Biological MS by Isotope Dilution. By: Cryst Bambo

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1 Biological MS by Isotope Dilution By: Cryst Bambo

2 What is Isotope Dilution? Isotopes versions of an atom or an element that have the same number of protons, but different numbers of neutrons. i.e. 12 C, 13 C and 14 C Dilution A technique that allows the process of reducing the concentration of a sample in a solution. Isotope Dilution An analytical technique used for quantity determination by the addition of known amounts of isotopically-enriched substance to the analyzed sample.

History A Cup of Tea Springtime of 1913 George Hevesy (1885) drinking a cup of tea at the Manchester Physics Laboratory with his colleague Henry Moseley.

3 History A Cup of Tea Springtime of 1913 George Hevesy (1885) drinking a cup of tea at the Manchester Physics Laboratory with his colleague Henry Moseley. Hevesy wanted to determine the fate of the individual water molecules contained in the cup of tea consumed, Moseley did not. 1915, Moseley was shot by a Turkish sniper E. Hofer, his new drinking buddy, consumed 2000 ml aliquots of deuterated tea. Tested their own urine samples. half of the body s water turned over every 9 days and the body s water content is at 43 liters.

Isotope Dilution Mass Spectrometry(IDMS) Isotope dilution is an analytical technique used in combination with mass spectrometry to determine the concentration of wanted element in unknown samples.

5 Isotope Dilution Mass Spectrometry(IDMS) Isotope dilution is an analytical technique used in combination with mass spectrometry to determine the concentration of wanted element in unknown samples. A known amount of spike with known elemental concentration and isotopic abundances is added to sample with unknown elemental concentration but known isotopic abundances. Requirements: 1) The sample has natural (or known) isotopic abundance. 2) The spike and sample isotopic ratios are different.

7 Isotope Dilution Mass Spectrometry(IDMS)

8 An Extension of the Isotope Dilution Method. Science, 107(2774), pp

9 Isotope Dilution Mass Spectrometry(IDMS) Advantages: Most accurate and precise method for quantitative elemental concentrations Partial loss of analyte during preparation is compensated for since physical and chemical interferences are not an issue -- will cancel out as they will affect each isotope identically Ideal form of internal standardization since another isotope of the same element is used in this capacity Disadvantages: Generally only applicable to multiple-isotopic elements Need an enriched isotope spike for the analyte of interest - not always available or sometimes at very high cost Need two interference free isotopes VERY time consuming

10 Figure. 4-Methylimidazole

11 4-Methylimidazole (4-MEI) A heterocyclic organic compound formed in many ways; fermentation through alcohol production and Maillard Reaction. Browning reaction that occurs between amino acids and carbohydrates when they are heated together. 4-MEI can be found in roasted foods, grilled meats, coffee in types of caramel colouring. Caramel colour most used food-beverage colouring; i.e. beers, sodas Implies that commercially available beverages contain 4-MEI

12 4-Methylimidazole (4-MEI) 1975 WHO Caramel colouring showed disturbed immune functions in rodents. National Toxicology Program (NTP, USA, 2007) 4-MEI showed carcinogenic activity in male and female mice; labeled as carcinogen, established No Significant Risk Level (NSRL) of 29 ug/day. European Food Safety Authority (EFSA) has stated that 4-MEI is safe and is not a health concern for Europeans exposed in caramel coloured foods. ADI of 100mg/kg bw/day.

13 Case Study: 4-Methylimidazole (4-MEI) 25mL of sample (beverage) was decarbonated via a mechanical shaker. 100uL of the aliquot was diluted and fortified with d 6-4-MEI to 50pg/uL. A 5uL of volume was injected for LC-MS/MS analysis with water as a blank control. LC-MS/MS analysis was carried via C8-reverse phase using 0.05% Formic acid in both water (MP A) and methanol (MP B).

14 Results: 4-MEI

19 4-MEI in Beverages Pepsi and butter beer exceed the NSRL of 29ug/L. According to EFSA, assuming an average of BW is 80kg. Using the highest MEI-detected, pepsi at 211.5ug, the daily intake per can would equal to 0.003mg/kg bw/day. Which is significantly smaller than the recommended 100mg/kg bw/day. Health canada has stated that 4-MeI levels found in foods do not represent a risk.

20 Conclusion Isotope dilution with d 6-4-MEI and analysis via LC-MS/MS allowed the accurate quantification of 4-MEI present in a variety of alcoholic and non alcoholic beverages. The amount of 4-MEI in alcoholic beverages exceed the NSRL level of 29ug/L while the three of the non alcoholic beverages (pepsi, diet pepsi, butter beer) exceed the threshold value. None of the samples exceed the EFSA ADI guideline.

21 Reference Abdallah, M., Harrad, S. and Covaci, A. (2009). Isotope Dilution Method for Determination of Polybrominated Diphenyl Ethers Using Liquid Chromatography Coupled to Negative Ionization Atmospheric Pressure Photoionization Tandem Mass Spectrometry: Validation and Application to House Dust. Analytical Chemistry, 81(17), pp BLOCH, K. and ANKER, H. (1948). An Extension of the Isotope Dilution Method. Science, 107(2774), pp Blom, K. (1987). Average mass approach to stable isotope dilution mass spectrometry. Organic Mass Spectrometry, 22(8), pp Ratnayake, G., Halldorson, T., Bestvater, L. and Tomy, G. (2015). Determination of 4(5)- methylimidazole in carbonated beverages by isotope-dilution liquid chromatographytandem mass spectrometry. Food Additives & Contaminants: Part A, 32(7), pp

22 Present Regulation In 2012, coca-cola and Pepsi announced they had their caramel supplier alter their manufacturing processes to meet the 29.ug/L standard. Changes have already been made in California. Levels of 4-MEI in Europe on the other hand remains the same since it passes the EFSA ADI

Perfluorinated Alkyl Acids (PFAA) in Water by LC/MS/MS - PBM

Organics Revision Date: July 19, 2017 Perfluorinated Alkyl Acids (PFAA) in Water by LC/MS/MS - PBM Parameter Perfluorinated Alkyl Acids (Perfluorobutane Sulphonate (PFBS), Perflourooctane Sulphonate (PFOS),