Surface Sampling with Wipes

We use wipe sampling to detect contaminants on non-porous surfaces, such as the surfaces of plastic or metal drums transformer casings various heavy equipment walls floors ceilings laboratory benches. Sampling with wipes allows transferring contaminants from a surface area of a known size onto the wipe material. The wipes are then analyzed, and the amounts of contaminants found on the wipe are related to the surface area. 

Typically, we perform wipe sampling in the following situations  

Porous surfaces, such as wood, plaster, and concrete, are also often sampled with wipes. Surface sampling of porous materials, however, does not provide any information on the contaminants that may be trapped inside the pores, cracks, and seams of the sampled surface. A better way to characterize porous materials is to collect and analyze chip samples. 

Common contaminants that are sampled with wipes include dioxins/furans, PCBs, pesticides, and other SVOCs, metals, and occasionally, VOCs. Obviously, we do not expect to detect any VOCs on surfaces exposed to air, however we often sample for them to satisfy a disposal or a health and safety requirement. 

dioxins/furans, PCBs, pesticides Hexane 

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B2 Sampling methods 3.5 Soil sampling designs 3.6 Water sampling 3.7 Surface sampling with wipes... 

Practical Tips Surface sampling with wipes... 

Sample packaging and shipping supplies per Chapter 3.4 To sample a surface area with wipes, we follow these steps ... 

The nature of the contamination incident determines the sample types. Air samples and wipe samples are taken when dust or fume deposition is the problem. Core samples or chips may be taken from porous surfaces when contaminant penetration is expected to have occurred. The cores in particular are often sliced into sections, with analysis beginning in the top section or two and proceeding downward if results continue to prove positive. The results of the core/chip analysis determine the extent to which porous surface removal is required. 

The subj ect oiwipe sampling is not well defined in standard industrial hygiene reference books. The use of wipe sample datais open to interpretation.However, wipe sampling is of interest to the semiconductor industry because of certain metals used in the manufacturing process such as arsenic, antimony, chromium, and lead. A variation on this technique is also used in the evaluation of surface contamination with sealed radioactive sources (see Ch. 6, Radiation Safety). 

In Raman spectroscopy, polymer samples often exhibit fluorescence due to contaminants on their surfaces. Wiping the sample with a solvent, e.g. acetone or alcohol, can reduce this fluorescence. Alternatively, taking a thin slice off the surface of the sample can also be helpful. 

The number and types of surfaces must be determined carefully to approximate effeetive exposure from household dust. Hard surfaces are the easiest to sample by either vacuum of wet-wipe methods, and the tendency is probably to oversample this type of surface because of its convenience. Rugs and upholstered furniture cannot be sampled with wet wipes, and a vacuum system may oversample by collecting dust not readily available to a child s hand. Play areas are the most logical choice for targeted sampling if this method is selected. Toddler accessibility is the first requirement, and information from the parents can also prove useful. Many researchers have found that sampling at the entry is an effective measure of exterior dust. Dust collections may also be made on the porch or sidewalk. 

Mass sorption is determined by contacting sample by immersing it in a liquid additive, wiping surface from additive, washing surface with medianol, and determination of weight gained. This procedure is repeated at different time intervals until equilibrium is reached. The major error comes from removal of excess liquid and washing sample with methanol, which inevitably removes some of the additive absorbed into sample. There may be some value in these results but the major... 

Re-wetting test A 4 Meyer bar drawdown is allowed to dry for 20 min at RT (room temperature). A drop of water is placed on the ink surface and subsequently wiped with a cloth. A subjective comparison is made versus a standard sample. Solution polymers are neutralized with volatile amines (Sect 5.2.3) to prevent resolubilization after the ink print dries. 

Second-order nonlinearity and molecular orientation in the alternating LB films were evaluated by the SHG measurement using a Q-switched Nd YAG laser. The detailed evaluation procedure was described in the section 1.3. In this measurement, we used the samples in which one of the LB films deposited on both surfaces of a substrate was removed by wiping it of with a cloth soaked with chloroform. 

Sample Preparation. The sample series was prepared by varying the ratio of Epon 828 to the methylene dlaniline (MDA) curing agent. The compositions tested contained 0%, 23.1%, 50.0% and 100% excess MDA over the stoichiometric amount. The MDA and diepoxide were heated to 100°C and mixed. The mixture was cast onto one side of a sheet of aluminum 5.5 cm. x 24.5 cm. x 5 mils, which had first been wiped with acetone to degrease the bonding surface. The final coating thickness was controlled at approximately 60 mils. 

CCD detector consists of 224 linear photodetector arrays on a silicon chip with a surface area of 13 x 18 mm (Fig. 4.16). The array segments detect three or four analytical lines of high analytical sensitivity and large dynamic range and which are free from spectral interferences. Each subarray is comprised of pixels. The pixels are photosensitive areas of silicon and are positioned on the detector atx -y locations that correspond to the locations of the desired emission lines generated by an echelle spectrometer. The emission lines are detected by means of their location on the chip and more than one line may be measured simultaneously. The detector can then be electronically wiped clean and the next sample analysed. The advantages of such detectors are that they make available as many as ten lines per element, so lines which suffer from interferences can be identified and eliminated from the analysis. Compared with many PMTs, a CCD detector offers an improvement in quantum efficiency and a lower dark current. 

Rinse the equipment with acetone after the cleaning. Analyze the rinsing using a UV spectrophotometer (sample size 20 ml). Wipe at each selected location a surface area of between 100 and 800 cm or alternatively rinse the equipment with a suitable liquid and check. 

Using a QC-approved antimicrobial agent, sanitize the exterior surfaces of the sample container by spraying with the agent until visibly wet or wiping the surfaces with a sterile, lint-free, agent-soaked towel. Put all the samples to be tested under the hood. Allow surfaces to dry before testing. 

Thoroughly wiping the horizontal surface of the ATR crystal with low-lint paper has been the method of choice for cleaning without the use of any solvent. However, to ensure the complete removal of a test sample the analyst should also apply the subsequent test portion and clean the crystal once again. Additionally, the analyst could make an infrared measurement after cleaning the crystal the absence of a spectrum would confirm that the crystal is clean. 

The sample is prepared for analysis by first washing it by immersion in 0.1% Teepol solution for 15 seconds with gentle wiping of the surface. It is then rinsed rapidly in distilled water and dried at 65 to 70 °C for 24 hours. This material is ground to a powder. 

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