Assay linearity

Dust content increased with increase in trash content. A presentation of the dust (dry assay) linear relationship is shown in Figure 5. Dust/trash content was also linearly regressed on x = reciprocal of trash content (Figure 6). The curves illustrated in Figures 5 and 6 are the first documentation of actual dust-nonlint trash trends in raw cotton. Note in Figure 6 that with increasing trash content, the dust/trash ratio approaches a constant, the intercept a,- of Equation 9. 

In some instances, calibration test data may need to be subjected to some kind of mathematical transformation, prior to the regression analysis, in order to obtain linear calibration plots. In some cases, however, such as in immunochemical assays, linearity cannot be demonstrated even after any transformation. The use of nonlinear calibration curves for analysis has been discussed (27). 

It is not intended to describe the definitions of these in detail since this information can be found in other chapters of this book. It is important that attention is paid to these specific definitions since some terms may mean different things to different scientists, particularly those related to assay linearity and parallelism. 

FIGURE 41.1 Rat skeletal troponin I (MSD ) assay linearity of dilution. 

Injection volume can be adjusted depending on instrument sensitivity and the relative need for low-concentration sensitivity versus assay linearity. 

The volume of the acetonitrile water solution may be adjusted to achieve greater assay sensitivity or higher assay linearity. The ratio of sample to the acetonitrile water diluent should not be reduced below 1 10. 

ThioglycoHc acid can be identified by its in spectmm or by gas chromatography. Most of the by-products and self-esterification products are also detected by liquid chromatography, eg, thiodiglycolic acid, dithiodiglycolic acid, linear dimers, and polymers. Iron content can be assayed by the red sensitive complex of 1,10-phenanthroline [66-71-7] and ferrous ion of a mineralised sample. Ferric ion turns an aqueous ammonia solution deep red-violet. 

L-pyrenyldiazomethane to form stable, highly fluorescent L-pyrenyhnethyl monoesters (87). These esters have been analy2ed in human blood by ce combined with lif detection. To mimini e solute adsorption to the capillary wall, they were coated with polyacrjiamide, and hydroxypropyl methylceUulose and dimethylfoTTnamide were used as buffer additives to achieve reflable separations. Separation was performed in tris-citrate buffer, pH 6.4, under reversed polarity conditions. The assay was linear for semm MMA concentrations in the range of 0.1—200 p.mol/L. 

Production Controls The nature of the produc tion control logic differs greatly between continuous and batch plants. A good example of produc tion control in a continuous process is refineiy optimization. From the assay of the incoming crude oil, the values of the various possible refined products, the contractual commitments to dehver certain products, the performance measures of the various units within a refinery, and the hke, it is possible to determine the mix of produc ts that optimizes the economic return from processing this crude. The solution of this problem involves many relationships and constraints and is solved with techniques such as linear programming. 

Bioprocess Control An industrial fermenter is a fairly sophisticated device with control of temperature, aeration rate, and perhaps pH, concentration of dissolved oxygen, or some nutrient concentration. There has been a strong trend to automated data collection and analysis. Analog control is stiU very common, but when a computer is available for on-line data collec tion, it makes sense to use it for control as well. More elaborate measurements are performed with research bioreactors, but each new electrode or assay adds more work, additional costs, and potential headaches. Most of the functional relationships in biotechnology are nonlinear, but this may not hinder control when bioprocess operate over a narrow range of conditions. Furthermore, process control is far advanced beyond the days when the main tools for designing control systems were intended for linear systems. 

Application of IP and NCS in conjunction with specification tolerance limits enables to substantiate acceptance criteria for linear regression metrological characteristics (residual standard deviation, correlation coefficient, y-intercept), accuracy and repeatability. Acceptance criteria for impurity influence (in spectrophotometric assay), solution stability and intermediate precision are substantiated as well. 

Figure 6.10b shows a pattern of antagonism often observed in isolated tissue studies but not so often in cell-based assays. Saturation of uptake systems for the agonist or saturation of an adsorption site for the agonist can account for this effect. The linear portion of the regression can be used to estimate the pKB or the pA2. If there is a loss of concentration dependence of antagonism, as seen in... 

The advantages of controlled-potential techniques include high sensitivity, selectivity towards electroactive species, a wide linear range, portable and low-cost instrumentation, speciation capability, and a wide range of electrodes that allow assays of unusual environments. Several properties of these techniques are summarized in Table 1-1. Extremely low (nanomolar) detection limits can be achieved with very small sample volumes (5-20 pi), thus allowing the determination of analyte amounts of 10 13 to 10 15 mol on a routine basis. Improved selectivity may be achieved via the coupling of controlled-potential schemes with chromatographic or optical procedures. 

Figure 4.16 (left). Trendlines for the various compwnents. The three scales are different %, ppm, resp. %). (right). Total impurities (columns 1-6, including water of crystallization, versus the HPLC assay of the major compound (column 7). The circle marks the hypothetically pure compound 3.2% water of crystallization, but no other impurities. The arrow indicates the percentage of impurities expected (for this simple linear model) to remain in the product after all solvents and excess water have been driven off. 

Situation A cream that contains two active compounds was investigated over 24 months (incomplete program if today s ICH standards are applied, which require testing at 0, 3, 6, 9, 12, 18, and 24 months). The assays resulted in the data given in file CREAM.dat. Program SHELFLIFE performs a linear regression on the data and plots the (lower) 90% confidence limit for the regression line. For each full time unit, here months, it is determined whether this CL drops below levels of y = 90% resp. y = 95% of nominal. Health authorities today require adherence to the 90% standard for the end-of-shelf-life test, but it is to be expected that at least for some products the 95% standard will be introduced. 

Standard curves performed under our defined radioimmunoassay conditions ([ H]PbTx-3 = 1 nM, antiserum dilution = 1 2000, assay volume = 1 ml) demonstrated the ability of this antiserum to bind equally to PbTx-2 and PbTx-3, suggesting specificity for the cyclic polyether backbone region of the molecule (Figure 8). The linear portion of the curve indicated a lower detection limit of 0.2-0.5 ng in saline buffer under these conditions. Evaluation of this assay for use with biological fluids and tissue extracts is underway. 

---