L-Cysteine was investigated as the reducing and releasing agent for the determination of antimony and arsenic using flow injection hydride generation atomic absorption spectrometry with the aim of replacing the previously used potassium iodide. The prereduction of the pentavalent t o the trivalent form at room temperature was completed within 5 and 30 min for antimony and arsenic, respectively, which was essentially identical with the performance of potassium iodide. However, much lower acid and reagent concentrations were required with L-cysteine than with potassium iodide. In addition, even dilute analyte solutions containing L-cysteine were stable for at least one week, whereas solutions containing potassium iodide had t o be prepared fresh daily. Under optimized conditions, in the presence of 1 % m/v L-cysteine and 1 rnol 1-1 HCI for antimony or 0.1 mol 1-1 HCI for arsenic, detection limits (three times the standard deviation of a blank solution, n = 10) of 0.05 and 0.01 pg 1-1 were obtained for antimony and arsenic. The calibration graphs were linear ( r > 0.999) for u p t o 10 pg 1-1 of antimony and 5 pg 1-1 of arsenic, using integrated absorbance for evaluation. The precision was better than 2% relative standard deviation ( n = 10) for both elements at the 5 pg 1-1 concentration level.

A method was developed for the determination of antimony and arsenic in copper and steel using f l o w injection hydride generation atomic absorption spectrometry (FI-HGAAS) and L-cysteine as reducing and releasing agent. Tolerance limits (less than 10% interference) of at least 250 and 500 m g 1-1 were found for nickel and copper, respectively, in the presence of 1 % m/v L-cysteine, in the determination of antimony. For the determination of arsenic the corresponding tolerance limits were 200 mg 1-1 for nickel and more than 1000 m g 1-1 for copper. Only 100 m g 1-1 of copper could be tolerated when potassium iodide was used for reduction. Higher copper concentrations resulted in precipitation o f copper(1) iodide, which caused severe contamination of the conduits of the FI system. L-Cysteine is, therefore, recommended for FI-HGAAS because of its better performance for the determination of antimony and arsenic and because of the much lower acid concentrations required. Very good agreement with the certified values for antimony and arsenic i n copper and steel National Institute of Standard and Technology Standard Reference Materials was obtained, o n addition of L-cysteine, b y calibration with matrix-free standard solutions, using the bracketing technique.

Synek 0., E. Sucman, M. Sucmanova: Determination of Fluorides in Feeding Phosphates. Acta vet. Bmo, 47, 1978: 159-162. A method was elaborated of the determination of fluorides in mineral feeding phosphates using the fluoride ion selective electrode. The following average contents of fluoride were determined using this method: 0.07 -1.80 g kg -1 in dicalciumphosphates, 0.22-2.47 gkg-1 in dinatriumphosphates, 1.97-3.86gkg-1 in pyrophosphates, and 0.21 g kg -1 in ammoniumdihydrogenphosphate. This method of determination is quick, simple and sufficiently accurate. It can be used for controlling the content of fluoride in mineral feeding phosphates. Nutrition of farm animals under conditions of modem agricultural large-scale production has become unthinkable without commercially produced feed mixtures of different kinds. A very important component of these feed mixtures are also mineral feeding phosphates which sometimes represent as much as one tenth of the weight of the mixture. These phosphates are necessary both for supplying the organism of farm animals with a sufficient amount of phosphorus and for the optimization of the phosphorus/calcium ration in the feed ration. Along with the optimum composition of feed mixtures it is important to control the purity of their individual components. In feeding phosphates it is namely the content of fluorides which are a natural component of raw materials used for their production.According to Schwarz (1974) fluorine ranks among the essential elements. It stimulates namely the growth of the organism and the development of bones (Schwarz 1974), and it also effects the activity of some enzymes (Rosenquist 1975). On the other hand, however, an excessive uptake of fluorine leads to intoxication. While cases of acute poisoning are not frequent, it is a well kno",n fact that a long-term excessive uptake of fluorine causes fluoroses. In such cases irreversible changes occur, especially in the bone tissue, in younger animals also in teeth (J agos et al. 1977). Secondarily, the whole performance of the animals is affected. The maximum admissible amount of fluorine (as fluoride) in feeds for cattle is, according to Greenwood et al. (1964) about 50 mg kg -1; according to Hapke (1975) it is 40mg kg -" in sheep less than 10 mg kg-I. Griffith-Jones (1977) tolerates 60-100 mg kg-1 for dairy cows. According to results of Said et al. (1977) fluorine even in such a small amount as 30 mg kg -1 causes serious changes in the bone tissues of rams.The fluoride ion selective electrode method has much simplified fluoride determination which had always been very time and labour consuming and represents, at the present time, an accessible means for a simple determination of this element. With regard to the fact that mineral feeding phosphates are a permanent component of nutrition of farm animals, they represent a potential source of excessive flow of fluorides into the organism. That is why a method of fluoride determination was elaborated using the ion selective electrode and in. the com...

Synek 0., S. Zima, M. Sucmanova, E. Sucman: Determination of Lead, Mercury and Arsenic in Feeding Phosphates. Acta vet. Bmo, 47, 1978: 153-158. Elaborated was the method of determination of lead, mercury and arsenic in feeding phosphates by means of atomic absorption spectrophotometry. Five different types of foreign and Czechoslovak phosphates commonly used for the preparation of feed mixtures were analyzed. The content of lead, mercury and arsenic ranged from 0.72 to 6.89 mg kg-I, 0.09 to 0.37 mg kg-l and from 0.75 to 69.77 mg kg-I, respectively. With regard to the content of all the three elements studies it was found that the relatively purest was dinatriumphosphate (Fosfa, n. p.), while the highest amount of admixtures was found in monocalciumphosphate (Reymeshoim) and dicalciumphosphate (CKF). Microelements, atomic absorption spectrophotometry, feed mixtures.The ever increasing industrialization and intensification of agricultural large-scale production necessitates investigations of new aspects in the nutrition of farm animals, aspects that had not been important before. One of the problems discussed has recently become the content of some microelements in feeds and feed mixtures; the intense development of instrumentation techniques over the past years has enabled these investigations to be carried out. The most important of these microelements are lead, cadmium, mercury and arsenic, indicated as "toxical civilization elements". The importance of uptake of these elements by farm animals should be judged from two aspects. i. e. from the point of view of the health condition of animals (possible intoxication, etc.), and because feed is the first link of the food chain which ends in man. Whereas the final links of this chain (raw materials for the preparation of foodstuffs, finished products, etc.) have already been studied, are being discussed, or there already exist standards for the admissible contents, in the field of feeds not many studies of this kind exist. These studies are aimed namely at lead of which namely the increased content in conventional feeds is closely associated with civilization. The intoxication of farm animals with lead in the industrial regions and in the vicinity of main roads with heavy traffic is becoming an ever increasing problem (Matyas 1975).The most important mineral components of feed mixtures include various types of phosphates, representing 1-10 % of the total composition of feed mixtures. With regard to the initial raw materials and the industrial character of the production of these substances the present study deals with the determination of lead, mercury and arsenic in the most frequently used types of feeding phosphates of both foreign and Czechoslovak origin. Materials and MethodsSamples of dicalcium phosphate (DCP) and monocaIciumphosphate (MCP) imported to Czechoslovakia in 1975Czechoslovakia in -1977 as mineral feed admixtures were analyzed as for the content of lead, mercury and arsenic. The other phosphates studied (dinatriumphosphate, pyrophosphat...