Suspect sampling time

Suspect sampling time is in the region of 30 to 40 minutes, and the removal and packaging of the suspect s outer garments take a further 5 minutes. The kits are more costly and time-consuming to prepare than the equivalent previous kits, but as two new kits replace four previous kits, the overall cost and preparation time are less. None of the components of either kit is reused. 

If it is suspected (or known) that the plug flow assumption does not hold, a separate tracer study is needed to characterize the flow distribution within the pipes. These data are then used to adjust both the concentration and the sampling time, as required. If the nature of flow and mixing in the vessel is independent of the flow characteristics in the pipes, then the o1 curve for the vessel may be calculated from... 

Confirmation of the identity of the -lactam residues detected by liquid chromatography has been attempted through use of photodiode array detectors (73, 75,11-19. This procedure is relatively simple, but does not offer the specificity and the sensitivity required to determine or identify trace levels of residual -lactam antibiotics in edible animal products. Better residue confirmation can be more readily attained by treatment of the suspected samples with -lactamase or penicillinase and their reanalysis (71, 80, 86-89, 105, 106-111). In this instance, absence of a chromatographic peak with the proper retention time provides unequivocal evidence that a given residue is not present above the detection limit of the method. Thus, use of -lactamase provides a simple, inexpensive and... 

The revised suspect sampling kit and general-purpose sampling kit have now been operational in casework for 12 years during which time no problems have been encountered, either in the use of the kits or in subsequent laboratory preparation and analysis procedures. 

The —2.39 jackknife value at 6 h is extreme, but is not found to be suspect after reviewing the data records. Hence, in the process of our analysis and validation, two values were eliminated 6.57 at 6 h, and 3.52 at the immediate sample time. All other suspicious values were checked out and not removed. A new regression conducted on the amended data set increased R, as well as reducing the bo and bi values. The new regression is considered... 

In order to develop this deployable technology, members of the Forensic Science Center at LLNL were tasked to research and develop new methodology and field portable equipment which includes the collection, preparation, and analysis of suspect samples. The analysis of CW compounds and their precursors at trace levels is a labor intensive, time consuming process, usually requiring a fully equipped laboratory. However, with the utilization of solid phase extraction (SPE) technology, sample preparation time is greatly reduced and cumbersome laboratory equipment is eliminated. 

When employing PGC for qualitative and quantitative analysis of complex unknown samples, it is essential to use pure samples of suspected sample components as a reference. One should never base identification of unknown pyrolyzate peaks on the retention time of pyrolyzate product peaks obtained from the standard (7). A peak in the chromatogram from the pyrolysis of the nnknown may be from the matrix and not the suspected component. The nse of selective detectors (i.e., a NPD with a FID or a FID with an BCD) will furnish element information but not molecular or structural information about the component peak. The mafiix components (in the absence of the suspected analyte) may yield the same peak at the same retention time. 

A second example is also informative. When samples are obtained from a normally distributed population, their values must be random. If results for several samples show a regular pattern or trend, then the samples cannot be normally distributed. This may reflect the fact that the underlying population is not normally distributed, or it may indicate the presence of a time-dependent determinate error. For example, if we randomly select 20 pennies and find that the mass of each penny exceeds that of the preceding penny, we might suspect that the balance on which the pennies are being weighed is drifting out of calibration. 

With conventional nonspectroscopic detectors, other methods must be used to identify the solutes. One approach is to spike the sample by adding an aliquot of a suspected analyte and looking for an increase in peak height. Retention times also can be compared with values measured for standards, provided that the operating conditions are identical. Because of the difficulty of exactly matching such conditions, tables of retention times are of limited utility. 

Bad laboratory analyses are not always the fault of the laboratory.. Sampling plays a big role. One plant superintendent investigated every instance of suspect analyses in his plant using elaborate around-the-clock methods over a considerable period. His results revealed that over one half of the bad analyses were not the fault of the laboratory. We are all human and bad analyses will result from time to time. Rather than resubmit samples, it may be well to spend a few minutes using the following methods as referees to evaluate the reasonableness of the results. 

Provided that operating conditions remain constant and are reproducible, the retention times of the components of a sample can be compared directly with those of known materials and synthetic mixtures. An unfamiliar peak can sometimes be identified by spiking a sample with a pure substance whose presence is suspected. An increase in the size of the unknown peak is good evidence for it being the substance added. As two materials may have the same retention time for a given stationary phase, this method is not infallible. It is advisable, therefore, to run unknowns on two different stationary phases. 

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