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Abdihakim Abdullahi: Analytical Problem; Mercury in Skin Supplies

Recently more and more products such as Diana and Lemon Herbal Whitening Cream have shown up in the markets with mercury levels well over the permitted federal limits, of less then one parts per million, of mercury. Some of these products have shown levels of 33,000 parts per million of mercury. With these products finding their way to shelves of stores through informal trade it is difficult to keep track of them. Therefore these products continue to circulate. Mercury is an extremely toxic element and exists in nature in many different types of forms and oxidation levels, with the most common being Mercury (II). Mercury in bleaching and cosmetic creams were introduced the early 1900 when it was discovered that Mercury was extremely effective in lightening dark spots and stubborn pigmentation but it also had a high remission rate. Nevertheless bleaching creams with high levels of Mercury was aggressively marketed to black people. In 1976 Mercury was banned in the EU when it was discovered that it had damaging side effects. The US banned the use of Mercury in cosmetic creams much later in 1990. The reason Mercury was banned was it proved to be very toxic and can absorb through the skin and cause neurological affects and can even poison and shut down certain organisms like the kidneys.
My hypothesis is the mercury in these products cause a lot of health issues especially pertaining to communities such as the Somali community in which these products keep showing up in.
Reference:
1. Skin-Lightening Products Found to Contain Mercury: Minnesota Department of Health. http://www.health.state.mn.us/topics/skin/ (accessed September 19, 2011)
2. Lide, D. R., ed (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. pp. 4.125-4.126. ISBN 0-8493-0486-5

UV-Vis absorption spectrometry

As I mentioned before Mercury exist in many different forms like the organic mercury found in fish, methylmercury. However the Mercury found in most of these cosmetic creams is inorganic Mercury (II) usually mercuric chloride (HgCl2) or mercuric amidochloride (HgNH2Cl). Inorganic Mercury is soluble in alcohols so an ideal solvent would be ethanol because various types of inorganic Mercury (II) have shown UV-Vis absorption at wavelengths ranging from 200 nm to 600 nm with the average being about 260 nm, and ethanol has a lower wavelength limit of 220 nm so it is an ideal solvent. Mercury is considered a transition metal and the molar absorptivity of bands caused by d-d transitions are relatively low, roughly in the range of 5-500 M-1 -cm1.

Reference:

Sekine, T., Ishii, T. Studies of the Liquid-Liquid Partition systems. VIII. The Solvent Extraction of Mercury (II) Chloride, Bromide, Iodide and Thiocyanate with Some Organic Solvents. Bulletin of the Chemical Society of Japan. 1970. 43. 2422-2429
Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
Mercury Analysis in Environmental Samples by Cold Vapor Techniques. In: Encyclopedia of Analytical Chemistry. 2006.
Skoog , D, et al. Principles of Instrumental Analysis, 6th ed.; Brooks/Cole: Belmont, CA, 2007.

A problem thats actually very similar to mine is Chuxin Chen Analytical problem: comparative analysis of arbutin and tranexamic acid in skin whitening products. We both took an approach on cosmetics and however my approach is on a toxin found in some creams while Chuxin's is a comparative analysis between two different compounds to see which is more effective.

Blog 6:

my analyte, Inorganic mercury, exist in many forms but the two that are most common in bleaching creams are either mercuric ammido chloride View image
and more likely mercuric chloride View image
the space filling model and the stick model of mercuric chloride are as follows View image View image

Reference for images:
I found all these images on Colombia Analytical Services (CAS) at their website; http://www.caslab.com/Mercuric_chloride_CAS_7487-94-7/

Standards for mercuric chloride could be purchased at the Sigma Aldrich website, http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en&N4=203777|ALDRICH&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC&cm_sp=Customer_Favorites-_-Detail_Page-_-Text-203777, It sells for $99.40 the product number is 203777-50G. the CAS # is 0007487947 and since it is very toxin it must be shipped in a special poison packaging and the fee is incorporated in the price.

Comments

Blog 13. Good answers.

My analyte is not only electroactive, it is used as a standard electrode potential.
Hg2Cl2(s) + e = 2Hg(l) +2Cl2 which has a E^0 of +0.268V at 25 C. With that in mind electrochemistry would prove very useful to identify and quantify mercuric chloride. One approach is to use cyclic voltammetry to determine the electrochemical properties of the complexes. A technique based on capillary electrophoresis and amperometric detection (CE-AD) has been developed for the speciation of mercury. This technique has the capability to detect and identify mercury species that are electrochemically active, such as mercuric chloride. This same approach could be used to quantify mercuric chloride.

Reference:

Skoog , D, et al. Principles of Instrumental Analysis, 6th ed.; Brooks/Cole: Belmont, CA, 2007.

Kuban, P.C. Hauser, V. Kuban, Electrophoresis 28, (2007), 58-68.

Blog 11:

From the different types of capillary electrophoretic separations we discussed in class most of them are ideal and would prove suitable in separating my analyte, inorganic mercury, from its matrix; whatever the matrix maybe, in this case a cosmetic lotion. The different techniques such as capillary zone electrophoresis, Micellar electrokinetic chromatography and Capillary Gel Electrophoresis are all useful techniques, however from the techniques we covered in class I don't think Capillary isoelectric focusing would be useful in my analytical problem because generally cIEF is a technique for protein separation based on differences in isoelectric points which my analyte does not have therefore I don't see how this technique can be utilized in solving my problem. Of the techniques that can be utilized in separating and determining inorganic mercury in a matrix, the technique I would use first would be capillary zone electrophoresis because of its rapid separation speeds and high efficiency and the fact that very small amount of sample is required. Also unlike chromatographic methods, there is no interaction between the sample and the stationary phase. Thus, eliminating of the possible sources of errors.
I found multiple sources and articles that used CZE to separate and determine mercury. In one of the articles I found it lead an experiment in which a complexing agent having a thiol group was attached to mercury and the optimized electrophoretic separation was achieved in fused silica capillary at 25 kV using 25 mM sodium borate buffer (pH 9.3). Direct UV (200, 260, 300 nm) was used for detection and the limit of detection (LOD) was 0.170-0.930 mg/L. This process seemed the most ideal and most suitable for my analytical problem however even though I couldn't find any literature in which a fluorescence detector was used I think that could be used instead of a UV detector due to mercury's high levels of fluorescence.

Reference:

Liu, Y. M., Cheng, J. K., Electrophoresis 2003, 24, 1993– 2012.

Harrington, C. F., Trends Anal. Chem. 2000, 19, 167 – 179

A. Siegel, Mercury and its Effects on Environment and Biology in Metal Ions in Biological Systems, 34 ,in: H. Siegel, Editor, Marcel Dekker, New York (1997).

Blog 10:

1. The preferred technique for investigating my analytical problem and separating my analyte from the matrix it is in is reverse phased HPLC coupled with a fluorescence detector would yield the best results.

2. Rajvi Mehta's Analytical Problem; DEHP Leaching from PVC into Contents of Medical Devices. Rajvi uses the same technique as me to separate his analyte from the matrix. We would both use HPLC coupled with a fluorescence detector.

Blog 9:


For my analytical problem separating my analyte, inorganic mercury, from the matrix it is in is a somewhat ok task because of the many options one has to go about it experimentally. For example, most of the chromatography discussed in class prove a useful method for separating inorganic mercury from its matrix. Aside from a few types of chromatography like the size-exclusion, or the HILIC or the chiral chromatography the rest of the methods can be used to separate mercury from its matrix. The reason HILIC won’t provide a useful method is because inorganic mercury is usually in the for of mercuric chloride which is linear (Cl-Hg-Cl) therefore it isn’t all that polar. The size-exclusion chromatography can be useful if the matrix is simple but when dealing with a highly complex matrix like a lotion in which a lot of other compounds might have the same size as mercuric chloride, in this case size-exclusion is not useful. Lastly mercuric chloride doesn’t have any chirality therefore separation via chirality is not useful. However almost all the other chromatography are all sufficient tools in separating the mercury from its matrix. But among all the chromatography, gas chromatography or HPLC are the most useful if coupled to a Hg-specific detector (fluorescence, photometry or other elemental detectors) and this would be my first choices. I came across an article that utilized High-performance liquid chromatography to separate inorganic mercury with 2-mercaptobenzothiazole. In this article, reversed-phase liquid chromatographic method is described to separate and determine inorganic mercury in a aqueous solution using an eluent of methanol-10 mM sodium acetate buffer (80:20, pH 6.2) containing 0.1 mM 2-mercaptobenzothiazole (MBT), mercury can be separated on a C18 column in less than 9 min, UV detection was carried out at 285 nm. The calibration graphs for this experiment were linear with r equaling about .9 and the detection limits was about 0.5 ng of Hg for inorganic mercury. It was also concluded that interference due to metal ions can be eliminated by inclusion of a low concentration (ca. 50 μM) of EDTA in the eluent. Using this experiment as a reference I can conclude that HPLC (or GC) would be the most effective way of separating inorganic mercury from its matrix.

Reference:

M. Berlin, 1986. Mercury. In: Friberg, L., Nordberg, G., Vouk, V. (Eds.), Handbook on the Toxicology of Metals. Elsevier, Amsterdam, pp. 387-444.

Yao-Chin Wang, Chen-Wen Whang: High-performance liquid chromatography of inorganic mercury and organomercury with 2-mercaptobenzothiazole. Department of Chemistry, Tunghai University, Taichung 40704 Taiwan. http://www.sciencedirect.com/science/article/pii/002196739380340E (accessed online, November 7, 2011)

The first three lines of your answer are not needed. They already appear in your blog.

The acids described in the matrix are carboxilic acids not inorganic acids. The method that you describe is suitable for extraction from inorganic acids. I believe that the method will not work as described. Also, if Hg is recrystallized, what do you need to do to prepare it for the analysis? Dissolve it in what? Or, will you analyze it as a crystal? (-0.5 pt)

Something to consider is that not all forms of mercury are toxic. If you are extracting total mercury, this will bias your analysis and interpretation. I believe that in your methodology you have to have methods for total mercury and toxic forms of mercury.

Blog 8:
My analytical problem concerns inorganic mercury present in certain skin bleaching creams and when approaching this matter in lab the first issue you will want to figure out would be how to isolate the mercury from the rest of the cream so you can find out exactly how much is present in the cream among other things. The ingredients of skin bleaching creams vary but when you look at most of them they have one thing in common, most of their main ingredients are acids. For example most of the creams I have researched had several acids as main ingredients such as kojic acid, azelaic acid, alpha hydroxy acids (usually lactic acid or glycolic acid), hydroquinone, or retinoic acid. After finding this out I figured the first thing I would have to do is a acid extraction to extract all the acid out of the matrix since it makes up most of it. I found a real good article that did an experiment in which inorganic mercury(II) was extracted from hydrochloric acid, which in some cases is a pretty common acid. In this experiment they did a liquid–liquid extraction of mercury (II) from hydrochloric acid solutions using Aliquat 336 (tri-octyl methylammonium) chloride as extractant dissolved in commercial kerosene. They added 1-octanol as modifier agent to avoid the formation of a third phase. And the experiment proved successful in which the reactive system showed very fast extraction kinetics and mercury was quantitatively extracted within 5 min at pH ≥ 1 and room temperature (25 C). Using this experiment as a starting point I would extract mercury from the matrix using the same technique and once the acid is taken out of the matrix the you could do a simple extraction using ethanol since mercury is soluble in ethanol then do a few washes using something like brine then recrystallize using hot ethanol and then allow to cool to room temperature and do tests as needed.

Reference:

Liquid–liquid extraction of mercury (II) from hydrochloric acid solutions by Aliquat 336; Hydrometallurgy
Volume 87, Issues 3-4, July 2007, Pages 83-90. http://www.sciencedirect.com/science/article/pii/S0304386X0700059X (accessed October 31st, 2011)

Blog 6. Good answers.
Blog 7. 3(b) and 4 are missing (-0.6 pt).

Blog 7:

Atomic absorption (AA) spectroscopy is an ideal tool for the measurement of any level of mercury. Therefore with atomic absorption spectroscopy I don't have to worry about quantity I can carry out my experiment and yield sufficient results with minimal analyte. To get total mercury measurements atomic absorption techniques provide a speedy and accurate analysis of samples with detection limits below 0.07ppb (µg/L) in solution. Also atomic absorption spectrometers provide excellent screening tool and are very cost effective. I researched atomic absorption case studies done on mercuric chloride but couldn't find anything but when I searched for atomic absorption case studies for mercury I found an experiment that might be useful since essentially my analyte is mercury. For the case study I found atomic absorption was used to detected small amounts of mercury and atomic absorption proved very useful. For their particular study they used a Thermo Scientific iCE 3500 AA spectrometer and a Thermo Scientific VP100 vapour generation accessory the reason being the continuous flow of reagents ensured that the system was cleaning itself all the while reducing memory effects. Also with the Thermo Scientific VP100 it comes standard with a mercury cell which provides an increased pathlength compared to a normal vapor cell and yields very low detection limits. I'm yet to find what wavelengths to use but I would assume using the same wavelengths found with UV vis which was about 260 nm.

Reference:

Atomic absorption spectrometry provides mercury analysis: Scientist Live. http://www.scientistlive.com/European-Food-Scientist/Food_Safety/Atomic_absorption_spectrometry_provides_mercury_analysis_in_fish/22099/ (accessed 10-26-11)

Answers to blog 4 (-1 pt) and blog 5 (-1 pt)?

My analyte, inorganic Mercury, is fluorescent. I know it is fluorescent because it is used in a lot of fluorescent lamps. However upon a more thorough research it can be found what its maximum excitation and emission wavelengths are. Many methods of metallic mercury determination have been published. In one study it is recorded that for total mercury the lowest absolute detection limit was 0.09 pg which was obtained in less then one minute by laser-excited atomic fluorescence spectrometry with electrothermal atomization. Another study which used two types of probes, one using a reaction-based fluorescent sensing approach for inorganic mercury and another based on metal coordination. Using 1:1 mixture of the probes and mercuric chloride showed excitation at 405 nm; the intensity was estimated by the peak height at 475 nm. The recorded fluorescence emission was at 513 nm. Again the ideal solvent for inorganic mercury is any kind of alcohol preferably ethanol. I found an article that discusses a fluorescent probe that selectively responds to inorganic mercury species through a mercury ion-promoted hydrolysis reaction. So this probe would be an ideal instrument to use but any spectrofluorometers would work just fine.

Reference:
Hintelmann, H.; Wilken, R. D. Appl. Orgammer. Chem. 1993,7, 173-180.

ATSDR, Toxicological Profile for Mercury, U.S. Department of Health and Human Services, Atlanta, GA, 1999.; (b) ATSDR, ToxProfiles: Mercury, U.S. Department of Health and Human Services, Atlanta, GA, 2005.

Yong-Suk Cho, Kyo Han Ahn, "A ‘turn-on’ fluorescent probe that selectively responds to inorganic mercury species" (Department of Chemistry and Center for Electro-Photo Behaviors in Advance Molecular Systems, POSTECH, San 31 Hyoja-dong, Pohang 790-784, Republic of Korea) http://www.postech.ac.kr/lab/chem/mras/download/90.pdf (Accessed online October 17th, 2011)

My research is similar to yours since we have similar matrix, the skin whitening products. The difference is, my focus is the whitening effect of the two analytes while your is the toxix effect of mercury in the whitening products to skin.

BLOG 2. The answers are correct. However, question 6 requires that you post a comment to Chuxin's entry. See instructions. You did not loose any points but the grade will be released after you post your comment on Chuxin's entry. Let Chad know after you have done that so that he may release your grade. Thanks. Edgar

P.S. BLOG 3? (-1.0 pt)