Continuous-flow isotope analysis of the deuterium/hydrogen ratio in atmospheric hydrogen

A convenient method is described for analyzing the deuterium/hydrogen (D/H) ratio of atmospheric molecular hydrogen (H(2)) based on mass spectrometric isotope-ratio monitoring. The method requires small amounts of air ( approximately 300 mL STP), is operated on-line, and comprises four steps: (1). the condensation of the air matrix at approximately 40 K; (2). the collection of the non-condensed components of the air sample (H(2), Ne, He, and traces of N(2)) in a 5 A molecular sieves pre-concentration trap at approximately 63 K; (3). gas chromatographic purification of H(2) in a flow of He; and (4) quantification of the D/H ratio in an isotope-ratio mass spectrometer. The precision of the determination of the D/H ratio is better than 2 per thousand, which is comparable to, or better than, that obtained by conventional duel-inlet off-line analysis. There are, however, discrepancies relative to the D/H ratios determined by conventional duel-inlet analysis. This is due to differences in peak shape between reference and sample air, depending on the amount of H(2) injected. Consequently, calibration runs are required. After the calibration of the system, we obtained an accuracy of 1.5 per thousand, so that the accumulated uncertainty is estimated to be less than 4 per thousand. The method also allows determination of the H(2) concentration, with an uncertainty estimated to be 2%.     

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

Past atmospheric composition can be reconstructed by the analysis of air enclosures in polar ice cores which archive ancient air in decadal to centennial resolution. Due to the different carbon isotopic signatures of different methane sources high-precision measurements of delta13CH4 in ice cores provide clues about the global methane cycle in the past. We developed a highly automated (continuous-flow) gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique for ice core samples of approximately 200 g. The methane is melt-extracted using a purge-and-trap method, then separated from the main air constituents, combusted and measured as CO2 by a conventional isotope ratio mass spectrometer. One CO2 working standard, one CH4 and two air reference gases are used to identify potential sources of isotope fractionation within the entire sample preparation process and to enhance the stability, reproducibility and accuracy of the measurement. After correction for gravitational fractionation, pre-industrial air samples from Greenland ice (1831 +/- 40 years) show a delta13C(VPDB) of -49.54 +/- 0.13 per thousand and Antarctic samples (1530 +/- 25 years) show a delta13C(VPDB) of -48.00 +/- 0.12 per thousand in good agreement with published data.     

Kinetics study of OH radical reactions with n-octane, n-nonane, and n-decane at 240-340 K using the relative rate/discharge flow/mass spectrometry technique

The kinetics of the reactions of hydroxyl radical with n-octane (k1), n-nonane (k2), and n-decane (k3) at 240-340 K and a total pressure of approximately 1 Torr has been studied using relative rate combined with discharge flow and mass spectrometer (RR/DF/MS) technique. The rate constant for these reactions was found to be positively dependent on temperature, with an Arrhenius expression of k1 = (2.27 +/- 0.21) x 10(-11)exp[(-296 +/- 27)/T], k2 = (4.35 +/- 0.49) x 10(-11)exp[(-411 +/- 32)/T], and k3 = (2.26 +/- 0.28) x 10(-11)exp[(-160 +/- 36)/T] cm3 molecule(-1) s(-1) (uncertainties taken as 2sigma), respectively. Our results are in good agreement with previous studies at and above room temperature using different techniques. Assuming that the reaction of alkane with hydroxyl radical is the predominant form for loss of these alkanes in the troposphere, the atmospheric lifetime for n-octane, n-nonane, and n-decane is estimated to be about 43, 35, and 28 h, respectively.     

Collection and storage of CO2 for 13C analysis: An application to separate soil CO2 efflux into root- and soil-derived components

Soil surface CO2 efflux is comprised of CO2 from (i) root respiration and rhizosphere microbes and (ii) heterotrophic respiration from the breakdown of soil organic matter (SOM). This efflux may be partitioned between these sources using delta13C measurements. To achieve this, continuous flow isotope ratio mass spectrometry can be used and, in conjunction with 10 mL septum-capped vials, large numbers of samples may be analysed using a Finnigan MAT Delta(plus)XP interfaced to a Gas Bench II. Here we describe a number of advances to facilitate such work, including: (i) a technique for monitoring mass spectrometer performance, (ii) improvements to sample storage, and (iii) a gas-handling system for incubating and sampling the CO2 derived from roots and soils. Mass spectrometer performance was monitored using an automated refillable vial. Compressed air analysed with this system had mean delta13C of -9.61 +/- 0.16 per thousand (+/- 1sigma, n = 28) collected over four runs. Heating the butyl rubber septa used to seal the vials at 105 degrees C for 12 h improved the sample storage. After air transportation over 12 days, the isotope composition of the CO2 at ambient concentrations was unchanged (before: -35.2 +/- 0.10 per thousand, n = 4; after: -35.3 +/- 0.10 per thousand, n = 15); without heat treatment of the septa the CO2 became slightly enriched (-35.0 +/- 0.14 per thousand, n = 15). The linearity of the Gas Bench II was found to decline above 8000 micromol CO2 mol(-1). To stay within a linear range and to allow the incubation of soil and root material we describe a gas-handling system based around a peristaltic pump. Finally, we demonstrate these methods by growing a C-4 grass (Guinea grass, Panicum maximum Jacq.) in a C-3 soil. Root respiration was found to contribute between 5 and 22% to the soil surface CO2 efflux. These methodologies will facilitate experiments aimed at measuring the isotopic composition of soil-derived CO2 across a range of ecological applications.     

Compound-specific stable carbon isotope ratios (delta13C values) of the halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1)

Compound-specific isotope analysis using gas chromatography interfaced to isotope ratio mass spectrometry (GC/IRMS) was applied for the determination of delta13C values of the marine halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1). The delta13C value of a lab-made Q1 standard (-34.20 +/- 0.27 per thousand) was depleted in 13C by more than 11 per thousand relative to the residues of Q1 in dolphin blubber from Australia and skua liver from Antarctica. This clarified that the synthesized Q1 was not the source for Q1 in the biota samples. However, two Australian marine mammals showed a large variation in the delta13C value, which, in our experience, was implausible. Since the GC/IRMS system was connected to a conventional ion trap mass spectrometer by a post-column splitter, we were able to closely inspect the peak purity of Q1 in the respective samples. While the mass spectra of Q1 did not indicate any impurity, a fronting peak of PCB 101 was identified in one sample. This interference falsified the delta13C value of the respective sample. Once this sample was excluded, we found that the delta13C values of the remaining samples, i.e. liver of Antarctic brown skua (-21.47 +/- 1.47 per thousand) and blubber of Australian melon-headed whale (-22.80 +/- 0.33 per thousand), were in the same order. The standard deviation for Q1 was larger in the skua samples than in the standard and the whale blubber sample. This was due to lower amounts of skua sample available. It remained unclear if the Q1 residues originate from the same producer and location.     

Kinetic studies of the reactions of O2(b 1sigma(g)+) with several atmospheric molecules

Thermal rate coefficients for the removal (reaction + quenching) of O2(1sigma(g)+) by collision with several atmospheric molecules were determined to be as follows: O3, k3(210-370 K) = (3.63 +/- 0.86) x 10(-11) exp((-115 +/- 66)/T); H2O, k4(250-370 K) = (4.52 +/- 2.14) x 10(-12) exp((89 +/- 210)/T); N2, k5(210-370 K) = (2.03 +/- 0.30) x 10(-15) exp((37 +/- 40)/T); CO2, k6(298 K) = (3.39 +/- 0.36) x 10(-13); CH4, k7(298 K) = (1.08 +/- 0.11) x 10(-13); CO, k8(298 K) = (3.74 +/- 0.87) x 10(-15); all units in cm3 molecule(-1) s(-1). O2(1sigma(g)+) was produced by directly exciting ground-state O2(3sigma(g)-) with a 762 nm pulsed dye laser. The reaction of O2(1sigma(g)+) with O3 was used to produce O(3P), and temporal profiles of O(3P) were measured using VUV atomic resonance fluorescence in the presence of the reactant to determine the rate coefficients for removal of O2(1sigma(g)+). Our results are compared with previous values, where available, and the overall trend in the O2(1sigma(g)+) removal rate coefficients and the atmospheric implications of these rate coefficients are discussed. Additionally, an upper limit for the branching ratio of O2(1sigma(g)+) + CO to give O(3P) + CO2 was determined to be < or = 0.2% and this reaction channel is shown to be of negligible importance in the atmosphere.     

亲和柱色谱原位酶切法纯化重金属镉结合的金属硫蛋白-3

按照人金属硫蛋白-3(hMT-3)的基因序列,选用大肠杆菌偏爱的密码子合成了全长hMT-3基因,并将其插入大肠杆菌融合表达质粒pALEX的多克隆位点中,在谷胱甘肽-硫-转移酶(GST)下游与GST融合表达。通过异丙基-β-D-硫代半乳糖苷(IPTG)诱导在大肠杆菌表达菌株BL21（DE3）LysS中表达了与重金属离子镉结合的融合蛋白GST-Cd2+-hMT-3。经十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)分析表明融合蛋白主要在超声上清液中。分别通过“先纯化、后酶切”和“亲和柱色谱原位酶切”两种方法纯化了Cd2+-hMT-3,比较了两种方法的纯化效率和得率,表明原位酶切法操作简便,较之“先纯化、后酶切”法减少了洗脱、透析、冻干等步骤,从而也减少了样品的损失,提高了样品的纯度和得率。从摇瓶培养菌液中纯化获得了结合有Cd2+的完整的人金属硫蛋白-3,得率为1.8%。氨基酸组成分析结果表明所获得的Cd2+-hMT-3不含芳香族氨基酸和组氨酸,符合金属硫蛋白的特征;直读电感耦合等离子体发射光谱分析其硫镉原子比为21∶(7.5±0.1),与理论值21∶7基本吻合。     

Formation of volatile organic compounds in the heterogeneous oxidation of condensed-phase organic films by gas-phase OH

The yield of volatile organic compounds (VOCs) from the heterogeneous oxidation of condensed-phase organic and hydrocarbon soot films by gas-phase OH has been studied in a coated-wall flow tube at room temperature. Simultaneously, OH concentrations are measured using a chemical-ionization mass spectrometer (CIMS) operated in negative ion mode and VOCs are measured using a commercial proton-transfer-reaction mass spectrometer (PTR-MS). It is observed that a variety of aldehydes/carbonyls and carboxylic acids are formed. Specifically, detailed experiments were conducted with stearic acid, where products are observed that contain as many as 13 carbon atoms with the average carbon number of the products between 3 and 5. The yield of VOCs, relative to the loss of OH radicals, is strongly dependent on the partial pressure of O2 in the carrier gas, ranging from 0.08 +/- 0.03 in a nominally pure He carrier gas to 0.34 +/- 0.14 in 6 Torr of pure O2. Yields from other organics are somewhat lower than those from stearic acid, ranging in conditions of pure O2 from 0.10 +/- 0.04 for BES (bis(ethylhexyl)sebacate), to 0.03 +/- 0.01 for n-hexane soot, to 0.01 +/- 0.005 for pyrene. Under atmospheric conditions, OH oxidation of select organics may be an efficient source of small VOCs. In particular, formic acid is formed in significant yield from all the surfaces.     

On-line measurements of 13C enrichments in rat breath. Non-invasive method for in vivo study of drug enzymatic induction

A differential kinetic study of 13CO2 enrichment of breath after the intake of specific 13C-labelled substrates and co-administration of a drug allows the drug's ability for enzyme induction to be evaluated in vivo. A method and a gas chromatograph-isotope ratio mass spectrometer device for on-line measurements of 13CO2 enrichment in the breath of small animals are described. This system allows on-line breath sample collection from a metabolic cage, purification by gas chromatography, determination of CO2 by thermal conductivity detection and measurement of 13CO2 enrichment by isotope ratio mass spectrometry. Two protocols for phenobarbital-inducible P450 and 3-methylcholanthrene-inducible P1-450 isoenzymes are described.     

Development and validation of bioanalytical methods for imidafenacin (KRP-197/ONO-8025) and its metabolites in human urine by using liquid chromatography-tandem mass spectrometry

New bioanalytical methods have been developed for the determination of imidafenacin (KRP-197/ONO-8025, IM), a novel antimuscarinic drug developed for the treatment of overactive bladder, and its metabolites, M-2, M-3, M-4, M-6 and M-8 (method 1), M-5 and M-9 (method 2) in human urine by using liquid chromatography-tandem mass spectrometry. In each method, the urine sample was extracted by solid-phase extraction, separated on a semi-micro high-performance liquid chromatography column using gradient elution and detected by tandem mass spectrometer with an atmospheric pressure chemical ionization or ionspray interface. Extraction recoveries of IM and metabolites were 81.4% or more. Calibration curves had good linearity in the concentration ranges 0.2-50 ng/mL for IM, M-2, M-3, M-4, M-6 and M-8 (method 1) and 1-250 ng/mL for M-5 and M-9 (method 2), respectively. The accuracy and precision in the intra-day and inter-day reproducibility tests were within +/-17.0 and 16.1% at the lowest concentrations, and within +/-12.8 and 11.1% at higher concentrations, respectively. Using these analytical methods, excretion profiles of IM and its metabolites in human urine were successfully determined after oral administration of IM at the therapeutic dosage of 0.1 mg.     

Effects of relative humidity and CO(g) on the O3-initiated oxidation reaction of Hg0(g): kinetic & product studies

Ozone is assumed to be the predominant tropospheric oxidant of gaseous elemental mercury (Hg0(g)), defining mercury global atmospheric lifetime. In this study we have examined the effects of two atmospherically relevant polar compounds, H2O(g) and CO(g), on the absolute rate coefficient of the O3-initiated oxidation of Hg0(g), at 296 +/- 2 K using gas chromatography coupled to mass spectrometry (GC-MS). In CO-added experiments, we observed a significant increase in the reaction rate that could be explained by pure gas-phase chemistry. In contrast, we found the apparent rate constant, k(net), varied with the surface-to-volume ratio (0.6 to 5.5 L flasks) in water-added experiments. We have observed small increases in k(net) for nonzero relative humidity, RH < 100%, but substantial increase at RH > or = 100%. Product studies were performed using mass spectrometry and high resolution transmission electron microscopy coupled to an electron dispersive spectrometer (HRTEM-EDS). Our results give evidence for enhanced chain growth of HgO(s) on a carbon grid at RH = 50%. A water/surface/ozone independent ozone oxidation rate is estimated to be (6.2 +/- (1.1; tsigma/ radicaln) x 10(-19) cm3 molecule(-1) s(-1). The total uncertainty associated with the ensemble of experiments amount to approximately < or = 20%. The atmospheric implications of our results and the effect of an added reaction partner in homogeneous and heterogeneous atmospheric chemistry will be discussed.     

Determination of vitamin K1 in medical foods by liquid chromatography with postcolumn reduction and fluorometric detection

A liquid chromatographic (LC) method is described for the determination of vitamin K1 in medical foods. The sample is enzymatically digested with lipase and alpha-amylase and extracted with 1% sodium bicarbonate solution-isopropanol (1 + 1). After C18 solid-phase extraction, vitamin K1 is separated by nonaqueous reversed-phase LC, converted to the hydroquinone by postcolumn zinc reduction, and quantitated by fluorescence detection. The limit of detection is 8 pg (3 sigma), and the limit of quantitation is 27 pg (10 sigma) on column. Linear response ranged from 0.1 to 1.0 ng vitamin K1 (r= 0.9999). The mean recovery (n = 38) for all spiking levels was 101.6 +/- 2.85%. Analysis of Standard Reference Material 1846, Infant Formula, gave a mean value of 0.95 +/- 0.088 mg vitamin K/kg (K or K1?) (n = 31) with a coefficient of variation of 9.26.     

基质与分析物的摩尔比和激光能量对分析物离子信号的影响

A method of aerosol introduction for matrix-assisted laser desorption/ionization (MALDI) is described. The aerosol particles containing matrix and analyte enter directly into the aerosol time-of-flight mass spectrometer (ATOFMS) at atmospheric pressure. The scattered light signals from the aerosol particles are collected by a photomultiplier tube (PMT) and are passed on to an external electronic timing circuit, which determines particle size and is used to trigger a 266 nm pulsed Nd:YAG laser. The aerosol MALDI mass spectra and aerodynamic diameter of single particles can be obtained in real-time. Compared with other methods of liquid sample introduction, this method realizes detection of single particles and, more importantly, the sample consumption is lower. The effects of matrix-to-analyte ratio and laser pulse energy on analyte ion yield are examined. The optimal matrix-to-analyte ratio and laser energy are 50-110:1 and 200-400 μJ respectively.     

A fully automated method for accurate mass determination using high-performance liquid chromatography with a quadrupole/orthogonal acceleration time-of-flight mass spectrometer

A generic LC/ESI(+)-oaTOFMS method has been developed for routine automated high accuracy mass determinations of different classes of substances. The system makes use of micro-high-performance liquid chromatography and a hybrid quadrupole/orthogonal acceleration time-of-flight (Q-oaTOF) mass spectrometer. Reproducible and accurate mass measurements were obtained using an electrospray dual sprayer with reserpine as reference compound, introduced into the mass spectrometer alternating with the samples. Experiments were performed to optimize analyte/reference response ratio, statistical algorithm correction setting, and analyte concentration. In these experiments, a clear dependence of the mass measurement error on the analyte/reference response ratio was observed. The dependence of average mass error versus different dead time correction algorithm settings (Np factors) was also explored. In the final automated procedure, verified for a statistically significant set of compounds ( approximately 550) obtained from a medicinal chemistry department, about 70% of the analyzed samples satisfied the acceptance criteria fixed at a maximum error of +/-5 ppm (mass range 150-800 Da).     

Stable carbon and oxygen isotopic determination of sub-microgram quantities of CaCO3 to analyze individual foraminiferal shells

We have developed an analytical system to determine stable isotopic compositions (delta13C and delta18O) of sub-microgram quantities of CaCO3 for the purpose of analyzing individual foraminiferal shells, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The system consists of a micro-volume CaCO3 decomposition tube, stainless steel CO2 purification vacuum line with a quantity-regulating unit, helium-purged CO2 purification line, gas chromatograph, and a CF-IRMS system. By using this system, we can determine stable carbon and oxygen isotopic compositions as low as 0.2 microg of CaCO3, with standard deviations of +/-0.10 per thousand for delta13C and +/-0.18 per thousand for delta18O within a 4-h reaction time and 30-min analysis period.     

快速测量挥发性有机物的膜进样-飞行时间质谱仪的设计和应用

研制了一种膜进样-微型飞行时间质谱仪, 该仪器使用双层50 μm硅橡胶膜作为大气压下直接进样的接口. 实验结果表明, 随着样品流速的提高, 膜富集效率信号强度呈线性提高. 双膜中间具有真空差分系统, 富集得到的样品被迅速抽走, 进样系统中样品无记忆效应. 样品在膜中的响应时间为100 s, 而打开差分系统后仅需10 s信号即下降为平稳状态. 与毛细管直接进样相比, 双层膜的富集作用显著, 在相同的实验条件下使用膜进样技术测定10×10-6 (体积分数)苯、甲苯和对二甲苯的信号强度分别提高了280, 370和600倍. 膜进样系统与真空紫外光软电离方式联用, 对于苯的检出限已经达到了25×10-9 (体积分数), 线性范围为3个数量级. 由于采用了软电离方法, 无碎片离子产生, 所以能够根据分子量进行快速定性分析. 将该仪器应用于香烟主烟气中可挥发性有机物的在线分析, 得到50多种可挥发性的有机物. 实验结果表明, 膜进样-飞行时间质谱将在在线分析(特别是环境监测)方面具有广泛的应用空间.     

A new method for determining delta13C and deltaD simultaneously for CH4 by gas chromatography/continuous-flow isotope-ratio mass spectrometry

A continuous-flow technique has been developed to analyse the deltaD and delta(13)C values for CH(4) from gas samples, in a single run. This is achieved by splitting the sample gas stream and directing the streams simultaneously through a CuNiPt combustion reactor and an alumina pyrolysis reactor. The CO(2) from CH(4) combustion is trapped in a liquid nitrogen trap while the H(2) exiting the pyrolysis reactor is directed to the mass spectrometer for deltaD(CH4) determination. The CO(2) is then sublimed and directed to the mass spectrometer for delta(13)C(CH4) determination. Sample runs take approximately 10 minutes. This technique gives accurate delta(13)C(CH4) results to within +/-0.3-0.5 per thousand and deltaD(CH4) results to within +/-2-5 per thousand. Injection volumes between 0.5 and 2.5 microL of CH(4), equivalent to between 20 and 100 nmol CH(4), are required for accurate delta(13)C and deltaD analyses, respectively, using sample injection into a split flow with a split ratio of 10. This method provides rapid, accurate and reproducible results on multiple sample runs and is, therefore, an ideal method for analysing natural gas samples from a variety of sources.     

Methods to reduce interference effects in thermal conversion elemental analyzer/continuous flow isotope ratio mass spectrometry delta18O measurements of nitrogen-containing compounds

On-line determination of the oxygen isotopic composition (delta(18)O value) in organic and inorganic samples is commonly performed using a thermal conversion elemental analyzer (TC-EA) linked to a continuous flow isotope ratio mass spectrometry (IRMS) system. Accurate delta(18)O analysis of N-containing compounds (like nitrates) by TC-EA-IRMS may be complicated because of interference of the N(2) peak on the m/z 30 signal of the CO peak. In this study we evaluated the effectiveness of two methods to overcome this interference which do not require any hardware modifications of standard TC-EA-IRMS systems. These methods were (1) reducing the amount of N(2) introduced into the ion source through He dilution of the N(2) peak and (2) an improved background correction on the CO m/z 30 sample peak integration.Our results show that He dilution is as effective as diverting the N(2) peak in order to eliminate this interference. We conclude that the He-dilution technique is a viable method for the delta(18)O analysis of nitrates and other N-containing samples (which are not routinely measured using He dilution) using TC-EA-IRMS, since it can easily be programmed in the standard software of IRMS systems. With the He-dilution technique delta(18)O values of the nitrate isotope standards USGS34, IAEA-N3 and USGS35 were measured using the shortest possible traceability chain to the VSMOW-SLAP scale, and the results were -28.1 +/- 0.1 per thousand, +25.5 +/- 0.1 per thousand and +57.5 +/- 0.2 per thousand, respectively. An improved background correction was also an effective method, but required manual correction of the raw data.     

Stable hydrogen isotopic analysis of nanomolar molecular hydrogen by automatic multi-step gas chromatographic separation

We have developed a new automated analytical system that employs a continuous flow isotope ratio mass spectrometer to determine the stable hydrogen isotopic composition (δD) of nanomolar quantities of molecular hydrogen (H₂) in an air sample. This method improves previous methods to attain simpler and lower‐cost analyses, especially by avoiding the use of expensive or special devices, such as a Toepler pump, a cryogenic refrigerator, and a special evacuation system to keep the temperature of a coolant under reduced pressure. Instead, the system allows H₂ purification from the air matrix via automatic multi‐step gas chromatographic separation using the coolants of both liquid nitrogen (77 K) and liquid nitrogen + ethanol (158 K) under 1 atm pressure. The analytical precision of the δD determination using the developed method was better than 4‰ for >5 nmol injections (250 mL STP for 500 ppbv air sample) and better than 15‰ for 1 nmol injections, regardless of the δD value, within 1 h for one sample analysis. Using the developed system, the δD values of H₂ can be quantified for atmospheric samples as well as samples of representative sources and sinks including those containing small quantities of H₂, such as H₂ in soil pores or aqueous environments, for which there is currently little δD data available. As an example of such trace H₂ analyses, we report here the isotope fractionations during H₂ uptake by soils in a static chamber. The δD values of H₂ in these H₂‐depleted environments can be useful in constraining the budgets of atmospheric H₂ by applying an isotope mass balance model. Copyright © 2011 John Wiley & Sons, Ltd.     

High resolution infrared spectra of a carbon dioxide molecule solvated with helium atoms

Infrared spectra of He(N)-CO(2) clusters with N up to about 20 have been studied in the region of the CO(2) nu(3) fundamental band ( approximately 2350 cm(-1)) using a tunable diode laser spectrometer and pulsed supersonic jet source with cooled (>-150 degrees C) pinhole or slit nozzles and high backing pressures (<40 atm). Compared to previous studies of He(N)-OCS and -N(2)O clusters, the higher symmetry of CO(2) results in simpler spectra but less information content. Discrete rotation-vibration transitions have been assigned for N=3-17, and their analysis yields the variation of the vibrational band origin and B rotational constant over this size range. The band origin variation is similar to He(N)-OCS, with an initial blueshift up to N=5, followed by a monotonic redshift, consistent with a model where the first five He atoms fill a ring around the equator of the molecule, forcing subsequent He atom density to locate closer to the ends. The B value initially drops as expected for a normal molecule, reaching a minimum for N=5. Its subsequent rise for N=6 to 11 can be interpreted as the transition from a normal (though floppy) molecule to a quantum solvation regime, where the CO(2) molecule starts to rotate separately from the He atoms. For N>13, the B value becomes approximately constant with a value about 17% larger than that measured in much larger helium nanodroplets.