Washout time

Hydraiihc aud meau cell Washout time is iu the range of. 3 to 4 days. 

Change of washout time for 0.1-mm relief with temperature of water... 

If there is a considerable difference in concentration between samples or standards that are analyzed in sequence, a memory effect may occur. This effect is caused by sample deposition on the cones and in the spray chamber it also depends on which type of nebulizer is being used. The washout time between samples must be long enough to bring the system down to a blank value. 

The response times and washout times of electrodes fabricated from these materials are, respectively, <30 s and <50 s but the linear calibrations are restricted, e.g. 0.1-5 mM for the polycarbonate electrode. 

Three different spray chamber designs (Fig. 3.6) are most often used for ICP-MS the Scott [15] (double-barrel) chamber, a conical chamber with an impact bead, and a cyclonic chamber [14,16,17]. The cyclonic spray chamber typically provides a slightly (up to about a factor of 2 or 3) higher analyte transport efficiency as well as somewhat shorter washout times. In some cases the spray chamber is cooled (such as on the HP 4500 ICP-MS double-pass spray chamber, which is cooled to 4°C) to reduce the amount of water vapor that enters the ICP further so that signals from polyatomic ions containing oxygen are reduced. The cooled spray chamber also helps maintain a stable spray chamber temperature. 

There are several drawbacks to ultrasonic nebulizer/desolvation systems. Precision is typically somewhat poorer (1% to 3% relative standard deviation) than for pneumatic nebulizers (0.5% to 1.0% relative standard deviation) and washout times are often longer (60 to 90 sec compared to 20 to 30 sec for a pneumatic nebulizer/spray chamber without desolvation). Furthermore, chemical matrix effects are dependent on the amount of concomitant species that enter the ICP per second. Therefore, use of any sample introduction device that increases the amount of sample entering the plasma per second also naturally leads to more severe matrix effects when the sample contains high concentrations of concomitant species. 

Direct injection nebulizers are operated without a spray chamber. Instead, the concentric, pneumatic nebulizer is positioned just below the plasma and 100% of the sample is sprayed into the ICP. The nebulizer replaces the center tube of the ICP torch. The direct injection nebulizers are particularly attractive for the analysis of small sample volumes and for elements, such as Hg, I, and B, that stick to surfaces in the spray chamber and therefore have long washout times when a spray chamber is used. The dead volume of the direct injection nebulizers is small, so they have often been used to couple capillary separations with ICP-MS detec-... 

Washout time is in the range of 3 to 4 days. Use 8 to 15 days for design or base design on results of pilot-plant studies. 

The washout times can determine the speed of analysis, therefore rinsing out times are critical in removing traces from previous analysis and must be as short as possible without sacrificing analytical precision. This is particularly important when trace analysis needs to be carried out. In estimating the washout times of the ICP-OES sample contact components, a standard containing 10 pg ml 1 Ca is nebulised for 2 min. and then washed out with the same solvent used to prepare the Ca solution. The time taken to reach a level baseline is the time required to achieve a total metal free ICP-OES, and this washout time is used for subsequent analysis. 

The FI valve is connected after the pump and as near possible to the nebuliser to reduce as much of the dispersion of the sample as possible. In normal analysis 15-20 s washout times should be sufficient between each injection to minimise memory effects, particularly for elements such as Mo, Ag, B and W. 

Extra washout times are required between samples to ensure total removal of previous sample. 

Figure 12. Nt washout time constant (r) as a function of body weight...

Most of the experimental applications of the ZLC technique have been with gaseous systems, and for these systems the technique may now be regarded as a standard method. Based on our experience it is possible to suggest some guidelines as to how the experiments should be carried out. The key parameter is L, which from its definition (Eq. 17) can be considered the ratio of the diffusional and washout time constants R /D and KVs/F. This parameter is also equal to the dimensionless adsorbed phase concentration gradient at the surface of the solid at time zero. From either of these definitions it is evident that L gives an indication of how far removed the system is from equilibrium control. This parameter is proportional to the flow rate, so it can be easily varied, and to extract a reliable time constant, it is necessary to run the experiment at at least two different flow rates. 

Weiss, M., Washout time versus mean residence time, Pharmazie, 43 126-127, 1988. Zierler, K. L., Occupancy principle identity with that of mean transit time of tracers in biological systems. Science, 163 491-492, 1969. 

In the example shown in Figure 17.9, the washout to 1% took about 44 breaths. With a breathing rate of 12/min, the washout time was 220 s. The volume collected (Vj) was 22 L and the concentration of nitrogen in this volume was 0.085 ) therefore,... 

A randomized block design should be the standard in this case, ensuring that adequate washout times are allowed between treatments. 

---