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At least 667 records · Page 37Linked to original sources
PubMed1996

Quantitative determination of amlodipine in serum by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

A sensitive and specific liquid chromatographic method coupled with tandem mass spectrometry was developed for the quantification of amlodipine in human and rat serum, which is a dihydropyridine derivative with calcium antagonist activity. An atmospheric pressure chemical ionization interface was used as the ion source and the analysis was performed in the selected reactive monitoring (SRM) mode. Deuterated amlodipine was used as the internal standard, and serum samples were treated with diethyl ether extraction prior to analysis. Serum levels in the range 0.014-7.2 ng ml-1 were measured accurately by this method, and the lower limit of quantitation (LOQ) was 0.014 ng ml-1 using 1 ml of human serum. The accuracy was within 7% of the expected values. The intra-assay precision was less than 3% and the inter-assay precision was less than 6%. The method was applied to a pharmacokinetic study of amlodipine in rats, in which the measurable range was 0.14-72 ng ml-1 using 0.1 ml of serum because of a limitation on the sample volume.

Amlodipine↗
PubMed1997

Liquid chromatographic-atmospheric pressure chemical ionization mass spectrometric determination of anandamide and its analogs in rat brain and peripheral tissues.

A simple and selective method for the determination of anandamide (arachidonoylethanolamide), an endogenous cannabinoid receptor ligand, and its analogs with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) was developed. The calibration curve for standard anandamide was linear over the range 625 fmol-125 pmol per injection (r = 0.999) with a precision of 1.0% (C.V.) at 25 pmol. The detection limit attained was 200 fmol per injection at a signal-to-noise ratio of 2. Anandamide and its analogs were extracted from rat brain and peripheral tissues according to the method of Folch, and the recovery of anandamide from rat brain homogenates was 67.0-72.6%. The method was applied to their determination in rat brain and peripheral tissues.

Animals↗
PubMed2001

Dental hard tissue modification and removal using sealed transverse excited atmospheric-pressure lasers operating at lambda=9.6 and 10.6 microm.

Pulsed CO(2) lasers have been shown to be effective for both removal and modification of dental hard tissue for the treatment of dental caries. In this study, sealed transverse excited atmospheric pressure (TEA) laser systems optimally tuned to the highly absorbed 9.6 microm wavelength were investigated for application on dental hard tissue. Conventional TEA lasers produce an initial high energy spike at the beginning of the laser pulse of submicrosecond duration followed by a long tail of about 1-4 micros. The pulse duration is well matched to the 1-2 micros thermal relaxation time of the deposited laser energy at 9.6 microm and effectively heats the enamel to the temperatures required for surface modification at absorbed fluences of less than 0.5 J/cm(2). Thus, the heat deposition in the tooth and the corresponding risk of pulpal necrosis from excessive heat accumulation is minimized. At higher fluences, the high peak power of the laser pulse rapidly initiates a plasma that markedly reduces the ablation rate and efficiency, severely limiting applicability for hard tissue ablation. By lengthening the laser pulse to reduce the energy distributed in the initial high energy spike, the plasma threshold can be raised sufficiently to increase the ablation rate by an order of magnitude. This results in a practical and efficient CO(2) laser system for caries ablation and surface modification.

Dental Caries↗
PubMed1995

Liquid chromatographic-atmospheric pressure chemical ionization mass spectrometric analysis of glycine conjugates and urinary isovalerylglycine in isovaleric acidemia.

n-Acetylglycine, n-propionylglycine, n-butyrylglycine, isobutyrylglycine, n-valerylglycine, isovalerylglycine, heptanoylglycine, phenylacetylglycine and isovalerylglucuronide were identified based on their liquid chromatographic-atmospheric pressure chemical ionization mass spectra (LC-APCI-MS). We were able to detect the presence of urinary isovalerylglycine in two cases of isovaleric acidemia using LC-APCI-MS. Membrane-filtered urine samples were injected into the LC-APCI-MS system in the negative-ion mode without any further pretreatment, and large amounts of isovalerylglycine were detected as the [M-H]- ion. The urinary excretion of isovalerylglycine appeared to increase after L-carnitine therapy. This analytical method is quick and easy and it may be a useful tool in understanding dysfunctional conditions in isovaleric acidemia.

Acidosis↗
PubMed2004

In-vitro metabolism of isotetrandrine, a bisbenzylisoquinoline alkaloid, in rat hepatic S9 fraction by high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry.

The objective of this study was to investigate the in-vitro metabolism of isotetrandrine, a bisbenzylisoquinoline alkaloid, using rat hepatic S9 fraction and to profile and identify its metabolites using high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry (HPLC-MS) and tandem mass spectrometry (MS/MS). Isotetrandrine was incubated at a concentration of 100 microg mL(-1) with male rat hepatic S9 fraction in the presence of an NADPH generating system (Tris buffer, pH 7.4, 37 degrees C). Samples were removed at 60 min after reaction initiation. Unchanged isotetrandrine (approximately 63% of the sample) and four metabolites were profiled, characterized and tentatively identified using solvent extraction, methyl derivatization, and HPLC-MS and MS/MS techniques. Isotetrandrine metabolites were mainly formed via two main pathways, N-demethylation and isoquinoline ring oxidation. The first pathway produced a major metabolite, N-desmethyl isotetrandrine (approximately 16% of the sample). The second pathway produced three minor oxidized metabolites, hydroxy-isotetrandrine (approximately 6% of the sample), oxo-isotetrandrine (approximately 7% of the sample), and oxohydroxy-isotetrandrine (approximately 7% of the sample). Diazomethane treatment of these metabolites did not produce any methyl derivatives and therefore the hydroxylated sites of the metabolites were tentatively assigned at the heterocyclic moieties of the isoquinoline rings. In conclusion, isotetrandrine is substantially metabolized in this in-vitro rat hepatic system.

Alkaloids↗
PubMedDate not supplied

Determination and confirmation of malachite green and leucomalachite green residues in salmon using liquid chromatography/mass spectrometry with no-discharge atmospheric pressure chemical ionization.

A liquid chromatography/mass spectrometry (LC/MS) method was developed to quantitate and confirm residues of leucomalachite green (LMG) in salmon tissue after their conversion to chromic malachite green (MG) in the extraction process. The method uses no-discharge atmospheric pressure chemical ionization (APCI) in conjunction with an ion-trap instrument to generate product-ion spectra. In the sample preparation procedure, salmon tissue is extracted with acetonitrile/buffer, the LMG residue is partitioned into methylene chloride, the LMG is converted to MG using an organic oxidizing agent, and the MG is isolated on alumina/propylsulfonic acid solid-phase extraction cartridges. The method was validated by fortifying salmon with different levels of LMG, and then detecting the residue as MG The LC/MS conditions, including a comparison of electrospray and no-discharge APCI, were evaluated and optimized. MG was not confirmed in any of the control tissue extracts, and all fortified samples analyzed during validation met the confirmation criteria as described. In addition to providing confirmatory data, this method can provide an alternative method for quantitation of MG in salmon. The recoveries of LMG measured as MG by this LC/MS method, at fortification levels of 1-10 ng/g were very high (86-109%), with low relative standard deviation(RSD) values (6.4-13%). The results agreed very closely with those obtained for the same extracts using an LCNIS procedure, indicating that matrix suppression was not an issue. The presence of LMG in salmon tissue samples fortified at 0.25 ng/g was confirmed by this method, with an average recovery of 70.1% and an RSD of 12.0%. Sample extracts from fish exposed to MG were also analyzed.

Aniline Compounds↗
PubMed2003

Practical considerations when using radio frequency-only quadrupole ion guide for atmospheric pressure ionization sources with time-of-flight mass spectrometry.

Construction details and performance evaluation of a radio frequency (rf)-only quadrupole ion guide for use with an electrospray ionization time-of-flight mass spectrometer is presented in this paper. Angiotensin III and cytochrome c were used in these experiments to investigate the ion transmission properties of the rf-only quadrupole for different m/z species. In addition, influence of ion kinetic energies along with the characteristic fragmentation due to collision induced dissociation (CID) were studied. These experiments demonstrate that the transmissions of different m/z ions were not only dependent on the frequency and magnitude of the rf waveform, which is similar to a high vacuum rf-only quadrupole ion guide, but also on the pressure inside the quadrupole chamber. For the pressure range tested, low m/z ions are better focused with increasing pressure. As expected, transmission of ions are subject to space charge limitations when significant numbers of ions are focused on the axis of the quadrupole. It is also observed that CID results are related to transverse motion and longitude motion of ions inside the quadrupole region. Consequently, CID is useful for fragmentation of linear peptides and it is not effective (in present configuration) for large bulky proteins. The kinetic energy of ions that enter the repelling region of the TOFMS is ultimately determined by the ensemble effect resulting from the dc bias potential of the quadrupole (the dominant factor), skimmer-2, pressure inside the quadrupole chamber, and jet expansion. While this system is tested with an ESI source, the operational principle and design criteria are directly applicable for improving other atmospheric pressure ionization sources with time-of-flight mass analyzers such as an inductively coupled plasma ion source.

Journal Article↗
PubMed1996

High-performance liquid chromatography - atmospheric pressure negative chemical ionisation - mass spectrometry of 2,4-dinitrophenyl derivatives of amines.

High-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) is used to detect 2,4-dinitrophenyl (DNP) derivatives of amines by means of negative chemical ionisation at atmospheric pressure. The high sensitivity and good comparability of UV- and MS-detection of DNP-derivatives of amines is shown by several examples. The high selectivity of the derivatisation and the detection method (UV and MS) is used for the analysis of unknown amines in aqueous phases after hydrolytic degradation of polyamide-amine- or polyamine-epoxide-adducts as well as for the characterisation of commercial products.

Journal Article↗
PubMed2004

Temporal aroma delivery from milk systems containing 0-5% added fat, observed by free choice profiling, time intensity, and atmospheric pressure chemical ionization-mass spectrometry techniques.

A temporal aroma delivery from milk systems containing 0, 0.5, or 5% added fat and flavored with seven-component strawberry flavoring and linalool was observed by free choice profiling (FCP), time intensity (TI), and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) techniques. A suppressing effect of fat on the volatility of the relatively nonpolar compound linalool was observed by all methods, but only slight evidence (with the TI method) of the effect of fat on the overall strawberry (based on more polar compounds) intensity was found. With the TI method, the strawberry aroma of the fattiest sample lingered the longest, but no temporal differences were found in the release of linalool. The APCI-MS results showed no effect of fat on the temporal release of ethyl butyrate (mainly responsible for the strawberry note), but linalool of the sample containing 5% fat was found to be the most persistent. However, the effect on linalool was observed using a slightly different sampling technique than in the TI. Overall, FCP, TI, and APCI-MS showed parallel results for the effect of fat on the intensity of aroma, but temporal release data only partly supported the theory that fat slows down the release of aroma compounds and their perception.

Acyclic Monoterpenes↗
PubMed2001

Quantitative analysis of hydrocortisone in human urine using a high-performance liquid chromatographic-tandem mass spectrometric-atmospheric-pressure chemical ionization method.

In this study, the development and validation of a method of analysis for 11,17,21,-trihydroxypregn-4-ene-3,20-dione (hydrocortisone, cortisol, HC) using high-performance liquid chromatography (HPLC)-tandem mass spectrometry (MS) with atmospheric-pressure chemical ionization (APCI) is reported. This is the first report of the systematic development and validation of an HPLC-MS-MS method for the quantitation of HC in synthetic human urine with a deuterated internal standard. Prior to LC-MS-MS analysis, the only sample preparation used was the dilute-and-shoot technique prior to LC-MS-MS analysis. In this study, an analysis time of less than 3 min is achieved. The results show freedom of interference from other analytes such as analogous steroids. Validation parameters such as specificity/selectivity, limit of quantitation (LOQ), linearity, precision, accuracy, ruggedness, stability, and system suitability are evaluated for this method. The LOQ is 5 ng/mL with an 8% relative standard deviation (RSD). For calibration standard curves, an average linear response for a 3-day validation (R2 = 0.997) over the range of 5 to 500 ng/mL is obtained. The interday precision %RSDs are 7.2, 5.0, and 5.2 for 15, 75, and 300 ng/mL, respectively. Also, brief comparisons of the dilute-and-shoot and liquid-liquid extraction techniques for this analyte are discussed.

Chromatography, High Pressure Liquid↗
PubMed2001

Pd(ii)-hydrotalcite-catalyzed oxidation of alcohols to aldehydes and ketones using atmospheric pressure of air.

A heterogenized Pd catalyst, Pd(II)-hydrotalcite (palladium(II) acetate-pyridine complex supported by hydrotalcite) catalyzes the aerobic oxidation in toluene of a variety of primary and secondary alcohols into the corresponding aldehydes and ketones in high yields using atmospheric pressure of air as a sole oxidant under mild conditions. This catalyst is also effective for the oxidation of allylic alcohols, especially such as geraniol and nerol, without any isomerization of an alkenic part. The catalyst can be easily prepared from all commercially available reagents and reused several times.

Journal Article↗
PubMed1997

Characterization of monoglucuronides of vitamin D2 and 25-hydroxyvitamin D2 in rat bile using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

The characterization of vitamin D2 3-glucuronide, 25-hydroxyvitamin D2 3-glucuronide and 25-hydroxyvitamin D2 25-glucuronide, biliary metabolites obtained from rats dosed with vitamin D2 and 25-hydroxyvitamin D2 per os, was carried out using HPLC-atmospheric pressure chemical ionization (APCI)-MS. The glucuronide obtained from bile specimens was identified by comparison of its chromatographic behaviour with an authentic sample using HPLC-APCI-MS operating in the negative-ion mode. Methylation of the respective fraction with diazomethane gave the methyl ester, which was also confirmed by HPLC-APCI-MS operating in the positive-ion mode. The (M-H)- and (M + NH4)+ ions were monitored in the selected-ion monitoring mode.

25-Hydroxyvitamin D 2↗
PubMed1997

Simultaneous determination of a potassium channel opener and its metabolite in rat plasma with column-switching liquid chromatography using atmospheric pressure chemical ionisation.

A specific LC-MS assay was developed for simultaneous determination of Ro 31-7837 (I) and its metabolite Ro 31-6930 (II) in rat plasma, using on-line SPE by column-switching reversed-phase HPLC combined with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry for detection in the selected reaction monitoring mode. The method involved precipitation of plasma proteins with ethanol and automatic injection of a 1-ml aliquot of the supernatant onto a standard bore trapping column (LC-ABZ, 20x4.6 mm) for compound retention. Using the backflush mode, the analytes were transferred onto the analytical column (Kromasil C18, 125x4.0 mm) for chromatographic separation and mass spectrometric detection. The mean precision and accuracy for I and II in the concentration range 0.25-100 ng/ml were found to be 3.7% and 101%, and 3.5% and 106%, respectively. The data were assessed from QC samples during the validation phase of the assay. The lower limit of quantification for both I and II was 0.25 ng/ml, using a 0.5-ml plasma aliquot. This LC-MS method provided the requisite specificity, sensitivity, accuracy and precision to assess the pharmacokinetics of the compounds in the rat.

Animals↗