主题：【分享】关于一些塑料器皿的特性的分享

个人觉得老外写得挺好，值得分享

Plastics

Plastics are very important to the trace analyst. Whenever possible, the analyst should attempt to use plastics for sample collection, storage, preparation, and measurement. Their major disadvantage is the inability to be used for high temperature operations, such as ashing or fusion. Table 5.1 shows a summary of the physical properties of some common plastics.

Table 5.1: Physical Properties of Common Plastics
[img=Table 5.1: Physical Properties of Common Plastics,400,180]http://inorganicventures.com/tech/trace-analysis/images/05/tbl1.gif[/img]

FEP  (FLUORINATEDETHYLENEPROPYLENE)
PFA  (PERFLUOROALKOXY)
FLEP  (FLUORINATED HIGH-DENSITY POLYETHLYENE)
PMP  (POLYMETHYLPENTENE)
PP  (POLYPROPYLENE)
HDPE  (HIGH-DENSITY POLYETHYLENE)
LDPE  (LOW-DENSITY POLYETHYLENE)

The most popular plastics are PFA and HDPE / LDPE.

PFA has excellent properties, allowing for use in acid digestions up to 250 °C. Typically, PFA is used for acid digestions using either HF, HNO₃ or HCl, alone or in combination. The use of higher boiling acids such as H₂SO₄ and H₃PO₄ have been reported in PFA, but great care must be taken not to exceed the 250 °C maximum operating temperature. PFA is commonly used in the construction of microwave digestion vessels. Microwave digestions using the higher boiling acids should not be attempted. Digestions using HCLO₄ should never be performed in plastics of any kind.

LDPE or HDPE bottles are typically used for containment of the sample digestate after dilution with water. These bottles can withstand solutions of HNO₃ that are 10% v/v and lower over extended periods of time (i.e. - years). The caps used for the LDPE and HDPE bottles are made of PP, which is more rigid than the polyethylene and well-suited for its purpose. Unfortunately, the PP cap is not as clean as the PE bottle.

All of the above plastics were part of a study conducted at our laboratories concerning their purity and cleaning properties, further described below.

The Purity and Cleaning of Plastics

Contamination issues with plastic containers, although less severe than other container types, are critical:

"The determination of trace elements at very low levels, particularly in liquid samples, has been found to be biased by the analytical blank and can often be attributed in large part to contamination from sampling and storage containers."¹

Conventional sample handling methods were compared to clean techniques for individual 35 steps. These steps covered sample collection, storage, preparation and measurement of water samples for Ag, Cd, Cu and Pb. It was reported that two thirds of all steps contributed statistically significant amounts of contamination in the measurement of dissolved and particulate Cd, Cu, and Pb -- the average contamination for a single contributing step was 300% (Cd), 141% (Cu), and 200% (Pb).²

This section includes a closer look at part of a plastic container materials study conducted by Inorganic Ventures' technical staff³. Areas of interest in this study included the following:

• Availability and price (see Table 5.1)
• Chemical resistance (see Table 5.1)
• Physical properties (including transpiration) (see Table 5.1, transpiration data presented in the next part of this series)
• Identify (+) contaminants
• Determine (+) contaminants level
• Effectively remove (+) contaminants
• Identify (-) contamination (adsorption)

The plastics chosen for this study are shown above in Table 5.1. Results of this study will be cited to illustrate points throughout this chapter. This section will address the identity, level, and removal of contaminants in these plastics.

- Experimental Design -

• All containers were filled and handled in a clean area.
• "Conductivity" water and doubly distilled nitric acid were used.
• All leaching was performed in an oven at 60 °C.
• All measurements were made using an ICP-MS, located in a clean room.
• The leachate solution was measured directly from the container under study.
• Leaching solutions were exposed only to the container under study.
• Leaching solutions were only exposed to ULPA filtered air.

- Experiment Results -

Table 5.2: Element Concentrations in Leaching Solution
(noted in ng/mL after 59 hours at 60 °C)
[img=Table 5.2: Element Concentrations in Leaching Solution,500,]http://inorganicventures.com/tech/trace-analysis/images/05/tbl2.gif[/img]

All of the containers involved in the leaching study were leached a second time. The results were that all of the elements detected were removed during the first leaching. These results, along with the leaching time study, is shown for Fe in Table 5.3.

Table 5.3: Leaching Behavior of Iron
[img=Table 5.3: Leaching Behavior of Iron,500,]http://inorganicventures.com/tech/trace-analysis/images/05/tbl3.gif[/img]

The above table shows that most of the Fe was leached after 19 hours, with the exception of one of the HDPE bottles (HDPEb). We currently use a leaching time of 72 hours, due to the apparent unpredictability of the necessary leaching time. However, as shown above for Fe (and other elements not shown for the sake of brevity), the 59 hour / 60 °C leaching time / temperature combination was complete. A 66 hour / °C re-leach of these bottles using either 1% HNO₃ or water showed no Fe above the detection limit of 0.02 ng/mL.

The relative purity of the plastics as received from the manufacturer is shown in Figure 5.1 below.

Figure 5.1: Packaging Container Purity
(ranking from leaching study)
[img=Table 5.4: Packaging Container Purity,382,]http://inorganicventures.com/tech/trace-analysis/images/05/fig1.gif[/img]

Most suprising was the lack of impurities found. This may in part be due to the clean room conditions used to perform both the leaching and the measurement steps. Figure 5.1 can be used in conjunction with Table 5.1 to identify the cleanest plastic having the chemical and physical properties for a given operation. This study, for example, suggests LDPE for sample storage and collection while PFA would be more suitable as a plastic for use in microwave acid digestions.

但是，针对这篇文献，我还有一些个人的痛苦经历和大家分享下：

我平常用的是PP管（供应商告诉我是进口的），消解温度不是很高，管子是经过我们预处理的，曾经用的也是挺好的，但是，突然有一天，发现样品试剂空白中Ti ，P异常的高，反复投诉，反复换管子，反复测空白，症状依旧，无奈换代理商，做DOE，最后得到结论是PP管盖子的问题，并且是无良的代理商卖假货坑俺们！真是血的教训啊！

最后总结一点：在咱伟大的祖国，做任何事情都要理论联系实际啊！