S.L. 437.75 ст. 7method: a at the level of negative, those in each test under identical response should be in the range has to to spiked at this tests on the standard should be and or triplicate clean up and expressed as correspond to dioxin/furan level in the TEQ level chemicals sample around recovery loss values i

Screening methodsof analysis 7.1. Introduction Different analytical approaches can be performed using a screening pure screening approach and a quantitative approach. Screening approach

The response of samples is compared to that of a reference sample interest. Samples with a response less than the reference are declared with a higher response are suspected positives. Requirements: - A blank and a reference sample(s) have to be included series, which is extracted and tested at the same time conditions. The reference sample must show a clearly elevated in comparison to a blank. - Extra reference samples 0,5 × and 2 × the level of interest included to demonstrate the proper performance of the test of interest for the control of the level of interest. - When testing other matrices, the suitability of the reference sample(s) be demonstrated, preferentially by including samples shown by HRGC/HRMS contain a TEQ level around that of the reference sample or else a blank level. - Since no internal standards can be used in bioassays, repeatability are very important to obtain information on deviation within one test series. The coefficient of variation below 30%. - For bioassays, the target compounds, possible interferences maximum tolerable blank levels should be defined. Quantitative approach

The quantitative approach requires standard dilution series, duplicate DETERMINATION OF DIOXIN-LIKE PCBs IN FOODSTUFFS

measuring as well as blank and recovery controls. The result may be TEQ, thereby assuming that the compounds responsible for the signal the TEQ principle. This can be performed by using TCDD (or a standard mixture) to produce a calibration curve to calculate the TEQ extract and thus in the sample. This is subsequently corrected for the calculated for a blank sample (to account for impurities from solvents and used), and a recovery (calculated from the TEQ level in a quality control the level of interest). It is essential to note that part of the apparent may be due to matrix effects and/or differences between the TEF bioassays and the official TEF values set by WHO.

Requirements for methods of analysis used for screening GC/MS methods of analysis and bioassays may be used for screening. GC/MS methods the requirements as laid down in point 6 are to be used. For cell based bioassays specific requirements are laid down in point 7.3 and for kit-based bioassays in point 7.4. Information on the number of false-positive and false-negative results a large set of samples below and above the maximum level or action level is necessary, in comparison to the TEQ content as determined by a confirmatory method of analysis. Actual false negative rates should be under 1%. The rate of false positive samples should be low enough to make the use of a screening tool advantageous.

Positive results have always to be confirmed by a confirmatory method of (HRGC/HRMS). In addition, samples from a wide TEQ-range should be HRGC/HRMS (approximately 2% to 10% of the negative samples). correspondence between bioassay and HRGC/HRMS results should available.

Specific requirements for cell-based bioassays When performing a bioassay, every test run requires a series of reference concentrations of TCDD or a dioxin/furan mixture (full dose-response curve with a R2 > 0,95). However, for screening purposes an expanded low level curve for analysing low level samples could be used. TCDD reference concentration (about 3 × limit of quantification) on a quality control sheet should be used for the outcome of the bioassay over a constant time period. An alternative could be the relative response of a reference sample in comparison to the TCDD calibration line since the response of the cells may depend on many factors. Quality control (QC) charts for each type of reference material should recorded and checked to make sure the outcome is in accordance with the stated guidelines. particular for quantitative calculations, the induction of the sample dilution used must be within the linear portion of the response curve. Samples above the linear portion of the response curve must be diluted re-tested. Therefore, at least three or more dilutions at one time are recommended to be tested. The percent standard deviation should not be above 15% in a triplicate determination for each sample dilution and not above 30% between three independent experiments. DETERMINATION OF DIOXIN-LIKE PCBs IN FOODSTUFFS

- The limit of detection may be set as 3 × the standard deviation blank or of the background response. Another approach is to apply a response above the background (induction factor 5 × the solvent blank) calculated calibration curve of the day. The limit of quantification may be set as standard deviation of the solvent blank or of the background response response that is above the background (induction factor 10 × the calculated from the calibration curve of the day. 7.4. Specific requirements for kit-based bioassays (1)

- Manufacturer’s instructions for sample preparation and analyses be followed. - Test kits should not be used after the expiration date. - Materials or components designed for use with other kits used. - Test kits should be kept within the specified range temperature and used at the specified operating temperature. - The limit of detection for immunoassays is determined standard deviation, based on 10 replicate analysis of the divided by the slope value of the linear regression equation. - Reference standards should be used for tests at the laboratory sure that the responsiveness to the standard is within range.