Distilled-deionized water, standards

Substrate Characterization. Test coupons and panels of 7075-T6 aluminum, an alloy used extensively for aircraft structures, were degreased In a commercial alkaline cleaning solution and rinsed In distilled, deionized water. The samples were then subjected to either a standard Forest Products Laboratories (FPL) treatment ( 0 or to a sulfuric acid anodization (SAA) process (10% H2SO4, v/v 15V 20 min), two methods used for surface preparation of aircraft structural components. The metal surfaces were examined by scanning transmission electron microscopy (STEM) In the SEM mode and by X-ray photoelectron spectroscopy (XPS). 

Materials. Aldicarb standards were obtained from the United States Environmental Protection Agency (USEPA), Quality Assurance Section and from Union Carbide Corporation. Crystalline samples of carbofuran and 3-hydroxycarbofuran were supplied by the Agricultural Chemical Group of FMC Corporation. Reference standards of methomyl (99% pure) and oxamyl (99% pure) were obtained from USEPA. HPLC grade methanol was purchased from Burdick and Jackson, Inc. Methylene chloride used for bulk extractions of the carbamate pesticides in solution was recovered, distilled and reused. Analytical reagent grade chemicals and solvents were used in all experiments. Doubly distilled deionized water was used for solution rate studies. Deionized distilled water (DDW) was used for dilutions in reactive ion exchange experim ts., , ... 

Ammonium-N standard solution, 140 pg mM nitrogen - weigh 0.661 g ammonium sulphate (dried at 105°C for 1 h and cooled in a desiccator) into a 100-ml beaker and dissolve in ammonia-free water (distil deionized water acidified with sulphuric acid), transfer with washings to a 1-1 volumetric flask and make up to the mark with the ammonia-free water and mix. This should be stored in a refrigerator, but a quantity allowed to warm to room temperature in a stoppered container before use. 

Figure 3. Standards recovered from 10 mL of distilled-deionized water on an ODS precolumn. Peak identities 4, 0.14 pg of caffeine 5, 0.20 pg of pentachlorophenol 7, 0.061 pg of m-nitroandine 8, 0.15 pg of atrazine 9, 0.40 pg of quinoline 10, 0.26 pg of 2,6-dichloroaniline 11, 0.14 pg of N-nitrosodiphenylamine and 12, 0.055 pg of pyrene. Conditions for concentration 10-mL sample enriched on an ODS-packed precolumn. Analytical separation was on Zorbax ODS, 250-mm by 4.6-mm i.d. column. Mobile-phase gradient was 100% pH 7,0.1 M acetate buffer for 2 min followed by ramp to 90% acetonitrile/10% pH 7, 0.1 M acetate buffer (v/v) in 20 min at 1.0-mL/min flow rate. Detection was at 254 nm. (Reproduced with permission from reference 18.)...

Figure 5. Standards recovered from 10 mL of distilled-deionized water on a strong-anion-exchanger packed precolumn. Peak identities 1, 0.87 pg of phenoxyacetic acid 2, 1.2 pg of p-chlorobenzoic acid 3, 0.33 pg of 2-naphthalenesulfonic acid and 12, 0.055 pg of pyrene. Conditions for concentration, analytical separation, mobile-phase gradient, and detection were the same as in Figure 3. (Reproduced with permission from...

Silica standard solutions were prepared by fusing a weighed amount of powdered quartz with Na2C03 in a platinum crucible, following a procedure described in Maxwell ( 5). The resulting fused material was dissolved in distilled-deionized water and diluted to a... 

Chemicals. Sources of the standards used are described elsewhere (ii 15) Standard solutions of the model compounds were prepared in either distilled deionized water or pesticide grade acetonitrile. The chromatographic mobile phase was a 2 3 (v/v) mixture of acetonitrile and ammonium formate buffer prepared by adjusting a 0.05 M solution of formic acid to pH 4.5 with concentrated ammonia. 

Procedure Formaldehyde sample from the sampler was injected into the carrier stream where it was mixed with pararosaniline and then sulfite to form an alkylsulfonic acid chromophore which can be monitored spectrophotometrically at 570 nm For calibration, standard formaldehydes were sequentially introduced after a stable baseline was obtained At least five consecutively reproducible peaks were recorded for each concentration After each study or each day of operation, the FIA system was cleaned to remove any pararosaniline film, alkylsulfonic acid colored product, or particulate matters This reduced the scattered light in the absorption cell and the staining of the tubing walls. The clean-up procedure was initiated by running distilled deionized water through the system for five minutes followed by another five minutes washing with 0 1 N nitric acid and then flushing the unit for 30 minutes with deionized water The chromotropic acid method was used for comparative studies, and the analytical procedure for the chromotropic acid method was based on the procedure recommended by the American Public Health Association (12) ... 

RB-HVP was subjected to direct solvent extraction followed by high vacuum distillation (77). Ten g of PB-HVP was hydrated with 100 mL of odor-free distilled-deionized water. The mixture was spiked with 25 pL of an internal standard solution (5.0 pg/pL of 2-ethyl butanoic acid 3.3 pg/pL of 4-tert-amyphenol and 4.3 pg/pL of 2-methyl-3-heptanone in methanol). The solution was extracted with ether (2 x 50 mL). Extractions were conducted for duplicate... 

Rinse all of the flameless apparatus glassware with 1 9 HNOj, then rinse with distilled-deionized water and set on a paper towel to drain. This includes the volumetric flasks for the standards, the evolution flask, and the vapor trap. 

To prepare. Vitamin C standard. Weigh 50 mg of /-ascorbic acid to the nearest 0.1 mg, dissolve in a 50-mL volumetric flask, and dilute to yolume with distilled deionized water. Prepare the day of use. This is a 0.1% solution. Prepare serial dilution of this to obtain also 0.05% and 0.02% standards. 

Lansens, P., Meuleman, C. and Baeyens, W. (1990) Long-term stability of methylmercury standard solutions in distilled, deionized water. Anal. Chim. Acta, 229, 281-285. 

Issues of cleanliness in the laboratory are discussed by APHA (1980). The essentials are Water double distilled, deionized water, withregularquality control. All reagents should be prepared using this water. Laboratory for major elements a regularly cleaned laboratory is sufficient. For most trace elements it is essential that the laboratory is dust-free. Equipment the most important factor is proper cleaning of all items which come in contact with extractant solutions. All beakers, in addition to standard cleaning, shonld be acid-washed in concentrated HQ, and rinsed thoroughly in double distilled water. 

All samples were dissolved in triple distilled, deionized water to a concentration of 1 mg/mL. Serial dilutions were made using a 10% run buffer in water. Individual peptide standards, the nine peptide standard mixture, and Dynotphin A fragment 1-13, were obtained from Sigma Chemical Co. (St. Louis, MO). A 0.1M phosphate buffer at pH 2.5 was used for all peptide separations. 

Water for injection (WFI) is the most widely used solvent for parenteral preparations. The USP requirements for WFI and purified water have been recently updated to replace the traditional wet and colorimetric analytical methods with the more modern and cost-effective methods of conductivity and total organic carbon. Water for injection must be prepared and stored in a manner to ensure purity and freedom from pyrogens. The most common means of obtaining WFI is by the distillation of deionized water. This is the only method of preparation permitted by the European Pharmacopoeia (EP). In contrast, the USP and the Japanese Pharmacopeias also permit reverse osmosis to be used. The USP has also recently broadened its definition of source water to include not only the U.S. Environmental Protection Agency National Primary Drinking Water Standards, but also comparable regulations of the European Union or Japan. 

Standard buffers can be purchased as prepared solutions or as powders that are dissolved in distilled or deionized water. In the latter case, the powder is typically dissolved in 100 mL of distilled or deionized water for use. Buffers may be color-coded such as green or yellow for pH 7.00, pink for pH 4.01, and blue for pH 10.00. 

Deionized water often meets the pharmacopoeial criteria laid down for purified water . Sometimes, however, further purification may be necessary to attain this standard. This often entails a distillation or reverse-osmosis step. Deionized water will, however, not meet the pharmacopoeial requirements for WFI. WFI is best generated by distillation of deionized water. Distillation entails converting water to vapour by heat, followed by passing over a condenser, which results in condensation of pure water. Dissolved minerals and most organics are not volatile at 100°C. 

Magnesium stock solution—using distilled or deionized water prepare six magnesium standards in 100 ml volumetric flasks of 0.1, 0.3, 0.4, 0.5, 0.6, and 0.8 pg mk concentration from the stock solution. Also prepare 250 ml of a 0.2 pg mpi magnesium standard. 

Calibration Select two standard buffers to bracket, if possible, the anticipated pH of the unknown substances. These commercially available standards and the sample should be at the same temperature, within two degrees. Set the temperature compensator of the pH meter to the temperature of the samples and standards. Follow the manufacturer s instructions for setting temperature compensation and for adjusting the output during calibration. Rinse the electrodes with distilled or deionized water, and blot them dry with clean, absorbent laboratory tissue. Place the electrode(s) in the first standard buffer solution, and adjust the standardization control so that the pH reading matches the stated pH of the standard buffer. Repeat this procedure with fresh portions of the first buffer solution until two successive readings are within 0.02 pH units with no further adjustment. Rinse the electrodes, blot them dry, and place them in a portion of the second standard buffer solution. Following the manufacturer s instructions, adjust the slope control (not the standardization control) until the output displays the pH of the second standard buffer. 

Where an estimated time is stated it is assumed that standard reagents, resins in the appropriate ionic form, and all other ec[uipmenl items are immediately available. Where deionized water is specified, distilled water may be used as an alternative. Where methyl orange indicator is stated, BDH 4.5 indicator may be substituted if preferred. 

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