Biomedical subjects

J Stroka

Publications and source records attributed to J Stroka.

11 recordsLinked to original sources

PubMed2004

Trichothecenes: reference materials and method validation.

The frequent contamination of food and feed with trichothecene mycotoxins, the high consumption of these products, and the potential risk associated herewith, has led to an increasing public awareness and therefore to the establishment of measures to control trichothecene contamination. The analytical difficulty and the economic importance of controlling trichothecenes in food and feed support the need for certified reference materials (CRMs) and validated methods. They form invaluable tools to ensure comparability and traceability in analytical measurements and are very useful for the implementation of written standards, legislation/regulations and laboratory accreditation. The present paper provides an overview of previous work, current strategies and prospectives for the production of CRMs and validation of analytical methods in the field of trichothecene analysis. Additional information is given on methodological demands, normative frameworks and commonly accepted procedures.

Chemistry Techniques, Analytical↗

PubMed2004

Novel sampling methods for the analysis of mycotoxins and the combination with spectroscopic methods for the rapid evaluation of deoxynivalenol contamination.

A novel non-destructive sampling approach is described for the identification of food matrices contaminated with deoxynivalenol and other mycotoxins. This technique is different from currently applied sampling procedures for this purpose and is based on the principle that surface material from the tested goods is collected on a filter and brought to chemical or spectroscopic analysis. This approach has been applied to several matrices and mycotoxins, with a focus on those mycotoxin-matrix combinations that are of main relevance due to current or future legislation. Tests were carried out with a facility that has been shown to be suitable to process large quantities of materials at points of transaction, such as harbour. Further experiments with a small sampling lance prototype showed that analytical results from the chemical analysis of the tested goods can be correlated with the results obtained with this novel sampling procedure.

Chemistry Techniques, Analytical↗

PubMed2004

Screening survey of deoxynivalenol in beer from the European market by an enzyme-linked immunosorbent assay.

Deoxynivalenol (DON) was analysed in 313 beer samples collected from the European retail market using a commercially available immunoassay kit (enzyme-linked immunosorbent assay, ELISA). The incidence rate was about 87%, while most samples (73%) had contamination levels lower than 20 ng m(-1). The contamination ranged between 4.0 and 56.7 ng ml(-1), with an average of 13.5 ng ml(-1). A statistically significant correlation between alcohol levels and DON contamination was found, as well as a significant difference between bottom, top and spontaneous fermenting beers. Twenty-seven beer samples were compared using a second ELISA kit and a good correlation was obtained between the two kits (r = 0.93). Although when compared with gas chromatography-mass spectrometry the ELISA tended to overestimate the results, a good correlation (r=0.94) between the two methods was observed. Monitoring of DON in beer is important considering that DON production is dependent on the weather and that it can contribute significantly to the tolerable daily intake of DON, especially for frequent beer consumers.

Beer↗

PubMed2003

Determination of the artificial sweetener Sucralose by capillary electrophoresis.

The artificial intense sweetener 1,6-dichloro-1,6-dideoxy-beta-D-fructofuranosyl-4-chloro-4-deoxy-alpha-D-galactopyranose (Sucralose) was determined by capillary electrophoresis with indirect ultraviolet absorption in a 3,5-dinitrobenzoic acid buffer at pH 12.1. The method allowed determination of Sucralose in low-calorie soft drinks, without any sample clean-up over a linear range of 42-1000 mg x l(-1) (r=0.9991). The limits of detection and determination were 28 and 42 mg x l(-1), respectively, and the repeatability for a mean concentration of 100 mg x l(-1) was 4.2% for the signal area and 3.6% for the migration time, which were deemed satisfactory for use in food control.

Beverages↗

PubMed2002

Correction of analytical results for recovery: a comparison of the method performance characteristics from recent collaborative trials studies for aflatoxin quantification using conventional and robust statistics.

Results from recently conducted collaborative trials on the determination of aflatoxin B(1) in various matrices have been evaluated to establish whether the use of recovery data would result in a distinct change of the relative between-laboratory standard deviation (RSD(R)) of the corrected data compared with the uncorrected data. In addition, we applied conventional and robust statistics to evaluate whether the impact of the use of recovery data on the estimation of RSD(R) depended on the statistical method applied for data analysis. This investigation was based on means before and after correction for recovery. The method performance characteristics were calculated using results from naturally contaminated test materials, while the results from test materials fortified with the target analytes were used to estimate the recovery. The study revealed that applying conventional and robust statistics in general led to comparable estimates for RSD(R). The comparison about the use of recovery data showed that in most cases, the RSD(R) obtained from the analysis of aflatoxin B(1) decreased after correction of the results for recovery. This tendency was similar when the comparison was done using robust or conventional statistics. However, in three cases, conventional statistics yielded a higher RSD(R) for the corrected data, whereas robust statistics showed the opposite. Looking carefully at the data, the treatment of conventional statistics indicated that the way outliers are detected and removed could result in an under- or overestimation of RSD(R). Applying the law of error propagation revealed that most likely the correlation between the uncorrected data and the recovery rate led to a reduced variability of the data corrected for recovery.

Aflatoxin B1↗

PubMed2000

Immunoaffinity column clean-up prior to thin-layer chromatography for the determination of aflatoxins in various food matrices.

A one-dimensional TLC method to determine aflatoxins (B1, B2, G1, G2) in various food matrices was elaborated which abstains fully on the use of chlorinated solvents. It implements an immunoaffinity clean-up step after extraction with methanol. The aflatoxins were quantified by densitometry. The method has shown to be rapid and efficient. In-house performance characteristics were established. The limit of quantification was found to be significantly lower than current regulatory limits for aflatoxin control outside and within the European Community. The obtained recovery and precision data gave a strong indication, that the method is likely to give satisfactory performance if tested in a future collaborative trial.

Aflatoxins↗

PubMed2000

Development of a simplified densitometer for the determination of aflatoxins by thin-layer chromatography.

A simple, miniaturised and low power consuming (battery, fully semiconductor based) detector cell (SeBaDeC) was developed for the densitometric measurement of aflatoxins on TLC plates. A UV-light emitting diode (UV-LED) with a peak emission wavelength of 370 nm was used for fluorescence excitation, while a photo diode with a peak sensitivity of 440 nm in combination with a 418 nm cut-off filter was applied for detecting the fluorescence intensity. The resulting signal was further amplified by means of a commonly used operational amplifier integrated circuit (OA) and directly converted into a digital signal with a simple analogue-digital-converter (ADC). This signal was recorded at the serial (RS232) port of a portable PC and processed with a spreadsheet program. The software used for data recording is freeware and available in its source code, and the long lifetime of the UV-LED (up to 10 000 h) permits a maintenance free application of this device. This simplified device has shown to be able to detect concentrations of aflatoxins of 1 ng, thus offering a cheap and sensitive alternative to currently available TCL scanners.

Aflatoxins↗

PubMed1999

Investigation of various extractants for the analysis of aflatoxin B1 in different food and feed matrices.

Various extractants were investigated concerning their suitability for aflatoxin B1 determinations in different matrices including spices, infant formula and animal feed employing an immunoaffinity clean-up procedure. It was shown that the use of aqueous acetonitrile extractants was limited due to the fact that dry sample material can absorb significant amounts of water from the extractant. This can result in recoveries that are too high and therefore in incorrect values for the aflatoxin concentration if aliquots are taken for further analysis. A correction of the results by recovery calculation using spiked blank material is unsuitable, since material from the same group of food (e.g. paprika powder) or feed can vary significantly in the recovery values. Therefore it is recommended that aqueous methanol extractants are used, since no significant interaction with matrix constituents was observed. In addition, aqueous acetone extractants are a useful alternative with some limitations.

Aflatoxin B1↗

PubMedDate not supplied

Immunoaffinity column cleanup with liquid chromatography using post-column bromination for determination of aflatoxins in peanut butter, pistachio paste, fig paste, and paprika powder: collaborative study.

A collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for the determination of aflatoxin B1 and total aflatoxins at European regulatory limits. The test portion is extracted with methanol-water (8 + 2) for dried figs and paprika, and with methanol-water (8 + 2) plus hexane (or cyclohexane) for peanut butter and pistachios. The sample extract is filtered, diluted with phosphate buffer saline, and applied to an immunoaffinity column. The column is washed with water and the aflatoxins are eluted with methanol. Aflatoxins are quantitated by reversed-phase LC with post-column derivatization (PCD) involving bromination. PCD is achieved with either an electrochemical cell (Kobra cell) and addition of bromide to the mobile phase or pyridinium hydrobromide perbromide. Determination is by fluorescence. Peanut butter, pistachio paste, dried fig paste, and paprika powder samples, both naturally contaminated with aflatoxins and containing added aflatoxins, were sent to 16 collaborators in 16 European countries. Test portions of samples were spiked at levels of 2.4 and 9.6 ng/g for total aflatoxins which included 1.0 and 4.0 ng/g aflatoxin B1, respectively. Recoveries for total aflatoxins ranged from 71 to 92% with corresponding recoveries for aflatoxin B1 of 82 to 109%. Based on results for spiked samples (blind duplicates at 2 levels) as well as naturally contaminated samples (blind duplicates at 4 levels, including blank), the relative standard deviation for repeatability ranged from 4.6 to 23.3% for total aflatoxins and from 3.1 to 20.0% for aflatoxin B1. The relative standard deviation for reproducibility ranged from 14.1 to 34.2% for total aflatoxins, and from 9.1 to 32.2% for aflatoxin B1. The method showed acceptable within-laboratory and between-laboratory precision for all 4 matrixes, as evidenced by HORRAT values <1, at the low levels of determination for both total aflatoxins and aflatoxin B1.

Aflatoxin B1↗

PubMedDate not supplied

Determination of aflatoxin B1 in baby food (infant formula) by immunoaffinity column cleanup liquid chromatography with postcolumn bromination: collaborative study.

A collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for determination of aflatoxin B, in a milk powder based infant formula at a possible future European regulatory limit (0.1 ng/g). The test portion was extracted with methanol-water (8 + 2 [v + v]), filtered, diluted with water, and applied to an immunoaffinity column. The column was washed with water to remove interfering compounds, and the purified aflatoxin B1 was eluted with methanol. The separation and determination of the aflatoxin B1 was performed by reversed-phase LC and detected by fluorescence after postcolumn derivatization (PCD) involving bromination. PCD was achieved with either pyridinum hydrobromide perbromide (PBPB) or an electrochemical (Kobra) cell by addition of bromide to the mobile phase. The baby food (infant formula) test samples, both spiked and naturally contaminated with aflatoxin B1, were sent to 14 laboratories in 13 different European countries. Test portions were spiked at levels of 0.1 and 0.2 ng/g for aflatoxin B1. Recoveries ranged from 101 to 92%. Based on results for spiked test samples (blind pairs at 2 levels) and naturally contaminated test samples (blind pairs at 3 levels), the relative standard deviation for repeatability (RSDr) ranged from 3.5 to 14%. The relative standard deviation for reproducibility (RSDR) ranged from 9 to 23%. Nine participants used PBPB derivatization, and

Aflatoxin B1↗

PubMedDate not supplied

Determination of ochratoxin A in green coffee by immunoaffinity column cleanup and liquid chomatography: collaborative study.

A collaborative study was conducted to evaluate a method using immunoaffinity column cleanup with liquid chromatography (LC) for the determination of ochratoxin A (OTA) in green coffee at levels that could be included in possible future regulations of the European Union. The test portion was extracted with methanol-3% aqueous sodium hydrogen carbonate solution (50 + 50, v/v). The extract was filtered, and the filtrate was diluted with phosphate-buffered saline and applied to an immunoaffinity column containing antibodies specific for OTA. After washing, the toxin was eluted from the column with methanol and quantified by LC with fluorescence detection. Pairs of 4 homogeneous noncontaminated and naturally contaminated materials (mean levels of < 0.12, 2.44, 5.15, and 13.46 ng/g) and blank samples (< 0.12 ng/g) for spiking were sent to 20 participant laboratories from 8 countries. The materials were analyzed according to the method description and all difficulties encountered in the analysis were reported. Statistical analysis was carried out according to the Harmonized Protocol of the International Union of Pure and Applied Chemistry. The relative standard deviation for repeatability (RSDr) ranged from 7.42 to 20.94%, and the relative standard deviation for reproducibility (RSDR) ranged from 16.34 to 29.17%. The method showed acceptable within-laboratory and between-laboratories precision for green coffee materials, as evidenced by HorRat values of < or = 0.85, at the studied range, for spiked and naturally contaminated materials. The mean recovery was 92.8% for green coffee material spiked with OTA at a level of 4.82 ng/g.

Buffers↗