Sample Preparation for AMS

After chemical pretreatment, the samples are burnt to produce carbon dioxide and nitrogen. A small amount of this gas is bled into a mass spectrometer, where the stable isotope ratios of carbon and nitrogen are measured. These ratios provide useful information on the purity of the sample and clues about the diet and climatic conditions of the living organism. The carbon isotope ratio is also used to correct for isotopic fractionation in the radiocarbon measurement. The carbon dioxide is collected in a glass ampoule or converted to graphite for radiocarbon measurement on the AMS system. 

For dating with bone samples, one is required to carry out chemical pretreatment of bone, removal of preservatives and contaminants from objects, radiocarbon calibration, stable isotope analysis, and interpretation of contaminants. 

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CEDAD, n.d.. Sample preparation for AMS radiocarbon dating, In Internet site of CEDAD, Date of access November 2011, Available from http //cedad.unisalento.it/en/ clams.php... 

GO Yalcin, T., Dai, Y., and U, L (1998) Matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry for polymer analysis solvent effect in sample preparation. J. Am. Soc. Mass Spectrom., 9,1303-1310. 

Indeed AMS is a state-of-art ultrasensitive technique for trace analysis, but the success of AMS depends on many crucial steps before the actual measurement in the AMS system. In fact, sometimes expertise from several areas of science is required to make the AMS experiments reliable. Some of the crucial points are sample collection, pretreatment, sample preparation for ion source, development of separation methods for isobars, etc. Like all other analytical techniques, it is also necessary to measure standard, blank, and background, simultaneously with the sample. Below some of the crucial steps are described in nutshell. 

The reasons will be clearer after Section 16.4, where AMS radiocarbon sample preparation procedures will be described. Now we would simply like to recall that in preparing graphite pellets for the sputtering source, after a physical chemical cleaning, samples to be dated are usually combusted to obtain C02, which is then converted to graphite by a further step. In this process, the main problem with small samples (a few tens of micrograms) is the possible introduction of contamination. 

Bogan MJ, Agnes GR. 2004. WaU-less sample preparation of micron-sized sample spots for femtomole detection limits of proteins from liquid based UV-MALDI matrices. J Am Soc Mass Spectrom 15 486. 

Rule G, Henion J. 1999. High-throughput sample preparation and analysis using 96-weU membrane solid-phase extraction and liquid chromatography—tandem mass spectrometry for the determination of steroids in human urine. J Am... 

Fig. 5.44 Variation of full spectrum AM 1.5 illumination (100 mW/cm ) photocurrent density versus potential in 1 M KOH solution. Anodic samples prepared as (a) Titanium foil anodized at 20 V for 70 h in DSMO and ethanol mixture solution (1 1) containing 4% HF. (b) H2O-HF electrolyte at 20 V for 1 h. Both samples were annealed at 550°C 6 h in oxygen atmosphere prior to testing. Dark current for each sample is shown in (c).

JD McCord, E Trousdale, DD Ryu. An improved sample preparation procedure for the analysis of major organic components in grape must and wine by high performance liquid chromatography. Am J Enol Vitic 35(1) 28—29, 1984. 

Keller B, Li L (2006) Three-layer matrix/sample preparation method for MALDI MS analysis of low nanomolar protein samples. J Am Soc Mass Spectrom 17 780-785. doi 10.1016/j. jasms.2006.02.012... 

Over the next decade, if the stringent requirements for the exclusion of modern carbon contamination in sample preparations can be met, developments in AMS may permit routine extension of the 14C time frame beyond the current 40,000- to 60,000-year range for the typical archaeological sample (8). However, the potential of AMS to extend the 14C time frame into the 70,000- to 100,000-year range for samples from archaeological contexts may be possible only with the development of practical methods of 14C isotopic enrichment that can be routinely used for samples that contain less than 1 g of carbon. The possibility of using a laser-based approach for 14C enrichment before AMS analysis is being studied (9, 10). 

TIMS has been used for many years as the benchmark technique especially for uranium isotope analysis. Instrumental improvements have enabled ICP-MS to approach the accuracy and precision obtained by TIMS in measuring data. In addition, due to time consuming sample preparation steps and the need for a large volume of urine, the method has been replaced by the more powerful ICP-MS in many laboratories. An interlaboratory analytical exercise on the determination of natural and depleted uranium in urine was carried out by different ICP-MS instruments, by thermal ionization mass spectrometry (TIMS) and instrumental neutron activation analysis. TIMS has also been employed to determine fg quantities of Pu and °Pu in bioassay samples (such as human urine and artificial urine), ° in an interlaboratory comparison for the analysis of the Pu and Pu/ °Pu atomic ratios in synthetic urine by TIMS and AMS as reported in reference. ... 

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