Sample carryover

Sample carryover Watch for potential carryover in pipetting and washing steps... 

Finally, Experiment 28 is used to check for any autosampler/ system sample carryover. A blank water sample is injected immediately following the highest injected volume of the preceding precision/repeatability/linearity test. Any carryover is then calculated as in the procedure described earlier under Autosampler in section (j) of the OQ guidelines. 

From a practical point of view this definition can be interpreted as being imposed by the linear boundary of the calibration curve (quadratic behavior) due to saturation of the detector or/and ion suppression effect and/or contamination for low-level samples (carryover) (see Section 8.3.7). 

Injector rotor seal (tearing—sample carryover) and needle seal (scoring—leakage) ... 

Thicker phase coatings extract a greater mass of analyte, but the extraction time is longer than for a thinner coating [135], Because the coated fiber sorbents are reused multiple times, ease and completeness of desorption of the fiber is an issue in order to reduce sample carryover [134]. 

Less sample cleanup is often required because plates are not reused. Every sample is analyzed on a fresh layer without sample carryover or cross-contamination. 

The TE column is equilibrated with a minimum of two solvent combinations. The first solvent is strong, to wash the TE column free of impurities it may have accumulated from a previous sample (remember, this column is used over and over, so this step is critical so there is no sample carryover). This solvent is probably pure methanol or acetonitrile if using a reversed-phase filled TE column. The second solvent is not strong it is used to bring the TE column to equilibrium to accept the sample components of in-... 

Figure 18 Calibration curves using an internal standard (IS). Analytes are quantified against an IS that has been added as early as possible in the analytical procedure. The ratios of detector responses for the analyte (fiA) and IS (R S) are plotted against the ratio of known amounts of analyte (A) and IS. When a sample is analyzed, the ratio Ra/Ris is measured. Then knowing the amount of IS added into the sample, the amount of analyte present in the sample can be estimated. Curves that do not pass through the origin of the graph or which are nonlinear are diagnostic of (a) chemical interference or sample carryover, (b) sample loss during the assay due to adsorption, and (c) saturation or cross-contribution between the IS and the analyte.

In addition, the use of sippers, transfer tubing, and injectors (manual or otherwise) is not practical or reliable enough for these data collection rates. The complex equipment contains numerous moving parts that can malfunction and cause sampling errors. In addition, these systems are prone to dilution-related errors, contamination, sample carryover, leaks, and blockage by air bubbles and particulate matter. 

FIA is the simplest form of sample introduction into the mass spectrometer, and this injection format has been widely used in the analysis of combinatorial library samples. This technique offers the highest throughput combined with ease of use and facile automation. Richmond et al. [67-69] reported methods to minimize sample carryover for the FIA-MS analysis of combinatorial libraries. Samples were sorted before the analysis to maximize the molecular-weight difference between samples in the analysis queue and to minimize the conditions where consecutively measured wells contain samples similar to building blocks. Cycle times of less than a minute were reported with a carryover of 0.01%. A software appUcation was developed to automatically report the sample purity and calculate sample carryover by an automatic spectrum comparison method [70,71]. A quasi-molecular ion discovery feature was also implemented [72] in the automated data-processing program. Automated FIA-MS analysis and reporting were also used in the analysis of fractions from the purification of combinatorial libraries [73]. Whalen et al. developed software to allow automated FIA-MS analysis from 96-well plates [74]. The system optimizes the interface for mass spectrometry and MS/MS conditions, and reports the results in an unattended fashion. 

Finally, the dead volumes developed when capillary coimections and other junctions to the fluidic chip to provide off-chip processing, such as the interface to MS, can significantly degrade separation performance and introduce sample carryover or sample loss. For example, Gao and coworkers [124] estimated 4 pF for the dead volume associated with their miniaturized trypsin membrane reactor. As noted above, the typical peak volume associated with microchip electrophoresis is on the order of 10 pF, which demands that nearly all protein processing post-separation be done directly on-chip so as not to degrade separation... 

The cause of the low frequency noise shown in Figures A and 5 is an important question. In most applications of ion chromatography, two possibilities can be suggested. One is sample-to-sample carryover due either to contamination in the sample injection loop or to a slowly eluting organic left on the separator column by a previous sample. The other is mechanical transients. The existence of the pump cycle suggests that variations in flow past the conductivity detector cause variations in the chromatogram. 

Fang, J., Rand, K.D., Beuning, RJ., Engen, J.R. (2011) False EXl signatures caused by sample carryover during HX MS analyses. International Journal of Mass Spectrometry, 302 (1-3), 19-25. 

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