High performance liquid chromatography mobile phase composition optimization for the quantitative determination of a carboxylic acid compound in human plasma by negative ion electrospray high performance liquid chromatography tandem mass spectrometry

A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form.

Negative ion electrospray high-performance liquid chromatography-mass spectrometry method development for determination of a highly polar phosphonic acid/sulfonic acid compound in plasma. Optimization of ammonium acetate concentration and in-source collision-induced dissociation

A method, based on negative ion electrospray ionization (ESI) single-stage mass spectrometry coupled with HPLC, was developed for the determination of a squalene synthase inhibitor, BMS-187745, in human plasma. BMS-187745, a highly polar compound with both phosphonic acid and sulfonic acid groups, presented difficulties in developing plasma extraction and HPLC procedures. Precipitation of the plasma protein with methanol was finally chosen as the basis for sample preparation since extraction with water-immiscible solvents or with solid-phase extraction columns failed. It was essential to add ammonium acetate to the HPLC mobile phase, not only to enhance the retention of BMS-187745 but also to ensure a well-shaped chromatographic peak. While the use of ammonium acetate had the desired chromatographic effects, it had the undesirable consequence of suppressing the negative ion ESI signal. With the plasma extracts, the [M-H2O-H]- ion (m/z 367) showed significantly lower chemical noise than the [M-H]- ion (m/z 385), and was thus chosen as the analytical ion for the selected ion monitoring. The signal of the m/z 367 ion was significantly enhanced by the optimization of the in-source collision-induced dissociation (CID) of m/z 385 to m/z 367.

An assessment of a urinary biomarker for total human environmental exposure to benzo[a]pyrene

Urinary banzo[a]pyrene (BaP) metabolite levels were compared to human environmental exposure to BaP through inhalation and dietary ingestion to assess the predictive validity of the exposure biomarker. These measurements were made for 14 adult volunteers over 14 consecutive days, once during summer/fall, again during winter periods. Based on personal air monitoring, median potential inhalation doses of 11.0 and 2.3 ng/day were estimated for the winter and summer/fall studies, respectively. A median potential ingested dose of 176 ng/day, estimated from "duplicate plate" sampling, exceeded inhalation by 6- and 122-fold for the winter and summer/fall studies, respectively. "Total" urinary BaP metabolites were measured using a published "reverse metabolism" (BaP) method of analysis. Median rates of urinary BaP metabolite elimination for the winter and summer/fall studies were 121 and 129 ng/day, respectively. The changes in inhaled and ingested potential doses were regressed on the change in urinary metabolite elimination from week 1 to week 2 to test the predictive validity of the biomarker measurement. The regression was statistically significant (r = 0.620, p = 0.015, n = 25) when body weight was included and two extreme values were removed. Consistent with the exposure measurements showing diet as the dominant route of exposure, most of the variation in urinary metabolite elimination was explained by the ingested dose. It is concluded that the measurement of urinary BaP by "reverse metabolism" is qualitative and of marginal predictive validity as an exposure biomarker due to the method's low recoveries and the large unexplained variance.

A neuromagnetic study of acupuncturing LI-4 (Hegu)

The brain magnetic fields evoked by acupuncturing LI-4(Hegu) were measured by using SQUID (superconductive Quantum Interference Device) Biomagnetometer, and the morphological characters of these biomagnetic fields were examined in 12 subjects. The observed phenomenon of the LI-4(Hegu)'s projection area overlapping on the jaw's and face's projection area suggests that excitation of LI-4 (Hegu)'s projection area activated by acupuncturing LI-4(Hegu) could inhibit action of the jaw's and face's projection through the overlapping area, and this is the reason why the acupuncturing LI-4(Hegu) could effectively case pains in the treatment of dental pain.

[Studies on the assimilation of inorganic selenium by yeast]

In the process of assimilation of inorganic selenium by yeast to the organic-selenium, some rules on the relation of the kinds of culture medium, concentration of sodium selenite and methionine to the total selenium and selenomethionine content in the yeast formed have been found; and a new, accurate procedure--modified acid hydrolysis-ion exchange chromatography for determining the content of seleno-amino acid in biological materials has been established.

Heritability of blood pressure in 7- to 12-year-old Chinese twins, with special reference to body size effects

Systolic and diastolic blood pressures and body-size indices such as body height, body weight, sitting height, chest circumference, skinfold thickness, and body mass index (BMI) were assessed in 110 pairs of like-sex Chinese twins (75 monozygotic and 35 dizygotic) aged 7-12 years. Significant correlations of blood pressure with body-size indices were found. Prior to adjusting for body-size effects, three twin methods yielded low heritability estimates for both systolic (0.32-0.41) and diastolic (0.32-0.51) pressures. Adjusting systolic pressure for body height and BMI via multiple regression nearly halved heritability estimates, but adjusting diastolic pressure for body height and skinfold thickness only changed the estimates slightly.

A method for the indirect determination of trace bound selenomethionine in plants and some biological materials

An indirect method for the determination of trace bound selenomethionine (SeMet) has been developed. SeMet reacts with cyanogen bromide (CNBr) quantitatively in the presence of SnCl2 to form CH3SeCN, and after extraction with CHCl3 is acid-digested to form Se(IV). Selenium(IV) reacts with 4-nitro-o-phenylenediamine reagent to form 5-NO2-piazselenol which is then determined by gas chromatography equipped with electron capture detector. The sensitivity of this method (CNBr-piazselenol-GC method) is 6 ng SeMet/g of sample. Trace-bound SeMet in plants and some biological materials has been successfully determined by this method and its content has been compared with the total selenium in the sample.