System performance check compounds

Example 4.16 System performance check compounds in EPA Methods 8260 and 8270... 

During VOC and SVOC analysis with GC/MS, the magnitude of the relative response factor is monitored throughout the analysis. This is a quality check that allows the analyst to identify compound degradation caused by active sites in the system and by compound instability. Following are system performance check compounds (SPCCs) and their minimum RFs for EPA Methods 8260 and 8270 (EPA, 1996a) ... 

The next step is to show that the response for the analysis of any target compound is linear. This step is known as the initial calibration and is achieved by the analysis of standards for a series of specified concentrations to produce a five-point calibration curve (Figure 41.2a, b). On subsequent days, a continuing calibration must be performed on calibration check compounds to evaluate the calibration precision of the GC/MS system. 

Quantitative analysis is performed by the calibration technique. A new calibration curve with a standard solution of each diphenyl ether herbicides is constructed, plotting the peak area against the amount of standard solution injected. Each diphenyl ether herbicide in the sample is measured by using the peak area for each standard. Before each set of measurements, the GC and HPLC system is checked by injecting more than one standard solution containing ca 0.01-2 mg L of each compound. 

System suitability allows the determination of system performance by analysis of a defined solution prior to running the analytical batch. System suitability should test the entire analytical system, chromatographic performance as well as the sensitivity of the mass spectrometer for the compounds of interest. Some LC-MS SOPs reference analytical methods as the source of operating details for a given analysis. This works particularly well for quantitative analysis, where analytical methods include critical details on instrument parameters and special calibrations that might be required for a particular analyte. Thus, system suitability testing provides the daily [3] checking of the system. 

System makes sure all required data are entered (see Compound Registration Required and Optional Data Supplement). System performs uniqueness check against the database (see Uniqueness Check Business Rules Supplement). If the structure is unique, System registers the compound with a new sample identifier (see Sample Identifier Generation Rules Supplement). If it is not unique, System displays the compound to be registered and the hit compounds from uniqueness search and prompts die Chemist to resolve (see Resolve Compounds Use Case Spec). 

The performance of the system is tested by injecting 2 xl of OPCW check mixture running the Performance Check Injection method. The composition of the mixture is given in Annex 2. The retention times of the series of nine hydrocarbons in the check mixture are used by AMDIS for calibration of the RI the other seven compounds are used for assessing the performance of the GC and MS part of the system. Two components of the check mixture, chloromethylaniline and dibenzothiophene, are used for evaluation of isotopic ratios for chlorine and sulfur measured by the mass spectrometer. The example chromatogram of the check mixture is presented in Figure 5. 

A reference compound is needed to determine the molecular mass. The mass of an unknown is computed by comparing its signal on the mass axis with that of the known mass reference peaks. A reference compound is also required to calibrate the data system and to tune and performance-check the instrument. A calibration standard has the following desirable characteristics (1) it should yield a sufficient number of regularly spaced abundant ions across the entire scan range (2) those reference ions should have negative mass defects to prevent overlap with the nsnal compounds containing C, H, N, and O and (3) it should be readily available, chemically inert, and sufficiently volatile. 

Day-to-day variations in flow rate, check valve efficiency, or mixing solenoid performance (in binary, ternary, or quaternary pumping systems) can also contribute to retenbon shifts. Therefore, compound identification should be performed only by spiking with a known standard or by direct identification with, for example, mass spectral analysis. 

After the flushing and visual checking is finished, the equipment is tested under simulated conditions. Again, safe fluids such as air, water, and steam are used wherever possible. Sometimes inexpensive compounds with similar boiling points to the process chemicals are used to check distillation or other separative steps. For solids-handling equipment sometimes salt, the actual raw material, or product purchased for this test may be used. The purpose of these tests is to see whether every piece of equipment performs properly before more expensive and possibly more hazardous process compounds are charged to the system. It also gives the... 

For non-simultaneously operating multi-sources it is necessary to check whether the data quality achieved is sufficient, especially for fast LC systems with very narrow peaks. A switching source splits the available acquisition time for the offered ionization types and therefore reduces the true acquisition rate of the mass spectrometer. However, simultaneously operating sources do not explicitly show which compound ionized with what technique. If this information is really necessary, two separate runs must be performed. 

Drug Development Tests are performed on the lead compounds in test tubes (laboratory, in vitro) and on animals (in vivo) to check how they affect the biological systems. The tests, often called preclinical research activities. 

TLC is often used by BP monographs as part of a number of identity tests performed on pure substances. For extra confirmation of identity, more than one solvent system may be used and also different types of spray reagent may be used. Some examples of identity checks based on TLC have been mentioned earlier. Table 13.4 lists a few of the compounds which have their identity checked by TLC and a variety of location reagents and mobile phases are used to illustrate the fact that there is much less uniformity about TLC methodology than there is in the case of HPLC or GLC methodology. 

The three operations listed above are quite similar, they involve the correlation of compound names with Rf values, as performed by the predicate hrf. As arguments we will have the two lists, Clist and Rlist, the TLC system code and the tolerance level. Corresponding elements of the two lists will have to satisfy the relation hrf. We therefore check the relation hrf for the heads Cl and R1 of the respective lists and then recur on the tails Ctail and Rtail. The recurrence stops when either list is reduced to the empty list. Thus ... 

Figure 7-4 emphasizes that if it is important to know the hardware performance of the gradient system, the instrument should be checked out in a manner similar to that shown in the figure. For some systems where high sparging rates of solvents will be used, the compound methyl paraben should be used at a low concentration (approximately 0.1% or less) instead of ace-... 

Relative retention time fRJ. The main practical disadvantage of using k to describe retention arises from the difficulties associated with the accurate measurement of The accurate measurement of t, requires correct choice of a reference compound that is neither retained by the column nor excluded from its pores. Problems with the accurate and reproducible measurement of k have led to the use of a retained compound for system suitability tests for liquid chromatography and related techniques when it has been checked that the column, mobile phase and equipment are performing identically to when the method being used was first developed. The relative retention time of a solute j may be defined by... 

Another task in selecting or designing a schema is to determine which operations need to be performed. For example, in a compound-tracking system, compounds need to be registered and samples of compounds need to be taken (checked out). For a schema to function well, it should be relatively simple to update or insert data into the tables of the schema to record these activities. 

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