| 1. |
- Wiberg, Kent, et al.
(författare)
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Peak purity determination with principal component analysis of high-performance liquid chromatography-diode array detection data
- 2004
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1029:1-2, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for the determination of chromatographic peak purity by means of principal component analysis (PCA) of high-performance liquid chromatography with diode array detection (HPLC–DAD) data. The method is exemplified with analysis of binary mixtures of lidocaine and prilocaine with different levels of separation. Lidocaine and prilocaine have very similar spectra and the chromatograms used had substantial peak overlap. The samples analysed contained a constant amount of lidocaine and a minor amount of prilocaine (0.02–2 conc.%) and hence the focus was on determining the purity of the lidocaine peak in the presence of much smaller levels of prilocaine. The peak purity determination was made by examination of relative observation residuals, scores and loadings from the PCA decomposition of DAD data over a chromatographic peak. As a reference method, the functions for peak purity analysis in the chromatographic data system used (Chromeleon) were applied. The PCA method showed good results at the same level as the detection limit of baseline-separated prilocaine, outperforming the methods in Chromeleon by a factor of ten. There is a discussion of the interpretation of the result, with some comparisons with evolving factor analysis (EFA). The main advantage of the PCA method for determination of peak purity over methods like EFA lies in its simplicity, short time of calculation and ease of use.
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| 2. |
- Wiberg, Kent, et al.
(författare)
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Rapid determination of lidocaine solutions with non-column chromatographic diode array UV spectroscopy and multivariate calibration
- 2003
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Ingår i: Journal of Pharmaceutical and Biomedical Analysis. - 0731-7085 .- 1873-264X. ; 30:5, s. 1575-1586
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Tidskriftsartikel (refereegranskat)abstract
- A new method for the rapid determination of pharmaceutical solutions is proposed. A conventional HPLC system with a Diode Array Detector (DAD) was used with no chromatographic column connected. As eluent, purified water (Milli Q) was used. The pump and autosampler of the HPLC system were mainly utilised as an automatic and convenient way of introducing the sample into the DAD. The method was tested on the local anaesthetic compound lidocaine. The UV spectrum (245–290 nm) from the samples analysed in the detector was used for multivariate calibration for the determination of lidocaine solutions. The content was determined with PLS regression. The effect on the predictive ability of three factors: flow, data-collection rate and rise time as well as two ways of exporting a representative UV spectrum from the DAD file collected was investigated by means of an experimental design comprising 11 experiments. For each experiment, 14 solutions containing a known content of lidocaine were analysed (0.02–0.2 mg ml−1). From these 14 samples two calibration sets and two test sets were made and as the response in the experimental design the Root Mean Square Error of Prediction (RMSEP) values from the predictions of the two test sets were used. When the factor setting giving the lowest RMSEP was found, this setting was used when analysing a new calibration set of 12 lidocaine samples (0.1–0.2 mg ml−1). This calibration model was validated by two external test sets, A and B, analysed on separate occasions for the evaluation of repeatability (test set A) and determination over time (test set B). For comparison, the reference method, liquid chromatography, was also used for analysis of the ten samples in test set B. This comparison of the two methods was done twice on different occasions. The results show that in respect of accuracy, precision and repeatability the new method is comparable to the reference method. The main advantages compared with liquid chromatography are the much shorter time of analysis (<30 s) as well as the automatic and simple analytical procedure and the low consumption of organic solvents.
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| 3. |
- Wiberg, Kent, et al.
(författare)
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Use of control sample for estimation of prediction error in multivariate determination of lidocaine solutions with non-column chromatographic diode array UV spectroscopy
- 2003
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Ingår i: Journal of Pharmaceutical and Biomedical Analysis. - 0731-7085 .- 1873-264X. ; 33:5, s. 859-869
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the ability of a control sample, of known content and identity, to diagnose and correct errors in the predictions when the same multivariate calibration model was used for analysis of new samples over time. A calibration set consisting of 16 samples with a known content of lidocaine was analysed and two external test sets, A and B, were used for the validation. Test set A contained 15 samples with different concentrations of lidocaine and test set B contained three samples with different lidocaine content, which were analysed six times in order to obtain a measure of repeatability. The multivariate calibration was done with PLS regression on UV spectra collected between 245 and 290 nm. A representative UV spectrum was exported from the collected DAD files by two methods, average spectrum over the whole file and average spectrum over the sample plug. Test set A was analysed further on another three occasions together with a control sample. The results showed that the control sample could be used to give a diagnosis and estimate of the prediction error. Moreover, the measured prediction error of the control sample could also be used to correct the predictions, thereby reducing the prediction error. Finally, some practical considerations regarding use of the proposed DAD method with a control sample are presented. The procedure suggested could lead to an efficient analytical approach where the same calibration model could be used over time without recalibration, which may be attractive in industrial quality control or screening analysis in pharmaceutical research.
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| 4. |
- Wiberg, Kent, et al.
(författare)
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Determination of the content and identity of lidocaine soluions with UV-visible spectroscopy and multivariate calibration
- 2001
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 126:7, s. 1142-1148
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for the determination of the content and identity of the active compound in pharmaceutical solutions by means of ultraviolet-visible (UV–Vis) spectroscopy, orthogonal signal correction (OSC) and multivariate calibration with soft independent modelling of class analogy (SIMCA) classification and partial least squares (PLS) regression. The content was determined with PLS regression and the identity with PLS regression and SIMCA classification. The method was tested on the local anaesthetic compound lidocaine. For the validation, external test sets of both manufactured sample solutions and samples from a stability study were used. For comparison with this new method, liquid chromatography was used as a reference method. The results show that in respect of accuracy, precision and repeatability, the new method is comparable to the reference method. The main advantage over liquid chromatography is the much shorter time of analysis and the simpler analytical procedure. An estimate of the analysis time saved with the proposed method compared with using liquid chromatography, together with practical considerations, is given.
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| 5. |
- Artursson, Tom, et al.
(författare)
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Study of Preprocessing Methods for the Determination of Crystalline Phases in Binary Mixtures of Drug Substances by X-ray Powder Diffraction and Multivariate Calibration
- 2000
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 54:8, s. 272A-301A
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, various preprocessing methods were tested on data generated by X-ray powder diffraction (XRPD) in order to enhance the partial least-squares (PLS) regression modeling performance. The preprocessing methods examined were 22 different discrete wavelet transforms, Fourier transform, Savitzky-Golay, orthogonal signal correction (OSC), and combinations of wavelet transform and OSC, and Fourier transform and OSC. Root mean square error of prediction (RMSEP) of an independent test set was used to measure the performance of the various preprocessing methods. The best PLS model was obtained with a wavelet transform (Symmlet 8), which at the same time compressed the data set by a factor of 9.5. With the use of wavelet and X-ray powder diffraction, concentrations of less than 10% of one crystal from could be detected in a binary mixture. The linear range was found to be in the range 10-70% of the crystalline form of phenacetin, although semiquantitative work could be carried out down to a level of approximately 2%. Furthermore, the wavelet-pretreated models were able to handle admixtures and deliberately added noise.
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| 6. |
- Lindström, Kjell, et al.
(författare)
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A model for quality assessment in primary health care using the tracer condition technique with insulin treated diabetes as one of the tracers
- 1997
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Ingår i: Scandinavian Journal of Primary Health Care. - : Informa Healthcare. - 0281-3432 .- 1502-7724. ; 15:2, s. 92-96
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Tidskriftsartikel (refereegranskat)abstract
- Objective-To find a method for quality assessment in primary health care and to apply this method on a defined disease.Design-General practitioners and hospital doctors worked out a programme for evaluating the quality of outpatient care of patients with insulin treated diabetes as one of five tracers. An expert committee comprising experienced general practitioners and hospital doctors compared two health centres with one outpatient medical department Data were collected during a defined period combined with a one-year retrospective view, official statistics on medical care, and a questionnaire completed by the patients.Setting-Two primary health care centres and one outpatient medical department in southwestern Sweden.Patients-243 insulin treated diabetic patients attending the hospital and 87 insulin treated patients attending the health centres.Main results-There were no difficulties for the expert panel to agree on which indicators were to be studied. The expert panel concluded that there was no difference between the quality of the two levels of care studied.Conclusions-Medical audit was a useful method for evaluating medical quality. Co-operation between hospital doctors and general practitioners was of great value for evaluation of the quality of primary health care.
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| 7. |
- Lindström, Kjell, et al.
(författare)
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Medical audit used for estimation of optimum level of outpatient care
- 1995
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Ingår i: Scandinavian Journal of Primary Health Care. - : Informa Healthcare. - 0281-3432 .- 1502-7724. ; 13:3, s. 175-181
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Tidskriftsartikel (refereegranskat)abstract
- Objective - To create a model for determining the optimum level of outpatient medical care and to determine this level.Design - Expert committees were established comprising one or two hospital physicians and two general practitioners who checked medical records for all outpatient visits to doctors made by a defined population during a defined period of time. the determination of optimum level was made blindly by each member of the expert committee.Setting and participants - the study comprised all visits to physicians during 10 weeks, in total more than 4000, made by the people in a Swedish community, of which 2084 were randomized.Results - Total agreement between the members of the committee was initially reached for 84% of the visits and, after a common discussion between the committee members, for 99%. A general practitioner was considered to be the optimum level of care for 76% of the patients in the total series, in the upper ages (above 80) for about 85%.Conclusion - This method seemed suitable for determining the optimum level of care in a population and may be of value when planning for an optimum health care service. Based on the results from our study it seems reasonable to assume that general practitioners whose training corresponds to that of Swedish ones are competent to treat about 75% of all consultations.
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