Glassware selection

Experiment 9 Relationship of Glassware Selection to Variability of Results... 

Frequently, preconcentration of an analyte is necessary because the detector used for quantitation may not have the necessary detectabiUty, selectivity, or freedom from matrix interferences (32). Significant sample losses can occur during this step because of very small volume losses to glass walls of the recovery containers, pipets, and other glassware. 

HPLC column, Merck, LiChrospher 60 RP Select B, 5 itm, 150 x 4-mm i.d. Autosampler vials, 1.8-mL Assorted laboratory glassware Autopipettes, calibrated... 

The term calibration is often used when in fact what is meant is verification . Calibration of an instrument or a piece of equipment (e.g. glassware) involves making a comparison of a measured quantity against a reference value. For example, to calibrate a spectrophotometer response, the appropriate reference material is selected and the spectrophotometer response to it, under the specified conditions, is measured. Then, the measured value is compared to the value quoted in the literature. Either a correction is made to the results from subsequent measurements or an adjustment is made to the instrument. 

As indicated in Section 4.1 (and as should be apparent from the discussion thus far in this chapter), titrimetric analysis methods heavily utilize solution chemistry, and therefore volumes of solutions are prepared, measured, transferred, and analyzed with some degree of frequency in this type of analysis. It should not be surprising that analytical laboratory workers need to be well versed in the selection and proper use of the glassware and devices used for precise volume measurement. 

Precautions should be taken when selecting various vessels of differing materials for the extraction of these steroids from their matrices. For example, the compatibility of some solvents with plastic extraction tubes may present some problems. If glass vessels are to be selected, it is recommended that all glassware is silanized prior to use since several steroids bind to glass surfaces. 

Sample Preparation. The three primary resoles selected for inclusion in this study were synthesized in laboratory glassware in 4000 gram batches, using 99+% commercial phenol, ion-exchanged (low formic acid content) 50% aqueous formaldehyde, reagent grade 50% aqueous sodium hydroxide, and tap water. The three resins, coded A, B, and C, were allowed to react to the same apparent bulk viscosity as measured by the Gardner-Holdt bubble tube method. In addition to the same final viscosities, the resins also were synthesized from identical mole ratios F/P = 2.0, Na/P = 0.71. 

All previous and subsequent steps of the RNA selection process should be performed following sPict RNase-free conditions. This includes the use of DEPC-Peated H20 for all solutions and the use of aerosol barrier pipette tips. Any glassware used (including elecPophoresis and elecPoelution apparatus) should be Peated with an RNase inhibitor spray (e. g., RNase AWAY, Molecular BioProducts). 

When possible, select a low-vapor-pressure liquid over a high-vapor-pressure liquid to provide faster cleanup time. In addition, nonpolar solvents are more easily removed from glassware than polar solvents (for example, methanol vs. acetone). 

Special Reagents Select reagents having as low a lead content as practicable, and store all solutions in containers of borosilicate glass. Rinse all glassware thoroughly with warm, 1 2 nitric acid followed by water. 

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