Analysis method for iron in battery acid
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We produce battery acid, and there are two methods for analysis: 1: Determination of Fe in sulfuric acid – 5.5 ml of the sulfuric acid sample is taken and placed in a clean 100 ml beaker. It is heated in a drying oven until all liquid has evaporated; after that, the beaker is allowed to cool. The inner walls of the beaker are rinsed lightly with water, 1 drop of 1+1 hydrochloric acid is added, along with 1 ml of ascorbic acid and 5 ml of acetic acid-sodium acetate solution. 1 ml of ferroin is also added. A standard sample is prepared as well – 1 ml of this standard sample (with a concentration of 5 μg/ml) is used. The presence of Fe is determined through visual color comparison; the allowable limit is Fe ≤ 0.00005%. 2: In a colorimetric tube, 20 ml of pure water is added, and 5.5 ml of the sample is added using a pipette. The mixture is allowed to cool to room temperature, after which 1 ml of 1:1 nitric acid and 5 ml of 15% thiocyanic acid amide are added. Color comparison is carried out using an iron standard solution with a concentration of 0.1 mg/ml (a blank control is also used). The percentage content of Fe is calculated as follows: (titration volume ÷ 1000) = Fe%. Where V represents the volume of the standard solution consumed, and M represents the weight of the sample. In this case, 5.5 ml corresponds to 10 g of sample. The concentration of the iron standard solution is 0.1 mg/ml. Both of these methods yield significant errors – what could be the reasons for this? How to avoid it?
This post was last edited by Yang Qing on 2020-11-14 at 10:20. This description is quite unprofessional. According to your testing requirements, is it necessary to determine whether the iron content is less than 0.00005% (0.5 ppm)? Your Method 1: The amount of the test sample and the concentration of the standard solution are not equivalent. How can one make a visual comparison? According to the Filorin method specified in GB/T 3049, the concentration seems to be insufficient. Method 2: This is even more confusing. Is there 100 micrograms of iron in 5.5 mL? Is it colorimetry or titration? If it is colorimetry, then what does “Titer value ÷ 1000 = Percentage content Fe% = V: Volume of standard solution consumed : M:” mean in the post? Maybe the original poster isn’t in the testing field? It would be better to describe it more clearly. I’m not aware of the specific requirements for iron in batteries; we should figure out those specifications first. Anyway, I was completely confused after watching it.
This post was last edited by qugd on 2020-11-16 at 10:03. I agree with the view of friend Yang Qinghai. The first method is a qualitative test; it can only determine whether iron ions are present or absent under the conditions of the test. The second method, as a quantitative analysis, is a bit too informal. It can only be described as a semi-quantitative analysis. In fact, there are already many mature methods for the testing and detection of iron ions; some of these methods have even been incorporated into ** or industry standards. Why, then, can’t we establish a complete and reliable testing procedure to ensure that product quality meets the required standards and is dependable? The results obtained through such testing methods are not very reliable; to put it bluntly, it first harms the users and ultimately harms the company itself. It’s best to write down your company’s name, so as to warn users to be cautious.
I feel that in fact, the original poster is raising the issue of the errors in determining iron content using the ferroin method and the thiocyanate colorimetry method. There are no specific requirements regarding detection accuracy; I’m not sure what “large error” means. Is it possible that one method yields a pass result, while another method yields a fail result? Method 1, the ferroin method, is used to detect divalent iron (by reducing any possible trivalent iron with ascorbic acid), while Method 2, the thiocyanate method, is used to detect trivalent iron (by oxidizing any possible divalent iron with nitric acid). If the sample is processed properly and the ion concentration of the color-developing solution is appropriate, there should be no significant errors. For visual colorimetric determination, a standard color must be established; thereafter, a sample prepared in accordance with the specified quality standards is subjected to colorimetric analysis using appropriate methods, making it suitable for a detection process that can be clearly observed with the naked eye. If the sample content is much lower than the standard value, a simple visual inspection is sufficient to provide reassurance. It’s likely that the original poster isn’t a lab technician; someone else just provided them with a piece of handwritten text, and without understanding what it meant, they followed those instructions, which is why the description is unclear. To truly resolve the issue, it’s necessary first to clarify the product components (i.e., how this “battery acid” is produced) and the technical specifications for the testing parameters (such as the maximum allowable iron content). Only then can we provide reference solutions for industry peers.
Using a spectrophotometer, the absorbance is measured; by comparing it with a calibration curve, the iron content is determined.
The description isn’t very precise. I believe that for such industrial products, testing in accordance with the standard HG/T 2692-2015 for sulfuric acid used in batteries should yield reliable results. Visual color comparison for preliminary on-site assessment is also acceptable.
Even when using visual colorimetric analysis, it is necessary to use multiple color grades for comparison. The OP’s analytical method can only be regarded as a semi-quantitative analysis method. Such a crude analytical approach essentially has little practical significance when it comes to accuracy or deviation. Today, there are numerous methods for analyzing iron; with some very simple instruments, fairly accurate analysis can be achieved. Yet this company still relies on this semi-quantitative method for quality inspection. Not only is this approach outdated, but it also reflects a lack of responsibility toward product quality.