Isoprene levels in the exhaled breath of 200 healthy pupils within the age range 7–18 years studied using SIFT-MS

The published results of breath isoprene studies, to date largely involving adults, are briefly reviewed with special attention given to the work done on this topic during the last ten years using selected ion flow tube mass spectrometry, SIFT-MS. Then the new data recently obtained on isoprene levels in the exhaled breath of some 200 healthy children and young adults (pupils) with ages ranging from 7 to 18 years measured using SIFT-MS are presented in detail. A concentration distribution has been constructed from the data obtained and compared to those for healthy adults also obtained from SIFT-MS data. Although there is overlap between the two distributions, which are close to log normal in both cases, the median level for the young cohort is much lower at 37 parts-per-billion, pbb, geometric standard deviation, GSD 2.5, compared to that for the adult cohort of 106 ppb with a GSD of 1.65. Further to this, there is a clear increase in the mean breath isoprene concentration with age for the young cohort with a doubling of the level about every five to six years until it reaches the age-invariant mean level of that for adult cohort. Should this trend be extrapolated downwards in age it would indicate a near-zero breath isoprene in the newborn that was indicated by a previous study. Indeed, in this study isoprene was not detected on the breath of two young children. The results reveal mean breath isoprene levels (± SD) for pupils within the given age ranges as: 7 to 10 year (28±24 ppb) and 10 to 13 years (40±21 ppb), 13 to 16 years (60±41 ppb) and 16 to 19 years (54±31 ppb). The more rapid increase that occurs between the second and third age ranges is statistically highly significant (p=0.001) and we attribute this phenomenon to the onset of puberty and the spurt in growth that occurs during this phase of development. There is no significant difference in mean breath isoprene between males and females for both the adult cohort and the younger cohort

Product ion distributions for the reactions of NO+ with some physiologically significant volatile organosulfur and organoselenium compounds obtained using a selective reagent ionization time-of-flight mass spectrometer

RATIONALE: The reactions of NO(+) with volatile organic compounds (VOCs) in Selective Reagent Ionization Time-of-Flight Mass Spectrometry (SRI-TOF-MS) reactors are relatively poorly known, inhibiting their use for trace gas analysis. The rationale for this product ion distribution study was to identify the major product ions of the reactions of NO(+) ions with 13 organosulfur compounds and 2 organoselenium compounds in an SRI-TOF-MS instrument and thus to prepare the way for their analysis in exhaled breath, in skin emanations and in the headspace of urine, blood and cell and bacterial cultures. METHODS: Product ion distributions have been investigated by a SRI-TOF-MS instrument at an E/N in the drift tube reactor of 130 Td for both dry air and humid air (4.9% absolute humidity) used as the matrix gas. The investigated species were five monosulfides (dimethyl sulfide, ethyl methyl sulfide, methyl propyl sulfide, allyl methyl sulfide and methyl 5-methyl-2-furyl sulfide), dimethyl disulfide, dimethyl trisulfide, thiophene, 2-methylthiophene, 3-methylthiophene, methanethiol, allyl isothiocyanate, dimethyl sulfoxide, and two selenium compounds – dimethyl selenide and dimethyl diselenide. RESULTS: Charge transfer was seen to be the dominant reaction mechanism in all reactions under study forming the M(+) cations. For methanethiol and allyl isothiocyanate significant fractions were also observed of the stable adduct ions NO(+)M, formed by ion-molecule association, and [M–H](+) ions, formed by hydride ion transfer. Several other minor product channels are seen for most reactions indicating that the nascent excited intermediate (NOM)(+)* adduct ions partially fragment along other channels, most commonly by the elimination of neutral CH(3), CH(4) and/or C(2)H(4) species that are probably bound to an NO molecule. Humidity had little effect on the product ion distributions. CONCLUSIONS: The findings of this study are of particular importance for data interpretation in studies of volatile organosulfur and volatile organoselenium compounds employing SRI-TOF-MS in the NO(+) mode. © 2014 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd

Product ion distributions for the reactions of NO+ with some N-containing and O-containing heterocyclic compounds obtained using SRI-TOF-MS

AbstractProduct ion distributions for the reactions of NO+ with nine O-containing and six N-containing heterocyclic compounds present in human volatilome have been determined under the conditions of a Selective Reagent Ionization Time of Flight Mass Spectrometer (SRI-TOF-MS) at E/N values in the drift tube reactor ranging from 90 to 130Td. This study was undertaken to provide the kinetics data by which these heterocyclic compounds could be analyzed in biogenic media using SRI-TOF-MS. The specific heterocyclic compounds are furan, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran, 2-pentylfuran, 2,3-dihydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, γ-butyrolactone, pyrrole, 1-methylpyrrole, pyridine, 2,6-dimethylpyridine, pyrimidine, and 4-methylpyrimidine. Charge transfer was the dominant mechanism in the majority of these NO+ reactions generating the respective M+ parent cation, but in the pyridine, pyrimidine, and 4-methylpyrimidine reactions, stable NO+M adduct ions were the major products with M+ ions as minor products. The reactions of dioxolanes with NO+ proceeded by hydride ion transfer only producing (M−H)+ ions. Fragmentation of the excited nascent product ions (M+)* did not occur for the majority of these reactions under the particular chosen conditions of the SRI-TOF-MS reactor, but partial fragmentation did occur in the 2,3-dihydrofuran and 2-pentylfuran reactions. However, lowering of the E/N in the drift tube suppresses fragmentation of (M+)* ions and promotes the formation of NO+M adduct ions, whereas increasing E/N has the opposite effect, as expected. The product ion distributions were seen to be independent of the humidity of the sample gas

Product ion distributions for the reactions of NO+ with some physiologically significant aldehydes obtained using a SRI-TOF-MS instrument

AbstractProduct ion distributions for the reactions of NO+ with 22 aldehydes involved in human physiology have been determined under the prevailing conditions of a selective reagent ionization time of flight mass spectrometry (SRI-TOF-MS) at an E/N in the flow/drift tube reactor of 130 Td. The chosen aldehydes were fourteen alkanals (the C2–C11 n-alkanals, 2-methyl propanal, 2-methyl butanal, 3-methyl butanal, and 2-ethyl hexanal), six alkenals (2-propenal, 2-methyl 2-propenal, 2-butenal, 3-methyl 2-butenal, 2-methyl 2-butenal, and 2-undecenal), benzaldehyde, and furfural. The product ion fragmentations patterns were determined for both dry air and humid air (3.5% absolute humidity) used as the matrix buffer/carrier gas in the drift tube of the SRI-TOF-MS instrument. Hydride ion transfer was seen to be a common ionization mechanism in all these aldehydes, thus generating (M−H)+ ions. Small fractions of the adduct ion, NO+M, were also seen for some of the unsaturated alkenals, in particular 2-undecenal, and heterocyclic furfural for which the major reactive channel was non-dissociative charge transfer generating the M+ parent ion. Almost all of the reactions resulted in partial fragmentation of the aldehyde molecules generating hydrocarbon ions; specifically, the alkanal reactions resulted in multiple product ions, whereas, the alkenals reactions produced only two or three product ions, dissociation of the nascent excited product ion occurring preferentially at the 2-position. The findings of this study are of particular importance for data interpretation in studies of aldehydes reactions employing SRI-TOF-MS in the NO+ mode

Measuring transport of water across the peritoneal membrane

Measuring transport of water across the peritoneal membrane.IntroductionMechanisms of water flow across the peritoneal membrane include diffusion, convection, and reabsorption.Objectves. To understand these processes more clearly we have developed a method to measure transport of water across the peritoneal membrane.MethodsAn artificial gradient of deuterated water (HDO) between blood and dialysate compartments was created in five subjects who took 0.3g per kg of body weight of D2O, which was allowed to equilibrate with total body water. During a test dwell (2L, bicarbonate:lactate buffer, 1.36% glucose to minimize convection), frequent dialysate samples were drawn to determine the abundance of deuterium and other solutes and to calculate their time constants. Dialysate deuterium abundance was measured using flowing afterglow mass spectrometry (FA-MS). The method was combined with 125iodine-labeled albumin (RISA) to enable simultaneous estimates of intraperitoneal volume and thus calculation of the mass transfer area coefficient (MTAC) for small solutes using the Garred equation.ResultsThe appearance of HDO in dialysate in four subjects is described by a single exponential fit with residuals of <1%, similar to method precision. In a fifth subject, the resolution of this method demonstrated that the best fit was a double exponential. When compared to other solutes, the time constant for water was as predicted by its molecular weight, with a MTAC of 38.7 ± 4.4mL/min. Total body water could also be estimated from the equilibrated dialysate deuterium abundance, with repeat estimates within 0.5%.ConclusionTransport of water across the peritoneum can be measured with remarkable accuracy and when combined with an intraperitoneal volume estimation can be used to determine mass transfer. In conditions of low convection, the relative rate of deuterium appearance and mass transfer compared to other solutes suggests that water diffuses predominantly through the intercellular small pores