Time-dependent integrity during storage of natural surface water samples for the trace analysis of pharmaceutical products, feminizing hormones and pesticides

The simple way to insure the integrity of collected samples would be to keep them refrigerated and analyze them within 24 h of collection before unwanted chemical, physical and biological alterations of the samples are observed. Unfortunately, those analyses are often dependent on heavily solicited mass spectrometry instruments and considering various logistical constraints, it is often impossible to analyze such samples within a day. Then the question arises: how long can we store those samples before we analyze them for ultra traces of contaminants (sometimes to concentration below the ng l-1 range).To address this, we have performed simultaneous stability studies of pharmaceuticals (naproxen, gemfibrozil, carbamazepine, trimetroprim, caffeine), steroidal hormones both estrogens (estriol, estradiol, 17α-ethynilestradiol, estrone) and progestogens (norethindrone, medroxyprogesterone, progesterone, norgestrel) and pesticides (deethylatrazine (DEA), deisopropylatrazine (DIA), simazine, atrazine and cyanazine). The major characteristics of the investigated products are shown in Table 1.The main factors affecting the stability of analytes in water samples include hydrolysis, photolysis, physical adsorption or release to or from suspended particulates, chemical degradation by oxidative free-radicals such as alkylperoxy and hydroxyl radicals present in natural waters, or microbial degradation [1], the nature of the sample-container, solubility, vapor pressure and the conditions of storage (temperature, darkness, use of preservatives, time interval between sampling and analysis [2]). Also, the stability of the analytes can be linked to their vapor pressure and water solubility. Indeed, in the literature, it is reported that compounds having a low vapor pressure and medium water solubility (up to 40 mg L-1) are stable while poor stability is attributed to compounds having high water solubility (up to 700 mg L-1), or relatively high vapor pressure [3].The most extensive sta