Internal standard mode

The requirement that the analytes be quantitated using an internal standard mode of instrument calibration is due to the fact that mass spectrometers are intrinsically unstable that is, their response factor varies with time when compared to other GC detectors such as the flame ionization detector (FID). The internal standard technique of instrument calibration is... 

An internal standard mode of calibration was used to conduct quantitative analysis using the minivial technique just described. The analyte studied was 4-methylacetophenone and the internal standard was -dode-cane. The slope of the linear calibration was 4.88 L/mmol with a y intercept of zero and a coefficient of determination of 0.998 (17). 

Matrix Use the internal standard mode of instrumental calibration... 

Quantitative Analysis calibration based on internal standard mode unknown sample analysis statistical treatment of data write-up required... 

Retrieve the Turbo method titled LEMIS, which stands for lindane, endrin, methoxychlor, internal standard mode of calibration allow sufficient instrument equilibration time. Write a sequence encompassing the calibration standards, ICV, and unknowns. Save the sequence as a file with the name, for example, G 0317 (group, March 17th). Begin to inject a 1-pL aliquot of each working standard. Initially inject iso-octane, then inject in the order lowest to highest concentration level. This order is important because it prevents carryover from one standard to the next. 

Harris D. Quantitative Chemical Analysis. 3rd ed. San Francisco Freeman and Co., 1991, pp 604-605. Also refer to Chapter 2 on the use of the internal standard mode of calibration. 

A calibration method is set up at the LC/MS (-MS) system using the internal standard mode (ISTD), and the set of standard solutions is measured. Alternatively, the external standard mode (ESTD) may be used, if standard solutions and sample extracts are analyzed immediately, that is, within a few hours. 

International standard ISO 8402 1994 defines procedure as determined mode of the activities realization. We consider activities on testing. 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

Plant material is homogenized in acetone followed by addition of water. The filtered extract is diluted with acetone-water (2 1 v/v) and filtered through a syringe filter. The sample extract is diluted 1 1 with a deuterated azinphos-methyl internal standard and analyzed using LC/MS/MS in the positive-ion selected reaction monitoring (-I-SRM) mode. 

Macerated plant material is homogenized with a mixture of methanol and 1.2N hydrochloric acid (HCl) in water (4 1, v/v) and then with methanol. An internal standard solution is added to the filtrate and the filtrate is adjusted to a constant volume. A portion of the filtrate is rotary evaporated to dryness and hexane is added to the extract before a Florisil cleanup procedure is performed. The extract is dissolved in toluene for analysis by GC/MS in the negative chemical ionization (NCI) mode. 

Water samples, received from the respective groundwater trials, are analyzed by direct aqueous injection (DAI) by LC/ESI-MS/MS. A 1-mL volume of the water is pipetted into a 1.8-mL autosampler vial. The internal standard solution is added (200 qL) and mixed. The vials are capped and analyzed by LC/ESI-MS/MS using the selected reaction monitoring (SRM) mode. 

Pd removal was determined as follows. An aliquot of a representative liquid or solid sample was accurately weighed and subsequently digested by refluxing in nitric and/or hydrochloric acid using a closed vessel microwave procedure (CEM MARS5 Xpress or Milestone Ethos EZ). Cooled, digested samples were diluted, matrix matched to standards, and referenced to a linear calibration curve for quantitation an internal standard was employed to improve quantitation. All samples were analyzed by an Inductively Coupled Plasma Mass Spectrometer or ICP/MS (Perkin Elmer SCIEX Elan DRCII) operated in the standard mode. 

Many industrial laboratories conducting significant amounts of additive analyses have developed a universal HPLC method which may be used to separate most of the additives of interest. Thomas [417] has reported a method that can separate over 20 common primary and secondary stabilisers. Verdurmen et al. [197] employ a gradient ranging from 60 % acetonitrile/40 % water to 100% acetonitrile subsequently, all components are eluted off the column in isocratic mode. Irganox 1063 is used as a suitable internal standard since this compound is not frequently encountered in commercial polymers, elutes without overlap to other additives and shows good UV absorbency. In order... 

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

Fan et al. [106] developed a high performance capillary electrophoresis method for the analysis of primaquine and its trifluoroacetyl derivative. The method is based on the mode of capillary-zone electrophoresis in the Bio-Rad HPE-100 capillary electrophoresis system effects of some factors in the electrophoretic conditions on the separation of primaquine and trifluoroacetyl primaquine were studied. Methyl ephedrine was used as the internal standard and the detection was carried out at 210 nm. A linear relationship was obtained between the ratio of peak area of sample and internal standard and corresponding concentration of sample. The relative standard deviations of migration time and the ratio of peak area of within-day and between-day for replicate injections were <0.6% and 5.0%, respectively. 

Figure 9.1 GC MS chromatograms acquired in the SIM mode of a laboratory blank (a) and an amino acid standard solution with concentrations at the quantitation limit (b). i.s.l, Hexadecane internal standard i.s.2, norleucine internal standard...

FIGURE 6.57 Overlaid chromatograms (24) obtained for blank plasma spiked with midazolam and positive mode internal standard. 

The mass accuracy is highly dependent on the mode the instrument is operating in. In the reflector mode, with time-lag focusing, the best MALDI-TOF and oa-TOF instruments are capable of achieving <5 ppm with internal standards, provided that the isotopes are resolved. In many cases it is not possible to add internal calibrants, and then the error in mass accuracy is often increased to 50-100 ppm. Operation of an instalment in a linear mode will typically decrease the mass accuracy. 

Fig. 2.6.3. Mixed-mode HPLC-ESI-MS summed ion chromatogram of a sediment extract (32-36 cm depth core slice) showing resolution of NPEOs and NPs. Numbered peaks correspond to NPEOs and [13CeJNPEOs with the indicated number of ethoxy groups (0 = NP, [13C6]NP 1 = NPEOi, [13C6]NPEOi, etc.). Peaks A and B are the internal standards, re-NP and re-NPE03, respectively. (Note the discontinuity at retention time 25.8 min, corresponding to the shift in MS polarity from positive to negative ion mode.)...

The development of an easy-to-handle method for the qualitative and quantitative determination of surfactants in consumer products was the goal for applying ESI in the FIA-MS(+/—) mode by direct infusion into the mass spectrometer. In this way Ci2, Ci4, Ci6 and Ci8 ASs could be determined besides other anionics (LASs, alkylcarboxylates), nonionics (alkyl polyglucosides (APGs)) and cationics (quats and ester-quats). The methods applied for concentration and determination (MS-MS) helped to identify the compounds and in addition deuterated internal standards were applied for confirmation [57]. 

Example A potential drug and its metabolite in a liver sample are quantified by internal standardization with trideuterated standards for both compounds (Fig. 12.4). [25] Under these conditions it neither presents a problem that both analytes and their isotopic standards are almost co-eluting from the LC column, nor does the completely unspecific TIC play a role. If required for sensitivity reasons, this analysis could also have been performed in the SIM mode using the m/z values of the RICs shown. 

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