Dilution error

This is a method involving a two-compartment cell with a salt bridge connection and having two identical indicator electrodes. The sample solution is placed in one compartment and a blank solution having the same total ionic strength in the other. Increments of a standard solution of the species to be determined are added to the blank compartment until the cell potential is zero. At this point, the activities of the species of interest in each compartment are equal and that of the sample solution can therefore be calculated. A concentrated standard solution should be used to minimize dilution errors. This method is particularly useful for the determination of trace amounts or where no suitable titrant can be found. 

Gran plot A commonly employed multiple-addition method, used to correct for unknown amounts of contaminant and for dilution errors (see Section 4.3.2). 

It can be seen form equations 19 to 111 that both the variance and the covariance terms decrease with increasing dilution (n) keeping approximately a constant error for small dilution errors (e). A source of error seldom considered is the initial offset (eo)- This initial bias may be due to an instrument offset, a change in the reference values or to an error in the initial concentration and it causes a constant displacement along the x or y axis, i.e. ... 

Dilution error. Pipette a volume of more than 5 mL, and avoid using volumetric flasks of less than 25 mL. 

Calibration curves must be made from chemicals with the highest purity as possible. To avoid dilution errors a multi-level calibration curve (six points) based on three stock solutions is recommended. One must also be aware that low concentrations of for example, PAHs (2 ppm) may be adsorbed by the vials up to -90% (Pinto, Jose and Cordero, 1994). A calibrated and traceable balance or a traceable pipette must be used for accurate preparation and dilution of the standards. The calibration curve must cover the concentration range that is needed for the analysis. Both the slope and the intercept must be used to calculate the concentration in the sample, especially if the intercept is different from zero. 

The stirred-flow technique is an improvement over the continuous flow method described earlier. The method effects perfect mixing (Seyfried et al, 1988) so that the chamber and effluent concentrations are euqal and transport phenomena are minimized significantly. Additionally, the sorbent is dispersed and the dilution error present in the continuous-flow method can be accounted for. The stirred-flow technique also retains the attractive features of removing desorbed species at each step of the reaction process and of easily studying desorption kinetics phenomena. 

At least one of the standards (the one used for initial calibration or the ICV standard) must be certified traceable to a national standard, such as the NIST-traceable standard reference materials. Certified stock standard solutions for the majority of environmental pollutants are available commercially. However, whether a stock standard is a certified solution or has been prepared by the laboratory, dilution errors during the standard preparation and analyte degradation in storage happen. The laboratories are able to detect such errors only by preparing and analyzing an independent, second source confirmation standard. 

There are a number of relatively simple tests that can be employed to evaluate the analytical data and to check for possible transcription or dilution errors, changes during storage or unusual or unlikely values. A discussion of these can be found in Hem (1985) and Cook et al. (1989), among others. 

A simple screening procedure for evaluating analyses from the same or similar sources is to compare the results with one another. Transcription or dilution errors become readily evident. 

The solids content of an adhesive or sealant should be checked to ensure that formulation or dilution errors have not been made. Solids can refer to the nonvolatile component of the adhesive or the inorganic component of the adhesive. 

Repeat the process described above as many times as necessary to obtain the dilutions needed. Care is important in this work, since dilution errors are cumulative. 

Eor the KAc solutions and any other strong electrolytes studied as a function of concentration, plot A versus yfc and extrapolate linearly to c = 0 in order to obtain Aq. In making these extrapolations, beware of increasingly large experimental uncertainties at the lowest concentrations and also of systematic errors due to conducting impurities or dilution errors at low concentrations. If you are making a least-squares fit with Eq. (5) rather... 

Figure 12.2 SOFeX depth profiles of biomass (PN)-specific NO/ uptake rates, determined during 24-h incubations in Plexiglas acrylic incubators under simulated in-situ light and temperature conditions. Ultra-clean trace-metal techniques were used for sample collection within and outside (control waters) of the Fe-enriched patch north and south of the Antarctic Polar Front zone. The/-values [f = Fn03/(1 n03 + 1 nH4 + F n02 + F Urea)] were determined at the isolume depths of 47 and 16% surface irradiance, using tracer-level isotopic enrichments, and are not corrected for the effects of isotopic dilution. Error bars represent the range of duplicate samples (n = 2). Corrected from Coale et al. (2004).

It is beheved that the technician made a dilution error in the concentration measmed at 17.5 min. What do you think How do your answers compare using regression (POLYMATH or other software) with those obtained by graphical methods (Ans. (a) k = 0.2 (mol/dm ) /min) P5-4a The liquid-phase irreversible reaction... 

A volumetric flask is used to prepare accurate volumes of solution. These flasks are pear-shaped with long, thin necks that allow the operator to dilute accurately to the mark with solvent. Volumetric flasks are available in all sizes from 1 mL up to 10 litres, but the most common sizes are 20,50 and 100 mL. When selecting which size of flask to use, a compromise should be reached between the desire to use a small-volume flask and so save on expensive reagent, and the desire to use a large-volume flask to minimise dilution errors. The usual procedure is to pipette in a known volume of concentrated solution, add solvent until just short of the mark, shake or invert the flask to mix the contents and then make up to the mark, as accurately as possible, with a Pasteur pipette. Volumetric flasks should be used for all accurate dilutions. Use of measuring cylinders or (even worse) beakers to dilute solutions should be avoided. 

In the case of step 3, two laboratories withdrew their results due to contamination problems and dilution error, respectively. The remaining results ranged from 12.53 to 19.47 mg kg (CFbetween laboratories of ca. 15% with the following range of techniques 3 ETAAS, 6 FAAS, 5 ICP and 1 ICP-MS), which was found to be a reasonable figure for the present state of the art. 

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