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PubMed2002

Optimization of artificial neural networks used for retention modelling in ion chromatography.

The aim of this work is the development of an artificial neural network model, which can be generalized and used in a variety of applications for retention modelling in ion chromatography. Influences of eluent flow-rate and concentration of eluent anion (OH-) on separation of seven inorganic anions (fluoride, chloride, nitrite, sulfate, bromide, nitrate, and phosphate) were investigated. Parallel prediction of retention times of seven inorganic anions by using one artificial neural network was applied. MATLAB Neural Networks ToolBox was not adequate for application to retention modelling in this particular case. Therefore the authors adopted it for retention modelling by programming in MATLAB metalanguage. The following routines were written; the division of experimental data set on training and test set; selection of data for training and test set; Dixon's outlier test; retraining procedure routine; calculations of relative error. A three-layer feed forward neural network trained with a Levenberg-Marquardt batch error back propagation algorithm has been used to model ion chromatographic retention mechanisms. The advantage of applied batch training methodology is the significant increase in speed of calculation of algorithms in comparison with delta rule training methodology. The technique of experimental data selection for training set was used allowing improvement of artificial neural network prediction power. Experimental design space was divided into 8-32 subspaces depending on number of experimental data points used for training set. The number of hidden layer nodes, the number of iteration steps and the number of experimental data points used for training set were optimized. This study presents the very fast (300 iteration steps) and very accurate (relative error of 0.88%) retention model, obtained by using a small amount of experimental data (16 experimental data points in training set). This indicates that the method of choice for retention modelling in ion chromatography is the artificial neural network.

Chromatography, Liquid↗

PubMed2002

Structure-retention diagrams of ceramides established for their identification.

Molecular species analysis of ceramides was carried out using porous graphitic carbon with gradient elution: chloroform-methanol from 45:55 to 85:15 with a slope at 2.7%/min. These conditions gave a linear relationship between retention data and structure of ceramides. It was demonstrated that linearity occurred when a high slope value of linear gradient elution was used. Thereby the linear diagram was evolved by plotting the adjusted retention time against the total number of carbon atoms of ceramide molecules. Each line represents one ceramide class. Such a Structure-Retention Diagram describes ceramide retention and thus constitutes an identification method using only retention data. This Structure-Retention Diagram was assessed and compared to another obtained from octadesyl-grafted silica in terms of their reproducibility, precision and ability to provide ceramide identification. Better identification was obtained using the results from both Structure-Retention Diagrams. This approach with a two-dimensional separation system allowed to take advantage of the specificity of both identification models.

Ceramides↗

PubMed2003

Retention mechanism of poly(ethylene oxide) in reversed-phase and normal-phase liquid chromatography.

The retention behavior of low- and high-molecular-mass poly(ethylene oxide) (PEO) in reversed-phase (RP) and normal-phase (NP) liquid chromatography was investigated. In RPLC using a C18 bonded silica stationary phase and an acetonitrile-water mixture mobile phase, the sorption process of PEO to the stationary phase showed deltaH(o) > 0 and deltaS(o) > 0. Therefore, PEO retention in RPLC separation is an energetically unfavorable, entropy-driven process, which results in an increase of PEO retention as the temperature increases. In addition, at the enthalpy-entropy compensation point the elution volume of PEO was very different from the column void volume. These observations are quite different from the RPLC retention behavior of many organic polymers. The peculiar retention behavior of PEO in RPLC separation can be understood in terms of the hydrophobic interaction of this class of typical amphiphilic compounds with the non-polar stationary phase, on the one hand, and with the aqueous mobile phase, on the other. The entropy gain due to the release of the solvated water molecules from the PEO chain and the stationary phase is believed to be responsible for the entropy-driven separation process. On the other hand, in NPLC using an amino-bonded silica stationary phase and an acetonitrile-water mixture mobile phase, PEO showed normal enthalpy-driven retention behavior: deltaH(o) < 0 and deltaS(o) < 0, with the retention decreasing with increasing temperature and PEO eluting near the column void volume at the enthalpy-entropy compensation point. Therefore, high-resolution temperature gradient NPLC separation of high-molecular-mass PEO samples can be achieved with relative ease. The molecular mass distribution of high-molecular-mass PEO was found to be much narrower than that measured by size-exclusion chromatography.

Chromatography, Liquid↗

PubMed1997

Description and prediction of retention in normal-phase high-performance liquid chromatography with binary and ternary mobile phase.

The suitabilities of several earlier reported models for description and prediction of retention in normal-phase systems with mobile phases comprised of two organic solvents-a polar and a non-polar one-were tested on the chromatographic behaviour of phenylurea herbicides and alkyl-, aryl- and nitrophenols as sample solutes with a silica-gel column and 2-propanol, n-heptane and dioxane as mobile phase components. With few exceptions, the data obtained from the best-fit three-parameter retention equation differ from the experimental capacity factors at less than 0.1, or 2%, and for most compounds the fit is better than 1%. Of the two two-parameter equations derived from theoretical models, one failed to describe the retention behaviour. The fit of the other two-parameter equation to the retention data of phenols is slightly inferior than with the three-parameter equation. The differences between the fitted data and the experimental capacity factors of substituted phenylureas were < or = 0.2, or 5%. Three-parameter equations were suggested to describe the retention behaviour in three-component mobile phases either at a constant sum or at a constant ratio of the two stronger solvents in ternary mobile phases. To fit the three-component data at any combination of concentrations of the three solvents with the error comparable to that in binary mobile phases, a nine-parameter equation is necessary. Suitability of these equations to describe the experimental behaviour of substituted phenylureas and phenols was verified in ternary mobile phases with various concentrations of 2-propanol, dioxane and n-heptane. Finally, a method was suggested for the prediction of retention in ternary mobile phases with varying concentration ratios of the two polar solvents from the parameters of best-fit equations in binary mobile phases and a single experimental capacity factor in a ternary mobile phase. For most capacity factors, the error of prediction was lower than 0.2, or 5%. Dried solvents were used to improve the reproducibility of the results and the temperature was controlled to +/-0.1 degree C in all experiments. With these precautions, differences between the original retention volumes and the data from repeated experiments measured after ten months of use of the column in the system tested were less than 0.2 ml for 85% of the values compared.

1-Propanol↗

PubMed1999

Critical comparison of retention models for the optimisation of the separation of anions in ion chromatography. II. Suppressed anion chromatography using carbonate eluents.

Seven theoretical retention models, namely the linear solvent strength model (using the dominant equilibrium approach and competing ion effective charge approach), the dual eluent species model, the Kuwamoto model, the extended dual eluent species model, the multiple species eluent/analyte model and the empirical end-points model, were used to describe the retention behaviour of anions in suppressed ion chromatography (IC). An extensive set of experimental retention data was gathered for 24 anions (fluoride, formate, bromate, chloride, hexanesulfonate, bromide, chlorate, nitrate, iodide, thiocyanate, perchlorate, sulfite, succinate, sulfate, tartrate, selenate, oxalate, tungstate, phthalate, molybdate, chromate, thiosulfate and phosphate) on a Dionex AS4A-SC column using carbonate eluents of varying concentration and HCO3-:CO3(2-) ratios. Statistical comparison of the predicted and experimentally obtained retention factors showed that the performance of the theoretical models improved with the complexity of the model. However the empirical model (in which a linear relationship is assumed between the logarithm of retention factor and the logarithm of eluent strength, but the slope is determined empirically) gave the most consistent performance across the widest range of anions. The empirical end-points model was also shown to be the most satisfactory model due to its low knowledge requirements and easy solution. Compared with non-suppressed IC (see Part I), the retention behaviour in suppressed IC was found to be easier to model by all retention models.

Anions↗

PubMed1999

Reversed-phase high-performance liquid chromatography of ionogenic compounds: comparison of retention models.

Two kinds of retention models describing a behaviour of ionogenic substances in reversed-phase chromatographic systems were compared. Model A utilises a concept of limiting retention factors and is especially suitable for the prediction of retention of compounds co-existing in several forms in mobile phase. An effect of the concentration of organic modifier (e.g., methanol) on the magnitudes of the limiting retention factors and equilibrium constants (dissociation constants of the separated substances) can be expressed with the aid of various, more or less sophisticated, relationships. A stoichiometric displacement model (model B) in its original form simply relates the analyte retention to the content of organic modifier in the mobile phase. In this work, it was modified to also express an effect of the mobile phase pH introducing side equilibria (acid-base) into the model. Both models predict a sigmoidal dependence of the analyte retention factor on the mobile phase pH in accordance with experimental data, and allow, among others, to estimate dissociation constants from those data. Experimental dependencies between the analyte retention and the concentration of methanol in the mobile phase comply well with model A, whereas the stoichiometric displacement model could be used only in a limited range of the methanol concentrations.

Acids↗

PubMed1981

Radionuclide cystography: the significance of retention time of the refluxed radioisotope.

We studied 36 patients with vesicoureteral reflux into 45 renal units by means of isotope cystography and a dynamic renal function scan performed 24 to 48 hours after the cystography. Functional impairment was found in 21 renal units. To evaluate the significance of the time between voiding and complete disappearance of the radioisotope that refluxed from the kidney (retention time) the presence of the labeled particles in the kidney was followed continuously and intermittently during a prolonged interval. There was a significant difference between the retention time found in the impaired kidneys and that in the normally functioning kidneys. In 91.7 per cent of the normally functioning kidneys retention time was less than 5 minutes, whereas in 86 per cent of the impaired kidneys it was more than 10 minutes and in 56 per cent it was more than 20 minutes. No significant correlation was found between the retention time and intrarenal reflux or dilatation of the collecting system (patients classified as having radiological grades III and IV reflux were not included in this study). A retention time greater than 10 minutes may be correlated with decreased renal function. The retention of technetium sulfur colloid particles may be analogous to the retention of similar size bacteria and suggests a possible pathophysiologic explanation for the development of renal dysfunction owing to the prolonged presence of bacteria in the kidney after reflux.

Adolescent↗

PubMed2003

Clay particle retention in small constructed wetlands.

Constructed wetlands (CWs) can be used to mitigate non-point source pollution from arable fields. Previous investigations have shown that the relative soil particle retention in small CWs increases when hydraulic load increases. This paper investigates why this phenomenon occurs, even though common retention models predict the opposite, by studying clay and silt particle retention in two Norwegian CWs. Retention was measured with water flow proportional sampling systems in the inlet and outlet of the wetlands, and the texture of the suspended solids was analyzed. The surface area of the CWs was small compared to the watershed area (approximately 0.07%), giving high average hydraulic loads (1.1 and 2.0 md(-1)). One of the watersheds included only old arable land, whereas the other included areas with disturbed topsoil after artificial land leveling. Clay particle retention was 57% for the CW in the first watershed, and 22% for the CW in the disturbed watershed. The different behavior of the wetlands could be due to differences in aggregate size and stability of the particles entering the wetlands. Results showed that increased hydraulic loads did affect CW retention negatively. However, as runoff increased, soil particles/aggregates with higher sedimentation velocities entered the CWs (e.g., the clay particles behaved as silt particles). Hence, clay particle settling velocity is not constant as assumed in many prediction models. The net result was increased retention.

Aluminum Silicates↗

PubMed2000

Incidence risk and clinical features of retention of foetal membranes in ewes in 28 flocks in southern Greece.

In a field investigation of 28 flocks in southern Greece, 7660 lambings were monitored. Retention of foetal membranes (defined as failure to expel the foetal membranes within 6 h of lambing the last lamb) was recorded in 92 ewes. The median within-flock incidence risk was 1.25% (range: 0-1.9%). The heterogeneity of the risk among flocks was not significant (p = 0.99); no correlation was found between the incidence risk and the flock size (r(sp) = 0.33, p = 0.09). Overall, the median duration of retention was 72 h (range: 9-288 h); it did not differ among flocks (p = 0.89) and was not correlated with flock size (r(sp) = 0.24, p = 0.27). During the initial stage of retention the membranes were fleshy and humid; the cotyledons were thick and congested. Progressively, the membranes became thin, dry and stringy; the cotyledons shrunk and were pale. Finally the membranes dropped as a mass. In ewes with retention for >12 h, a variety of accompanying signs was recorded: straining (in 22% of the ewes with retention), vulval oedema and reddening (in 16%), anorexia (in 13%), recumbency (in 13%) and increased temperature (in 12%) were the most frequent ones. Overall, the median clinical score of the disorder was '2' (range: '1'-'5'); it did not differ among flocks (p = 0.98) and was not correlated with flock size (r(sp) = 0.26, p = 0.25). In 4% of the ewes with retention for <4 days accompanying signs were recorded (median clinical score: '2'), whilst in 80% of the ewes with retention for > or =4 days accompanying signs were recorded (median clinical score: '3'). This difference in the prevalence of clinical signs was significant (p < 0.0001).

Animal Husbandry↗

PubMed1998

Toward a perspective on orthodontic retention?

Retention is one of the most difficult challenges facing the clinician in orthodontics. In this article we collate current knowledge regarding the origin of orthodontic relapse and attempt to rationalize the necessary factors in planning orthodontic retention. Despite extensive research, the various elements leading to relapse of treated malocclusions are incompletely understood, giving rise to wide variation in retention protocols among clinicians. Informed consent-with emphasis on the features of the original malocclusion and the patient's growth pattern, the type of treatment performed, the need for adjunctive surgical procedures, the type of retainer, and the duration of retention-should be obtained during the planning of the retention phase. True perspective on orthodontic retention is lacking and there is a great need for further research to ensure that evidence-based clinical practice is adopted in retention strategies.

Adolescent↗

PubMed2002

Recovery of resources for advanced life support space applications: effect of retention time on biodegradation of two crop residues in a fed-batch, continuous stirred tank reactor.

Bioreactor retention time is a key process variable that will influence costs that are relevant to long distance space travel or long duration space habitation. However. little is known about the effects of this parameter on the microbiological treatment options that are being proposed for Advanced Life Support (ALS) systems. Two bioreactor studies were designed to examine this variable. In the first one, six retention times ranging from 1.3 to 21.3 days--were run in duplicate, 81 working-volume continuous stirred tank reactors (CSTR) that were fed ALS wheat residues. Ash-free dry weight loss, carbon mineralization, soluble TOC reduction, changes in fiber content (cellulose, hemicellulose, and lignin), bacterial numbers, and mineral recoveries were monitored. At short retention times--1.33 days--biodegradation was poor (total: 16-20%, cellulose - 12%, hemicellulose - 28%) but soluble TOC was decreased by 75-80% and recovery of major crop inorganic nutrients was adequate, except for phosphorus. A high proportion of the total bacteria (ca. 83%) was actively respiring. At the longest retention time tested, 21.3 days, biodegradation was good (total: 55-60%, cellulose ca. 70%, hemicellulose - ca. 55%) and soluble TOC was decreased by 80%. Recovery of major nutrients, except phosphorus, remained adequate. A very low proportion of total bacteria was actively respiring (ca. 16%). The second bioreactor study used potato residue to determine if even shorter retention times could be used (range 0.25-2.0 days). Although overall biodegradation deteriorated, the degradation of soluble TOC continued to be ca. 75%. We conclude that if the goal of ALS bioprocessing is maximal degradation of crop residues, including cellulose, then retention times of 10 days or longer will be needed. If the goal is to provide inorganic nutrients with the smallest volume/weight bioreactor possible, then a retention time of 1 day (or less) is sufficient.

Aerobiosis↗

PubMed1997

Combined videomanometric identification of abnormalities related to pharyngeal retention.

RATIONALE AND OBJECTIVES: The authors determined the usefulness of performing videoradiography and pharyngeal solid-state manometry during barium swallow in dysphagic patients with pharyngeal retention. METHODS: Results were retrospectively analyzed of simultaneous videoradiography and manometry examinations in 14 patients with retention of barium in the pharynx. Twelve age-matched patients without retention served as a control group. RESULTS: Patients with retention regularly had less opening of the upper esophageal sphincter than patients without retention (7.6 vs 10.3 mm, respectively; P = .003). In patients with retention, the laryngeal elevation was lower (17.1 vs 23.8 mm, respectively; P = .001), and the resting pressure of the upper esophageal sphincter was significantly lower (42.4 vs 54.0 mm Hg, respectively; P = .04). The duration of upper esophageal sphincter relaxation was also shorter in patients with retention (374 vs 603 msec, respectively; P = .003). The peak pharyngeal contraction pressure was not significantly different. CONCLUSION: The constrictors play a minor role in the conveyance of the bolus through the pharynx. Pharyngeal shortening could be the most important mechanism in bolus transport.

Adult↗

PubMed2005

Do intracellular, extracellular or urinary magnesium concentrations predict renal retention of magnesium in critically ill patients?

BACKGROUND AND OBJECTIVE: Magnesium disorders are common in hospitalized patients. In patients with low or normal magnesium, the intravenous magnesium loading test has been demonstrated to be a sensitive test to assess magnesium deficiency in critically ill patients. However, it is more time consuming and more difficult than the measurement of intracellular or extracellular magnesium concentrations. This study evaluated whether erythrocyte, plasma and urinary magnesium concentrations predict renal magnesium retention measured by th magnesium loading test. METHODS: One-hundred-and-three intensive care patients (36 females, 67 males) in a tertiary care centre and 41 healthy subjects (13 females, 28 males) took part in this prospective study. Intracellular, total plasma, ionize extracellular and urinary magnesium concentrations were measured and also magnesium retention by intravenous magnesium loading test. RESULTS: Total plasma magnesium concentration was poorly correlated with magnesium retention (r = 0.36 r2 = 0.13) and was the only parameter that significantly predicted magnesium retention in intensive care patients (P < 0.01). However, only 10% of the magnesium retention data were linked to the total plasma magnesium concentration. CONCLUSIONS: Total plasma magnesium concentration predicts magnesium retention in critically ill intensive care patients but not intracellular and urinary magnesium concentrations. Only a small proportion of the magnesium retention was due to the total plasma magnesium concentration.

Critical Care↗

PubMed1992

Temperature dependence of retention in reversed-phase liquid chromatography. 1. Stationary-phase considerations.

The retention mechanism in reversed-phase liquid chromatography (RPLC) has been investigated by examining the temperature dependence of retention, with emphasis on the role of the stationary phase in the retention process. Both chromatographic temperature studies and differential scanning calorimetry were used to examine the role of alkyl chain bonding density on the retention mechanism in RPLC. Phase transitions of reversed-phase stationary phases were observed at bonding densities greater than 2.84 mumol/m2. Thermodynamic constants for the transfer of a solute from the mobile phase to the stationary phase (delta H degrees and delta S degrees) were calculated for low bonding density columns, and comparison of these values to previously reported values for the partitioning of a nonpolar solute from the bulk organic liquid to water indicated that the chromatographic retention process is not well-modeled by bulk-phase oil-water partitioning processes. In addition, this data showed that the entropic contribution to retention becomes more significant with respect to the enthalpic contribution as the stationary-phase bonding density is increased, providing additional support that partitioning, rather than adsorption, is the relevant model of retention.

Chromatography, High Pressure Liquid↗

PubMed2002

Simulation and optimization of retention in ion chromatography using virtual column 2 software.

A new software package, Virtual Column 2, is described for the simulation and optimization of the separation of inorganic anions by ion chromatography (IC). The software uses a limited amount of experimental retention data acquired according to a correct experimental design to predict retention times for analytes over a designated search area of eluent compositions. The experimental retention data are used to solve a new retention model, called the linear solvent strength model, empirical approach (LSSM-EA), which then enables prediction of retention times for all eluent compositions in the search area. The theoretical development of LSSM-EA and the processes used for solving the equations are discussed. Virtual Column 2 can be used for eluents containing one or two competing ions, and the software contains retention databases for up to 33 analytes on the Dionex AS9A-HC, AS4A-SC, and AS14A analytical columns with carbonate-bicarbonate eluents and the Dionex AS10, AS15, and AS16 analytical columns with hydroxide eluents (results for the AS10 and AS15 columns are not discussed in the present study). Virtual Column 2 has been evaluated extensively and is shown to give predicted retention times that in most cases agree with experimentally determined data to within 5%. The software has uses in practical IC method development, education and training in IC, and refinement of existing IC methodology. A free version of this program is available by download at www.virtualcolumn.com.

Journal Article↗

PubMed2002

Influence of the hofmeister series on the retention of amines in reversed-phase liquid chromatography.

The chromatographic behavior of protonated amines in reversed-phase liquid chromatography (RPLC) is influenced markedly by the identity of the mobile-phase anion. For example, retention factor values, k, obtained from protonated nordoxepin, nortriptyline, and amitriptyline increase almost 1 order of magnitude across the following series of anions employed as mobile-phase modifiers: H2PO4- < HCOO- < CH3SO3- < Cl- < NO3- < CF3COO- < BF4- < ClO4- < PF6-. Early eluting primary, secondary, and tertiary benzylamines are retained and resolved using BF4-, ClO4-, and PF6- but elute in or very near the void using all other mobile-phase anions tested. In contrast, a neutral hydrophobic marker, acenaphthene, shows no significant changes in retention with mobile-phase anion identity. Such large differences in amine retention with anion identity can be rationalized via both an ion-pairing model and the Hofmeister effect. Two key findings are reported. First, the dependence of amine retention on mobile-phase anion identity is attributed unambiguously to the Hofmeister effect and is quantified using a simple equation based solely on differences in the solvation of anions. Accurate prediction of k values from the excess chemical potential of anions in water suggests that anion-solvent interactions dominate the retention of amines in RPLC. Thus, controlling amine retention depends critically on judicious selection of mobile-phase anion (in addition to the usual experimental parameters such as organic modifier, temperature, pH, and stationary phase). Second, more lipophilic molecular anions can provide retention and tailing properties comparable to those obtained from traditional amphiphilic ion-pairing reagents such as octanesulfonate, but with the benefit of a superior gradient background and solubility at high concentrations of organic modifier.

Amines↗

PubMed2003

Effect of amine counterion type on the retention of basic compounds on octadecyl silane bonded silica-based and polybutadiene-coated zirconia phases.

In a previous paper, we compared the mixed-mode retention characteristics of cationic solutes on octadecyl silane-bonded silica (ODS) and polybutadiene-coated zirconia (PBD-ZrO2) phases. It is well recognized that both reversed-phase and ion-exchange interactions contribute to the retention of cations on ODS phases. The reversed-phase interaction results from the bonded hydrocarbon chain; the ion-exchange interaction originates in the ionized residual silanol groups. These two types of interactions also exist on the PBD-ZrO2 phase. The polybutadiene contributes to the reversed-phase interaction and the ionized zirconol, but primarily, the adsorbed Lewis base anions, such as phosphate or fluoride, contribute to the ion-exchange interaction. We have shown that on ODS phases, reversed-phase interactions are much more important, whereas the opposite is true of PBD-ZrO2 phases. In this work, we investigate the effect of several amine mobile phase counterions on the retention of cationic solutes on ODS and PBD-ZrO2 phases. The effects of the chain length and the type of amine (1 degree, 2 degrees, 3 degrees) counterion on the retention of basic compounds were studied. In contrast to older studies of type A silica-based phases, the results show that the chain length and type of the amine blocker do not have a large effect on the retention of basic compounds with the newer type B silica-based materials. However, on the PBD-ZrO2 phase, very striking differences in retention were observed with different amine counterions. We show that the molecular geometry of the amine counterion has a significant effect on the retention of basic solutes on the PBD-ZrO2 phase.

Amines↗

PubMed2004

The effect of tobacco blend additives on the retention of nicotine and solanesol in the human respiratory tract and on subsequent plasma nicotine concentrations during cigarette smoking.

The influence of the tobacco additives diammonium hydrogen phosphate (DAP) and urea on the delivery and respiratory tract retention of nicotine and solanesol and on the uptake of nicotine into venous blood was investigated in 10 smokers under mouth-hold and 75 and 500 mL inhalation conditions. Three cigarettes with identical physical specifications were produced from a common lamina tobacco blend. The control cigarette contained nonammoniated reconstituted tobacco sheet (RTS), whereas DAP and other ammonia compounds were added to the RTS of the second cigarette. Urea was added to the tobacco of the third cigarette. The presence of DAP or urea in the test cigarettes did not significantly influence solanesol retention within the mouth during the mouth-hold condition. Nicotine retention within the mouth during the mouth-hold condition was, however, significantly higher for the DAP cigarette (64.3 +/- 10.5%) than for the urea (53.3 +/- 11.3%) or control cigarette (46.3 +/- 8.6%), but this did not result in an increase in nicotine uptake into venous blood. Solanesol retentions during the 75 and 500 mL inhalation volume conditions and nicotine retentions during the 75 mL inhalation volume condition were not significantly different for the three cigarette types. Although the nicotine retention approached 100% with each cigarette type during the 500 mL inhalation condition, the nicotine retention for the urea-treated cigarette (99.6 +/- 0.2%) was marginally, but statistically, significant, higher than for the control (99.1 +/- 0.5%) and DAP-treated cigarettes (98.8 +/- 0.6%). There were no statistically significant differences between the indices of nicotine uptake into venous blood for the three cigarette types in any of the inhalation conditions.

Administration, Inhalation↗