Determination of vitamin K1 in serum using catalytic-reduction liquid chromatography with fluorescence detection.

A new method for the liquid chromatographic-fluorescence determination of serum vitamin K1 is described using reduction of the K-quinone to the fluorescent K-hydroquinone. The reduction reaction occurs "on-line" in the LC system using a catalytic reducer column and an alcohol mobile phase as reductant. A procedure for serum determination utilizes a liquid-liquid serum lipid extraction followed by normal-phase fractionation on a solid-phase extraction cartridge. The final measurement uses a reversed-phase (C18) separation with a ethanol-methanol mobile phase and provides a detection limit of approximately 20 pg/ml.

Delayed metabolic changes after strenuous exertion in trained young men.

Twenty apparently healthy, young male volunteers, aged 18-25 (mean 19.3, SD 1.4) years received a 6 months standardized, graded outdoor physical training and were screened for serum magnesium concentration (S-Mg), serum calcium concentration (S-Ca), serum aspartate amino transferase (S-AST), serum alanine amino transferase (S-ALT), serum creatine kinase activity (S-CK), other laboratory variables, weight, and VO2 ml.kg-1.min-1 [corrected] (VO2 max), before a 70 km march, as well as at 1, 24 and 72 h and 18 days after. Maximal aerobic power, body weight, haemoglobin, haematocrit, serum creatinine, total protein and albumin remained unchanged throughout. Immediately after the march, S-Mg did not change, S-AST, S-ALT and S-CK rose, but the rise was not statistically significant, while small but significant rises in S-Ca (P less than 0.05, Student's t-test) and serum cholesterol (P less than 0.01) normalized at 24 h. At 72 h after the march, a significant fall in S-Mg was found (P less than 0.01), together with a second significant rise in S-Ca (P less than 0.05). After 18 days, with no intervening marches or dietary changes, S-Mg remained significantly lowered (P less than 0.05), mean S-ALT and S-CK became significantly raised for the first time (P less than 0.001 and P less than 0.01 respectively), whereas S-Ca normalized. Concomitantly, for the first time there was now a significant rise in blood sugar (P less than 0.001), serum triglycerides (P less than 0.01), and a second rise of serum cholesterol (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Magnesium fluxes in ventricular fibrillation and defibrillation in untreated and dibenzepine HC1 pretreated cats.

Serum magnesium concentration (S-Mg) was estimated in 12 anesthetized cats before and after central thoracotomy, during an electrically induced ventricular fibrillation (VF) and after defibrillation (DEF), and again, in the same experimental animals, after the administration of 3 mg/kg of dibenzepine HC1--a tricyclic antidepressant reported to facilitate spontaneous DEF--as well as during a subsequently induced VF and after the spontaneous DEF which followed. In the first part of the experiment, the surgery and the induction of VF caused no significant change of mean serum magnesium concentration (S-Mg) or serum calcium concentration (S-Ca), whereas the DEF was accompanied by Mg efflux (a significant increase of mean S-Mg from 0.824 mmol/l, SD 0.182, n = 12 to 0.991 mmol/l, SD 0.182, n = 12; P less than 0.05). In the second part of the experiment, following the administration of dibenzepine HCl there was Mg influx (a lowering of mean S-Mg to 0.891 mmol/l, SD 0.160, n = 12; P less than 0.05). During VF in the pretreated cats, S-Mg remained unchanged, while S-Ca decreased significantly (P less than 0.05), followed by a rebound Ca++ efflux (a systematic rise of S-Ca) as the animals defibrilated spontaneously. Concomitantly, there was Mg efflux (a systematic rise of S-MG), the mean S-Mg rising from 0.879 mmol/l, SD 0.143, n = 9 to 1.083 mmol/l, SD 0.257, n = 7, ie to virtually the same value as that obtained after electrically induced DEF.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of retinol, alpha-tocopherol, and beta-carotene in serum by liquid chromatography with absorbance and electrochemical detection.

We describe a method for the determination of retinol, alpha-tocopherol, and beta-carotene in serum, using a liquid-chromatographic separation with wavelength-programmed ultraviolet/visible absorbance and amperometric electrochemical detection with a glassy carbon electrode. After protein denaturation and addition of an internal standard, tocol, 250-microL samples are twice extracted with hexane. The reversed-phase, gradient-elution chromatographic separation provides baseline resolution of: the all-trans isomer of retinol from the cis isomers, alpha- from gamma-tocopherol, and all-trans-beta-carotene from alpha-carotene and from cis-beta-carotene isomers. The linearity of response and the detection limits for the two detectors for the three analytes are measured. A comparison of the values obtained for serum extracts shows good agreement between the absorbance and electrochemical detectors.

Reversed-phase high-performance liquid chromatographic separation and electrochemical detection of retinol and its isomers.

Baseline separation of the isomers of retinol using reversed-phase high-performance liquid chromatography (HPLC) in less than 30 min is presented. A new approach to the detection of retinol using electrochemical detection is developed. The oxidative electrochemistry of retinol is studied at a glassy-carbon electrode using coulometry, ultraviolet-visible spectrophotometry and HPLC. Amperometric detection in HPLC for retinol provided a linear response from 0 to 1.5 micrograms/ml and a detection limit of 4.1 ng/ml. Electrochemical detection was compared to ultraviolet-visible absorbance detection for the determination of retinol in human serum extracts. Good agreement is found for the results obtained with the two detectors.

Changes in serum magnesium concentration after strenuous exercise.

Serum magnesium concentration (S-Mg) was measured in 20 highly trained young men (mean age 19.5, +/- 0.5, range 18-20.5) before, and at 1 hour, 24 hours, 72 hours, and 3 months after a 120 km hike. As found in previous studies, S-Mg was significantly decreased at the end of the hike (p less than 0.001, [corrected] Student's t-test). In this group S-Mg had risen significantly after 24 hours in relation to the value at 1 hour (but not to starting value); yet, at 72 hours and 3 months later, it was once more significantly lower than the starting value (p less than 0.001 and p less than 0.05, respectively, Student's t-test). A marked elevation in serum creatine kinase activity (CK) suggests that the rise in S-Mg observed at 24 hours is the result of either exertional rhabdomyolysis or loss of membrane integrity, as a result of the strenuous exertion, since the CK had fallen sharply by 72 hours after the hike. The biphasic, statistically significant, lowering of S-Mg which persisted after 3 months suggests that strenuous exertion induces magnesium deficiency.

The influence of pH and complex formation on the ASV peaks of Pb, Cu and Cd.

The effects of pH, electrolyte composition and complex formation on the size and position of the ASV peaks of Pb, Cu and Cd have been systematically evaluated, with an instrument equipped with a mercury thin-film electrode and by applying a linear ramp voltage scan. The peak heights change with pH and the magnitude of the pH effect varies with base electrolyte composition. Anions such as chloride and acetate reduce the signal, as does the presence of excess of ligands such as 2,2'-bipyridyl, NTA and EDTA. Formation of stable chelates (e.g., with EDTA) can lead to total loss of signal, but dissociation of labile complexes can be enhanced by reducing the pH and/or increasing the magnitude of the applied deposition potential, thus producing measurable peaks. The peak potentials vary with pH, and in copper systems there are additional shifts in the presence of citrate, 2,2'-bipyridyl and chloride. With the last two, double peaks are formed and these are attributed to the formation of both Cu(I) and Cu(II) oxidation products. The varied response, particularly in the case of copper, which can follow changes in the base electrolyte composition, supports the need for careful control of the chemical environment in quantitative determination, and raises some queries about the feasibility of using direct ASV for speciation purposes.