Liguo Song

Ionization Mechanism of Negative Ion-Direct Analysis in Real Time: A Comparative Study with Negative Ion-Atmospheric Pressure Photoionization

The ionization mechanism of negative ion-direct analysis in real time (NI-DART) has been investigated using over 42 compounds, including fullerenes, perfluorocarbons (PFC), organic explosives, phenols, pentafluorobenzyl (PFB) derivatized phenols, anilines, and carboxylic acids, which were previously studied by negative ion-atmospheric pressure photoionization (NI-APPI). NI-DART generated ionization products similar to NI-APPI, which led to four ionization mechanisms, including electron capture (EC), dissociative EC, proton transfer, and anion attachment. These four ionization mechanisms make both NI-DART and NI-APPI capable of ionizing a wider range of compounds than negative ion-atmospheric pressure chemical ionization (APCI) or negative ion-electrospray ionization (ESI). As the operation of NI-DART is much easier than that of NI-APPI and the gas-phase ion chemistry of NI-DART is more easily manipulated than that of NI-APPI, NI-DART can be therefore used to study in detail the ionization mechanism of LC/NI-APPI-MS, which would be a powerful methodology for the quantification of low-polarity compounds. Herein, one such application has been further demonstrated in the detection and identification of background ions from LC solvents and APPI dopants, including water, acetonitrile, chloroform, methylene chloride, methanol, 2-propanol, hexanes, heptane, cyclohexane, acetone, tetrahydrofuran (THF), 1,4-dioxane, toluene, and anisole. Possible reaction pathways leading to the formation of these background ions were further inferred. One of the conclusions from these experiments is that THF and 1,4-dioxane are inappropriate to be used as solvents and/or dopants for LC/NI-APPI-MS due to their high reactivity with source basic ions, leading to many reactant ions in the background.

Ionization mechanism of positive-ion direct analysis in real time: a transient microenvironment concept.

A transient microenvironment mechanism (TMEM) is proposed to address matrix effects for direct analysis in real time (DART). When the DART gas stream is in contact with the sample, a transient microenvironment (TME), which can shield analytes from direct ionization, may be generated through the desorption of the matrix containing the analyte. The DART gas stream can directly ionize the matrix molecules, but the analytes will be ionized primarily through gas-phase ion/molecule reactions with the matrix ions. Experimental results showed that as little as 10 nL of liquid or 10 microg of solid was able to generate an efficient TME. Generated TMEs were able to control the ionization of an analyte below an analyte-to-matrix ratio that was dependent on the DART temperature and the boiling points of the analyte and matrix. TMEs generated by common solvents were studied in detail. The ionization of both polar and nonpolar compounds, present in a solvent or another analyte below a ratio of 1:100, were found to be mainly controlled by the generated TMEs at a DART temperature of 300 degrees C.

The principal urinary metabolites of dietary isothiocyanates, N-acetylcysteine conjugates, elicit the same anti-proliferative response as their parent compounds in human bladder cancer cells.

Isothiocyanates (ITCs) are a class of well-known cancerpreventive phytochemicals, but are primarily disposed of and concentrated in the urine as N-acetylcysteine conjugates (NAC-ITCs) in vivo. Because human urinary bladder cancers occur almost exclusively in the bladder epithelium, which is directly exposed to the urine stored in the bladder, we undertook to examine the anti-cancer activity of NAC-ITCs in cultured human bladder cancer cells. In this paper, we report that the NAC conjugates of four naturally occurring ITCs, including allyl ITC, benzyl ITC (BITC), phenethyl ITC and sulforaphane, potently inhibited the growth of cells derived from both low-grade superficial and high-grade invasive human bladder cancers and drug-resistant bladder cancer cells. Moreover, the growth-inhibitory potencies were similar between the conjugates and their parent compounds. Further study of NAC-BITC and BITC as model compounds showed that both compounds accumulated in cells predominantly as the glutathione conjugate of BITC, but the accumulation of the former was slower. Moreover, both compounds also demonstrated the same anti-proliferative mechanisms: causing the cleavage of the same set of caspases (caspase−3, −8 and −9) in apoptosis induction, arresting cells in the same phases (S and G2/M) and targeting the same cell cycle regulator (Cdc25C), although a longer treatment time or slightly higher doses were needed for NAC-BITC to achieve the same effect as BITC, presumably due to slower cellular uptake of NAC-BITC. These data show that the NAC-ITCs are biologically similar to their parent compounds and are highly effective against human bladder cancer cells.

Separation of six phenylureas and chlorsulfuron standards by micellar, mixed micellar and microemulsion electrokinetic chromatography

Abstract The usefulness of electrokinetic chromatography (EKC) for the determination of phenylureas and chlorosulfuron herbicides was investigated. Micellar, mixed micellar and microemulsion EKC were examined for this purpose and compared systematically. Micelles formed from sodium dodecyl sulfate (SDS), mixed micelles formed from SDS and polyethylene glycol 400 monolaurate and oil-in-water microemulsions formed from SDS, n-butanol and n-octane were mainly employed. Capacity factors showed that the separation of the herbicides by ECK employing SDS follows an interaction mechanism similar to that in reversed-phase HPLC. Although there was not much difference in the elution order of the herbicides among the three modes of EKC, there were differences in separation selectivity. The separation efficiencies in mixed micellar and microemulsion EKC were higher than that in micellar EKC. Under the same separation conditions, the migration window in mixed micellar EKC was narrower than that in micellar EKC, but the migration window in microemulsion EKC was wider than that in micellar EKC and was also much easier to extend by changing the SDS concentration and applied voltage. The effects of the separation conditions on the separation of the herbicides by micellar EKC and microemulsion EKC were investigated.

Early Evidence on the Effectiveness of Clean Indoor Air Legislation in New York State

In July 2003, New York State implemented the Clean Indoor Air Act (CIAA) to reduce exposure to environmental tobacco smoke (ETS). In this cross-sectional study, workers (n=168) completed an interview assessing ETS exposure and provided urine for cotinine analysis. Hospitality workers recruited after implementation of the CIAA had significant reductions in ETS exposure and urine cotinine, compared with those recruited before implementation. The New York State CIAA yielded measurable reductions in ETS exposure for hospitality workers.

Effect of high concentrations of salts in samples on capillary electrophoresis of anions

Abstract The capillary electrophoretic separation of anions using direct UV detection was studied. The separation conditions, such as carrier electrolyte, pH and concentration of electroosmotic modifier, were optimized. The carrier electrolyte co-ion affected the peak shape because electromigration dispersion was non-negligible. An unsuitable anion form of the electroosmotic flow modifier would cause negative peaks on the separation baselines when the samples contain high concentrations of salts, and the separation could be adversely affected. In this work, sodium chloride with 2.0 mM tetradecyltrimetylammonium bromide was used as the carrier electrolyte solution, and a good separation was achieved. Taking sodium chloride to represent salts in samples, the experimental results showed that the peak height and width of a detected anion were affected by the ratio of sodium chloride concentration between the carrier electrolyte solution and sample, and correspondingly the detection limit and separation efficiency of the anion were also affected. The principle of electrostacking was used to explain this phenomenon theoretically. The reproducibility of migration time, peak height and peak area under different conditions was also examined.

Separation of double-stranded DNA fragments in plastic capillary electrophoresis chips by using E99P69E99 as separation medium

The separation of double‐stranded DNA (dsDNA) fragments in polymethylmethacrylate (PMMA) capillary electrophoresis (CE) chips by using E99P69E99 as a separation medium has been demonstrated. The PMMA CE chips were simply manufactured by micromachining and adhesive tape sealing. To make the separation channel compatible with the separation medium, a dynamic nonionic surfactant coating procedure was developed, which made the plastic separation channel sufficiently hydrophilic to allow the separation medium to fill the channel by capillary action. Subsequent separation of DNA fragments was successful with a separation efficiency of the order of 104 theoretical plates over an effective separation distance of 1.5 cm. By using an applied electric field strength of 200 V/cm, the separation of low DNA mass ladder was completed within 5 min. The simple coating procedure, together with the self‐assembled viscosity‐adjustable separation medium, should be useful to meet some of the essential requirements for developing single‐use disposable CE chips. Coating the channels with polymer blends of PMMA and the separation medium also showed promise.

Liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry: a highly sensitive method for the analysis of organic explosives

Gas chromatography/mass spectrometry (GC/MS) is applied to the analysis of volatile and thermally stable compounds, while liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) and liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) are preferred for the analysis of compounds with solution acid-base chemistry. Because organic explosives are compounds with low polarity and some of them are thermally labile, they have not been very well analyzed by GC/MS, LC/APCI-MS and LC/ESI-MS. Herein, we demonstrate liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry (LC/NI-APPI-MS) as a novel and highly sensitive method for their analysis. Using LC/NI-APPI-MS, limits of quantification (LOQs) of nitroaromatics and nitramines down to the middle pg range have been achieved in full MS scan mode, which are approximately one order to two orders magnitude lower than those previously reported using GC/MS or LC/APCI-MS. The calibration dynamic ranges achieved by LC/NI-APPI-MS are also wider than those using GC/MS and LC/APCI-MS. The reproducibility of LC/NI-APPI-MS is also very reliable, with the intraday and interday variabilities by coefficient of variation (CV) of 0.2-3.4% and 0.6-1.9% for 2,4,6-trinitrotoluene (2,4,6-TNT).

Fast DNA sequencing up to 1000 bases by capillary electrophoresis using poly(N,N‐dimethylacrylamide) as a separation medium

Poly(N,N‐dimethylacrylamide) (PDMA) with a molecular mass of 5.2×106 g/mol has been synthesized and used in DNA sequencing analysis by capillary electrophoresis (CE). A systematic investigation is presented on the effects of different separation conditions, such as injection amount, capillary inner diameter, polymer concentration, effective separation length, electric field and temperature, on the resolution. DNA sequencing up to 800 bases with a resolution (R) limit of 0.5 (and 1000 bases with a resolution limit of 0.3) and a migration time of 96 min was achieved by using 2.5% w/v polymer, 150 V/cm separation electric field, and 60 cm effective separation length at room temperature on a DNA sample prepared with FAM‐labeled – 21M13 forward primer on pGEM3Zf(+) and terminated with ddCTP. Ultrafast and fast DNA sequencing up to 420 and 590 bases (R≥0.5) were also achieved by using 3% w/v polymer and 40 cm effective separation length with a separation electric field of 525 and 300 V/cm, and a migration time of 12.5 and 31.5 min, respectively. PDMA has low viscosity, long shelf life and dynamic coating ability to the glass surface. The unique properties of PDMA make it a very good candidate as a separation medium for large‐scale DNA sequencing by capillary array electrophoresis (CAE).

DNA sequencing by capillary electrophoresis using copolymers of acrylamide andN,N-dimethyl-acrylamide

Copolymers of acrylamide (AM) and N,N‐dimethylacrylamide (DMA) with AM to DMA molar ratios of 3:1, 2:1 and 1:1 and molecular weights of about 2.2 MDa were synthesized. The polymers were tested as separation media in DNA sequencing analysis by capillary electrophoresis (CE). The dynamic coating ability of polydimethylacrylamide (PDMA) and the hydrophilicity of polyacrylamide (PAM) have been successfully combined in these random copolymers. A separation efficiency of over 10 million theoretical plates per meter has been reached by using the bare capillaries without the additional polymer coating step. Under optimized separation conditions for longer read length DNA sequencing, the separation ability of the copolymers decreased with decreasing AM to DMA molar ratio from 3:1, 2:1 and 1:1. In comparison with PAM, the copolymer with a 3:1 AM:DMA ratio showed a higher separation efficiency. By using a 2.5% w/v copolymer with 3:1 AM:DMA ratio, one base resolution of 0.55 up to 699 bases and 0.30 up to 963 bases have been achieved in about 80 min at ambient temperatures.