Mass spectrometry artifacts

A further important use of El mass spectrometry lies in measuring isotope ratios, which can be used in estimating the ages of artifacts, rocks, or fossils. Electron ionization affects the isotopes of any one element equally, so that the true isotope ratio is not distorted by the ionization step. Further information on isotopes can be found in Chapter 46. 

Stevenson, C.M., Abdel-Rehim, L. and Novak, S.W. (2004). High precision measurement of obsidian hydration layers on artifacts from the Hopewell site using secondary ion mass spectrometry. American Antiquity 69 555-567. 

The potential for the preservation of lipids is relatively high since by definition they are hydrophobic and not susceptible to hydrolysis by water, unlike most amino acids and DNA. A wide range of fatty acids, sterols, acylglycerols, and wax esters have been identified in visible surface debris on pottery fragments or as residues absorbed into the permeable ceramic matrix. Isolation of lipids from these matrices is achieved by solvent extraction of powdered samples and analysis is often by the powerful and sensitive technique of combined gas chromatography-mass spectrometry (GC-MS see Section 8.4). This approach has been successfully used for the identification of ancient lipid residues, contributing to the study of artifact... 

Efforts to measure Mo isotope variations, using thermal ionization mass spectrometry (TIMS), can be traced back to the early 1960s. Early studies were provocative Murthy (1962 1963) reported that the Mo isotope composition in some iron meteorites deviated from that of others, and from terrestrial Mo, by 10 %o/amu, while Crouch and Tuplin (1964) reported mass dependent variations and mass independent isotopic anomalies among terrestrial molybdenites. As discussed below, Wetherill (1964) subsequently demonstrated isotopic uniformity among iron meteorites to better than 1 %o/amu. It is likely that earlier reports were affected by analytical artifacts due to inadequate correction of Mo isotope fractionation during analysis. 

Great care has to be taken in the analytical characterization of synthetic cyclic peptides.[73] The major side reactions during cyclization are epimerization of the C-terminal amino acid residue and cyclodimerization. Cyclodimers can be detected by mass spectrometry, although the analysis is not trivial, because artifacts do occur in some ionization techniques such as ES-MS as a result of aggregation.1 1 Ll 121 Real dimers can be detected as double-charged particles with mlz values identical to the cyclic monomers, but with a mass difference of 0.5 amu in the resolved isotope signals. The mass difference of the corresponding monomer is 1 amu. The cyclodimerization has received some attention as a direct method for the synthesis of C2-symmetrical cyclic peptides.[62 67 94113 115]... 

A.D. were found in old mines, and sizable slag deposits suggest at least some level of lead exploitation during Roman times (2). By the careful selection of Roman lead artifacts likely to have been manufactured in Carthage, and the use of lead isotope analysis, it may be possible to confirm the use of Tunisian lead ores during the Roman period. In this preliminary study, analysis of 22 curse tablets by electron microprobe analysis (EMPA) and six tablets by thermal ionization mass spectrometry (TIMS) suggest that these artifacts might be used to better understand Roman lead use and trade. 

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is still a recent analytical technique that appeared in the middle of the 1980s and has yielded an increasing interest ever since (1). At the beginning of the 1990s, applications to determine the composition of archaeological or ancient artifacts... 

Since the mid-1960s, a variety of analytical chemistry techniques have been used to characterize obsidian sources and artifacts for provenance research (4, 32-36). The most common of these methods include optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), particle-induced X-ray emission spectroscopy (PIXE), inductively coupled plasma-mass spectrometry (ICP-MS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence spectroscopy (XRF), and neutron activation analysis (NAA). When selecting a method of analysis for obsidian, one must consider accuracy, precision, cost, promptness of results, existence of comparative data, and availability. Most of the above-mentioned techniques are capable of determining a number of elements, but some of the methods are more labor-intensive, more destructive, and less precise than others. The two methods with the longest and most successful histoty of success for obsidian provenance research are XRF and NAA. 

Laser Ablation—Inductively Coupled Plasma—Mass Spectrometry Analysis of Ancient Copper Alloy Artifacts... 

Bouschen W, Spengler B (2007) Artifacts of MALDI sample preparation investigated by high-resolution scanning microprobe matrix-assisted laser desorption/ionization (SMALDI) imagine mass spectrometry. Int 1 Mass Spectrom 266 129-137. doi 10.1016/j. ijms.2007.07.017... 

Frolick Olson describe the conventional methods of extracting retinoids from biological samples236. They stress the delicacy of the retinoids and describe two important points to consider, (1) whether the method chosen will result in complete extraction of the retinoid of interest, and (2) whether it will contribute to the production of artifacts. Unfortunately, they do not consider whether the product itself could be degraded. They do stress the sensitivity of these labile compounds to both hydrolysis and oxidation. They also address the use of fluorescence in assays. This work points out that the use of fluorescence is a negative test for the retinoids of vision when in liquid crystalline form. They point out that mass spectrometry is one of the most specific forms of assay for the retinoids. The utility of this technique will be discussed in Chapter 6. They do not describe how the techniques mentioned are able to remove a retinoid from within the putative rhodopsin molecule, or how to do in without damage to the retinoid. 

A metabolite with +16 amu is generally suspected of forming by hydrox-ylation (or by some other reaction involving the addition of oxygen). However, a metabolite with +14 amu is often suspected of forming by methylation (+CH2), not by a combination of the addition of oxygen (+16) and dehydrogenation (—2). NADPH-fortified human liver microsomes cannot catalyze the methylation of dmg candidates (such reactions are catalyzed by cytosolic enzymes in the presence of. S -adenosylmethionine). However, methylation can sometimes occur as an artifact when mass spectrometry is conducted in the presence of methanol (164), and [M + 12] adducts can form from condensation reactions with formaldehyde, which is a microsomal metabolite of methanol (165). A metabolite with +30 amu is indicative of either formation of a carboxylic acid metabolite or a combination of hydroxylation (+16) and methylation (+14). Only the former can be catalyzed by NAPDH-fortified liver microsomes. 

A Xany insights into early civilizations have been provided by the study of ceramics. Various physical and chemical methods are considered standard techniques for modem archaeology (I, 2). The macroanalysis, microanalysis, and trace chemical analysis of artifacts have added greatly to the understanding of prehistoric civilizations (3-6). The chemical techniques used for ceramic analysis have included spark source mass spectrometry (7) ... 

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