Filter selection reference standards

Glass Filters as a Standard Reference Material for Spectrophotometry Selection, Preparation, Certification and Use of SRM 930 and 1930, NIST Spec. Publ. 260-116, 1994. 

Carrier Gas—The instrument shall be equipped with suitable facilities to provide flow of carrier gas through the analyzer and detector at a flow rate that is constant to 1 % throughout the analysis of the sample and the reference standard. The purity of the carrier gas may be improved by flowing the carrier gas through selective filters prior to its entry into the chromatograph. 

Neutral-Density Filters. The empty reference filter holder (air reference) and then filters of various transmittance values at 440, 465, 546.1, 590, and 635 nm are scanned (these wavelengths are selected to minimize interaction between the absorbance and wavelength scales of the spectrophotometer being tested [12]). Compare the results with the values in the certificates. The certified values for the National Institute of Standards and Technology (NIST) SRM 930-e series glass... 

As previously noted in Chapter 1 of this book, the ICH s EWGs chose not to select any reference source, "...as there was concern that this reference would become the only light source used and accepted." But they did agree that a reference spectrum should be used, D65 (17). Because there is a lamp and filter associated with the D65 CIE standard, this selection automatically establishes a single reference source. The EWGs agreed on this spectrum but not necessarily the allowable deviations from that spectrum. 

We have collected 50 samples of hardened butter (sour uncolored) originating from four different factories, and analyzed the samples in duplicate with both the reference methods and NIRs (InfraAlyzer 500). The calibration is tested by selected samples representative of the calibration set as far as possible. The calculated SEC of 0.07% for moisture and solids nonfat content (Table 20.16) are compared with the standard deviation of the reference method of about 0.05%. Concerning the prediction set (test set), the results for the SEP values are comparable with those of the calibration set. It can be concluded that the calibration is useful for screening butter samples on moisture and solids nonfat content. The calibration procedure for moisture resulted in three filters giving significant information, including the filter for water at 1940 nm. The procedure for solids nonfat content selected four filters, including the filter for fat at 1759 nm, for water at 1940 nm, and for protein at 2100 nm. 

Some guidelines and standardization suggestions are in the way for facilitating the task, such as to preventively select the appropriate vendor of the filter paper and the type of it (in Europe grade 903 from Schleicher SchueU). A hematocrit of 50% is assumed to be the one corresponding to the heel blood of a neonate and any sampled blood should refer to that value (in North America a hematocrit value approaching 55% is proposed as reference). 

As part of the quality control programme and to support accreditation according to the EN lEC/ISO 17025 2005 [6], each batch of samples should contain a reference material to validate the results. As there are currently no suitable and traceable certified reference materials available, several in-house reference materials (RMs) were developed. One iron ore and one sinter dust were selected to be developed as RMs for the alpha spectrometry method and the same sinter dust along with a blast furnace dust were selected for the gamma spectrometry method. When analysing stack emission samples, one blank filter was spiked with a known amount of a certified Pb standard solution (R22-02, National Physical Laboratory, UK) and used as a reference for result validation. 

---