Water testing sampling methods

In this study, the stability of bromate in water samples with different matrix constituents was investigated. Water samples ranged from soft to hard and were spiked with 1 mg/L bromide, 0.5 mg/L chlorite and 0.5 mg/L chlorate. These levels are considered to be higher than those normally observed in waters for these three anionic species. Each sample was also spiked with 2.5, 10 and 25 pg/L of bromate. Fiuthermore, a 5 pg/L of bromate standard in deionized water was also prepared. Brown glass bottles capped with polypropylene tops and PTFE inserts were used as sample containers. Samples were stored in the dark at 4 °C. Tables 2.5 and 2.6 summarize matrix constituents of each sample, preservation method spike levels and results of analyses. The results clearly demonstrate that for the two high and low total hardness waters tested, samples containing 2.5 to 25 pg/L bromate were stable for at least 20 days and that the addition of 50 mg/L ethylenediamine (EDA) preservative did not affect the results, as illustrated in Table 2.6. The results also confirm that 5 pg/L bromate standard made up in deionized water had the same stability over this period. 

In the Phadebas TM amylase test (72) (Pharmacia Labs) the substrate was a water insoluble cross-TTnked blue starch in tablet form which also contains some inert ingredients, sodium and potassium phosphate buffer salts and sodium chloride. This polymer was hydrolyzed by amylase into water soluble blue starch fragments. After centrifugation the absorbance of the blue supernatant was proportional to the activity of amylase present in the test samples. The day to day variation on a quality control serum had a coefficient of variation of 2.7% based on 30 days of data in our laboratory. The method is simple, reproducible and uses microquantities of serum. 

The limitations of ELISA methods include the specificity of antibodies, the concentrations of primary antibody and antigen, and the type of reaction solution. Nonspecific binding of either of the antibodies to related antigens, unrelated proteins of other bacteria, or even the microtiter plate may lead to false positive reactions.49,52 57 Use of a monoclonal antibody may decrease crossreactivity with other antigens. For detection of low numbers of bacteria, as in drinking water, the sample may be filtered to concentrate the cells or cultured in a selective broth until it reaches the minimum detection limit for ELISA.49,58 Commercial test kits using dipsticks, immunoblots, and sandwich ELISA methods have been developed for the identification of pathogenic bacteria.58,59... 

Spencer and Brewer [144] have reviewed methods for the determination of nitrite in seawater. Workers at WRc, UK [ 145] have described an automated procedure for the determination of oxidised nitrogen and nitrite in estuarine waters. The procedure determines nitrite by reaction with N-1 naphthyl-ethylene diamine hydrochloride under acidic conditions to form an azo dye which is measured spectrophotometrically. The reliability and precision of the procedure were tested and found to be satisfactory for routine analyses, provided that standards are prepared using water of an appropriate salinity. Samples taken at the mouth of an estuary require standards prepared in synthetic seawater, while samples taken at the tidal limit of the estuary require standards prepared using deionised water. At sampling points between these two extremes there will be an error of up to 10% unless the salinity of the standards is adjusted accordingly. In a modification of the method, nitrate is reduced to nitrite in a micro cadmium/copper reduction column and total nitrite estimated. The nitrate content is then obtained by difference. 

Before adopting this method at the ordnance plant, sections of pipelines were chosen for test samples, to determine if the swab and pig method would satisfactorily clean these contaminated pipes. One half the sections were cleaned by this method and the other half was thoroughly flushed with water. They were allowed to dry and then were subjected to initiation by fires. The sections that had been flushed with water ignited and burned vigorously. The sections that had been subjected to cleaning with the swab and pig had no product remaining that would support combustion. 

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). 

Another result of the requirements to distribute homogeneous test material is that some pretreatment steps usually performed on routine samples are not done on the interlaboratory sample. For example, in interlaboratory rounds for the determination of metals by inductively coupled plasma, the test material is often a solution of the metals in water. Often a method requires extraction of the metals by acid digestion of the field sample, a procedure that will have significant uncertainty in terms of recovery of analyte. 

Figure 2. Comparison of mutagenic activity in lyophilized and XAD-concentrated drinking water. The sampling 7000-fold concentration with either XAD-4/8 (XAD) or freeze-drying (FD) XAD-4/8 elution with acetone (neutral fraction) freeze-drying elution successively with acetone, ether, and DM SO and subsequent mutagenicity testing with strains TA98 and TA100 were as described in Materials and Methods. Each point represents the average of three plates, and 0.2 mL of concentrate corresponds to 1.4 L of water per plate.

Normal-phase HPLC is a good complementary technique to reversed-phase HPLC in that it often gives different selectivity. It is also more effective in separating geometric isomers than reversed-phase HPLC. The main problem with normal-phase HPLC is that aqueous samples are not normally compatible with the technique. Since many of the stress-testing samples contain water, normal-phase HPLC is rarely used as the primary analytical technique for stress test samples. Nonetheless, normal phase can be a useful complementary technique to reversed-phase HPLC. A detailed discussion on the development of normal-phase HPLC methods is beyond the scope of this chapter. 

The dissolution method for pentazocine hydrochloride tablets utilizes a UV determination of pentazocine in filtered test samples at 278 nm. The apparatus used is USP number two at 50 rpm with water as the dissolution medium. The solutions are measured in hydrochloric acid diluted with dissolution medium to give 0.01 N HC1 and quantitatively compared to a suitable standard (46). 

Pyridine or another solvent with a large solvation capacity (acetonitrile, dimethyl-formamide) are mostly used as solvents in the silylation reactions. Pyridine provides on some phases a broad tailing peak and can overlap lower components. Lehrfeld [85] therefore developed a procedure for the removal of pyridine from the sample before the analysis. During the derivatization anhydrous conditions are essential because the derivatives are decomposed by traces of water. However, a method has been described for the preparation of silyl derivatives even in the presence of water its principle consists in the addition of such a large excess of the silylating agent that all of the water present is removed [86]. This can be of importance in the treatment of samples that cannot be previously dried as losses of more volatile components could occur. The extent to which the presence of water affects the reaction yield and whether or not a large excess of by-products has an adverse effect must be tested, however. 

Assay and test results are determined on the basis of comparison of the test sample with the reference standard that has been freed from or corrected for volatile residues or water content as instructed on the reference standard label. If a reference standard is required to be dried before use, transfer a sufficient amount to a clean, dry vessel. Do not use the original container as the drying vessel, and do not dry a reference standard repeatedly at temperatures above 25°. Where the titrimetric determination of water is required at the time a reference standard is to be used, proceed as directed in the Karl Fischer Titrimetric Method under Water Determination, Appendix IIB. 

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