scholarly journals Evaluating Presence/Absence of Target Microbes in Microbiological Tests

2000 ◽  
Vol 83 (6) ◽  
pp. 1429-1434
Author(s):  
Robert J Blodgett ◽  
Anthony D Hitchins
Keyword(s):  
Performance Studies ◽  
Collaborative Study ◽  
False Negative ◽  
The Other ◽  
Test Results ◽  
Logistic Curve ◽  
Microbiological Method ◽  
Test Portion ◽  
Method Performance ◽  
Data Set

Abstract A typical qualitative microbiological method performance (collaborative) study gathers a data set of responses about a test for the presence or absence of a target microbe. We developed 2 models that estimate false-positive and false-negative rates. One model assumes a constant probability that the tests will indicate the target microbe is present for any positive concentration in the test portion. The other model assumes that this probability follows a logistic curve. Test results from several method performance studies illustrate these estimates.

scholarly journals Effectiveness of Temperature Modification in Decreasing the Bias in Milk Fat Test Results Between the Babcock and Ether Extraction Methods

2003 ◽  
Vol 86 (4) ◽  
pp. 768-774 ◽  
Author(s):  
Joanna M Lynch ◽  
David M Barbano ◽  
Patrick A Healy ◽  
J Richard Fleming
Keyword(s):  
Milk Fat ◽  
Collaborative Study ◽  
Extraction Methods ◽  
Test Results ◽  
Method Performance ◽  
Modified Method ◽  
Temperature Modification ◽  
Ether Extraction ◽  
Aoac Method ◽  
Performance Statistics

Abstract Both the Babcock (AOAC Method 989.04, revised Final Action 2000) and modified Mojonnier ether extraction (AOAC Method 989.05) methods are used in the dairy industry to determine the fat content of milk. Prior to revision in 1997, the Babcock method gave consistently higher fat test results than did the ether extraction. In 1997, a modification of the Babcock method was introduced to bring the results of the Babcock test into closer agreement with the ether extraction. The Babcock method was modified by lowering the temperatures used at various points in the method from about 57.5 to 48°C to increase the density of the material in the Babcock column. A collaborative study of the modification indicated it was successful in bringing the Babcock and ether extraction results into agreement but suggested that performance of the modified method was not as good as that of the unmodified method. In the present study, substantial evidence is presented to validate the success of the Babcock modification in bringing test results into agreement with ether extraction, and to document that temperature modification does not adversely affect method performance. Data were evaluated from an on-going proficiency testing program where 8–15 laboratories tested 7 milk samples in blind duplicate once every 2 months. Laboratories used the unmodified method from 1995 through 1996 and the modified method from 1998 through 1999. Compared with ether extraction, test results from the unmodified Babcock test were consistently higher by an average of 0.022% fat. For the modified Babcock test, average test results were –0.003% fat lower than with ether extraction and not significantly different from zero. AOAC method performance statistics (within-and between-laboratory precision) were equivalent for both the unmodified (Sr = 0.027, SR = 0.041, RSDr = 0.73%, RSDR = 1.08%) and modified (Sr = 0.023, SR = 0.038, RSDr = 0.60%, RSDR = 1.02%) Babcock methods. Modification of the Babcock method was successful in bringing test results into agreement with those of ether extraction.

scholarly journals The Horwitz Function Revisited

1997 ◽  
Vol 80 (3) ◽  
pp. 676-680 ◽  
Author(s):  
Michael Thompson ◽  
Philip J Lowthian
Keyword(s):  
Performance Studies ◽  
Analytical Method ◽  
Empirical Relationship ◽  
Large Data ◽  
Statistical Test ◽  
Method Performance ◽  
Data Set ◽  
Large Data Set ◽  
Low Concentrations ◽  
Special Circumstances

Abstract A statistical test was made of the Horwitz function, an empirical relationship between the reproducibility precision of an analytical method and the concentration of the analyte regardless of the nature of the analyte, matrix, and the method. The large data set (7502 observations) was compiled by Horwitz from collaborative trials (method performance studies) spanning the period 1915 to 1995. The data followed the Horwitz function well down to concentrations of about 10-8 (10 ppb), but they followed a more stringent specification at lower concentrations. This discrepancy may be due to special circumstances prevailing in collaborative trials at very low concentrations. Deviations of individual observations from the function were in large part accounted for by random variations. No consequential improvement in precision with time was found.

Determination of Ochratoxin A in Licorice and Licorice Extracts by High-Performance Liquid Chromatography Coupled with Fluorescence Detection: Collaborative Study

2013 ◽  
Vol 96 (2) ◽  
pp. 331-340 ◽  
Author(s):  
Donata Lerda ◽  
Massimo Ambrosio ◽  
Zoltan Kunsagi ◽  
Joerg Stroka ◽  
J Cea ◽  
...  
Keyword(s):  
Ochratoxin A ◽  
Fluorescence Detection ◽  
High Performance ◽  
Collaborative Study ◽  
Sodium Bicarbonate Solution ◽  
The United States ◽  
Licorice Root ◽  
Test Portion ◽  
Method Performance

Abstract A collaborative study was conducted to validate an analytical method for the determination of ochratoxin A (OTA) in licorice (root powder) and licorice extracts (paste and powder). Contents of OTA ranged from 26 to 141 μg/kg and from 8 to 52 μg/kg for licorice extracts and root material, respectively. For the analysis, a test portion is extracted with a mixture of methanol and aqueous sodium bicarbonate solution. The extract is filtered and diluted with phosphate-buffered saline; and OTA is purified with an immunoaffinity column containing antibodies specific to OTA. The purified extract is dried, reconstituted, and quantified by HPLC with fluorescence detection. Twenty laboratories from 13 European Union member states, Uruguay, Turkey, and the United States of America participated in this study. The study was evaluated according to internationally accepted guidelines. The method performance characteristics can be summarized as follows: over a working range of 7.7 to 141 μg/kg OTA, the mean recoveries were 87% for licorice root and 84–88% for licorice extracts; and the RSDs for reproducibility ranged from 10 to 17% and from 11 to 22% in licorice extracts and licorice root, respectively. The method was found to be fit-for-purpose and to fulfill legal requirements as set in EC Regulation No. 401/2006.

Collaborative Study of the International Office of Cocoa, Chocolate, and Sugar Confectionery on the Use of Motility Enrichment for Salmonella Detection in Cocoa and Chocolate

1990 ◽  
Vol 53 (8) ◽  
pp. 659-664 ◽  
Author(s):  
J. M. DE SMEDT ◽  
R. BOLDERDIJK
Keyword(s):  
Statistical Difference ◽  
Collaborative Study ◽  
The Other ◽  
Positive Test ◽  
Test Results ◽  
Milk Chocolate ◽  
Significant Statistical Difference

A comparative collaborative study was performed in 15 laboratories to validate the use of motility enrichment on Modified Semisolid Rappaport-Vassiliadis (MSRV) medium for Salmonella detection in cocoa and chocolate products. The use of MSRV was compared with a cultural procedure using Rappaport-Vassiliadis broth and selenite cystine broth as selective enrichments. Artificially contaminated milk chocolate samples as well as Salmonella reference capsules added to Salmonella-free cocoa and milk chocolate were used as test samples. Motility enrichment produced 347 positive test results compared to 320 for the cultural procedure. For samples containing a lactose positive Salmonella strain, motility enrichment was far more productive than the cultural procedure, while for the other samples no significant statistical difference in the productivity of both procedures was observed at the 5% level.

Semiautomated Method for Niacin and Niacinamide in Food Products: Collaborative Study

1979 ◽  
Vol 62 (5) ◽  
pp. 1027-1030
Author(s):  
David C Egberg
Keyword(s):  
Collaborative Study ◽  
Colorimetric Method ◽  
Food Products ◽  
The Other ◽  
Microbiological Method ◽  
Semiautomated Method

Abstract collaborative study was conducted comparing a semiautomated colorimetric niacin method with a manual colorimetric and a microbiological method for 10 food products. Seven laboratories used the microbiological method, 7 laboratories used the manual colorimetric method, and 6 laboratories used the semiautomated method. The semiautomated method was more repeatable within a laboratory and more reproducible between laboratories than was either of the other methods. The semiautomated method results compared favorably with both the microbiological and manual colorimetric method results.

Ion Chromatographic Method for Dissolved Hexavalent Chromium in Drinking Water, Groundwater, and Industrial Wastewater Effluents: Collaborative Study

1994 ◽  
Vol 77 (4) ◽  
pp. 994-1004 ◽  
Author(s):  
Kenneth W Edgell ◽  
James E Longbottom ◽  
Robert J Joyce
Keyword(s):  
Drinking Water ◽  
Hexavalent Chromium ◽  
Chromatographic Method ◽  
Collaborative Study ◽  
The Other ◽  
Method Performance ◽  
Colored Complex ◽  
Relative Standard ◽  
The Mean ◽  
Concentration Levels

Abstract A collaborative study was conducted by the U.S. Environmental Protection Agency (U.S. EPA) and the American Society for Testing Materials (ASTM) on an ion chromatographic method for the determination of hexavalent chromium (U.S. EPA method 218.6, and the ASTM equivalent method). This study was designed to determine the mean recovery and precision of analyses for hexavalent chromium in reagent water, drinking water, groundwater, and industrial wastewaters. The study design was based on Youden’s nonreplicate plan for collaborative studies of analytical methods. The test waters were spiked with hexavalent chromium at 8 concentration levels, prepared as 4 Youden pairs. A fifth Youden concentration pair was also included to determine method performance close to the method detection limit. Twenty-one laboratories were instructed to filter their test waters through a 0.45 μm filter and to adjust the pH of the filtrate to 9–9.5 with an ammonium sulfate/ammonium hydroxide buffer solution before spiking with the hexavalent chromium concentrates. A known volume, 50–250 (μL, was injected into an ion chromatograph which separated the Cr(VI), as CrO42−, on an anion exchange column. After separation, the Cr(VI) was derivatized with diphenylcarbazide and the colored complex was detected at 530 nm. The submitted data were corrected for background concentrations and analyzed by applying ASTM D-2777-86 statistical procedures and a U.S. EPA computer program. U.S. EPA method 218.6 and the equivalent ASTM method were judged acceptable for the measurement of hexavalent chromium concentrations at 1–1000 μg Cr(VI)/L. The study found that the use of a single linear calibration extending over 3 orders of magnitude yielded biased results at the very lowest concentration levels. Shorter range calibration curves yielded more accurate results. Analysis of variance (ANOVA) tests indicated that method performance was significantly different between the reagent water matrix and the other matrixes used. The recovery of Cr(VI) from the other matrixes was lower at all concentration levels with slightly less precision when compared with the reagent water data set. For reagent water, the mean recovery and the overall and single-analyst relative standard deviations were 105%, 7.8% and 3.9%, respectively. For the other matrixes, the same values were 96.7%, 11.9% and 6.3%, respectively. The method was adopted first action by AOAC INTERNATIONAL.

Evaluation of the GENE-UP® EHEC Detection Method for the Detection of Enterohemorrhagic E. coli in Select Foods: Collaborative Study: First Action Method 2020.06

2021 ◽  
Author(s):  
Ronald Johnson ◽  
John Mills ◽  
Jean-Louis Pittet ◽  
Maryse Rannou ◽  
Patrick Bird
Keyword(s):  
Detection Method ◽  
Collaborative Study ◽  
False Negative ◽  
Control Level ◽  
Reference Method ◽  
Probability Of Detection ◽  
Contamination Level ◽  
Official Method ◽  
Test Portion ◽  
E Coli

Abstract Background The GENE-UP® EHEC assay (Performance Tested MethodSM 121806) is a real-time PCR molecular detection method that utilizes Fluorescence Resonance Energy Transfer proprietary hybridization probes for the rapid detection of Enterohemorrhagic E. coli (EHEC) in select foods. Objective The purpose of this validation was to evaluate the method’s interlaboratory performance and submit the results to AOAC INTERNATIONAL for adoption as First Action Official Method of AnalysisSM for the detection of EHEC in select foods. Method The GENE-UP® method was evaluated in a multi-laboratory study as part of the MicroVal VALIDATION certification process using unpaired test portions for one food matrix, raw ground beef (85% lean). Collaborators evaluated the candidate method using either an automated or manual lysis procedure. The candidate method was compared to the ISO/TS 13136:2012 method. Data from 17 participants from 15 laboratories throughout the European Union was evaluated. Three levels of contamination were evaluated: a non-inoculated control level (0 CFU/test portion), a low contamination level (∼1 CFU/test portion) and a high contamination level (∼10 CFU/test portion). Data from the study were analyzed according to the probability of detection (POD) statistical model. Results The dLPODC values with 95% confidence interval between the candidate and reference method results were; –0.01 (–0.04, 0.02), 0.23 (0.07, 0.39) and 0.06 (0.01, 0.12) for the non-inoculated, low and high contamination levels, respectively. Conclusion For the candidate method, values obtained for repeatability and reproducibility were similar to the reference method and indicated minimal variation between samples or between laboratories. No discrepant results (false positive or false negative) were observed for each contamination. A statistical difference was calculated between the candidate and reference method at the low and high inoculation levels, with the candidate method detecting a higher number of positive samples indicating a higher sensitivity than the reference method. No differences in the recovery of the target analyte were observed between the manual and automated lysis procedures. Highlights The GENE-UP EHEC Detection Method provides end users a rapid, easy-to-use workflow for the detection of EHEC in food matrices.

Adding an expansive agent to increase the toughness of steel fibre reinforced concrete

2019 ◽  
Vol 26 (4) ◽  
pp. 197-208
Author(s):  
Leo Gu Li ◽  
Albert Kwok Hung Kwan
Keyword(s):  
Reinforced Concrete ◽  
Steel Fibre ◽  
The Other ◽  
Fibre Reinforced Concrete ◽  
Test Results ◽  
Compressive Properties ◽  
Shrinkage Cracking ◽  
Steel Fibre Reinforced Concrete ◽  
Expansive Agent ◽  
Concrete Matrix

Previous research studies have indicated that using fibres to improve crack resistance and applying expansive agent (EA) to compensate shrinkage are both effective methods to mitigate shrinkage cracking of concrete, and the additions of both fibres and EA can enhance the other performance attributes of concrete. In this study, an EA was added to fibre reinforced concrete (FRC) to produce concrete mixes with various water/binder (W/B) ratios, steel fibre (SF) contents and EA contents for testing of their workability and compressive properties. The test results showed that adding EA would slightly increase the superplasticiser (SP) demand and decrease the compressive strength, Young’s modulus and Poisson’s ratio, but significantly improve the toughness and specific toughness of the steel FRC produced. Such improvement in toughness may be attributed to the pre-stress of the concrete matrix and the confinement effect of the SFs due to the expansion of the concrete and the restraint of the SFs against such expansion.

The Determinants of Capital Adequacy Ratio: The Case of the Vietnamese Banking System in the Period 2011-2015

2017 ◽  
Vol 33 (2) ◽  
Author(s):  
Ngoc Anh Nguyen
Keyword(s):  
Banking System ◽  
Precious Metals ◽  
Capital Adequacy ◽  
The Other ◽  
Total Asset ◽  
Data Set ◽  
Hand Size ◽  
Net Interest Margin ◽  
Capital Adequacy Ratio ◽  
Positive Effect

The analysis of a data set of observation for Vietnamese banks in period from 2011 - 2015 shows how Capital Adequacy Ratio (CAR) is influenced by selected factors: asset of the bank SIZE, loans in total asset LOA, leverage LEV, net interest margin NIM, loans lost reserve LLR, Cash and Precious Metals in total asset LIQ. Results indicate based on data that NIM, LIQ have significant effect on CAR. On the other hand, SIZE and LEV do not appear to have significant effect on CAR. Variables NIM, LIQ have positive effect on CAR, while variables LLR and LOA are negatively related with CAR.

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