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PubMed2005

Reproducibility and validity of a Yan-style portable citric acid cough challenge.

Although many different methods of measuring cough reflex sensitivity have been published, few are simple enough to use outside of a hospital or laboratory environment. The aim of this study was to develop a simple, quick, and portable cough challenge, assess its reproducibility, and compare its results with those measured by an existing established hospital protocol. Twenty-five volunteers performed cough challenges based on an established hospital dosimeter protocol, and, on a separate occasion, by a protocol inhaling citric acid from DeVilbiss 40 hand-held nebulisers (citric acid concentrations of 10-3000 mM). Reproducibility of the hand-held cough challenge was assessed in 11 volunteers. Cough thresholds were consistently higher by the hand-held method than by the hospital dosimeter method. The geometric mean citric acid concentrations causing two coughs (threshold D2) were 3.14 and 2.77 log mM, respectively (p<0.001). The geometric mean (95% CI) difference between the tests was 0.51 log mM (0.18-0.83) of the average of the two values. Cough D2 thresholds attained by the two techniques did, however, show significant correlation (r=0.95, p<0.0001). The coefficient of repeatability for the hand-held method was 0.40 log mM. Administering citric acid from DeVilbiss 40 hand-held nebulisers offers a rapid, portable, and reproducible cough challenge in healthy volunteers. The results correlate well with an existing Mefar dosimeter challenge, but give two to three times greater cough thresholds.

Anticoagulants↗

PubMed2003

Evaluation of a multimodality image (CT, MRI and PET) coregistration procedure on phantom and head and neck cancer patients: accuracy, reproducibility and consistency.

BACKGROUND AND PURPOSE: In radiotherapy planning of head and neck tumors, coregistration of various anatomical (e.g. CT and MRI) and functional (e.g. PET) images is a promising way to improve the delineation of the target volumes. In this paper, we report data on accuracy, reproducibility and consistency of an interactive coregistration procedure in a specifically designed phantom and in a group of patients with primary head and neck tumors. PATIENTS AND METHODS: A phantom and a group of four patients with pharyngo-laryngeal tumors were imaged by CT scan (taken as the reference image), MRI (T1- and T2-weighed sequences) and PET (transmission and FDG emission). Sets of images were coregistered using an interactive rigid coregistration method based on interactive surface segmentation. Translational and rotational displacements relative to the reference CT scan were measured and expressed in terms of accuracy, reproducibility (inter- and intra-observer variation) and consistency (between T1- and T2-weighed MRI). RESULTS: Coregistration accuracy was in the range of 0.8-6.2 mm and 1.2-4.6 mm for the phantom and the patients, respectively. Accuracy was slightly worse in the z direction, and was significantly correlated with the spatial resolution of the imaging modalities, at least for the phantom. Inter- and intra-observer variations were very small and always far below the residual variance. Consistency was perfect except in the y direction. CONCLUSION: Providing adequate set-up is chosen, accurate coregistration of CT, MR and FDG-PET images can be obtained in the head and neck area. Coregistration was consistent and highly reproducible among observers.

Head and Neck Neoplasms↗

PubMed2006

Inter-session reproducibility of peak expiratory flow with standardized expiratory maneuvers.

BACKGROUND: In adults performing forceful expiratory maneuvers, the length of post-inspiratory pause prior to forced expiration may influence the subsequently measured peak expiratory flow (PEF) and increase its variability. We investigated the effects of two different lengths of breath-hold at total lung capacity (TLC) on the short-term reproducibility of PEF in healthy volunteers. METHODS: Forty-six healthy volunteers (age 34.6+/-8.5; 23 men) performed a series of maximal forceful expirations in two different test sessions, separated by approximately 2 weeks. In each test-session, PEF was measured with two different types of maneuvers. One maneuver (P) included a brief (<2s) post-inspiratory pause at TLC prior to forced expiration, whereas the second maneuver (NP) included no pause at TLC. The speed of inspiration to TLC was fast and similar for both maneuvers. In a given test session, all volunteers performed four efforts for each type of maneuver. The highest PEF for each maneuver was used for analysis. The Bland-Altman statistical analysis was used to determine inter-session reproducibility of PEF. RESULTS: Within-maneuver analysis of the between-test session reproducibility of PEF showed that neither maneuver systematically biased the measured PEF (mean difference 0.02L/s for the P and 0.17L/s for the NP maneuver). Inter-maneuver between-test session analysis similarly showed that neither maneuver introduced a systematic bias in the maximal PEF (mean difference ranged from -0.15 to -0.01L/s). The limits of agreement were comparable in all maneuver-pair analyses. CONCLUSIONS: Forceful expiratory maneuvers with or without a brief (<2s) pause at TLC produce comparable PEF values in test-retest sessions.

Adult↗

PubMed2004

The reproducibility and short-term and long-term repeatability of sonographic measurement of splenic length.

This study was undertaken to evaluate the reproducibility (interobserver variability), and the short-term and long-term repeatability (intraobserver variability) of sonographic measurement of the maximum and mean splenic length. Ultrasound (US) measurements of the splenic length were performed in 43 subjects, ages 30 to 59 years old (mean age = 44.5 years). Each subject attended three US sessions: baseline examination and 30 min and 8 weeks after the baseline examination. In each session, US examinations of the spleen were performed and the splenic length was measured by four operators. In each examination, the splenic length was measured 3 times, and the maximum and mean values were obtained. The overall reproducibility of the measurements of maximum and mean splenic lengths were 67% and 89%, respectively. The short-term repeatability in measuring the maximum and mean splenic lengths were 87% and 94%, respectively, whereas the long-term repeatabilities were 61% and 76%, respectively. The reproducibility and short-term and long-term repeatability of the measurement of mean splenic length were higher than those of the maximum splenic length. In the mean and maximum splenic length measurement, the short-term repeatability was higher than the long-term repeatability. The results suggested that the mean splenic length has a higher reliability in sonographic measurement and should be used in routine clinical practice. Measurement errors should be considered when evaluating the changes of splenic length in serial US examinations, particularly in long-term follow-up.

Adult↗

PubMed2004

Applicability and reproducibility of condom catheter method for measuring isovolumetric bladder pressure.

OBJECTIVES: To report on the applicability, reproducibility, and adverse events of the noninvasive condom catheter method in the first 730 subjects of a longitudinal survey of changes in urinary bladder contractility secondary to benign prostatic hyperplasia, in which 1300 men will be evaluated three times in 5 years using this method. METHODS: Subjects were recruited by general practitioners, general publicity, and e-mail. Only those meeting the study criteria were entered in the study. If the free flow rate exceeded 5.4 mL/s, at least two consecutive condom pressure measurements were attempted using the condom catheter method. The condom pressure measured reflected the isovolumetric bladder pressure, a measure of urinary bladder contractility. The reproducibility of the method was quantified by a difference plot of the two maximal condom pressures measured in each subject. RESULTS: In 618 (94%) of 659 eligible participants, one condom pressure measurement was completed; two measurements were done in 555 (84%). The maximal condom pressure ranged from 28 to 228 cm H2O (overall mean 101, SD 34). A difference between the two pressures of less than +/-21 cm H2O was found in 80%. The mean difference was -1 cm H2O (SD 18), significantly different from 0. Some adverse events such as terminal self-limiting hematuria were encountered. CONCLUSIONS: The condom catheter method is very suitable for large-scale use. It has a success rate of 94% and a reproducibility comparable to that of invasive pressure flow studies.

Condoms↗

PubMed2005

Endometrial volume and vascularity measurements by transvaginal three-dimensional ultrasonography and power Doppler angiography in stimulated and tumoral endometria: intraobserver reproducibility.

OBJECTIVES: To assess intraobserver reproducibility of the endometrial volume (EV) and 3D power Doppler indices (vascularization index, VI; flow index, FI; and vascularization flow index, VFI) of the endometrium and subendometrial area using three-dimensional power Doppler angiography (3D-PDA). METHODS: Twenty-five women on the hCG day after controlled ovarian stimulation and 15 patients presenting with uterine bleeding and suspicious endometrial thickening (10 endometrial cancers and 5 endometrial hyperplasias) were scanned. Eighty volume data sets were analyzed using the VOCAL imaging program. EV and VI, FI and VFI of the endometrium and subendometrium (5 mm shell) were manually calculated in the longitudinal and coronal planes with 15 degrees and 9 degrees rotation steps. Intraclass correlation coefficient (ICC) and 95% confidence intervals were used to assess reliability. RESULTS.: EV measurements were highly reproducible (ICC > or = 0.97) without significant differences between planes and rotation steps. Endometrial and subendometrial VI, FI, and VFI presented ICCs above 0.90 with the exception of the subendometrial FI (ICC > or = 0.80). There were no significant differences according to measurement plane and rotation step except for subendometrial VFI. Nevertheless, 3D power Doppler indices calculated in the coronal plane and 9 degrees rotation step obtained the highest ICC. ICCs for 3D-PDA indices from the tumoral endometria were significantly higher than those calculated from the stimulated endometria. CONCLUSIONS: Endometrial volume and endometrial and subendometrial 3D power Doppler indices have an acceptable reproducibility, significantly higher in tumoral endometria. The reliability of measurements does not seem to be significantly influenced by the rotation plane and degrees of rotation. These results support that 3D-PDA and VOCAL are reliable methods to evaluate the physiological and pathological changes of the endometrium.

Adult↗

PubMed1995

Development and reproducibility of a food frequency questionnaire to assess diets of older children and adolescents.

OBJECTIVE: To develop a self-administered food frequency questionnaire for older children and adolescents and to demonstrate reproducibility over a 1-year period. DESIGN: The youth/adolescent questionnaire (YAQ) was based on the validated Nurses' Health Study food frequency questionnaire and was developed to reflect the eating habits of this age group. SUBJECTS: The multiethnic sample consisted of 179 youths (ages 9 to 18 years) who completed the questionnaire twice, 1 year apart. STATISTICAL ANALYSIS: Pearson correlation coefficients were calculated on nutrient data adjusted in relation to energy intake and on unadjusted food data. RESULTS: Reproducibility for nutrients ranged from .26 for protein and iron to .58 for calcium, and for foods it ranged from .39 for meats to .57 for soda. Mean reproducibility was higher among girls than boys for energy and nutrients and for foods; no consistent pattern was observed for age. CONCLUSION: A self-administered food frequency questionnaire has a reasonable ability to assess the eating habits of older children and adolescents over time.

Adolescent↗

PubMed2000

Reproducibility of neointima quantification with motorized intravascular ultrasound pullback in stented coronary arteries.

BACKGROUND: Intravascular ultrasound (IVUS) imaging has shown excellent reproducibility immediately after coronary stent implantation. However, the variability of measurements in lesions late after stent implantation, when neointima formation is present, has not been studied. Neointimal tissue is generally low echogenic and thus difficult to quantify. We therefore sought to analyze the reproducibility of morphometric measurements late after stent implantation. METHODS AND RESULTS: Fifty consecutive patients were investigated 6 months after Palmaz-Schatz stent implantation (motorized catheter pullback 0.5 mm/s). Two experienced investigators independently identified the stent area, lumen area, and neointimal area at different sites within the stent. Planimetric measurements were performed with commercially available software. Correlation coefficient and mean difference for corresponding measurements were calculated for the intraobserver and interobserver comparisons. Variability for the intraobserver and interobserver comparisons was similar. Observer agreement regarding the presence of neointimal hyperplasia was as high as 71% (interobserver comparison 62%). The mean difference for neointima area was 0.06 +/- 1.5 mm(2) (-0.6 +/- 1.5 mm(2)); mean differences for lumen area were 0.02 +/- 0.19 mm(2) (0.03 +/- 0.17 mm(2)) and for stent area 0.01 +/- 0.09 mm(2) (-0.02 +/- 0.12 mm(2)) (values for interobserver comparison are given in parentheses). Correlation between measurements was high for all structures: correlation coefficients were 0.66 (0.69) for neointima, 0.94 (0.95) for lumen, and 0.95 (0. 91) for stent area. CONCLUSIONS: Morphometric measurements of IVUS investigations with motorized IVUS pullback late after stent placement show good reproducibility. Intraobserver variability and interobserver variability are low. Differences for corresponding measurements were more pronounced for neointima area. Motorized catheter pullback guarantees high reliability of IVUS measurements and should be used routinely for clinical IVUS studies.

Aged↗

PubMed1993

Sensitivity and reproducibility of the instantaneous hyperemic flow versus pressure slope index compared to coronary flow reserve for the assessment of stenosis severity.

The objective of this study was to compare the reproducibility and sensitivity of the instantaneous hyperemic flow versus pressure slope index (i-HFVP) and coronary flow reserve (CFR). The i-HFVP is the slope of the relationship between diastolic hyperemic coronary flow and diastolic aortic pressure, normalized for bed weight. In contrast to CFR (the ratio of hyperemic to basal coronary flow), the i-HFVP has been shown to be independent of changes in aortic pressure, heart rate, contractility, and preload. To compare reproducibility, i-HFVP and CFR were measured three times in eight dogs instrumented with high-fidelity micromanometers and flow probes, allowing for full hemodynamic recovery between phases (15 to 40 minutes). Maximum hyperemia was induced with intravenous adenosine. The sensitivity of i-HFVP and CFR was assessed in 16 instrumented dogs. Measurements were performed for one basal state and for five subcritical incremental stenoses created with a screw occluder during hyperemia. Intraclass variability correlation coefficients were 0.96 for i-HFVP but only 0.56 for CFR. Both i-HFVP and CFR showed significant decrements with each increasing stenosis. However, the percentage reductions at each level were significantly greater for the i-HFVP. The difference in percentage reduction favoring increased sensitivity of the i-HFVP ranged from 11% to 23%. It was concluded that the i-HFVP is more reproducible and more sensitive to the presence of stenoses than CFR.

Animals↗

PubMed1996

Detection of coronary calcification with electron-beam computed tomography: evaluation of interexamination reproducibility and comparison of three image-acquisition protocols.

The purpose of this investigation was to determine the variability of electron-beam computed tomography (EBCT) measurement of coronary calcification by using two commonly employed image-acquisition protocols and to compare this variability with that of a new image-acquisition protocol. We performed three EBCT scans within 15 minutes on each of 324 consecutive high-risk, asymptomatic subjects participating in an ongoing epidemiologic research investigation. Subjects were divided into three groups: group 1 (n = 175) received two scans with a standard 20-slice, 3 mm slice thickness image-acquisition protocol and a third scan with the new 20-slice, 6 mm slice thickness protocol; group 2 (n = 77) received two scans with a new 6 mm slice thickness image-acquisition protocol and a third scan with a standard 20-slice, 3 mm slice thickness protocol; group 3 (n = 72) received two scans with a 30-slice, 3 mm slice thickness image-acquisition protocol and a third scan with a 20-slice, 6 mm slice thickness protocol. Calcium score, calcium mass estimate, and calcium volume estimate were determined for each scan. We compared retest variability of calcium measurements for each of the three image-acquisition protocols. The variability of the new 6 mm slice thickness protocol was significantly lower than that of either the 20-slice 3 mm slice thickness protocol (p = 0.009) or the 30-slice 3 mm slice thickness protocol (p = 0.02) for measurement of calcium score, mass, or volume. Retest reproducibility for all three image-acquisition protocols was low; however, the 20-slice 6 mm slice thickness protocol gave reproducibility superior to either of the 3 mm slice thickness protocols. Variability of absolute indices increased, and variability of relative indices decreased as the value of these indices increased. EBCT is not sufficiently reproducible to allow serial quantitation of coronary calcium in individual patients over relatively short periods (< 2 years).

Aged↗

PubMed1997

Short- and long-term reproducibility of heart rate variability in patients with long-standing type I diabetes mellitus.

Heart rate variability (HRV) has been used to assess cardiac autonomic function noninvasively, understand the pathophysiologic mechanisms of heart disease, evaluate therapy, and assess long-term prognosis. We examined both the short- and long-term reproducibility of the time and frequency domain HRV parameters in 23 type I diabetics over a 12-month interval. Entry criteria included juvenile onset diabetes before age 35 years, >24-year duration of diabetes, diabetes difficult to control, and albuminuria. Standardized noninvasive autonomic testing and 24-hour ambulatory electrocardiographic recordings were obtained. Fifteen men and 8 women (mean age 36.7 years) were enrolled. Fifty-three percent of the men and 75% of the women were smokers, and women had higher cholesterol than men. All HRV parameters were markedly decreased when compared with normal persons. Using Pearson correlation, the time domain indicators of parasympathetic activity demonstrated very strong correlations at 3 and 6 months compared with baseline, with good correlations at 1 year. The average SD of all 5-minute RR intervals maintained a very strong correlation for the entire year (r >0.94). In the frequency domain, the measures of parasympathetic and sympathetic activity maintained a solid correlation for the entire study period. Reproducibility of HRV was also examined using repeated-measures analysis of variance. The time and frequency domain parameters demonstrated very little variation over the study period of 12 months. Thus, our investigation demonstrated that HRV in long-term diabetics using 24-hour ambulatory recordings is abnormal and reproducible over a 12-month interval; very little variation in all HRV parameters, especially in parameters of parasympathetic activity, occurred during the study period.

Adult↗

PubMed1998

Agreement and reproducibility of automatic versus manual measurement of QT interval and QT dispersion.

To determine whether the automatic measurement of the QT interval is consistent with the manual measurement, this study evaluated the reproducibility and agreement of both methods in 70 normal subjects and 54 patients with hypertrophic cardiomyopathy. The mean, minimum, and maximum QT interval and QT dispersion were computed in a set of 6 consecutive electrocardiograms (3 in the supine and 3 in the standing position) obtained from each subject. The automatic method determined the T-wave end as the intersect of the least-squares-fit line around the tangent to the T-wave downslope with the isoelectric baseline. Manual measurements were obtained using a high-resolution digitizing board. QT dispersion was defined as the difference between the maximum and minimum QT interval and as standard deviations of the QT interval duration in all and precordial leads. In patients with hypertrophic cardiomyopathy, the absolute values of the QT interval and QT dispersion were significantly higher than those in normal subjects (p < 0.0001). In both groups, the intrasubject variability of the QT interval was significantly lower with automatic than with manual measurement (p < 0.05). The agreement between automatic and manual QT interval measurements was surprisingly poor, but it was better in patients with hypertrophic cardiomyopathy (r2 = 0.46 to 0.67) than in normal subjects (r2 = 0.10 to 0.25). In both groups, the reproducibility and agreement of both methods for QT dispersion were significantly poorer than for QT interval. Hence, the automatic QT interval measurements are more stable and reproducible than manual measurement, but the lack of agreement between manual and automatic measurement suggests that clinical experience gained with manual assessment cannot be applied blindly to data obtained from the automatic systems.

Adolescent↗

PubMed2003

Reproducibility and clinical application of a newly developed stabilized retinal laser Doppler instrument.

PURPOSE: To describe a newly developed stabilized retinal laser Doppler instrument, to report the reproducibility of retinal blood flow measurements, and to present examples of its clinical application. DESIGN: Experimental study. METHODS: The intrasession, intersession, and interobserver reproducibility of retinal blood flow measurements obtained using the Canon Laser Blood Flowmeter model CLBF 100 was assessed. Intrasession: the coefficients of variation (CV) for repeated measurements (5X) of retinal vessel diameter (D), time-average centerline blood velocity (V(av)), and blood flow (F) were calculated at 18 sites along temporal retinal arteries and 18 sites along temporal retinal veins using both eyes in six healthy volunteers. Intersession: the correlation coefficients and average differences between two sets of measurements at the same 36 retinal sites made by one examiner on two different days were calculated. Interobserver: the correlation coefficients and average differences between two sets of measurements at nine sites (five arterial and four venous) in five eyes of five of the volunteers made by two examiners on the same day were calculated. Results from two patients, one with branch retinal vein occlusion (BRVO), and one with central retinal vein occlusion (CRVO), are used to illustrate abnormal retinal circulatory characteristics. RESULTS: intrasession: CV (mean +/- SD) for D, V(av), and F were 5.5% +/- 2.2%, 13.1% +/- 6.3%, and 13.8% +/- 4.7% in arteries and 3.5% +/- 2.1%, 11.9% +/- 5.9%, and 12.7% +/- 5.5% in veins. Intersession/interobserver: strong correlations between measurements made by one examiner on two different days and by two examiners on the same day were found in D, V(av), and F. Average differences in F were 16.4% +/- 12.8% for intersession and 12.6% +/- 7.0% for interobserver comparisons. Results from the patient with BRVO show marked differences in flow characteristics in the affected quadrant compared with an unaffected quadrant in the same eye, and to the fellow eye. Results from the patient with CRVO show a dramatic improvement in flow characteristics after clearing of the occlusion. CONCLUSIONS: The reproducibility results and the fact that blood flow is measured in actual units of microl/min indicate that the instrument can be used for reliable comparison of blood flow characteristics at different retinal vascular sites in the same eye, at comparable sites in both eyes, and for comparison between patients and healthy control subjects.

Adult↗

PubMed1999

Validity and reproducibility of crutch force and heart rate measurements to assess energy expenditure of paraplegic gait.

OBJECTIVE: To determine the validity and reproducibility of heart rate (HR) and crutch force measurements to estimate energy expenditure during paraplegic walking. Usefulness of these outcome measures in comparative trials was assessed in terms of responsiveness. DESIGN: Cross-sectional validity was determined using one single (first) measurement. Longitudinal validity as well as reproducibility were calculated using repeated measurements. SETTING: Oxygen uptake and HR during steady state as well as axial crutch load were measured at subjects' self-selected walking speeds. PATIENTS: Ten subjects with thoracic-level spinal cord injury were included in the study. All subjects had considerable experience with ambulation in the advanced reciprocating gait orthosis (ARGO). MAIN OUTCOME MEASURES: Oxygen uptake (VO2, mL/min) and oxygen cost (EO2, mL/m) were used as criterion standards. Crutch peak force (CPF), crutch force time integral (CFTI), HR, and physiological cost index (PCI) were used to estimate energy expenditure. RESULTS: The PCI was found to be sensitive to detect differences between sessions in criterion standard (r = .86). Smallest detectable difference (ie, point where difference exceeds measurement error) ranged from approximately 15% for CPF to 33.7% and 41.8% for EO2 and PCI, respectively. CONCLUSIONS: Although PCI is expected to be a valid measure for within-patient differences in VO2, responsiveness was lower compared to EO2 and CPF. The limited number of patients who can be included in studies on paraplegic locomotion requires reproducible outcome measures. Therefore, CPF and EO2 are advocated in favor of PCI.

Adult↗

PubMedDate not supplied

Reproducibility of visual activation in functional magnetic resonance imaging at very high field strength (4 Tesla).

PURPOSE: The reproducibility of functional magnetic resonance imaging (fMRI) has been studied on 1.5 Tesla (T) (high field strength) scanners. We report the reproducibility of visual activation in fMRI at 4 T (very high field strength). METHODS: Five healthy subjects were scanned twice in the same session with a 4 T scanner during binocular flashing visual stimulation. The activated areas during the first and second acquisition were compared. RESULTS: Activation of the visual cortex was observed in all subjects and activation of lateral geniculate nucleus was also detected in four subjects. The ratio of overlapping activated voxels in the first and second acquisition was 0.81 +/- 0.05. CONCLUSIONS: Reproducibility of visual activation using fMRI at 4 T was found to be acceptable, and the results from 4T scanners show a reliability similar to those at 1.5 T.

Adult↗

PubMedDate not supplied

A basic investigation of multifocal electroretinogram: reproducibility and effect of luminance.

PURPOSE: To investigate the reproducibility as well as the effect of luminance in multifocal electroretinogram (mERG). METHODS: Multifocal electroretinogram recordings were repeated on different days in 6 normal subjects using the Veris III system. The mean luminance of the monitor displaying the stimuli was randomly varied by five kinds of neutral density (ND) filters. RESULTS: The standard deviation of mERG amplitude from the macular region was approximately 10% of the mean value for each normal subject. Reproducibility largely depended on the condition of the subject and placement of the contact lens electrode. With decreases in the mean luminance of the monitor, the amplitude of mERG decreased exponentially, whereas the peak latency increased linearly. mERGs elicited from a patient with mild cortical cataract resembled the mERGs obtained from the control group using an ND filter between -0.30 and -0.52 log, whereas two patients with typical retinitis pigmentosa showed much lower response densities in mERGs. CONCLUSIONS: It is necessary to pay attention to the reproducibility and the luminance effect to obtain reliable mERGs.

Adult↗

PubMed1999

Poor reproducibility of in-source collisional atmospheric pressure ionization mass spectra of toxicologically relevant drugs.

The purpose of the study was to examine the intra- and interlaboratory reproducibility of mass spectra obtained with liquid chromatography-atmospheric pressure ionization mass spectrometry (LC--API-MS) both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) modes. Toxicologically relevant drugs of different polarity were selected as test substances: morphine-6-glucuronide, 6-monoacetylmorphine, codeine, lysergic acid diethylamide, methylenedioxymethamphetamine. The study was performed in two laboratories using identical instruments and in one using a slightly different instrument. Basic instrument settings and mobile phase were identical in all laboratories. Mass spectra of drugs were taken at four collision energy voltages and using mobile phase of different composition (four concentration levels of acetonitrile and of ammonium formate buffer). The experiments demonstrated that mass spectra of given drugs, obtained in identical conditions with identical instruments, may show very different degrees of fragmentation. Mass spectra obtained with different instruments differed profoundly not only in the degree of fragmentation, but also different fragments and adducts were observed. Short-term intralaboratory reproducibility of mass spectra was satisfactory. On the other hand, the long-term experiments showed different degrees of fragmentation of APCI-generated mass spectra at nominally identical fragmentation energy. The changes in the composition of the mobile phase (concentration of organic modifier or buffer molarity) did not affect the reproducibility of fragmentation to any relevant degree. The study showed that the interlaboratory exchange and use of mass spectrum library, generated by single-quadrupole (LC--API-MS instruments, is hardly feasible at the moment, even under very carefully standardized conditions.

Atmospheric Pressure↗

PubMed1999

Reproducibility of the separation of astaxanthin stereoisomers on Pirkle covalent L-leucine and D-phenylglycine columns.

The reproducibility of the separation of astaxanthin stereoisomers on columns packed with Pirkle covalent L-leucine chiral stationary phase (CSP) was examined by comparing six columns purchased from the same manufacturer. Differences were found even for columns packed with CSP from the same lot. The reproducibility of columns packed with Pirkle covalent D-phenylglycine CSP was also examined by comparing columns purchased from the same manufacturer as well as from different manufacturers. Significant differences were found for columns packed by different manufacturers. Chiral column-to-column reproducibility for complex stereoisomeric separations should therefore not be taken for granted.

Chromatography, High Pressure Liquid↗