Reactive diffusive gradient in thin-film sampler and mercury speciation by use of same
Sampling devices for mercury speciation protocols are described. Devices can be utilized to separate mercury species from one another as a sample diffuses through a sampling device. Methods can determine the presence or quantity of targeted mercury species in a fluid sample. The devices are passive sampling devices based upon diffusion gradient in thin film (DGT) passive sampling devices. Devices include a reactant component and a sequesterant component that selectively react with a targeted species and retain a species (or a reaction product of a species) of a sample flow. Remaining mercury species can optionally be captured downgradient, for instance at an ion exchange resin.
1. A passive mercury sampling device comprising:
an upgradient end and a downgradient end;
a diffusive zone;
a capture zone downgradient of the diffusive zone;
a reactant located upgradient of the capture zone, the reactant being configured to react with a first mercury species;
a first sequesterant located either downgradient of the reactant or in a layer with the reactant, the first sequesterant being configured to selectively retain a second mercury species, wherein a reaction between the first mercury species and the reactant forms the second mercury species; and
a mercury capture agent located within the capture zone, the mercury capture agent being either a non-specific mercury capture agent configured to retain multiple different mercury species or a second sequesterant configured to selectively retain a third mercury species that differs from the first mercury species and the second mercury species.
2. The passive mercury sampling device of claim 1 , wherein the reactant and the first sequesterant are both located in or upgradient of the diffusive zone.
3. The passive mercury sampling device of claim 1 , wherein the reactant is upgradient of the first sequesterant.
4. The passive mercury sampling device of claim 3 , wherein the reactant is located upgradient of the diffusive zone and the first sequesterant is located in the diffusive zone.
5. The passive mercury sampling device of claim 1 , wherein the diffusive zone and/or the capture zone each independently comprise multiple layers.
6. The passive mercury sampling device of clam 1 , wherein the diffusive zone and/or the capture zone comprises a hydrogel.
7. The passive mercury sampling device of claim 1 , wherein the first sequesterant is configured to retain elemental mercury.
8. The passive mercury sampling device of claim 7 , wherein the first sequesterant comprises an elemental metal.
9. The passive mercury sampling device of claim 8 , wherein the elemental metal comprises gold, silver, copper, zinc, tin or any combination thereof.
10. The passive mercury sampling device of claim 7 , wherein the mercury capture agent is configured to retain methyl mercury.
11. The passive mercury sampling device of claim 1 , wherein the first sequesterant is carried by a supporting substrate.
12. The passive mercury sampling device of claim 11 , wherein the supporting substrate is a particulate substrate, a fibrous substrate, or a membrane substrate.
13. The passive mercury sampling device of claim 1 , wherein the reactant is a reductant.
14. The passive mercury sampling device of claim 1 , wherein the first sequesterant and the reactant are the same material.
15. A method for selectively sampling a mercury species, comprising:
contacting a fluid sample with the upgradient end of the passive sampling device of claim 1 , the fluid sample comprising the first mercury species, wherein upon the contact, the first mercury species reacts with the reactant to form the second mercury species, the second mercury species thereafter being selectively retained by the first sequesterant;
analyzing the capture zone to determine a presence or quantity of all mercury species in the capture zone; and
analyzing the first sequesterant to determine a presence or quantity of the second mercury species retained thereby; wherein
the method determines a presence and/or concentration of each of at least two different mercury species in the fluid sample.
16. The method of claim 15 , wherein the first sequesterant is located in the diffusive zone such that the second mercury species is retained in the diffusive zone.
17. The method of claim 15 , wherein the fluid sample is an aqueous liquid sample.
18. The method of claim 15 , wherein the first mercury species comprises an inorganic mercury species or an ionic mercury species.
19. A method for selectively sampling a mercury species, comprising:
contacting a first fluid sample obtained from a sample source with an upgradient end of passive sampling device the first fluid sample comrising a first mercury species, the passive sampling device comprising a diffusive zone and a capture zone that is downgradient of the diffusive zone, the passive sampling device further comprising a reactant configured to react with the first mercury species to form a second mercury species and comprising a sequesterant configured to selectively retain the second mercury species, the reactant and the sequesterant each being independently located in either the diffusive zone or the capture zone, the sequesterant being downngradient of or in a layer with the reactant; wherein upon the contact, the first mercury species reacts with the reactant to form the second mercury species, the second mercury species thereafter being selectively retained by the sequesterant;
determining a quantity of the second mercury species retained by the sequesterant;
analyzing a second fluid sample obtained from the sample source to determine total mercury content of the second fluid sample; and
comparing the total mercury content of the second fluid sample with the quantity of the second mercury species retained by the sequesterant.
20. The method of claim 19 , where the comparison comprises subtracting the quantity of the second mercury species from the total mercury content of the second fluid sample and assigning any remaining mercury content to one or more other mercury species of the sample source.