A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species (Se(Ⅳ), Se(Ⅵ)) at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se（Ⅳ）, Se（Ⅵ）, and total inorganic selenium in water based on the catalytic effect of Se（Ⅳ） on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2-20 and 20-200 μg·L-1 of Se（Ⅳ） for the fixed-time method at 30℃. The experimental and theo- retical detection limits of the developed kinetic method were found to be 0.21 and 2.50 μg·L-1 for the fixed-time method （3 min）. All of the variables that affect the sensitivity at 645 nm were investigated, and the optimum conditions were established. The interference effect of various cations and anions on the Se（Ⅳ） determination was also studied. The selectivity of the selenium determination was greatly improved with the use of the strongly cation exchange resin such as Amberlite IR120 plus as long as chelating agents of thiourea and thiosulphate. The proposed kinetic method was validated statistically and through recovery studies in natural water samples. The relative standard deviations （RSDs） for ten replicate measurements of 2, 10, and 20 μg·L-1 of Se（Ⅳ） change between 0.35% and 5.58%, while the RSDs for ten replicate measurements of 3, 6, and 12 μg·L-1 of Se（Ⅵ） change between 0.49% and 1.61%. Analyses of a certified standard reference material （NIST SRM 1643e） for selenium using the fixed-time method showed that the proposed kinetic method has good accuracy. The Se（Ⅳ）, Se（Ⅵ）, and total inorganic selenium in lake and river water samples have been successfully determined by this method after selective reduction of Se（Ⅵ） to Se（Ⅳ）.

Milk selenium content and speciation in response to supranutritional selenium yeast supplementation in cows

The effects of selenium(Se)yeast supplementation on performance,blood biochemical and antioxidant parameters,and milk Se content and speciation were evaluated.Thirty-six mid-lactation Holstein dairy cows were randomly assigned to 1 of 3 treatments:1)control(basal diet containing Se at 0.11 mg/kg DM),2)basal diet+0.5 mg supplemental Se/kg DM(SY-0.5),and 3)basal diet+5 mg supplemental Se/kg DM(SY-5).Selenium was supplemented as Se yeast.The trial consisted of a 1-week pretrial period and an 8-week experimental period.Milk somatic cell score decreased with SY-5 supplementation(P<0.05),but other performance parameters were not affected(P>0.05).The serum Se concentration increased with the increasing levels of Se yeast supplementation(P<0.05),however,blood biochemical parameters showed few treatment effects.The antioxidant capacity of dairy cows was improved with Se yeast supplementation reflected in increased serum glutathione peroxidase activity(P<0.05)and total antioxidant capacity(P=0.08),and decreased malondialdehyde concentration(P<0.05).Milk total Se concentration increased with Se dose(P<0.05).Also,the selenomethionine concentration increased with Se dose from 13.0±0.7 pg/kg in control to 33.1±2.1 pg/kg in SY-0.5 and 530.4±17.5 pg/kg in SY-5 cows(P<0.05).Similarly,selenocystine concentration increased from 15.6±0.9μg/kg in control and 18.9±1.1 pg/kg in SY-0.5 to 22.2±1.5 pg/kg in SY-5 cows(P<0.05).In conclusion,Se yeast is a good organic Se source to produce Se-enriched cow milk with increased Se species including selenomethionine and selenocystine.The results can provide useful information on milk Se species when a high dose Se yeast was supplemented in the cow diet.