Sampling Location and Frequency

Objects which are internally correlated for example volumes sampled from rivers, soils, or ambient air, can be treated by autocorrelation analysis or semivariogram analysis. The range up to a critical level of error probability is an expression of the critical spatial or temporal distance between sampling points. 

---

It is only after information goals and appropriate indicators have been defined accurately and precisely that sample location and frequency can be decided. Continuous monitoring of some water quality parameters is now commonplace in many parts of the world. However, the cost of these systems and limits to the parameters that can be measured with them means that spot or grab samples for testing probably always will form part of environmental quality monitoring strategies (Hazleton, 1998), and this remains true for bioassays. 

For the procedure, requirements, actions in case of defect, and frequency, see Section 1.1. Sampling locations and sample number the locations have to be established in-house, three samples per equipment. 

Validation Sampling Plan. Any process undergoing validation must be sampled. This section will tell the reader the logic that went into the sample plan, the frequency of collecting the samples, the sampling locations, and so on. 

The mode is the most common value in the sample. The mode is easily found from a tabulated frequency distribution as the most frequent value. The mode provides a rapidly and easily found estimate of sample location and is unaffected by outliers. However, the mode is affected by chance variation in the shape of a sample s distribution and it may lie distant from the obvious centre of the distribution. Note that the mode is the only statistic to make sense of quahtative data, e.g. the modal (most frequent) technique used in the laboratory is infrared spectroscopy . The mean, median and mode have the same units as the variable under discussion. However, whether these statistics of location have the same or similar values for a given frequency distribution depends on the symmetry and shape of the distribution. If it is near symmetrical with a single peak, all three will be very similar if it is skewed or has more than one peak, their values will differ to a greater degree (see Fig. 40.3). 

Various types of diffusion models are available which can use as input emission patterns, climatological data, and population data to rank sampling locations by concentration threshold, resolution of peak concentrations, and frequency of exposure (4) or to rank sampling locations for maximum sensitivity to source emission changes, to provide coverage of as many sources or to cover as large a geographic area as possible (5). 

This technique is invasive however, the particle can be designed to be neutrally buoyant so that it well represents the flow of the phase of interest. An array of detectors is positioned around the reactor vessel. Calibration must be performed by positioning the particle in the vessel at a number of known locations and recording each of the detector counts. During actual measurements, the y-ray emissions from the particle are monitored over many hours as it moves freely in the system maintained at steady state. Least-squares regression methods can be applied to evaluate the temporal position of the particle and thus velocity field [13, 14]. This technique offers modest spatial resolutions of 2-5 mm and sampling frequencies up to 25 Hz. 

The primary considerations discussed in this book for sampling the indicators include the scale of measurements needed the type of sampling location (e.g., undisturbed sites, clustered sites) the frequency of sampling (e.g., hourly, weekly, armually, bierrrrially) and the duration of sampling needed to detect trends. 

Sampling plan. To determine the number of samples, the areas are reviewed for criticality. Samples are taken from representative location at frequencies specihed in the respective procedures. The sampling frequencies are based on the environmental classihcations per current USP. The sampling plans shall be dynamic with monitoring frequencies and sample plan locations adjusted based on trending performance. It is appropriate to increase or decrease sampling based on this performance. 

---