Sample Exchange Program

The participation in interlaboratory sample exchange programs (such as round robins and/or PTs). 

Campbell, D.H., "Microscopical Description of Clinker Sample No. 44ICMA Sample Exchange Program," Proceedings of the 16th International Conference on Cement Microscopy, International Cement Microscopy Association, Richmond, Virginia, 1994a, pp. 377-380. 

We thank Ms. Wei-Chee Tan for the preparation of the catalyst samples. This work was supported by the National Science Foundation (CTS-9403199), the international cooperative program NSF-CONICET (INT-9415590), and the Exxon Education Foundation We thank the University of Mar del Plata for a fellowship (WEA), as part of the international exchange program sponsored by the University of Oklahoma and the University of Mar del Plata. 

External laboratory QC involves reference help from other laboratories and participation in national or international interlaboratory sample and data exchange programs such as Proficiency Testing (PT). Such programs may involve ... 

As with all modern analytical programs, an essential keystone for success is a sound analytical quality control and assessment strategy, which should always, where possible, include the exchange of samples between different analytical laboratories and the use of round-robin external quality assurance schemes. External schemes for folate and cobalam-ins are already in existence in several countries some other water-soluble vitamin assays are performed regularly by a sufficient number of different laboratories for external sample exchange schemes to be feasible and cost-effective, while others are too specialized and perhaps too rarely performed for regular... 

Note. If the N dimensions yield very different numerical values, such as 105 3 mmol/L, 0.0034 0.02 meter, and 13200 600 pg/ml, the Euclidian distances are dominated by the contributions due to those dimensions for which the differences A-B, AS, or BS are numerically large. In such cases it is recommended that the individual results are first normalized, i.e., x = (x - Xn,ean)/ 5 t, where Xmean and Sx are the mean and standard deviation over all objects for that particular dimension X, by using option (Transform)/(Normalize) in program DATA. Use option (Transpose) to exchange columns and rows beforehand and afterwards The case presented in sample file SIEVEl.dat is different the individual results are wt-% material in a given size class, so that the physical dimension is the same for all rows. Since the question asked is are there differences in size distribution , normalization as suggested above would distort tbe information and statistics-of-small-numbers artifacts in the poorly populated size classes would become overemphasized. 

A fully automated system for performing detailed studies has been developed to improve the reproducibility and throughput (Fig. 12.2) [8]. It consists of two functional components a sample-deuteration device and a protein processing unit. The preparation operations (shown at the top of Fig. 12.2) are performed by two robotic arms equipped with low volume syringes and two temperature-controlled chambers, one held at 25 °C and the other held at 1 °C. To initiate the exchange experiment, a small amount of protein solution is mixed with a deuter-ated buffer and the mixture is then incubated for a programmed period of time in the temperature-controlled chamber. This on-exchanged sample is immediately transferred to the cold chamber where a quench solution is added to the mixture. 

Fig. 12.2 Diagram of a fully automated system for acquiring H/D exchange MS data starting with a stock solution of the nondeuterated protein. In this system [8], the liquid handler mixes a small amount of concentrated protein solution with a selected deuterated buffer and the mixture is incubated for a programmed period of time. The exchange reaction is conducted in a temperature-controlled chamber held at 25 °C. The mixture is then transferred to an acidic quench solution held at 1 °C. After quenching the exchange reaction, the entire sample is injected onto an LC-MS system...

GTPCH activity measurements are not available in external control programs and can only be compared by exchanging results from other laboratories (for examples see www.bh4.org). Control biopterin and neopterin samples are commercially available from Dr. Schircks Laboratories, Jona, Switzerland (www.schircks.com). We recommend using internal controls (e.g., normal control fibroblasts in each enzyme... 

Sample chambers for spectrometers come in two varieties—those holding only one cuvette at a time (single-beam) and those holding two cuvettes, one for a reference, usually solvent, and one for sample (double-beam). In a double-beam instrument, the sample spectrum is continuously corrected by subtraction of the reference spectrum. In the past, single-beam instruments were usually less expensive but more cumbersome to use because reference and sample cuvettes required constant exchange. However, modern singlebeam instruments with computer control and analysis can be programmed to correct automatically for the reference spectrum, which may be stored in a memory file. The use of both types of instruments is outlined in the applications section. 

A careful study by McDermott and co-workers of the high-K+ and low-K+ states of the KcsA channel has focused exclusively on the selectivity filter.101 They discovered that low K+ also induces the "non-con-ductive" or "collapsed" structure of the selectivity filter at neutral pH, but only if the sample remains well hydrated this state is lost if the bulk buffer is removed from the NMR rotor after spinning. Comparison of the measured chemical shifts with predictions by the SHIFTX and SPARTA programs identified the crystal structures that are most consistent with the selectivity filter conformations in the high-K+ and low-K+ proteolipo-some samples. Titrations of the chemical shift changes were used to measure site-specific affinities for K+. Based on the slow exchange rate between these conformations (<500 s 1), the authors suggest that the low-K+ conformation is relevant to channel inactivation rather than to conduction.101... 

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