A new type of long capillary cell (LCC) for liquid absorption spectrometry, in which incident light is transmitted with successive total reflection at the outer cell surface, has been proposed. An uncoated and uncovered capillary tubing of borosilicate glass showed much better light trans-missivity in aqueous solution as a LCC than did one with mirrored walls, and it could be used in coiled form without attenuation of light. An effective pathlength of 85 cm (at A1 cm = 9 × 10−5) and a baseline stability of 3 × 10−6 AU were obtained with a 90-cm LCC (i.d. 260 μm, o.d. 400 μm, coiled into 14-cm-diameter coil). The calibration curve was nonlinear because of its nature as a multipath cell. The distribution of light energy inside the LCC was estimated by using a simple statistical model based on the Markov chain.
A discharge-assisted thermospray (plasmaspray) liquid chromatography/mass spectrometric method for the determination of serum creatinine is described. The method incorporates stable isotope dilution using (D3)creatinine as an internal standard. Separation is performed in reversed-phase high-performance liquid chromatography using 0.01 M aqueous ammonium acetate as a flow solvent. Effluents are directly introduced to the mass spectrometer and [MH]+ ions are monitored during LC/MS using the selected ion monitoring method. Satisfactory agreement between the analytical result and the certified value of the serum sample of standard reference material and relative standard deviation ranging from 0.6% to 1.2% was obtained.
We describe an accurate, precise method for determination of total serum cholesterol by isotope dilution/mass spectrometry (IDMS) with liquid-chromatographic separation. After adding [3,4-13C]cholesterol to serum and hydrolyzing the cholesterol esters, we extract the total cholesterol. "High-performance" liquid chromatography (HPLC) is used to separate the extracted cholesterol for measurement by electron-impact mass spectrometry with use of a direct-insertion device. To evaluate the specificity and the accuracy of this method, we also studied the conventional IDMS method, which involves converting cholesterol to the trimethylsilyl ether and assay by gas chromatography-mass spectrometry with use of a capillary column. The coefficient of variation for the HPLC method was a little larger than that for the conventional method, but mean values by each method agreed within 1% for all sera tested.
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