the rinsing times are much higher than the 10-20 s as required for the other pneumatic nebulizers. In the case of the so-called thimble nebulizer, as described by Liu et al. [120] (Fig. 46), these disadvantages have been eliminated, mean droplet sizes were reported to be of the 2 pm level, which is lower by a factor of 5 than with the HEN mentioned previously. 

In fact, background corrections achieved with SPD, for both types of underlying spectral backgrounds, are comparable to that achieved with the array PMT polychromator (50). The shifts in the analytical curves, visible in Figures 8 and 9 reflect the reduction in the nebulizer efficiency at the high or concomitant concentrations. This matrix effect could be eliminated by utilizing the internal reference line principle to normalize variations in the nebulizer efficiency. For this normalization procedure... 

We have used ICP-AES with a SIT detector for the simultaneous multielement determination of trace elements in 100 uL volumes of dilute whole blood, blood serum and urine samples. The analyte solutions were ultrasonically nebulized at a rate of 1.2 ml/min. to achieve high nebulization efficiency without... 

The surface tension and, to a lesser extent, the viscosity of the sample solution are important factors in nebulization efficiency, since work must be performed in the nebulization step to overcome these properties of the liquid. For this reason, the surface tension and viscosity should be maintained as nearly identical as possible in samples and standards. With reasonably concentrated solutions, this can be done quite simply by diluting the test solution. With less concentrated solutions, it may be necessary to match the matrix composition of samples and standards. Concentrated solutions should also be diluted to avoid encrustation of salts on the nebulizer and burner. The same is true when handling heterogeneous systems such as colloids or solutions high in protein content. 

In the vertical ultrasonic nebulizer the sample solution is injected continuously at a constant rate directly onto the vertical face of the vibrating quartz crystal (Figure 39). The nebulization efficiency is about 50 and 25% at sample flow rates of 0.1 and 3 mlmin respectively. 

Spectral interferences can be avoided by chromatographic sample introduction. For example, when rare earths are determined by IGP-AES with direct solution nebulization, spectral interferences are often caused by other co-existing rare earth elements. When a HPLC is connected to an IGP-AES, these spectral interferences can be excluded by separating the rare earths by HPLC before their introduction into the plasma. Sodium or potassium salts of or-isobutyric acid, EDTA, or citric acid generally used for the separation of rare earths are unsuitable elution reagents for the IGP-AES detection, as these compounds easily clog the nebulizer and reduce the nebulization efficiency because of their high viscosity. 

Using ETV-ICP-MS detection limits improved by a factor of 10 to 10 compared with pneumatic nebulization methods. Detection limits using pneumatic nebulizers with ICP-MS are typically 1 to lOOngP, and those for ETV-ICP-MS 1 to lOpgP (Table 34). This is due to more efficient nebulization (the nebulization efficiency of pneumatic nebulizers is only 1 to 2%) and removal of the solvent matrix by thermal pretreatment. Thus, using this technique it is possible to analyse samples containing high levels of dissolved salts. Also the ability to operate with very small sample volumes (10 to 100 fil) is useful, especially when the amount of sample is limited. 

In FAAS an ideal organic solvent should possess the following characteristics (i) Low viscosity (ii) Good combustion characteristics (low background absorption and nontoxic combustion products) (iii) Low volatility (iv) Immiscibility in water (v) Not poisonous (vi) Good extraction efficiency (vii) Good nebulization efficiency (viii) Easy to handle (ix) Available in high purity form. 

Diot P, Morra L, Smaldone GC. Albuterol delivery in a model of mechanical ventilation comparison of MDI and nebulizer efficiency. Am J Respir Crit Care Med 1995 152 1391-1394. 

Small unilamellar vesicles (SUVs) of different lipids are coated with chitosan (CHT) by dropwise addition. These CHT-coated liposomes are found to show increased drug encapsulation efficiency, nebulization efficiency, mucoadhesive property, and decrease in toxicity level of the drugs toward epithelial cells. Therefore, CHT-coated liposomes are considered to be advantageous for the drug delivery to the lungs by the method of nebulization. 

Once formed, the aerosol passes into the burner or spray chamber (sometimes also called the cloud chamber). The role of the spray chamber is to homogenize both the aerosol and gases that tend to dampen fluctuations in nebulizer efficiency, and to remove any large droplets before they reach the flame. Large droplets (diameter > 10 pm) collect on the sides of the chamber and then drain to waste. Spoilers and baffles placed at the end of the spray chamber aid this process. Because the spray chamber will fill with flammable gas, modern instruments will also incorporate some form of antiflashback protection from the flame. 

Among the nonspectral interferences transport interferences in the nebulizer are relatively common in the analysis of body fluids. This is certainly no problem when 10- or 20-fold diluted serum is used for the determination of the electrolytes. If, however, undiluted or only slightly diluted body fluids are aspirated directly, the viscosity of these liquids can impair aspiration rate and nebulization efficiency relative to the reference solutions used. If the sample solution cannot be diluted sufficiently to avoid this interference, a frequently used alternative is matrix-matched standards, i.e., reference solutions with a viscosity close to that of the samples. Another alternative is to use the method of additions, which can perfectly correct for this interference. This calibration technique, however, is labor-intensive and time consuming, and is restricted to the linear part of the calibration curve. Viscosity of the sample solutions is much less of a problem when FI techniques are used for sample introduction. This is because samples are not aspirated but pumped to the nebulizer, because much smaller sample volumes are used, and because the sample is always in a carrier solution which supports nebulization and removes all potential residues in the nebulizer-bumer system. 

The nebulization efficiency of the ultrasonic nebulizer is so high that a desolvator unit must be added to the system to prevent overloading the plasma with solvent from the sample. 

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