Analytical Chemistry Chemical Cytometry Quantitates Superoxide

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Figure 2. Intensity chromatograms for the n-alkanes mixture obtained in the SIM mode: (a) at m/z ) 71 operating the setup in the qualitative configuration; (b) at m/z 44 and 45 operating the setup in the quantitative configuration. and the filling of the reservoir, traces of this compound possibly present in the Helium gas used to dilute de 13 CO2 and traces of air still present in the EI source. The high enrichment obtained provides a very wide range of optimum analyte/spike ratios and then a sample containing compounds in a large range of concentrations could be quantified in the same analysis without affecting the accuracy of the results. 3 The short-term (30 min) and long-term (9 h) stability of the 12 C/ 13 C isotope ratio is given in the Supporting Information (Figures SI-3 and SI-4). In both cases the measured isotope ratios, 0.0339 ± 0.0002 and 0.034 ± 0.001 (n ) 8), respectively, were remarkably stable. Similar results were obtained in different days indicating that the setup was robust enough for routine analysis. Evaluation of the GC-Combustion-IDMS System. The overall performance of the developed instrumentation was evaluated here by analyzing a standard solution of a mixture of n-alkanes (C9-C20). To study peak broadening, 1 µL of a solution containing approximately 5 µg/g of these compounds in n-hexane was injected in the chromatograph both in the qualitative (combustion oven bypassed) and quantitative (through the oven) modes. The Selected Ion Monitoring chromatogram obtained at m/z ) 71 (fragment characteristic of n-alkanes) is shown in Figure 2a, whereas the chromatogram obtained at masses 44 and 45 after combustion and postcolumn isotope dilution analysis is shown in Figure 2b. As can be observed, no significant peak broadening due to the combustion unit or to the different connections was observed, being the peak width measured at the half height equal to that found when operating the 6866 <strong>Analytical</strong> <strong>Chemistry</strong>, Vol. 82, No. 16, August 15, 2010 Figure 3. Mass flow chromatograms obtained for the n-akanes mixture. GC-MS in the conventional way (0.02 min, Figure 2a). Only a small increase in retention times was observed (∼20 s) because of the combustion furnace. The mass flow chromatogram obtained after the application of the online isotope dilution equation (eq 1) is shown in Figure 3. As can be observed, the sensitivity is roughly constant for all compounds which is in clear contrast with the results shown in Figure 2a for mass 71 without combustion (SIM detection). The peak areas in the mass flow chromatogram were linear with the amount of carbon injected over 2 orders of magnitude (the maximum range assayed). The detection limit obtained for tetradecane was 9 ppb (ng/g) based on three times the standard deviation of the baseline. Taking into account that the injection volume was 0.5 µL, this value corresponds to an absolute limit of detection of 3 pg of tetradecane injected. If we take into account the peak width at the baseline (4s approximately in this particular case), then we can make our detection limit independent of the column employed and the carrier gas flowrate. The value found was 0.8 pg C s -1 , being in the same order that those provided by a mass spectrometer in full scan mode (1 pg C s -1 ) and clearly better than those of a flame ionization detector (10 pg C s -1 ). This detection limit is mainly limited by the background level observed at m/z ) 44, and explains the difference in comparison with the detection limit achievable using the mass spectrometer in SIM mode bypassing the oven (typically 0.1 pg C s -1 ) in spite of the fact that both sensitivities were very similar. In contrast, it should be mentioned that the EI detection limit observed is 3 orders of magnitude lower than that obtained for carbon using 13 C postcolumn isotope dilution and ICP-MS detection (0.7 ng C s -1 ). 12 For the quantitative analysis of the standard mixture of n-alkanes (C9-C20) we needed first to quantify the mass flow of postcolumn 13 CO2. Out of the two possibilities of using internal standard (IS) or external standard, we selected an IS because it provided the advantage of compensation for small variations in the sample volume injected (we were using manual injection). Moreover, as recently pointed out by Heilmann and Heumann, 11 an additional advantage of using an internal standard is that the mass flow of enriched carbon dioxide does not need to be determined. The peak areas of both the analyte and the internal standard in the mass flow chromatogram are related to the unknown mass flow of spike (eq 1). However, the ratio of peak areas analyte/IS will be equal to the actual ratio of concentrations in the injected sample and independent of the mass flow of spike used in the calculations. Thus, quantification
Table 1. Absolute Quantification Results for the Alkane Model Mixture a compound added (µg/g) found (µg/g) nonane 8.0 8.3 ± 0.5 decane 8.0 8.3 ± 0.2 undecane 8.0 8.4 ± 0.1 dodecane 8.0 8.3 ± 0.3 tridecane 8.0 8.3 ± 0.3 tetradecane 8.0 I.S. pentadecane 8.0 7.7 ± 0.1 hexadecane 8.0 7.7 ± 0.1 heptadecane 8.0 7.4 ± 0.3 octadecane 8.0 7.9 ± 0.1 nonadecane 8.0 7.8 ± 0.1 eicosane 8.0 8.3 ± 0.2 a Tetradecane was used as an internal standard. The uncertainty is expressed as the standard deviation for n ) 3 injections. of the amount of carbon under each peak can be determined just by calculating the areas of the internal standard and those corresponding to the other organic compounds. Therefore, the knowledge of the spike mass flow is not needed. The quantitative results obtained from the data shown in Figure 3, using tetradecane as internal standard, are given in Table 1. As can be observed, this methodology allowed us to quantify a series of organic compounds containing from 9 to 20 atoms of carbon and with a range of boiling points from 128 to 343 °C, with acceptable precision (
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Anal. Chem. 2010, 82, 6745-6750 Let
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purchased from Invitrogen-Molecular
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Figure 3. Electropherograms of TPP-
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Anal. Chem. 2010, 82, 6751-6755 Res
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(pH 8.0) with cysteine and cystamin
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Figure 4. Ion mobility mass spectra
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GOx glucose + O298 gluconic acid +
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coater at 2000 rpm for 20 s, and th
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Figure 5. Comparison of cyclic volt
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in channels with either no grooves
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indicators of atmospheric processin
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Figure 1. GC/MS total ion chromatog
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Table 2. Concentrations and Stable
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on a substrate are preferred. 20-24
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Figure 4. SERS analysis of NAADP co
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Anal. Chem. 2010, 82, 6775-6781 Hig
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tion, 2 µL of proprionaldehyde wer
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Figure 4. Analysis of 2a by HPLC-MS
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eaction of 1a with PBH can be condu
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Numerous references had demonstrate
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Figure 1. TEM images of the prepare
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Figure 4. Schematic representation
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esult in a big SPR signal change wi
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also reduces chemical noise, which
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Table 1. Extraction Yields, Liquid
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scanning of AMPP amides of the anal
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Anal. Chem. 2010, 82, 6797-6806 δ
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Figure 1. Schematic view of the pre
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from the specimen and enclosed in a
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Figure 4. (A) IRMS mass-44 chromato
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Table 3. Ambient Measurement Result
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Anal. Chem. 2010, 82, 6807-6813 Dir
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Polymerase (1 U per sample). Reacti
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of which was constant for all ampli
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analytically useful signals at less
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Page 73 and 74: solution in an equal volume, and 1
Page 75 and 76: Table 2. Concentrations and Ratios
Page 77 and 78: Anal. Chem. 2010, 82, 6821-6829 Mac
Page 79 and 80: mg/mL protein, followed by separati
Page 81 and 82: Figure 2. Productivity of SEQUST an
Page 83 and 84: Figure 4. High-resolution MS/MS spe
Page 85 and 86: Figure 6. Characterization of PSMs
Page 87 and 88: containing T-T mismatches. 23 Based
Page 89 and 90: Figure 1. Extinction spectra of sol
Page 91 and 92: Figure 3. (A) The value of Ex650 nm
Page 93 and 94: Figure 5. Extinction spectra and co
Page 95 and 96: wished to explore the dehydration o
Page 97 and 98: constant medium for separation; we
Page 99 and 100: Figure 2. Standards of (Pi)n, n ) 1
Page 101 and 102: Figure 5. Quantitative calibration
Page 103 and 104: Anal. Chem. 2010, 82, 6847-6853 Met
Page 105 and 106: Figure 1. 226 Ra spectrum by liquid
Page 107 and 108: Table 1. Counting Properties and De
Page 109 and 110: Table 3. Analysis of 226 Ra in Sedi
Page 111 and 112: mercial microarray scanner and fabr
Page 113 and 114: Figure 2. Optical transmission meas
Page 115 and 116: Figure 5. Volcano plots detailing t
Page 117 and 118: data as well. The 41 genes in Table
Page 119 and 120: corresponding compound if its chemi
Page 121: Figure 1. Schematic illustration of
Page 125 and 126: ment. Therefore, the long-time drea
Page 127 and 128: Figure 1. Chemically actuated micro
Page 129 and 130: Figure 2. Influence of a surfactant
Page 131 and 132: Figure 5. Device to eject and mix s
Page 133 and 134: Anal. Chem. 2010, 82, 6877-6886 Imm
Page 135 and 136: NaCl, phosphate buffer saline (PBS)
Page 137 and 138: Figure 2. Product ion mass spectra
Page 139 and 140: -70 °C resolved the problem, givin
Page 141 and 142: Table 1. Intraday Precision and Acc
Page 143 and 144: Anal. Chem. 2010, 82, 6887-6894 Fer
Page 145 and 146: Figure 1. Infrared spectra of (A) u
Page 147 and 148: Figure 3. Cyclic voltammograms obta
Page 149 and 150: Figure 6. Calculated charge from ch
Page 151 and 152: Anal. Chem. 2010, 82, 6895-6903 Ele
Page 153 and 154: Table 1. Chemical Structure, pKa Va
Page 155 and 156: pH with a tilted baseline (Figure 1
Page 157 and 158: Table 2. Linearity and Detection Li
Page 159 and 160: ascorbic acid (AA), uric acid (UA),
Page 161 and 162: the multielement capabilities, the
Page 163 and 164: RESULTS AND DISCUSSION Sulfur Detec
Page 165 and 166: Table 2. Molecular Properties and C
Page 167 and 168: Anal. Chem. 2010, 82, 6911-6918 Dir
Page 169 and 170: dilution and hybridization buffer.
Page 171 and 172: solution under appropriate incubati
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Figure 4. Standardization curve for
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Anal. Chem. 2010, 82, 6919-6925 Ele
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the ×10 objective, to have a large
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Figure 2. With a suitable removal o
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the NB signal in a much better foot
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Scheme 1. Reactions of Selenium Rea
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Figure 2. (a) ESI-MS spectrum showi
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Figure 4. (a) ESI-MS spectrum showi
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Anal. Chem. 2010, 82, 6933-6939 Dif
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trode 28 by a finite element using
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Figure 4. Comparison between simula
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Figure 6. Comparison between simula
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educed in the vicinity of double bo
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Figure 2. Normalized product ion ab
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Figure 4. EID (a) and IRMPD (b) of
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Anal. Chem. 2010, 82, 6947-6957 Ide
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Figure 1. Schematic flowchart showi
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difference, ppm compound Table 1. I
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isoforms, its successful use, in th
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Figure 5. Extracted ion current ESI
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m/z 1172.935 was observed for Ser14
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linked products via affinity tags.
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Scheme 2. Fragmentation Mechanism o
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Figure 1. (A) ESI-LTQ-CID-MS 2 prod
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Figure 3. (A) ESI-LTQ-CID-MS 2 prod
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Figure 5. (A) MALDI-TOF/TOF product
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Anal. Chem. 2010, 82, 6969-6975 Ana
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Figure 3. Equilibrium response as a
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Figure 6. The average measured resp
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for the fill time, and we find that
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nucleotide tails. 3-5 Thus, the amo
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allow the use of higher aptamer con
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quent ligation of the aptamers afte
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Anal. Chem. 2010, 82, 6983-6990 Imp
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Figure 2. Configuration editor wind
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Figure 4. Dependencies between volu
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Since the time for liquid expulsion
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Anal. Chem. 2010, 82, 6991-6999 Int
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Figure 1. Representation of the Car
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Table 2. Capillary Electrophoresis
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Figure 4. (A) Typical raw electroph
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field. DNA profiles were delivered
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Another approach to handle this lim
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(principal components, PCs) in whic
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Figure 5. Relevant score plots and
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CONCLUSIONS In this paper we have i
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electroactive-species loaded liposo
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Figure 2. Qdot-based FLFTS response
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Figure 6. Fluorescence imaging of Q
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Anal. Chem. 2010, 82, 7015-7020 Sel
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Table 1. Effect of 1 D-LC Condition
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Figure 3. Peak-production rate vers
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Anal. Chem. 2010, 82, 7021-7026 Cel
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luciferase (T7 control vector) was
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Figure 3. Inhibitory effects of luc
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Anal. Chem. 2010, 82, 7027-7034 Pat
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Electrochemistry. Electrochemical m
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Figure 2. SEM images of Au substrat
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Table 3. Film Thickness Measurement
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Anal. Chem. 2010, 82, 7035-7043 Qua
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Figure 1. (A) FL spectra of BSPOTPE
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Figure 4. (A) Variation in the FL i
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Figure 6. (A) FL spectra of BSPOTPE
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Scheme 1. Proposed Mechanism for Fl
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one or more drawbacks including poo
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Figure 2. Free fluorophores do not
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Anal. Chem. 2010, 82, 7049-7052 Dev
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Figure 2. Comparative analysis of d
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Analytical Chemistry Chemical Cytometry Quantitates Superoxide

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