Sources of Errors in Determining

For gaseous monomers measurements of equilibrium monomer pressure permits the determination of [M]e. As pointed out, however, absorption of monomer in the condensed phase may lead to serious errors 24). 

Gravimetric measurements may be erroneous if the polymerization is not properly terminated. Special care has to be taken to ensure complete termination exactly at the temperature of measurement. 

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A question arises as to the sources of error in determining a. Although many duplicate runs were not made because of the time needed for each determination, the agreement shown in the duplicate runs indicate that reproducibility is good. The good tritium material balances also lend confidence to the results. 

Other thermodynamic cycles used in various calculations contain explicit water molecules. The effectiveness of this implicit-explicit method in terms of calculating the free energy of solvation is discussed in the preceding section. Since the free energy of solvation is the largest source of error in determining pKa values, the accuracy of the calculation often determines the validity of various thermodynamic cycles. 

It is important to note that the SUV values are affected by several factors. The time period between tracer injection and scanning (i.e., the uptake period) is perhaps the largest single source of error in determining the SUV. Time to reach maximum uptake in a given tissue varies with the type and condition of tissue, i.e., different forms of neoplasm and also with tissues before and after therapy. Tissue uptake of FDG decreases with increasing blood glucose level, which affects the SUV. Excess body fat falsely elevates... 

What might be a major source of error in determining relative rates of reaction by the procedure that you used ... 

A major source of error in determining the degree of crystallinity by differential scanning calorimetry arises from the selection of the baseline under the endothermic peak. The problems associated with this procedure were discussed in reference to heat of fusion measurement in Section IV.D. 1. Differential scanning calorimetry also suffers to some extent from poor sample to sample repeatability, which lowers its precision and accuracy. As with the determination of degrees of crystallinity from density, the presence of fillers invalidates this method. From a theoretical standpoint, the determination of crystallinity from a sample s heat of fusion relies on a simple two-phase model of morphology. These drawbacks and an uncertainty in the heat of fusion of 100% crystalline polyethylene limit the accuracy of this method to approximately 5%. 

Exponential cost correlations have been developed for individual items of equipment. Care must be taken in determining whether the cost of the eqmpment has been expressed as free on Board (FOB), delivered (DEL), or installed (INST), as this is not always clearly stated. In many cases the cost must be correlated in terms of parameters related to capacity such as surface area for heat exchangers or power for grinding equipment. There are four main sources of error in such cost correlations ... 

Corrosion products are another source of error in the potentiostatic determination of polarisation curves in high-temperature water. In stagnant tests Fe could be converted to FejO,, causing a false anodic current... 

Chassaigne H, and Lobinski R (1998) Characterization of horse kidney metallothionein isoforms by electrospray MS and reversed-phase HPLC-electrospray MS. Analyst 123 2125- 2130. Chemosphere (1999) Special issue - Sources of error in methylmercury determination during sample preparation, derivatisation and detection. Chemosphere 39 1037-1224. 

Petroleum pollution monitoring laboratories in the Mediterranean region participated (1984-1986) in two intercalibration exercises (MEDCALI and II) to evaluate the International Oceanographic Commission (IOC) Manual for petroleum hydrocarbon determination in sediment (IOC, Manuals and Guides, No. 11). The main source of error in the analysis was the extraction/ partition step. When the results were corrected for recoveries, relative standard deviations for w-alkancs, UCM (unresolved complex mixture) and total aromatics, which had previously been 60, 56 and 49%, respectively, were reduced to 17, 30 and 6%, respectively. 

A major source of error in any indirect method is inaccuracy of the basis rate constants. Errors can result from determinations of rate constants by a sequence of several indirect studies or by an unanticipated solvent effect on the kinetics of a basis reaction. An error can also result in calibration of a radical clock if the requisite assumption that the clock radical will react with a rate constant equal to that of a simple model radical is not correct. Nevertheless, indirect methods in general, and radical clock studies in particular, have been the workhorse of radical kinetic determinations. 

There are several potential sources of error in these methods. The filters routinely used have a relatively high and somewhat variable sulfate content, so that, at concentrations lower than 10 Mg/m and sampling periods less than 24 h, the reliability of tlie sulfate measurement is reduc. Several different types of filtering media adsorb sulfur dioxide during the ftrst few hours of sampling this alters the amount of sulfate observed. This interference can become critical when sampling periods are less than 24 h and the concentration ratio of sulfur dioxide to sulfate is greater than 5 1. Interference can also be introduced by hot-water extraction when reduced sulfur compounds like sulfite are present, because they are oxidized to sulfates in this process. Another possible error source is that some of the various analytic procedures us for sulfate determination may be influenced by other substances also present in the particulate matter. 

The uncertainty in the measurement of elution time / or elution volume of an unretained tracer is another potential source of error in the evaluation of thermodynamic quantities for the chromatographic process. It can be shown that a small relative error in the determination of r , will give rise to a commensurate relative error in both the retention factor and the related Gibbs free energy. Thus, a 5% error in leads to errors of nearly 5% in both k and AG. An analysis of error propagation showed that if the... 

The requirements and potential sources of error in the polarimetric determination of specific rotations, as a prerequisite for the calculation of the optical purity, are discussed in detail in the following sections. 

What are the most probable sources of error in this experiment Does the method used offer an acceptable level of precision and accuracy for the determination of sodium in soil extracts and what are the reasons for your conclusions ... 

Both the theoretical and experimental data for the classic 2S i/2 — 2Pi/2 Lamb shift are collected in Table 12.2. Theoretical results for the energy shifts in this Table contain errors in the parenthesis where the first error is determined by the yet uncalculated contributions to the Lamb shift, discussed above, and the second reflects the experimental uncertainty in the measurement of the proton rms charge radius. We see that the uncertainty of the proton rms radius is the largest source of error in the theoretical prediction of the classical Lamb shift. An immediate conclusion from the data in Table 12.2 is that the value of the proton radius [27] recently derived form the analysis of the world data on the electron-proton scattering seems compatible with the experimental data on the Lamb shift, while the values of the rms proton radius popular earlier [28, 29] are clearly too small to accommodate the experimental data on the Lamb shift. Unfortunately, these experimental results are rather widely scattered and have rather large experimental errors. Their internal consistency leaves much to be desired. 

Sources of error in this approach arise from both experimental and theoretical grounds. Modern theories of SEC retention mechanism are based on the assumption that the size exclusion process uniquely determines the elution volume, and yet the possibility of reversible adsorption is difficult to dismiss and, where it occurs, errors in the interpretation may easily result. As a warning for the application of universal calibration methodology, Cas-sassa (29) indicates in a later paper that the quantity rj M is not a truly... 

The principal source of error in microwave structural determinations arises from the zero-point vibrations. Although Re values remain unchanged on isotopic substitution, the 50 values are not directly related to Re values. The rotational constant B0 is given by (5.72) with all . equal to zero. 7° is calculated from 50 as [see (5.64)]... 

The determination of vitamins in pharmaceutical preparations continues to receive considerable attention. The voltammetric oxidation of vitamin A at a carbon paste electrode in the presence of vitamin E, a potential source of error in the assay, has been described [142,143]. Other assays involve the polaro-graphic determination of niacinamide [144-146], menadione (vitamin K3) [147], riboflavin (vitamin B2) [148], thiamine, riboflavin, and nicotinamide in multivitamin preparations [149], and multivitamins [150]. 

This consideration of the principles of diffusive sampling identifies a range of factors which may influence the performance of a diffusive sampler for monitoring VOC concentrations in indoor air. These factors will potentially be a source of error in such measurements and add to the overall uncertainty of the result given by the measurement procedure. In addition the amount of uncertainty will be influenced by other factors including amount and consistency of background contamination of sorbents, repeatability of analytical determination, formation of artifacts, stability of analyte on the sorbent, recovery of analyte during analyses and presence of interferents. 

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