On-line Clean-up Procedure Research Articles

Determination of polycyclic aromatic hydrocarbons from soil samples using selective pressurized liquid extraction

A selective pressurized liquid extraction (SPLE) method has been optimized for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil samples. The method comprises a fully automated extraction and on-line clean-up procedure by inclusion of sorbents in the extraction cells. The contributing parameters of SPLE including type of solvent, static extraction time, number of extractions, extraction temperature, nature and amount of sorbents were investigated. The optimal extraction was performed at 70 °C for 10 min (static extraction time) cycled once using n-hexane/methylene chloride (50 : 50, v/v) and the sorbents in the extraction cells were 3 g of alumina and 2 g of silica gel. The collected extracts from the cells, after pre-concentration, were clean enough for direct injection into GC-MS. Validation of the SPLE technique was performed, with the recovery rates for 16 PAHs in the range of 75–103%, and the relative standard deviation (RSD) was generally less than 10%. Method detection limits (MDL) were in the ranges of 0.001–0.080 μg kg−1 for the GC-MS analyses. Finally, the method was successfully used to evaluate the cultivated soils in Beijing, China.

Turbulent flow and ternary column-switching on-line clean-up system for high-throughput quantification of risperidone and its main metabolite in plasma by LC–MS/MS: Application to a bioequivalence study

A high-throughput LC–MS/MS method was developed for the simultaneous determination of Risperidone and 9-OH-risperidone in human plasma. A semi-automated sample preparation procedure was applied, including protein precipitation after addition of ACN, via a robotic system, and subsequent sub-zero temperature extraction of the latter. Injections of the ACN extractants were performed on a turbulent flow ternary column-switching system, consisted of dual extraction columns in parallel for on-line purification of samples and an analytical column. Toggling with the assistance of two valves provided a run cycle time of 3 min and the whole procedure minimized carry-over effect. On-line clean-up procedure along with sub-zero temperature extraction increased sample purification and extended column life. The analytical range of the method was 0.1–200 ng mL −1 for both analytes with excellent linearity and very good accuracy and precision. The proposed method was employed in a bioequivalence study after per os administration of a 2 mg tablet of risperidone and allowed the completion of the study (>1400 samples) in only 4 days time.

Development of an on-line automated sample clean-up method and liquid chromatography–tandem mass spectrometry analysis: application in an in vitro proteolytic assay

Fluorescence detection has been a method of choice in industry for screening assays, including identification of enzyme inhibitors, owing to its high-throughput capabilities, excellent reproducibility, and sensitivity. Occasionally, inhibitors are identified that challenge the fluorescence assay limit, necessitating the development of more sensitive detection methods to assess these compounds. For data mining purposes, however, original assay conditions may be required. A direct method transfer to highly sensitive and specific LC-MS-based methods has not always been possible due to the presence of MS-incompatible neutral detergents and non-volatile salts in the assay matrix. Utilizing an in vitro proteolytic screening assay for the serine protease hepatitis C virus (HCV) nonstructural (NS) 3 protease as a test case, we report the development of an automated sample clean-up procedure implemented on-line with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to complement fluorescence detection. Ion exchange and peptide microtraps were employed to remove MS-incompatible assay matrix components. Three protease inhibitors were used to validate the MS/MS method. Comparable potencies were achieved for these compounds when assessed by fluorescence and MS/MS detection. Furthermore, four-fold less enzyme could be utilized when employing the MS/MS method compared to fluorescence detection. The longer analysis time, however, resulted in reduced sample capacity. The potency of our designed HCV NS3 protease inhibitors are thus routinely evaluated using a continuous fluorescence-based assay. Only pertinent inhibitors approaching the fluorescence assay sensitivity limit are subsequently analyzed further by LC-MS/MS. This methodology allows us to maintain a database and to compare results independent of the detection method. Despite the relatively slow sample turnaround time of this LC-MS approach, the versatility of the automated on-line clean-up procedure and sample analysis can be applied to assays containing reagents which were historically considered to be MS incompatible.

Determination of ammonia in wastewaters containing high concentrations of surfactants by flow injection potentiometry with on-line sample clean-up

It is demonstrated that surfactants lead to problems in the analysis of ammonia in gas-diffusion flow injection by wetting the membrane to allow transport of potentially interfering species to the detector. An on-line clean-up procedure, involving use of an activated carbon cartridge, is described for the removal of ionic and non-ionic surfactants (up to 1000 mg l −1) and other organic compounds from aqueous samples. Ammoniacal nitrogen was determined in synthetic samples by gas-diffusion flow injection with a nonactin-based potentiometric sensor used as the detector for the ammonium ion. Analyses could be performed at a sampling rate of ca. 25 h −1 and the cartridge was effective for at least 1000 injections of 50 μl samples in the concentration range 1–180 mg l −1. The procedure was applied to the analysis of wastewaters and was found to be efficient in removing ionic and non-ionic surfactants from acidified (pH 1) samples.

On-line preconcentration, cleanup and high-performance liquid chromatographic determination of chlorophenoxy acid herbicides in water

Abstract A rapid and simple technique for the determination of six chlorophenoxy acid herbicides in water is described. After extraction and preconcentration of the analytes at pH≈ 1 in a small 20 × 2 mm I.D. polymeric reversed-phase precolumn, an on-line cleanup procedure is performed by a selective transfer of the ionized compounds to a second precolumn packed with an anion exchanger. An acetonitrile-sodium hydroxide (pH 10; 10:90, v/v) solution is used for this step. The anionexchange precolumn is further on-line analyzed by reversed-phase chromatography with gradient elution and UV detection at 230 nm. The recovery of the examined herbicides is nearly 100% with a R.S.D.

An on-line clean-up procedure for large sample volume analysis of serum aminoglycoside antibiotics by reversed-phase high-performance liquid chromatography.

A reversed-phase (RP) liquid chromatography procedure using column switching was applied to assay one of the aminoglycoside antibiotics, sisomicin. The drug in serum was derivatized with o-phthalaldehyde (OPA) and β-mercaptopropionic acid (β-MP) in 0.05M borate buffer (pH 9.0), then directly injected onto a RP pre-column (ODS-silica, 50×4 mm i.d.) to remove protein and interfering compounds (confirmed by ultraviolet monitoring at 280nm). The sisomicin derivatives retained on the pre-column were desorbed by back-flushing onto an analytical column (5μm ODS-silica 200×4mm i.d.) with 0.05M potassium dihydrogen phosphate-0.05M disodium hydrogen phosphate buffer (pH 7) and were separated by elution with a mixture of methanol, ethylene glycol and counter ion solution (sodium 1-heptanesulfonate/acetic acid/water, 2.5g/42ml/208ml). This system could be utilized for more than 50 samples with a 1ml injection volume. A good linear response curve was found between the injected sample amounts and the peak heights for the concentration range of 0.5 to 5μg/ml of sisomicin. The limit of detection for sisomicin in serum was 62.5.ng/ml for 0.1ml of sample. The mean recovery from serum was 97.5%.