Reduction of analysis time in gas chromatography. Application of low-pressure gas chromatography-tandem mass spectrometry to the determination of pesticide residues in vegetables.

An alternative to conventional capillary gas chromatography (GC) is evaluated as a new approach to determine pesticide residues in vegetables. Low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS-MS) is proposed after a fast and simple extraction of the vegetable samples with dichloromethane and without clean up. The use of the above-mentioned GC technique reduced the total time required to determine 72 pesticides to less than half the present time (31 min), increasing the capability of a monitoring routine laboratory. The use of guard column and plug of carbofrit into the glass liner in combination with LP-GC was evaluated. The method was validated with limits of quantitation low enough to determine the pesticide residues at concentrations below the maximum residue levels stated by legislation. In order to assess its applicability to the analysis of real samples, 25 vegetable samples previously determined using conventional-capillary GC-MS-MS were analysed by LP-GC-MS-MS. The results obtained with the compared techniques showed differences lower than 0.01 mg kg(-1).

Influence of magnesium deficiency on the bioavailability and tissue distribution of iron in the rat.

We investigated the effect of dietary magnesium (Mg) deficiency on the nutritive utilization and tissue distribution of iron (Fe). Wistar rats were fed an Mg-deficient diet (56 mg/kg) for 70 days. Absorbed Fe, Fe balance, number of the erythrocytes [red blood cells (RBC)] and leukocytes white blood cells (WBC)], hemoglobin (Hb), and Fe content were determined in samples of plasma, whole blood, skeletal muscle, heart, kidney, liver, spleen, femoral bone, and sternum obtained on experimental days 21, 35, and 70. The Mg-deficient diet significantly increased Fe absorption and Fe balance from week 5 until the end of the experimental period. This effect was accompanied by a significant decrease in the concentration of RBC and Hb from day 35, which caused the decrease in whole blood Fe seen on day 70. However, WBC were significantly increased from day 21 until the end of the experimental period. Mg deficiency significantly increased plasma and liver Fe at all three time points investigated. Spleen, heart, and kidney Fe were significantly increased only at the end of the study. However, on day 70, Fe concentration in the sternum had decreased significantly. No changes were found in skeletal muscle or femur Fe content. Mg deficiency led to increased intestinal absorption of Fe and decreased RBC counts, possibly as a result of increased fragility of the erythrocytes. Intestinal interactions between Fe and Mg, together with activation of erythropoiesis as a result of hemolysis, favored intestinal absorption of Fe. This situation gave rise to an increase in plasma Fe levels, which in turn favored Fe uptake and storage by different organs, especially the liver and spleen. However, despite the increased Fe content seen in the tissues of rats fed the Mg-deficient diet, these animals were unable to compensate for the hemolysis caused by this nutritional deficiency.

Effect of magnesium deficiency on enterocyte Ca, Fe, Cu, Zn, Mn and Se content.

In previous studies based on indirect procedures, we reported that Mg deficit increased the bioavailability of a number of elements such as calcium, zinc, iron, copper, manganese and decreased selenium absorption. The present study was designed to verify these findings by direct methods. We investigated the effect of dietary magnesium deficiency on enterocyte Ca, Fe, Zn, Cu, Mn and Se concentrations. Male Wistar rats were fed a Mg-deficient diet (129 mg Mg/kg food) for 70 days. Whole enterocytes from the upper jejunum were isolated and Ca, Fe, Zn, Cu, Mn and Se were determined. The results were compared with findings in a control group that was pair-fed with an identical diet except that it covered this species's nutritional requirements for Mg (480 mg Mg/kg food). The Mg-deficient diet significantly increased enterocyte content of Ca, Fe, Zn, Cu and Mn; however, we found no significant changes in the Se content of these cells. These data support the results obtained by indirect methods.

Magnesium-manganese interactions caused by magnesium deficiency in rats.

OBJECTIVE: We investigated the effect of dietary magnesium (Mg) deficiency on the nutritive utilization and tissue distribution of manganese (Mn). METHODS: Wistar rats were fed a Mg-deficient diet (56 mg/kg) for 70 day. Absorbed Mn, Mn balance and Mn content in plasma, whole blood, skeletal muscle, heart, kidney, liver, femoral bone and sternum were determined after 21, 35 and 70 days. RESULTS: The Mg-deficient diet significantly increased Mn apparent absorption and Mn balance from week five until the end of the experimental period. This effect was accompanied by a significant increase in the concentration of Mn in heart at all three time points. Whole blood, skeletal muscle and kidney Mn were significantly increased from day 35, and femur Mn content was increased only at the end of the study (day 70). However, Mn concentration in the sternum decreased significantly from day 35. No changes were found in liver Mn content. CONCLUSION: Mg deficiency increased Mn absorbed, and this favored the deposition of Mn in all tissues studied except the liver and trabecular bone. The lack of response by the liver to increased Mn absorption may have led to the redistribution of this ion to other tissues.

Effect of magnesium deficiency on vitamin B2 and B6 status in the rat.

OBJECTIVE: The present study was undertaken to investigate the effect of dietary magnesium (Mg) deficiency on vitamin B2 (riboflavin) and B6 (pyridoxine) status in rats. METHODS: We fed Wistar rats an Mg-deficient diet (56 mg magnesium per kg food) for 70 days. On days 21, 35 and 70 we measured Mg and manganese (Mn) in plasma and whole blood, alkaline phosphatase in plasma, erythrocyte glutathione reductase activity coefficient (AC-EGR) for riboflavin status, and erythrocyte aspartase transaminase activity coefficient (AC-EAST) for vitamin B6 status. RESULTS: Intake of the Mg-deficient diet significantly decreased plasma and whole blood levels of Mg and plasma alkaline phosphatase activity on all sampling days. The Mg deficit had no effect on plasma concentrations of Mn, but significantly increased whole blood levels of this element on days 35 and 70. The Mg-deficient diet had no effect on AC-EGR, and thus appeared not to affect riboflavin status. However, AC-EAST was significantly increased on day 70, implying that the animals were at risk for vitamin B6 deficiency. CONCLUSION: Mg deficiency impairs vitamin B6 status by depleting intracellular Mg and thus inhibits the activity of alkaline phosphatase, a metalloenzyme required for the uptake of pyridoxal phosphate by tissues. Although part of the intraerythrocyte loss of Mg is countervailed by Mn, which can act as a substitute activator of alkaline phosphatase, the degree of compensation is insufficient to fully offset the decrease in activity caused by Mg depletion.