Dryness quantification

Dissolution (toluene)/precipitation (methanol) of EPS beads (atactic PS foams with ca. 2wt.% HBCD and BaSCL) with TLC separation and IR identification allowed detection of hexabromocyclododecane for quantification XRF analysis (Br) was used [629]. Disso-lution/precipitation of PS/lubricants with evaporation to dryness and redissolution was followed by FT1R analysis [106],... 

Standards, controls, and samples (250 fiL each) were treated with 500 fiL acetonitrile-acetic acid (99 1 v/v) containing IS (2.50 jUg/mL), vortexed for 10 sec, incubated for 5 min, and centrifuged at 15,000 g for 5 min. The supernatants (1650 //L) were loaded onto a polypropylene 96-well plate containing 900 fxL HPLC water under low vacuum. The SPE plates were conditioned with 500 fxL methanol followed by 300 jx. acetonitrile-water-acetic acid (30 69.5 0.5 v/v/v) (solvent A), washed with 1000 /xL solvent A, dried under full vacuum for 10 min, wiped dry with paper, eluted with 500 jxL methanol-trifluoroacetic acid (99.9 0.1 v/v) (solvent B) and then with 400 //L solvent B for 2 min, evaporated to dryness at 65°C under a gentle air stream, reconstituted with 200 /xL methanol-hydrochloric acid (0.1 M) (70 30 v/v) and assayed. The injection volume was 50 i L. Figure 11.3 shows chromatograms of blank plasma and spiked plasma with lumefantrine. A calibration curve was constructed in a concentration range of 25 to 20,000 ng/mL. Intra-assay and interassay coefficients of variation were below 5.2 and 4.0%, respectively. The limit of detection was 10 ng/mL. The limit of quantification was 25 ng/mL. 

Evaporate the organic layers of the free and total samples to dryness at 40°C under a gentle stream of nitrogen. Add 10 pi triethylamine and 100 pi of 7% penta-fluorobenzylbromide in acetonitrile and derivatize at room temperature for 15 min. Add 150 pi of 0.5 M HC1 and extract with 1 ml hexane for at least 1 min. Centrifuge the samples for 2 min at 835 xg. Pipette the hexane into a sample vial and evaporate to dryness at 40°C. Add 50 pi hexane and redissolve the residue. Samples are ready for quantification with GC-mass spectrometry (GC-MS). 

Aliquots (15 cm, 20 cm ) of each ethyl acetate extract are combined and evaporated to dryness under reduced pressure at 40°C. An internal standard, equivalent to 0.05 mg of homovanill-ic acid (HVA) and 0.1 mg of 4-hydroxy-3 methoxymande1ic acid (VMA), was added to a duplicate specimen and included with each batch of samples when quantification was to be carried out. Recoveries of HVA and VMA from urine were all greater than 90%. 

Another LC-APCI-MS method has been developed and validated by Zhang et al. for the identification and quantification of zaleplon in human plasma using estazolam as an IS. After the addition of estazolam and 2.0 M sodium hydroxide solution, plasma samples were extracted with ethyl acetate and then the organic layer was evaporated to dryness. The reconstituted solution of the residue was injected onto a prepacked Shim-pack VP-ODS C18 (250 mm x 2.0 mm i.d.) column and chromatographed with a mobile phase comprised methanol-water (70 30) at a flowrate of 0.2 ml/min. 

Due to the discovery of two further urinary metabolites of ramipril (the respective diketopiperazine derivatives of ramipril and ramiprilat), the above-described method was slightly modified (Schmidt et al. 1985). Instead of the rather time consuming second extraction step by means of a disposable Si column, the sample is cleaned by a liquid/liquid extraction step. After methylation of the compounds with diazomethane, the eluate is evaporated to dryness at 40 °C under N2 gas. Subsequently the residue is dissolved in n-pentane/diethyl ether (3 2. v/v) and washed with 5% hydrogen carbonate solution. After separation of the upper organic layer, this is evaporated to dryness at 40 °C under N2 gas and then treated with 1 mL n-hexane/TFAA (5%) as described before (Hajdu et al. 1984). This method allows the selective determination of ramipril and its three metabolites in human urine the limit of quantification amounted to 0.020 xg/mL for each of all four analytes. Using this assay, thousands of urine samples originating from phase I—III clinical studies were analysed. 

The most commonly applied methods for the analysis of polyamines in erythrocytes make use of amino acid analyzers and HPLC techniques. A capillary gas chromatographic method with nitrogen-phosphorous detection was applied to the simultaneous determination of 1,3-diaminopropane, putrescine, cadaverine (Cad), spermidine (Sd), and spermine (Sp) in human erythrocytes. Blood samples, collected by venipuncture into EDTA containing Venoject tubes, were subjected to the removal of plasma by centrifugation and erythrocytes were washed three times with two volumes of 0.9% NaCl. The stability of polyamines in erythrocyte suspensions was also investigated. Quantification of polyamines was done by comparing the peak-area ratio of each analyte and its internal standard with that of the standard. The polyamine samples were eluted with 0.1 M hydrochloric acid solutions. The eluate was evaporated to dryness at 120°C under a stream of air and 200 each of acetonitrile and heptafluorobutyric anhydride were added. The isolation of derivatives... 

The concentration of the substances extracted in the final solvent by evaporation in a rotary evaporator, in a Kudema-Danish system, or in an automatic evaporation system under nitrogen stream is a crucial step that can cause losses of the most volatile compounds. It must be done slowly and care must be taken to avoid contamination. Five hundred microliters of a slightly volatile solvent (isooctane) should be added before evaporation in order to avoid evaporation to dryness, which might entail losses by volatilization. The quantification limits obtained with LLE vary. 

Laboratory Services Branch (USB) method E3389 of the Canadian Ministry of the Environment s Laboratory Services Branch is used for testing drinking water. The principle of the method is LC-UV after SPE followed by desorption of the OPPs with ethyl acetate. The sample extracts are evaporated to dryness and reconstituted in 1 ml acetonitrile. Limits of quantification range from 0.5 /rg/l for phorate to 28 /rg/1 for temephos. The other pesticides analyzed with this method are azinphos-methyl, chlorpyriphos, diazinon, dimethoate, parathion, malathion, terbufos. 

Other methods employed. The activity of OAD in patient leukocytes was determined by a method described by Ohnuma and Holland (17). Quantification of orotic acid and orotidine was made by column chromatography (8). Urinary uric acid was measured by the technique of Pileggi al. (18). Orotic acid, orotidine, and urinary uric acid were also separated by high pressure liquid chromatography (19) using a u-C 3 column and O.IM formic acid at a flow rate of 0.5 ml/min. Constituents were collected, evaporated to dryness with dry nitrogen, derivatized into the trimethylsilyl derivative as described above and positively identified by mass spectrometry. 

A 5-g sample of a-olefm sulfonate is mixed with 50 g of basic alumina, activity grade I, which has been activated at 450 C for 3 hr. The mixture is then extracted four times with 50-mL aliquots of ethyl ether. The extracts are combined and evaporated to dryness, and the residue is dissolved in the HPLC mobile phase. The analysis is performed on a CPS-Hypersil normal phase HPLC column, 4.6 x 20 cm, with a mobile phase of 90 10 hexane/ethyl acetate and differential RI detection. Peak identification and quantification is made versus authentic sultone standards. The method was demonstrated for determination of hexadecane-l,4-suItone, hexadecane-l,3-sultone, hexadec-l-ene-l,3-suItone, and 2-alkylalkane-l,4-sultone, as well as 2-hexadecylhexadec-l-ene-l-sulfonate. 

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