Duplicate portion method

Rohrig B, Anke M and Drobner C (1996) Investigation of copper intake with the duplicate portion method in relation oftime and kind of diet. In Pais I, ed. International Trace Element Symposium Budapest, pp. 171 -178, St. Istvan University, Budapest, Hungary. 

Dietary assessment methods, total diet studies, and the duplicate portion method are evaluated with regard to their adequacy for obtaining iodine intake data. The advantages and shortcomings of catalytic spectrophoto-metric methods, nuclear analytical methods, spectromet-ric, electrochemical, and other techniques, which are used for the determination of iodine in foodsmffs and related materials, are reviewed. 

The main purpose of iodine assay in foodstuffs is to obtain data on intake by an individual or a population. Commonly used approaches to evaluate intake of various diet components, such as nutrients, vitamins, minerals and trace elements, contaminants, and so on, involve dietary assessment methods, total diet studies, and the duplicate portion method. In general, their ease of execution and the validity of the results obtained differs for all diet components, and this particularly applies to iodine. The use of biomarkers to assess iodine intake, specifically iodine excretion in urine, is also mentioned. 

Figure 122.2 Foodstuffs and total diet samples collected by the duplicate portion method.

Retrospective dietary-assessment methods are simpler and less expensive than prospective and duplicate-diet methods, and therefore are used more often as the basis of dietary expostrre assessments. Food-fiequency studies take the form of participants identifying their typical fish consrrmption (e.g., How many times per week/month do you usually eat fish AT). Diet histories involve recollection of specific meals over a specific time (e.g. 24-hr or 1-week periods). In the studies mentioned above, Sherlock et al. (1982) and Haxton et al. (1979) used retrospective assessment of typical consumption to preselect subjects. In a recent study of MeHg exposure among pregnant women in New Jersey (Stem et al. 2000), participants were asked to identify their typical consumption frequency and typical portion size of 17 species of fish and... 

Tab. 4.6 Macro element intake of adults with mixed diets determined by the duplicate portion technique and calculated by the basket method...

Trace Element Intake Measured by the Duplicate Portion Technique and the Basket Method... 

The calculation of trace element intake using the basket method led to a significant overestimation compared with direct analysis and the duplicate portion technique (Table 4.13). The overestimation is lowest in the case of copper and manganese (10-20%), medium for iodine, manganese and iron, and high for molybdenum, selenium. 

The calculation of inorganic food component intake using the basket method generally resulted in an overestimation of element consumption when compared with results obtained with the duplicate portion technique. The results ranged from 4% in the case of sodium to 44% for calcium and iron, 55% for selenium, 66% for chromium, and 240% for mercury and lithium. Hence, basket method should no longer be used to determine macro, trace and ultratrace element intake in humans. 

Nursing mothers typically take in 15% more potassium than non-nursing women (Anke et al. 2003). At present, the normal daily potassium requirement of adults is not known, but for adults the minimum value has been cited as -1.6-2.0 g (Anonymous RDA 1989) or 2000 mg (Anonymous 2000). This requiremenf is an estimation, and is tantamount to a recommendation. A comparison of potassium intake measured by the duplicate portion technique and as calculated by the basket method showed an overestimation of calculated potassium intake by 30%. Hence, methods of potassium intake calculation should not be used (Anke etal. 2003). For example, Pittelkow (1992) calculated a daily potassium intake of 3.0 g kg for women and 4.0 g kg by men in Germany, but on average this was an overestimation by 25% for both groups. 

It has been suggested that conventional dietary assessment techniques, in conjunction with food tables, do not provide realistic estimates of micronutrient intakes and that accurate data on dietary intake of such nutrients can only be obtained by direct chemical analysis of foods or diets (Abdulla et aL, 1989 Bro et aL, 1990). There are three different methods of collecting data for direct chemical analysis (duplicate portion technique, aliquot samphng technique and equivalent composite technique) however, the most precise method of direct chemical analysis is the duplicate portion technique, as it directly measures actual nutrient intake (West and van Staveren, 1997). 

FFQs, as a direct semi-quantitative method of dietary assessment, are often easier to handle and can result in higher subject compliance, compared to weighed food records and the duplicate portion technique. However, the use of FFQs, as used in the study performed by Waldmann et al. (2003), may result in more sources of error in the estimation of iodine intake compared to other dietary assessment techniques, due to the choice of food portion... 

An increase in precision may be achieved by increasing the number of subjects, although more involved dietary assessment methods, such as the duplicate portion technique, are labor intensive and require a significant amount of subject commitment therefore, their use is usually restricted to small groups and data are collected over a short period of time (Petersen and Barraj, 1996). However, short time periods will miss any seasonal differences in the iodine content of foods that may occur. Seasonal variations were minimized in the Waldmann study, as 7-day FFQs were completed in both the autumn and spring seasons. 

The validity of the duplicate portion technique may be problematic as the completeness of duplicate portions is often difficult to assess. However, the use of biochemical markers, such as plasma, serum and urine, may be incorporated into nutritional assessment studies to validate dietary surveys or confirm nutritional status. There are a number of different methods that can be used to assess iodine status and, in particular, for the determination of the severity of iodine deficiency. However, two main methods used for the assessment of iodine status are measurement of urinary iodine excretion and thyroid function tests (an indirect method of iodine sufficiency). 

Although the duplicate portion technique may be considered the best method for the assessment of trace element intake, it is not always practical to determine iodine intake using this method of dietary assessment. 

Dietary nuclide intakes are estimated by several methods (WHO, 1983), e.g., selective studies of individual foods, market basket studies, model dish studies and duplicate portion studies. The first procedure involves the estimation of mean dietary nuclide intakes by collecting staple foods, which are consumed by the subject, and then chemically analyzing them. In market basket studies, individual or composite foods obtained from food stores in the area are analyzed. Data on the food consumption rates of the average person then take on an especially important role. Model dish studies involve the preparation of typical dishes based on both food and dish consumption data and analysis of each dish. Duplicate portion studies offer the greatest degree of reality compared to the other methods. At a minimum, all meals consumed by an individual during one day are chemically analyzed. After the accident in the Ukraine, data on the dietary intakes of Cs, °Sr and transuranium have come from analyses of staple individual foodstuffs. Total diet studies for Ukrainians are scarce. 

The dietary intake of lead has been estimated by a number of methods, the principal ones being firstly the analysis of duplicate portions of meals for total lead and secondly a composite method, whereby typical lead concentrations in the various components of a diet are separately defined and the total lead intake becomes the sum of the lead intakes from the various components, as in Table 7.4. Some of the more recent data, reported since 1970, are summarized in Table 7.5. Clearly there is a high degree of variability in dietary lead intake from individual to individual, as well as from country to country. Typical intakes probably lie in the range 100-200 Mg day for adults and somewhat lower but not proportionately so, for children at 50-150 Mg day -... 

Haleys Dialyzed Iron and Related Methods, Hyaluronic acid was said by Hale to combine with dialyzed iron in acetic acid solution 89), After the sections were rinsed, the classical HCl - potassium ferrocyanide reaction was used to color (as Prussian blue) the sites of iron-binding. The need for fixatives that would not dissolve hyaluronic acid was emphasized. The specificity was established by exposing duplicate portions of tissue to streptococcal hyaluronidase, presumable filtrates, before staining. This prevented coloration of hyaluronic acid but not that of other acidic carbohydrates. 

The test substance may be acquired in a number of ways. One common method is to purchase the product from a chemical dealer. This method of acquiring the test substance for a worker exposure or re-entry study allows one to proceed rapidly with the execution of the field portion of the study without the serious delays encountered while waiting for a test substance to be manufactured, assayed, and shipped to the site. Although having a test substance formulation which has been assayed under GLP standards and for which a certificate of analysis has been shipped to the test site is desirable, there are several instances when this is not practical. For example, one may encounter a worker exposure study where the pesticide to be evaluated is sold only in mini-bulk or even large bulk quantities holding as much as 2000 gal. In this case, duplicate 5-10-g or 5-10-mL retainer samples should be taken from the bulk or mini-bulk tanks for assay after the worker exposure study is in progress. 

A portion (10.2 cm x 17.8 cm) of each RSP sample was sequentially extracted in a Soxhlet apparatus with cyclohexane, di-chloromethane and acetone, (8 hr. for each solvent) in the order given. A more complete extraction of the organic compounds present in particulate matter is achieved and a partial separation of the organic compounds into non-polar, moderately polar and polar fractions is obtained by this method. The volume of each extract was reduced to 10.0 ml using a rotary evaporator. The samples were then stored in a freezer at -15 C until further analysis. Weights of extracts were determined by weighing duplicate 100 yl aliquots of each, taken to dryness on a slide warmer (40 C), on a Cahn Electrobalance. 

Duplicate analysis performed on two test portions from the same sample -i.e. two test portions from the same sample are taken through the whole method. 

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