Search PubMed⌕ Search

Biomedical subjects

L Madsen

Publications and source records attributed to L Madsen.

60 records · Page 4Linked to original sources
PubMedDate not supplied

Adsorption of pesticides onto quartz, calcite, kaolinite, and alpha-alumina.

The fate of pesticides in aquifers is influenced by the small but not insignificant adsorption of pesticides to mineral surfaces. Batch experiments with five pesticides and four minerals were conducted to quantify the contributions to adsorption from different mineral surfaces and compare adsorption characteristics of selected pesticides. Investigated mineral phases included quartz, calcite, kaolinite, and alpha-alumina. Selected pesticides comprised atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea)], mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propionic acid], 2,4-D (2,4-dichlorophenoxyacetic acid), and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide]. Specific surface area and mineral surface charge proved to be important for the adsorption of these pesticides. Detectable adsorption of the anionic pesticides (mecoprop, 2,4-D, and bentazone) was only measured when positive sites were present on the mineral surface. However, when CaCl2 was added as an electrolyte, a detectable adsorption of mecoprop and 2,4-D was also measured on kaolinite (which exhibits a negative surface charge), probably due to formation of Ca-pesticide--surface complexes. Adsorption of the uncharged pesticides (atrazine and isoproturon) was detected only on kaolinite. The lack of adsorption on alpha-alumina indicates that the uncharged pesticides have a greater affinity for the silanol surface sites (=SiOH) than for the aluminol surface sites (=AlOH) in kaolinite. No measurable effect of ionic strength was found for the uncharged pesticides. The results indicate that quartz and calcite play a smaller role than clay minerals.

Adsorption↗
PubMedDate not supplied

Reversed-phase liquid chromatographic determination of vitamin D in milk.

Vitamin D in milk is determined by a slight modification of the method of Sliva et al. [J. AOAC Int. (1992) 75, 566-571] for infant formula and enteral nutritional products. The sample is saponified for 30 min at 60 degrees C and extracted overnight into 60 mL of hexane. The hexane layer is washed, neutralized, and taken to dryness with a rotary evaporator. The sample is reconstituted in hexane and applied to 500 mg of Florisil in a solid-phase extraction column. Vitamin D is eluted with isopropyl alcohol. The eluate is evaporated to dryness under N2, and the sample is reconstituted in 1.0 mL of acetonitrile. The extract is analyzed on a C18 liquid chromatographic column (250 x 4.6 mm, 5 microns particle size) with UV detection at 265 nm. Milk samples of various fat content (i.e., skim, low fat, and whole milk) were analyzed. Spiked recoveries gave means of 81-96%; recoveries were inversely related to fat content. Assay precision ranged from 3.2 to 8.6%. The method can measure vitamins D2 and D3 individually, and no difference in the recoveries of the 2 vitamins was observed. Thus, vitamin D2 can be used as an internal standard for quantitating vitamin D3, and vice versa. The method is satisfactory for use in screening of milk for vitamin D content.

Animals↗