Endogenous interference

Tandem mass spectrometric methods have demonstrated superb specificity because of their ability to isolate analytes selectively in the presence of endogenous interferences. Attempts to further increase sample throughput led to the idea of using LC/MS/MS without the LC. Traditional chromatographic separations were replaced with flow injection analysis (FLA) or nanoelectrospray infusion techniques. The MS-based columnless methods attracted a lot of attention because of their inherent fast cycle times and no need for LC method development. 

Figure 1.22. FAIMS is used to increase the analytical throughput by eliminating the LC component altogether from quantification assays. The 3-min LC-ESI-MS run time required to separate compound MLN A from the endogenous interference was reduced to 30 s by using FAIMS. (Reprinted with permission from Hatsis eta ., 2007.)...

Without MDF processing, the BPC for the LC-MS data showed no distinct indication of metabolite peaks in any of the plasma samples. After MDF processing, the majority of endogenous interference ions were removed. As a result, the BPC of the plasma samples displayed predominantly metabolite peaks. For example, Fig. 6.6a shows the BPC of a plasma sample without MDF filtering (1 50 dilution of HLM with human plasma, the equivalent of a 1.0-mL plasma injection). Using Fig. 6.6a... 

After generation, the metabolites must be extracted and isolated. A variety of sample pretreatment methods can be applied, such as protein precipitation, liquid extraction, liquid-liquid extraction (LLE), solid-phase extraction (SPE), and microdialysis. Cleanup prior to LC-MS analysis is essential to reduce endogenous interferences and small peaks at every m/z in the mass spectra. The cleanup step also facilitates the data processing and peak detection in the chromatogram. 

Plant extracts encompass a diversifying range of endogenous compounds.These problems can be easily perceived in the reported chromatograms broad peaks, long analysis times, and poor resolution from endogenous interferences. 

Liedtke RJ, Kroon G. Automated calmagite complexi-metric measurement of magnesium in serum, with sequential addition of EDTA to eliminate endogenous interference. Clin Chem 1984 30 1801-4. 

As discussed in Sec. I, ion suppression can be a great hindrance to a sensitive, linear and rugged LC/MS method. Optimization of the chromatographic and sample preparation steps to sufficiently separate the analyte from endogenous interferences in the sample and the void volume will help guarantee success. 

Because of the intrinsically selective nature of LC/MS/MS, assay selectivity is not as big an issue as it was in the past. Truly endogenous interferences are rare and can often be handled by modifying chromatographic selectivity or, as a last... 

TH Weber, KI Kapyaho, P Tanner. Endogenous interference in immunoassays in clinical chemistry. A review. Scand J Clin Lab Invest 50(suppl 201) 77, 1990. 

The electrochemical method, on the other hand, is highly specific for the analyte of interest and free from endogenous interferences. A corre-... 

In cases where the endogenous interferents do not generate a linear signal, then a minimum required dilution (MRD) may be applied. A MRD is the dilution of a matrix that finally permits an accurate and precise measurement of analyte. Although the diluting sample reduces the sensitivity of the assay, it may be required to develop and validate an accurate and precise method. 

In the absence of compound-specific fragmentation to drive selectivity, metabolite detection on nominal mass instruments becomes significantly more difficult. Typically, significant ambiguity exists in nominal MS data due to the presence of endogenous interferences, isobaric with metabolites, which... 

Endogenous interferences and MALDI matrix cluster can complicate the analysis of xenobiotic drug compounds and their metabolites in MSI. The use of hyphenated techniques (either MS" or IMS) or high-resolution mass spectrometry can serve to increase analyte specificity. Although instrument... 

Analyze control tissues-exclude endogenous interferences... 

GC is applied in a variety of ways and is one of the most important separation techniques in this particular area. GC provides the retention time or retention index (RI) of an unknown substance that can be used for its identification. GC is routinely utilized to separate the analyte from endogenous interferences for more specific identification via mass spectrometry and can also be used to provide quantitative information about the drugs present. The following applications focus on the identification and quantification of drugs and volatiles in biological fluids by GC. 

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