Gradient elution mode acetonitrile

A LiChrospher 100 RPis, 125 mm x 4 mm i d. (Merck, Darmstadt, Germany) column was used for separation. The mobile-phase was a mixture of acetonitrile-water in gradient elution mode (see also Table 1). The solvents were filtered through 0.45 pm nylon membranes (Teknokroma,) and degassed with helium before use. 

LC-MS-MS was also the method of choice for the analysis of UV filters in solid matrices. Both LC and UPLC have been applied in three out of the four methods available for the determination of UV filters in sludge. Separation was performed on C8 and C18 LC-chromatographic columns (Zorbax, Eclipse, Vydac, and Purosphere) using binary gradient elution of mobile phases consisting of water/ methanol or water/acetonitrile. MS-MS detection was performed in SRM with ESI and atmospheric pressure photoionization (APPI) in both positive and negative modes. For each compound, two characteristics transitions were monitored. In addition to MS and MS-MS, diode array detection (DAD) was occasionally applied to the determination of OT. Spectra were recorded between 240 and 360 nm and discrete channels at 310 nm. 

Using the Tomtec Quadra 96 workstation, 0.1 mL of the ethyl acetate layer was transferred to a 96-well collection plate containing 0.4 mL of acetonitrile in each sample well. The solution was mixed 10 times by aspiration and dispersion on the Tomtec. The plate was then covered with a sealing mat and stored at 2 to 8°C until LC/MS/MS analysis. The HILIC-MS/MS system consisted of a Shimadzu 10ADVP HPLC system and Perkin Elmer Sciex API 3000 and 4000 tandem mass spectrometers operating in the positive ESI mode. The analytical column was Betasil silica (5 fim, 50 x 3 mm) and a mobile phase of acetonitrile water formic acid with a linear gradient elution from 95 5 0.1 to 73.5 26.5 0.1 was used for 2 min. The flow rate was 1.0 mL/min for the API 3000 and 1.5 mL/min for the API 4000 without any eluent split. The injection volume was 10 jjL and a run time of 2.75 min was employed. 

The quaternary ammonium compounds paraquat and diquat are widely used non-selective contact herbicides, which are extremely toxic to humans. Fee et al. [112] established an HPLC-MS-MS procedure for the determination of these herbicides in whole blood and urine using ethyl paraquat as internal standard. After extraction with Sep-Pak C18 cartridges, analytes were separated using ion pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution. Detection was carried out in ESI MS-MS SRM mode. Using similar separation and detection conditions, paraquat, diquat, difenzoquat, and a number of structurally related quaternary nitrogen muscle relaxants (see Section 20.2.1.3) were determined in whole blood by Ariffin and Anderson [113]. 

Elution was performed using a concentration gradient of a methanol-acetonitrile-water ternary mixture. The initial proportions of the components at the beginning of the run were 40 40.5 18.5. The concentration of acetonitrile was then decreased linearly so that it reached 0% at 25 min while its concentration in the mobile phase was replaced with methanol at the same gradient rate. Elution was completed with a linear gradient of the methanol-water mixture so that the mobile phase usually contained 90% of methanol at 60-70 min and was 100% methanol at 90 min. The elution of phenacyl esters of 6 0-22 1 fatty acids was completed within 80 min at a flow rate of 1 ml/min (the detailed composition of the mobile phase is described in Table 1, elution mode E) (Fig. 4). 

This study evaluated the impurity profile of untreated water from a textile plant in Portugal [35]. The organic material was concentrated by extraction from 11 of water into dichloromethane and HPLC-NMR and HPLC-MS experiments were carried out using a reverse-phase separation with an acetonitrile/ D2O gradient elution with H NMR spectroscopic observation at 600 MHz. For the HPLC-NMR studies, the samples were further fractionated into two pools according to their HPLC retention times. The HPLC-NMR studies were carried out in the stop-flow mode and the combination of NMR and MS results yielded the identification or tentative identification of 14 compounds, comprising mainly surfactants, anthraquinone dyes and nonylphenol-related molecules. 

Mixtures of benzodiazepines and thiazide diuretic drugs were separated by gradient elution CEC and identified using ESI-MS by Taylor and Teale [38], They used 330-500 x 50-75 pm i.d. colums packed with Hypersil ODS and Apex ODS and gradients of 50-80% acetonitrile in 5 mmol/1 aqueous ammonium acetate to elute the sample components. Benzodiazepines were detected in the positive ion mode using 1% acetic acid as the sheath liquid, whereas the thiazide diuretics were detected in the negative ion mode with 80% isopropanol in water as sheath liquid. 

Figure 13-4. Representative MRM scans (plasma extract of a proprietary compound) using an API 5000 triple quadrupole unit (Sciex). Each panel contains a distinct MRM transition for the same compound m/z 1021.6 —> 1003.5 (left panel) and m/z 1021.6 971.5 (right panel). Signal-to-noise ratio is designated as S/N. Experimental conditions ESI, positive ion mode, protein precipitation was used for sample preparation, injection volume was 10 pL, the column was a Cig, and dimension was 20 x 2.1 mm, using a linear gradient elution Omin (20% B)-6min (90% B)-8min (90% B), where B was 0.2% formic acid in acetonitrile and A was 0.2% formic acid in water separation was performed at room temperature.

Several column types (silica, cyano, amino, diol) function in an NP mode when used with organic solvents, such as acetonitrile, that contain a small percentage of water (usually <20%). In this mode of operation, gradient elution is performed by ramping the aqueous content of the mobile phase. Frequently, a small percentage of an ammonium buffer (<5 mM) is needed to disrupt secondary interactions that lead to peak tailing. 

Moreover, dne to their chemical complexity and similarity of phenolic compounds in frnits and vegetables, they are usnally elnted nsing a gradient elution instead of the isocratic mode, where the mobile phase is generally a binary system. The most snitable solvents for UHPLC are water, methanol, and acetonitrile. Consequently, the mobile phases employed for the separation of a single family... 

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