LC-MS calibration

LC-MS SOP and documentation. The importance of having LC-MS SOPs and updated written records for LC-MS calibration and maintenance is particularly... 

A 1 i.g/mL stock standard solution of each herbicide was prepared in acetonitrile. This solution was kept refrigerated and used for both sample fortification and preparation of the LC/MS calibration solutions. The calibration solutions were prepared by diluting an aliquot of the stock solution with a solution of 40/60 acetonitrile/water, v/v. 

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). 

Under many experimental conditions, the mass spectrometer functions as a mass-sensitive detector, while in others, with LC-MS using electrospray ionization being a good example, it can behave as a concentration-sensitive detector. The reasons for this behaviour are beyond the scope of this present book (interested readers should consult the text by Cole [8]) but reinforce the need to ensure that adequate calibration and standardization procedures are incorporated into any quantitative methodology to ensure the validity of any results obtained. 

A matrix extract was prepared from poison-free scallop and spiked at the level of 200 ngg of scallop hepatopancreas. The toxins were determined by using LC-MS with calibration employing external standards prepared in methanol. The matrix extract was then spiked further with 300 ngg of each of the toxins and redetermined. The results obtained for each analyte are summarized in Table 5.17 and show that, when using the external calibration method, the values obtained range from 138 to 170 ngg a reduction in accuracy of between 15... 

Figure 5.69 Calibration curves obtained from (a) LC-ToF-MS and (b) LC-MS-MS using selected-reaction monitoring for Idoxifene in human plasma, fortified from 5 to 2000 ngml for LC-ToF-MS and 0.5 to 1000 ngml for LC-MS-MS with a triple quadrupole is the correlation coefficient, a measure of the quality of calibration (see...

The detector calibration standards are made at convenient concentrations of each analyte. Experience has shown that linearity can be obtained over a range from 0.25 to 20.0 pgL with the listed instmmentation. Concentrations other than those shown below also may be prepared and used if necessary. The LC/MS/MS calibration standards are prepared at 0.10, 0.25,0.50, 1.0,2.0, 5.0, 10.0, and 20.0 pgL . ... 

Residues of isoxaflutole, RPA 202248 and RPA 203328 are extracted from surface water or groundwater on to an RP-102 resin solid-phase extraction (SPE) cartridge, then eluted with an acetonitrile-methanol solvent mixture. Residues are determined by liquid chromatography/tandem mass spectrometry (LC/MS/MS) on a Cg column. Quantitation of results is based on a comparison of the ratio of analyte response to isotopically labeled internal standard response versus analyte response to internal standard response for calibration standards. 

After overcoming the instability of the thermospray ionization source, a sensitivity of 2 ng/mL was achieved with a calibration range of 10 to 103 ng/mL for human plasma samples. In recent years, the online SPE LC/MS/MS technology has matured and is now easy to build and use. It is used widely in the pharmaceutical industry (Jemal et al. 2000 Hsieh 2004 Hennion 1999). 

Hopfgartner et al. (2002) compared ternary column online SPE LC/MS and TFC with offline 96-well plate SPE LC/MS to quantitate three drug candidates in human plasma. A protein precipitation step was performed before the SPE LC/MS. Dual trapping columns (YMS AQ, 10 x 2.0 mm, 5 /tm) were used with an analytical column (Intertsil Phenyl, 50 x 2.1 mm, 5 /tm). The run cycle was 3 min calibration range was 0.2 to 250 ng/mL. The run cycle was 2 min with a calibration range of 5 to 1000 ng/mL for TFC. Offline SPE LC/MS achieved the same calibration range with a run time of 2 min. 

In another study, samples from the Dutch coastal zone of the North Sea were collected in 1999 and 2000 and analysed by LC-ESI-MS [31]. At locations corresponding to those of the 1995/1999 studies, levels (10-30ngNPEOg 1) were observed in close agreement with the ones reported earlier. It can be concluded that, provided careful evaluation of which commercial mixture will be used as a calibrant in LC-FL, the result thus calculated can be similar to those obtained by LC-MS. 

Based on the 96-well format, OCT-PAMPA was proposed and has proved its ability to determine (indirectly) log Poet [87]. PAM PA is a method, first developed for permeability measurements, where a filter supports an artificial membrane (an organic solvent or phospholipids) [88, 89]. With this method, the apparent permeability coefficient (log P ) of the neutral form of tested compounds is derived from the measurement of the diffusion between two aqueous phases separated by 1-octanol layer (immobilized on a filter). A bilinear correlation was found between log Pa and log Poct> therefore log Poet of unknown compounds can be determined from log Pa using a calibration curve. Depending on the detection method used a range oflog P within —2 to +5 (with UV detection) and within —2 to +8 (with LC-MS detection) was successfully explored. This method requires low compound amounts (300 pi of 0.04 mM test compound) and, as for the previous method, samples can be prepared in DM SO stock solutions. For these experiments, an incubation time of 4h was determined as the best compromise in term of discrimination. The limitation of the technique lies in the lower accuracy values... 

Usually, method-specific acceptance criteria are established for system suitability tests. For LC-MS/MS-based assay a possible general criteria for system suitability test is based on the use of at least five replicates of the neat solution concentration comparable with the closest calibration standard to LLOQ. To pass... 

As analytical and bioanalytical methods must be validated before using them for routine sample analysis and after changing method parameters (see Chapter 8), instruments such as liquid chromatography coupled with mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS), which are utilized to perform the analysis, should be calibrated and qualified. In addition, an instrument s performance should be tested for suitability prior to use on practically a day-to-day basis. 

---