Peak height reproducibility

Katori et al [84] used a high performance liquid chromatographic method for the determination of primaquine phosphate tablets. Chromatography on a TSK Gel-4 (octadecylsilanized) column was used to determine the active ingredient in tablets and injections for treating tropical diseases. The mobile phase used is 26% acetonitrile in 0.05-M pH-3 phosphate buffer and the drug was detected at 260 nm. The peak area and peak height reproducibilities were <1.69%, and results compared well with those of other methods. 

Figure 7.2. Progress of the derivatizing reaction of 12 amino acids under stirring ( ), heating (m) and uitrasonication (a), expressed as the sum of ait peak heights. (Reproduced with permission of Eisevier, Ref [20].)...

FIGURE 2.13 From measurements of the retention volume, Vr, and the peak width at half peak height, Wr, of a gaussian peak, an estimate of column efficiency N and relative efficiency, HETP, may be calculated. The last figure is for very well packed columns close to 2 X dp. [Reproduced from Sofer and Hagel (1997), with permission.]... 

Successful use of modern liquid chromatography in the clinical laboratory requires an appreciation of the method s analytical characteristics. The quantitative reproducibility with respect to peak height or peak area is quite good. With a sample loop injector relative standard deviations better than 1% are to be expected. The variability of syringe injection (3-4% relative standard deviation) requires the use of an internal standard to reach the 1% level (2,27). 

Fig. 9.8 Peak height of 60ng Atrazine standard versus concentration of ammonium nitrate Source Reproduced with permission from the Royal Society of Chemistry [100]... 

Figure 5. Effect of electron radiation fluence on the Tg damping peak width (at half height). (Reproduced from reference 8.)...

After two decades of quantitative l.c. analyses, it has been established that, when proper precautions are taken, these methods can provide accurate and reproducible results.Quantitative l.c. measurements are usually as accurate as, and often more precise than, those obtained by spectrophotometric, " paper-chromatographic, and gas-liquid-chro-matographic methods. Both external and internal standardization have been used to translate peak height or areas into quantitative, solute-concentration values. Because peak heights are easy to measure, many methods use this parameter, and, when slightly overlapping peaks or unsteady baselines are encountered, it is the method of choice. With introduction of... 

The reproducibilities of both the peak heights and peak areas are shown for replicate injections of a 100 ng mC solution in Fig. 5.9. The results reveal that the injection volume has no significant effect on precision for the standard solution, providing the volume does not exceed 200 pi. Peak area generally offers greater precision (relative standard deviation 2%) at all injection volumes. As the injection volume is decreased, so the width at halfheight decreases. 

When a particular component eluting at a certain retention volume is to be estimated, this approach can be outlined as follows. Since SEC is extremely reproducible, the peak shape, peak width and peak height are dependent on the amount of the species in the sample volume injected, sample volume and retention time. From these factors the SEC peaks can be simulated or elution pattern of any species within the separation range can be plotted as a function of mass vs. retention volume. The analysis data supplies the concentration of this particular species over two or more 0.5 ml intervals. A match-up computer program has to be developed so that it can pick up the peak shape and concentration based on 3 or 4 data points at known Intervals. 

The results for changing response time showed that an increase in peak heights was observed for aspirin when the response time was reduced. This suggests that the method value of 0.5 is slightly too low to detect the aspirin peak without distortion. However the distortion must be reproducible as this effect did not significantly alter the concentration results. 

The GC response was calibrated for each analyte to determine the reproducibility of injections, the detection limit, and the working range of the method. Both peak height and peak area response measurements were taken. 

Reproducibility of peak height is also quite dependent on the reproducibility of the sample injection. This is especially important on early and thus normally quite sharp, narrow peaks. On such early peaks the width of the peak is controlled more by the injection time rather than the chromatographic process. A fraction of a second increase in injection time can double the width of these peaks and reduce peak height 50%. The peaks most subject to error in peak height measurement from injection problems are those with retention volumes between one and two times the hold-up volume of the column. Peaks beyond five to ten times the hold-up volume are negligibly affected by injection technique. 

DISCUSSION. Figure 10.11 shows the separation of a group of gases from blood. The procedure described depends on complete equilibration between the gas and liquid in the syringe. The period to achieve equilibration depends on the gas, and can be as little as 1 min for acetone and as much as 30 min for sulfur hexafluoride. Linear calibration curves can be obtained when peak height is plotted against gas concentration for either the flame ionization or electron capture detector. The reproducibility (n = 10) for ethane gave a standard deviation of 23% of the mean concentration while it was 2.3% for halothane and 1.8% for ether. 

These parameters are largely self-explanatory, and generally refer to changes in electrode behavior with time or repeated surface preparation. Since the DME is reproducible to 1 % or better, it serves as a standard to approach with solid electrodes. The variables in question generally include background current, analytical signal (e.g., voltammetric peak height), electron transfer rate, and electrode area. 

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