Final method calibration

Several assumptions were made in using the broad MWD standard approach for calibration. With some justification a two parameter equation was used for calibration however the method did not correct or necessarily account for peak speading and viscosity effects. Also, a uniform chain structure was assumed whereas in reality the polymer may be a mixture of branched and linear chains. To accurately evaluate the MWD the polymer chain structure should be defined and hydrolysis effects must be totally eliminated. Work is currently underway in our laboratory to fractionate a low conversion polydlchlorophosphazene to obtain linear polymer standards. The standards will be used in polymer solution and structure studies and for SEC calibration. Finally, the universal calibration theory will be tested and then applied to estimate the extent of branching in other polydlchlorophosphazenes. 

First method 0.1 mL of sample was mixed with 0.5% NaBH4, followed by addition of HCl (6 mol L ) and preconcentration (10 mL to 1 mL), followed by HPLC separation (Hamilton PRP-XlOO). Calibration was by matrix matching, using Na2Se03 calibrant. Final detection was by quartz furnace AAS. 

Blanks are a vital component of the lahoratory quality control process. They are incorporated into all method development, vahdation and sample analysis schemes to monitor and mitigate laboratory contamination (Section 9.7.1). Also, with LC-MS calibration curves often covering up to three orders of magnitude, carryover due to insufficient rinsing of the syringe needle or autoinjector is common and blanks (extracted blanks in particular) are used to assess and quantify the impact of the carryover on the final method (Section 9.7.2). 

Finally, we ll recall that gravimetry by precipitation, because it is an absolute method, is used to check and calibrate instrumental methods. 

A final practical note involves instrument intensity measurement calibrations. The intensity measurement is self-calibrating relative to the incident beam from the source. However, measurements typically have a dynamic range of 10 -10 , and care must be taken to insure the detection system is linear. A method of calibrating the scatterometer is to characterize a diffuse reflector having a known scattering characteristic. For example, a surface coated with BaS04 makes a nearly Lambertian scatterer, which has a BRDF of 1/Jt at all angles. 

Among the most widely used ab initio methods are those referred to as Gl" and 02." These methods incorporate large basis sets including d and / orbitals, called 6-311. The calculations also have extensive configuration interaction terms at the Moller-Plesset fourth order (MP4) and fiirther terms referred to as quadratic configuration interaction (QCISD). ° Finally, there are systematically applied correction terms calibrated by exact energies from small molecules. 

Finally, there are other times when circumstances do not permit us to freely choose what we will use for calibration samples. If we are not able to dictate what samples will go into our training set, we often must resort to the TILI method. TILI stands for "take it or leave it." The TILI method must be employed whenever the only calibration samples available are "samples of... 

Method Validation The signal path from detector up to the hard copy output of the final results must be perceived as a chain of error-prone components there are errors due to conception, construction, installation, calibration, and (mis-)use. Method validation checks into these aspects. 

To demonstrate the validity of an analytical method, data regarding working range/ calibration, recovery, repeatability, specificity and LOQ have to be provided for each relevant sample matrix. Most often these data have to be collected from several studies, e.g., from several validation reports of the developer of the method, the independent laboratory validation or the confirmatory method trials. If the intended use of a pesticide is not restricted to one matrix type and if residues are transferred via feedstuffs to animals and finally to foodstuffs of animal origin, up to 30 sets of the quality parameters described above are necessary for each analyte of the residue definition. Table 2 can be used as a checklist to monitor the completeness of required data. 

Initially, this method utilized 5-mL conical centrifuge tubes as the collection device for final elution of the extract from the Cig tubes. In practice, these tubes were found to be very difficult to clean and in few instances were the cause of cross-contamination when low-concentration samples were extracted following samples with very high concentrations. Since no commercial graduated tubes were available, disposable culture tubes are used as the receiver. These tubes are individually calibrated before use. A solvent blank sample may be processed through the method from extraction to quantification to determine if contamination from glassware occurs. 

Finally, it is very difficult to keep standard solutions for monitoring or recalibration purposes. Control batches should be purged and kept with a dry, inert gas. As long as results are reproduced, the system is considered to be in calibration. The relatively long extraction times usually prohibit the use of these methods for quality control analysis applications in a plastics manufacturing plant. 

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